Post by: Longcruise on January 29, 2021, 01:56:30 PM
This is in regard to glass/wood lam bows.
Which side of the bow should be optimized for to obtain highest performance? IOW is it better to have more tension than compression or vice versa. Or, should the two be in perfect balance?
What do you think and why?
Post by: EvilDogBeast on January 29, 2021, 02:46:05 PM
These are all just speculations on my part. I'm not an engineer by any means, but perhaps one will weigh in.
Post by: williwaw on January 29, 2021, 03:45:16 PM
Question for all if Michael doesn't mind,
When testing new designs by varying back/belly glass ratios, what is the most common type of limb failure?
Post by: Mad Max on January 29, 2021, 03:56:05 PM
Post by: Crooked Stic on January 29, 2021, 04:11:53 PM
They checked the bows at 28 in. with 10 GPP of draw weight. Then at 9 GPP with the same brace on each bow.
Post by: Shredd on January 29, 2021, 04:41:22 PM
Here's my speculation... First place I believe what you are really talking about in essence is shifting the neutral plane... Me and Flem never settled that one... :laughing:
Quotes from EDB and the Mad Man... "I would say you'd want as much tension as possible"...
"I would think thicker belly glass than the back would help"...
I think both of these statements have some air of truth about them... Tension and compression work together You really can't have one without the other in a bending limb... Since tension trumps compression in this case I believe the neutral plane is a hair more toward the tension side... Meaning the tension side is compressing a bit more of the limb than the compression side is stretching more of the limb on the tension side... I also believe the trick is to increase the strength of the compression side as to put more stress on the tension side without increasing the thickness of the limb... If you increase the thickness of the limb you will gain more tension and you will also increase arrow speed but you will also increase draw weight with no added performance of draw weight / arrow weight...
I like to call dabbling in this direction the Alchemy of Bow making... Kinda like turning Lead into Gold... How much can you cheat physics and stack more performance into something??
I just read Stics post and that proves my theory all wrong... Something to think about... But who wants a bow that is gonna self destruct...
Post by: Shredd on January 29, 2021, 04:49:42 PM
You don't really know until you spend month's of experimenting...
Alchemy I tell you... :thumbsup: :laughing:
Post by: williwaw on January 29, 2021, 05:06:01 PM
they found thinner belly glass give gains in speed. But not durable in the long run.
Stic,
"not durable".... can you recall how the bow(s) failed?
Post by: EvilDogBeast on January 29, 2021, 05:09:09 PM
On the topic of failure and glass thickness/overbuilding: Has anyone ever seen the glass itself fail? I don't recall ever seeing a bow that blew the glass. It always seems to be a disbond or a failure of the core.
Post by: Shredd on January 29, 2021, 05:10:35 PM
Post by: Mad Max on January 29, 2021, 06:05:07 PM
50-1/2" NTN 7-1/2" reflex
(https://i.imgur.com/f6GdJHx.jpg)
(https://i.imgur.com/iFNcFZ3.jpg?1)
(https://i.imgur.com/q5gx1qc.jpg)
Here is a link to Pete Ward bow review
"All readings were taken at one time, with a static release, Cavaler Elite Tab, Fresh Batery, and draw lenght's witnessed and coached by my wife Pat."
http://peteward.com/2007%20new%20pages/test.sheepeater.html
Post by: Bowjunkie on January 29, 2021, 06:13:34 PM
These bows were brought to me to refinish because in each instance the owners believed the stress marks were only in the finish. I refinished two of them, and they looked almost like new when I was done. Their glass was brown, and the faintest smokey shadow was barely visible afterwards. Even if I pointed it out to you, it was almost impossible to see. But after a few weeks or months of additional use, it came back, and then with continued use, the glass fibers eventually began to raise to the point you could feel them. This happened in an area about 2-3" long and the whole way across their limbs.
Post by: williwaw on January 29, 2021, 07:18:44 PM
Willi... I am pretty sure that they probably buckled...
If I understand the principles of materiel strength correctly, then it is reasonable to assume an excessively strained glass lam in compression will buckle on account of an underlying core failure?
I've seen glass fail on some recurves. They all failed on the back in the area of the fadeouts........... and then with continued use, the glass fibers eventually began to raise to the point you could feel them.
And an excessively strained glass lam in tension, seems to fail when the epoxy in the lam separates from the glass fiber?
Which side of the bow should be optimized for to obtain highest performance? IOW is it better to have more tension than compression or vice versa. Or, should the two be in perfect balance?
What do you think and why?
Since the strain levels at failure in tension and compression are failures of different natures, the "balance" for highest performance could be a design that maximizes the acceptable working strains on each side of the bow. They are most likely not equal.
The point is, not a single one failed in these compromised areas on the belly. It was always the glass on the back that fatigued and then failed. This leads me to believe glass is stronger in compression resistance than tension resistance, but I don't know that for a fact.
Jeff,
did your appraisal of the failed bows take into consideration the thicknesses and widths of the glass lams both back and belly? Your observations about the failures occurring in the fade areas complicates matters if the fades were not symmetrical front and back.
It always seems to be a disbond or a failure of the core.
Chris,
Did the failures you examined have pieces of the core still epoxied to the glass, ruling out a glue failure?
Post by: williwaw on January 29, 2021, 07:23:47 PM
This one is pushing the limits, No core problems
50-1/2" NTN 7-1/2" reflex
that's short, how wide are the limbs?
Post by: Mad Max on January 29, 2021, 07:29:11 PM
Post by: EvilDogBeast on January 29, 2021, 07:33:44 PM
Post by: mmattockx on January 29, 2021, 07:54:07 PM
Which side of the bow should be optimized for to obtain highest performance? IOW is it better to have more tension than compression or vice versa. Or, should the two be in perfect balance?
Perfect balance will be the most efficient way, but in this case 'perfect balance' would mean that both the belly and back are strained to the same percentage of their failure strain. The belly side should fail first because compression is an unstable condition and tension is stable, but that assumes perfection in the construction which may or may not be the case.
I would think thicker belly glass than the back would help
This goes along with the compression side failing first and makes sense to me.
I am pretty sure we are overbuilding with glass as it is right now, and the glass used could actually handle quite a bit more stress. Personally I suspect we are at the limits of wood cores.
We never use more than about 50-60% of what fibreglass has to offer. You are correct in thinking that the cores are often the weak link. Care must be taken to not overstress the cores as the wood can take ~1/3 the strain of fibreglass.
I've seen glass fail on some recurves. They all failed on the back in the area of the fadeouts, or fadeout lams, or wedges in the case of takedowns.
That's interesting and indicates there were other issues causing the failure beyond simple tension/compression loads. It also means the glue is doing a great job of a holding the belly lams onto the core.
Mark
Post by: Bowjunkie on January 30, 2021, 07:16:39 AM
Perhaps that's partly what I saw. But the glass fibers themselves were failing too. If you fold your hands by interlocking your fingers and then straighten your fingers so they stand up a little, that's what the glass fibers were doing. Did they 'come unglued' and then break, or vice versa? I don't know.
These bows had seen decades of regular use before failing.
No glue joint issues in those bows. They stayed together. Yes, there were other root causes concerning how the fadeout was executed, it acted like a hinge of sorts, creating much strain of both types in a very specific, isolated spot, and it seems to me at least that if glass was weaker in compression resistance, that it would have failed there in that spot in compression and not tension.
Has anyone ever seen glass fail only in compression? As in crushing, fretting etc... without wood or glue joint failure?
Post by: Roy from Pa on January 30, 2021, 08:31:31 AM
That area is a high stress area.
With thousands of shots out of a bow, sooner or later a weak spot is created there.
My old bear 1972 takedown, with prolly 10,000 shots out of it, broke just outside of the fade.
Wasn't a glue failure, just finally got weak enough and broke while at full draw.
That was exciting as hell:)
Post by: Walt Francis on January 30, 2021, 09:26:20 AM
.This one is pushing the limits, No core problems
50-1/2" NTN 7-1/2" reflex
that's short, how wide are the limbs?
If I remember correctly, Brent narrowed the limbs on The Sheepeater to 1.40”. I narrowed the ones made on his forms to 1.40 and 1.35. I bought one at an auction that was really beat up and narrowed it to 1.30” to clean up the edges and it still shoots like the other sheepeaters.
Post by: Flem on January 30, 2021, 09:35:16 AM
Post by: Mad Max on January 30, 2021, 09:44:44 AM
we are waiting on you Flem :bigsmyl:
Post by: Flem on January 30, 2021, 10:04:32 AM
[ You are not allowed to view attachments ]
Post by: Longcruise on January 30, 2021, 11:31:38 AM
I am seeking another path for the answer to the "neutral zone"
Guess I've been MIA here after getting this started. Had family commitments.
Im very impressed and intrigued by the contributions to this topic.
So, Flem, is it a neutral zone that is being sought? I kinda share that view but wonder what materials and placement will give the best results.
What is happening in the balancing act between back and belly? Is the belly a drag on the effort of the back? Does the belly need to push harder? Would that be an improvement in performance? Or, is it better to emphasize more tension in the back?
Flight bow builders are obviously maximizing to some degree even to the point that a highly performing Flight bow may have a very limited life span. When they die is it the back or belly that goes?
Post by: Shredd on January 30, 2021, 11:46:49 AM
Maybe Allen will chime in on flight bows...
Post by: Roy from Pa on January 30, 2021, 11:47:39 AM
Roy, do not click on this thread again:)
Post by: Shredd on January 30, 2021, 12:05:04 PM
Most glass bows break just outside of the fade.
That area is a high stress area.
With thousands of shots out of a bow, sooner or later a weak spot is created there.
My old bear 1972 takedown, with prolly 10,000 shots out of it, broke just outside of the fade.
Wasn't a glue failure, just finally got weak enough and broke while at full draw.
That was exciting as hell:)
I have come to the conclusion that most bows are like guitar strings... They are eventually gonna break from use...
Post by: Flem on January 30, 2021, 12:36:04 PM
Since everything in the physical world we know is trying to reach dynamic equilibrium, homeostasis, Yin/Yang or whatever you want to call it, we have to decide do we want our Bows to be in balance?
Do the materials we use store more energy and return to their resting position faster, when in tension or compression? What is the optimum balance between the opposing forces? Do we try to establish the position of the neutral zone or do we leave it to destiny? :pray:
Post by: Bvas on January 30, 2021, 12:54:28 PM
And before anyone says it........I have time to think about, not to do it.
Post by: kennym on January 30, 2021, 01:09:32 PM
Post by: Roy from Pa on January 30, 2021, 01:13:10 PM
Why doesn’t someone build a relatively simple bow. Perfectly flat limbs, with a perfectly centered riser. .040 glass one side, .030 other. Cut string grooves so bow can be strung and drawn either direction.
And before anyone says it........I have time to think about, not to do it.
Sure Bvass, come in here and throw wood on the fire and leave:)
Post by: Mad Max on January 30, 2021, 01:41:57 PM
So instead of looking at the neutral zone as something seen from the outside, I have decided to become one with the neutral zone. The view from inside, looking toward the back and belly is enlightening.
Since everything in the physical world we know is trying to reach dynamic equilibrium, homeostasis, Yin/Yang or whatever you want to call it, we have to decide do we want our Bows to be in balance?
Do the materials we use store more energy and return to their resting position faster, when in tension or compression? What is the optimum balance between the opposing forces? Do we try to establish the position of the neutral zone or do we leave it to destiny? :pray:
Maybe Gordans or who ever made the first glass figured that out for us. :knothead: :laughing:
And YES Safety would be calculate in that. :dunno:
Post by: Buemaker on January 30, 2021, 02:03:28 PM
Post by: williwaw on January 30, 2021, 03:46:15 PM
"And an excessively strained glass lam in tension, seems to fail when the epoxy in the lam separates from the glass fiber?"
Perhaps that's partly what I saw. But the glass fibers themselves were failing too. If you fold your hands by interlocking your fingers and then straighten your fingers so they stand up a little, that's what the glass fibers were doing. Did they 'come unglued' and then break, or vice versa? I don't know.
These bows had seen decades of regular use before failing.
No glue joint issues in those bows. They stayed together. Yes, there were other root causes concerning how the fadeout was executed, it acted like a hinge of sorts, creating much strain of both types in a very specific, isolated spot, and it seems to me at least that if glass was weaker in compression resistance, that it would have failed there in that spot in compression and not tension.
Has anyone ever seen glass fail only in compression? As in crushing, fretting etc... without wood or glue joint failure?
Jeff,
thanks for the followup of your observations. I should mention my "excessively strained" observation was of a test specimen, newly constructed and strained to complete failure, well beyond normal design stresses. As for the glass fibers failing in your repair bows. I have no doubt that long term usage at some stress near the working limit will cause some breakdown in the glass fibers. Also, if you take a strand of glass from new e-glass roving and dissolve away the sizing, it can be easily seen what appears as a "continuous" fiber is in fact only a collection of shorter strands.
Is the belly a drag on the effort of the back? Does the belly need to push harder? Would that be an improvement in performance? Or, is it better to emphasize more tension in the back?
I will venture a wild ass guess that if there were more drag or hysteresis in compression or tension, it would have been confirmed by now. The technology of fiberglass has not changed all that much in 70 years. Having all areas of the working limb, front and back, working as close to the limits you choose in your design, would seem to be the way to optimize.
Post by: mmattockx on January 30, 2021, 04:02:12 PM
Do the materials we use store more energy and return to their resting position faster, when in tension or compression?
For linear elastic materials they will store the same energy either way. I don't know if our composite lams behave close enough to linear elastic or not for that to work. Gordon's published info says their lams have the same elastic modulus in both tension and compression, which indicates they are very close to linear elastic behaviour.
Also worth noting is that Gordon's lists the tensile strength of the ULS lams as 152,000psi and the compressive strength as 119,000psi. The UL lams have a tensile strength of 152,000psi and a compressive strength of 111,000psi.
Good question on the rebound back to shape.
Do we try to establish the position of the neutral zone or do we leave it to destiny? :pray:
The neutral axis is easily calculated for any given cross section shape. You certainly don't need to know what it is to build a bow, but understanding its effects and controlling where it is located are useful things when trying to maximize performance.
Mark
Post by: Shredd on January 30, 2021, 07:40:31 PM
Note to self..
Roy, do not click on this thread again:)
:laughing: :biglaugh: :laughing: :biglaugh: :laughing:
Post by: Shredd on January 30, 2021, 07:44:22 PM
Why doesn’t someone build a relatively simple bow. Perfectly flat limbs, with a perfectly centered riser. .040 glass one side, .030 other. Cut string grooves so bow can be strung and drawn either direction.
And before anyone says it........I have time to think about, not to do it.
First sensible thing I heard all day... There yah go Longcruise... yah got all your answers right there...
Post by: Roy from Pa on January 30, 2021, 08:47:44 PM
:wavey:
Post by: Shredd on January 30, 2021, 09:49:02 PM
I am not trying to be cocky, a know it all or arrogant I am simply stating what I have been through, what I know and sharing with you what direction or directions I would take... And / or to give some advice when searching for high performance...
I busted my butt for about three years or more working toward making a high performance bow... In that period of time I made about 40 to 50 bows... Each bow went through a bunch of tests... The first test was vertical stability the second was speed... If a bow did not shoot over 182 or over I threw it to the side and made another one... At one time I had a pile of about 20 or more unfinished bows... All good bows but in my opinion slow... I experimented with split limb, prestressed and about 4 or 5 other exotic applications... I heard from someone that Ken Rohloff had a big pile of bow forms behind his workshop... All not up to par to his standards for a high performance bow... At the WTT contest he got 199 fps @ 10 gpp @ 28" with a 6" brace with carbon limbs and was a hot rod, which I am assuming that it had very narrow limbs ( maybe not suitable for constant and every day use).... My hat goes off to this guy... That is an amazing achievement... My fastest bow shot 196 fps @ 10 gpp @ 28" @ 6" brace and is a basic maple/ fiberglass lay up and with standard width (everyday use limbs)... I would have loved to be at that contest and talked with all those guys...
The reason I am sharing this is that there is no magic bullet... I see you all going off on these tangents talking about carbon fiber, numbers, stresses and such but not one time did I ever think I heard the word radius when talking about limb design... In my world it is all about radius's and angles plus a few other things... I feel as though I just scratched the surface in understanding how a bow works and what it takes to suck performance out of one... It takes a lot of work and hours upon hours of testing and experimentation unless you happen to get very lucky and stumble across a good design with a perfect taper rate....
So there is no magic bullet... If you have a sub par design and you throw some carbon on it or try some other exotic technique you may gain 2 to 3 fps which in my book is crap... Now you got and expensive bow with carbon shooting 178 fps instead of 175 fps... If you have an optimal design and cannot go any further with geometry then is the time to pull out the tricks with carbon fiber and such... Until then it's just talk and a waste of good $$ When you can do better with maple and f/g... It is ok and nice to understand how carbon and other things work but I think the real effort needs to go towards design and I am seeing very few on here making the efforts of making 15 to 20 bows to refine a single bow design's performance...
So the bottom line is if you all want to be real about this performance thing and want to work as a team to reach higher performance I would start comparing notes on geometry first until you cannot go any further in performance before you start discussing carbon and theories and such...
This is just my opinion...
After I reached a certain level I now see a little bit of the light on performance... (I feel years of hard work away from where I would like to be)... I now shed a little of that light on you... If you spend a lot of time researching and applying exotic applications to a sub par design I feel that you are stumbling in the dark... Although it probably does feel good talking about the Magic Bullet and having some kinda hope that an application of such an exotic is gonna take your 170 to 175 fps bow and bring it up to 190 fps... It's not happening...
Post by: Buemaker on January 31, 2021, 03:36:25 AM
https://www.thetradlab.com/reddbowrecurve
Post by: Roy from Pa on January 31, 2021, 06:11:04 AM
I wonder if the native Americans sat around the tee pee bickering about who had the fastest bow?:)
But I understand where ya all are coming from.
Post by: Shredd on January 31, 2021, 08:06:02 AM
This speed thing sometimes gets a bad rap... But some of the same guys talking chit about speed are shooting 65# bows... I would like them to explain that being a 40# bow can take down most game in the US... The only people I hear bickering or complaining about speed are the people that shoot slower bows... Maybe they feel they have to prove something...
I enjoy the challenge of making a fast bow just as much as you enjoy the challenge of making a wood one... We don't all have to be an Indian or think like one to get the pleasures of how we want to make a bow...
There are advantages to a fast bow... Smoother draw and less stacking run hand in hand with a fast bow and you can't beat a flatter trajectory...
I guess the bottom line is some like plinking with a 22 lr and some like a 223... It's no really big deal... It's what you like and you choose... But don't get down on other people for having their fun...
Hey maybe dem Indians making stick bows bitched about the ones using horn and sinew... :laughing:
Post by: Shredd on January 31, 2021, 08:09:15 AM
I have not sent my new design to Tradlab yet because it is a new design with only 5 bows made so far... I want to tweak it to hit 195 or higher... I am shooting to be first overall and with a simple maple / f/g layup... May have to go to carbon to get those last few fps... :dunno:
I am not trying to be a jerk or wanting to put a damper on these high tech discussions, I like the discussions to some degree but there comes a point where you draw the line between talk and actual real testing... That's where real progress is made... I am just trying to push some of you in the right direction... I constantly hear talk but I am not seeing any bows... Bows with numbers pushing the limits... I am not seeing any real numbers that matter, like string tension percentages, dfc's, arrow speeds, angles, radius's, ect....
I hope some of this hits home with you all and gets you in the right direction towards performance, if that's what you are really seeking...
Wishing the best for you all...
Post by: Roy from Pa on January 31, 2021, 08:14:30 AM
Relax Rich, I said I understand guys wanting faster bows.
It's just not my thing, I'm happy for you that's it's your thing.
I tried making one glass bow, it wasn't the same as carving one out of Osage and boo, so I didn't like it.
The only thing those fast bows do is miss faster:)
:wavey:
Post by: Shredd on January 31, 2021, 08:31:07 AM
By the way I would love to have one of your bows one day... Maybe we can do a trade off if you think you can handle the heat... :thumbsup: :biglaugh:
A fast bow with a very flat trajectory is least likely to miss... :thumbsup: :laughing:
Post by: Roy from Pa on January 31, 2021, 08:35:21 AM
:thumbsup:
Post by: Shredd on January 31, 2021, 08:42:44 AM
Post by: Roy from Pa on January 31, 2021, 08:45:50 AM
Post by: kennym on January 31, 2021, 08:53:07 AM
Post by: Roy from Pa on January 31, 2021, 08:57:31 AM
Post by: Shredd on January 31, 2021, 08:58:43 AM
Post by: Flem on January 31, 2021, 09:38:10 AM
"Do the materials we use store more energy and return to their resting position faster, when in tension or compression?
For linear elastic materials they will store the same energy either way. I don't know if our composite lams behave close enough to linear elastic or not for that to work. Gordon's published info says their lams have the same elastic modulus in both tension and compression, which indicates they are very close to linear elastic behaviour.
Also worth noting is that Gordon's lists the tensile strength of the ULS lams as 152,000psi and the compressive strength as 119,000psi. The UL lams have a tensile strength of 152,000psi and a compressive strength of 111,000psi.
Good question on the rebound back to shape."
The original question was not material specific. What about the other components? We are not building exclusively fiberglass bows. The downside of linear thinking, is all the important factors left in the wake of a myopic goal.
"Do we try to establish the position of the neutral zone or do we leave it to destiny? :pray:
The neutral axis is easily calculated for any given cross section shape. You certainly don't need to know what it is to build a bow, but understanding its effects and controlling where it is located are useful things when trying to maximize performance."
That is called tongue in cheek (joke)
Post by: Roy from Pa on January 31, 2021, 09:43:56 AM
Post by: Mad Max on January 31, 2021, 09:49:10 AM
And some people like Horse and buggy racing, Not me.
Nice work shredd :thumbsup:
Post by: Flem on January 31, 2021, 09:51:31 AM
Has anyone every talked to a neutral plane and asked it what it thought?
It's indifferent, happy to go with the flow. And since its intangible, hard to pin down.
Post by: Roy from Pa on January 31, 2021, 10:03:09 AM
Think I'm off the PC for a while here.
Gonna go put a fire in the bow shop wood burner and get it warm out there and clean up the basement after painting a wall.
28 degrees and snowing here, supposed to snow the next 3 days cause it's January in Pa.
And I love it just like it is:)
Post by: Mad Max on January 31, 2021, 10:10:46 AM
I did, I told it I was going to stretch it and glue 1 piece of glass to it with alot of reflex.
(https://i.imgur.com/rRcQIC8.jpg)
(https://i.imgur.com/k2EsBKN.jpg)
(https://i.imgur.com/84AZ7ot.jpg)
Now the neutral zone is compressed
Then I told it to get on that form so I could glue the second glass to it, but it jumped off and fell in the floor, true story
(https://i.imgur.com/f7m2uHG.jpg)
when I pulled it off the form it sprung in, not out.
this is how much it sprung in
(https://i.imgur.com/iOkaAdw.jpg)
Something to think about :bigsmyl:
What do you think this would do?????????????????????
Post by: Stagmitis on January 31, 2021, 10:39:19 AM
Post by: Roy from Pa on January 31, 2021, 10:42:27 AM
Post by: Mad Max on January 31, 2021, 10:47:03 AM
Max if you cut that in half and used green glass Will Ferrell would be proud :biglaugh:
????????????????????? :dunno:
Post by: Flem on January 31, 2021, 10:54:56 AM
Like Switzerland. Just hope I don't have to take the Autobahn to get there :bigsmyl:
Post by: Mad Max on January 31, 2021, 10:57:45 AM
Post by: Flem on January 31, 2021, 11:19:47 AM
Post by: Stagmitis on January 31, 2021, 11:22:37 AM
Post by: Shredd on January 31, 2021, 11:28:55 AM
Post by: Mad Max on January 31, 2021, 11:39:43 AM
Post by: Stagmitis on January 31, 2021, 12:58:44 PM
Shredd said:
So the bottom line is if you all want to be real about this performance thing and want to work as a team to reach higher performance I would start comparing notes on geometry first until you cannot go any further in performance before you start discussing carbon and theories and such
How true: Kinda like putting a bandaid on a cut that needs stitches.
Post by: EvilDogBeast on January 31, 2021, 02:35:06 PM
I think the intention of this thread was simply to theorycraft better performance through design. Discussion on design and materials can both lead us to better performance and both should be discussed. At the end of the day, this is really just to exercise our brains and may or may not lead to a breakthrough from one of our bowyers.
On a side note, I am not quite sure why every one of these discussions always has to break down into, "stop talking and go build something", or "graphite is the devil". Is it really such a crime to think something can outperform fiberglass? Composite industries have moved on to more modern materials, why can't we? Does it really detract anything from traditional bows to use graphite or some other advanced composite? There is a reason fifth and sixth generation fighters are utilizing advanced composites. They are objectively superior in every quality.
TL;DR: We should encourage thinking outside the box rather than smashing those thoughts back into the box.
Post by: Mad Max on January 31, 2021, 02:46:19 PM
When Carbon fiber came on the market everyone wanted it .
If it was that good, more Bowyers would be using it or selling it.
Most don't want it and it cost to much.
My 2 cents
Post by: Roy from Pa on January 31, 2021, 03:09:42 PM
That's the title of this thread:)
:wavey:
Post by: Shredd on January 31, 2021, 04:35:28 PM
Bvas had a great idea... Totally suited for this thread and somehow it went over everybody's head, no one even tried to discuss it or made a comment on it... If I saw this two or three years ago I would have been all over this... I am still itching to do it, but I just got about 15 other experiments that I would like to try in front of this one....
As for carbon fiber you gotta love the stuff... It is lightweight, stiff and ridgid... And in my book that is what is to be used for, something that you want lightweight, stiff and ridgid... You don't use a screwdriver when you need a wrench... ;) Bows are not ridgid when you use carbon fiber for the whole limb I think you start going in the wrong direction... I here of lots of problems with carbon fiber and failures happening... The stuff stresses easier than glass and is brittle... It really wants to be stiff and ridgid... I just proved to you in my post that you don't need carbon for a fast bow... Now take that carbon fiber and apply it to the last 8 to10" of the the limb and now you may have got something... That's where you want the limb stiff, ridgid and light weight... The trick is pulling that off and whether it will handle the shock and not seperate from the glass... Think of the ugly stick fishing rod but in reverse...
I love these tech threads I learn something from everyone of them but it seems sometimes you guys get talking in circles and I am not seeing anyone building bows and testing these theories... I thought this was a bow building sight... It would be great if once in a while somebody ran with one of these ideas and built a bow, and shared all the great info that you learned from the experience...
In my book, what is on paper usually does not match up with real life...
You guys keep talking this tech stuff all you want... I enjoy it to a degree and I usually learn something from it... But after two or three years if no one builds a bow applying some of these tech talk techniques and gets a bow shooting over 183 to 185 fps it seems that something is amiss here... You can't shoot a bow that is on paper... I would love to see one of you all build a high tech bow breaking 190 fps... I say raise the bar...
YOU CAN DO IT...!!! Just give it a try... I'll help you where I can... Call anytime...
Post by: EvilDogBeast on January 31, 2021, 04:59:17 PM
Post by: Shredd on January 31, 2021, 05:14:28 PM
Are you gonna try and make one with glass at the same poundage also to compare the two??
Post by: Flem on January 31, 2021, 05:26:44 PM
Prefaced with, I am not trying to be rude or attack anyone. This is simply something for everyone to think about.
I think the intention of this thread was simply to theorycraft better performance through design. Discussion on design and materials can both lead us to better performance and both should be discussed. At the end of the day, this is really just to exercise our brains and may or may not lead to a breakthrough from one of our bowyers.
On a side note, I am not quite sure why every one of these discussions always has to break down into, "stop talking and go build something", or "graphite is the devil". Is it really such a crime to think something can outperform fiberglass? Composite industries have moved on to more modern materials, why can't we? Does it really detract anything from traditional bows to use graphite or some other advanced composite? There is a reason fifth and sixth generation fighters are utilizing advanced composites. They are objectively superior in every quality.
TL;DR: We should encourage thinking outside the box rather than smashing those thoughts back into the box.
:thumbsup:
We have not even talked about Carbon/UHMWPE hybrid composites.
Is that pre-preg unidirectional? Whats the cure temp for your material?
Post by: EvilDogBeast on January 31, 2021, 05:46:21 PM
Post by: Flem on January 31, 2021, 06:57:35 PM
Post by: EvilDogBeast on January 31, 2021, 07:18:56 PM
Edit: The beauty of our pre-preg is it doesn't cure until heated.
Post by: EvilDogBeast on January 31, 2021, 07:24:11 PM
Post by: Flem on January 31, 2021, 09:29:05 PM
Either way I'm envious!
Post by: Longcruise on January 31, 2021, 09:39:14 PM
I think I am going to relocate my bow building to someplace where they know about neutral...
Like Switzerland. Just hope I don't have to take the Autobahn to get there :bigsmyl:
Yeah, all their planes are neutral. :)
Post by: EvilDogBeast on January 31, 2021, 09:44:26 PM
Post by: Longcruise on February 01, 2021, 03:46:22 PM
Post by: Roy from Pa on February 01, 2021, 03:50:55 PM
Since life forms are carbon based, doesn't a osage self bow have a higher percentage of carbon than a glass bow? :goldtooth:
Just don't you worry about that ole timer...
:wavey: :laughing:
Post by: Longcruise on February 01, 2021, 03:53:07 PM
Since life forms are carbon based, doesn't a osage self bow have a higher percentage of carbon than a glass bow? :goldtooth:
Just don't you worry about that ole timer...
:wavey: :laughing:
Just got outta bed. Kept me awake till 5:30 AM. :)
Post by: Flem on February 02, 2021, 12:02:34 PM
So you cure it first, then incorporate it into a lay-up?
:banghead:
Post by: EvilDogBeast on February 02, 2021, 01:51:29 PM
It really boils down to an ease-of-maintenance type thing. The only downside to pre-curing is you then need to use a separate adhesive to bond it to something else.
I really enjoy composite work as you may have gathered. Feel free to ask whatever questions you may have. If you want to see pictures of the non-bowyer related work we do here, PM me your number and I'll text some your way.
Post by: Longcruise on February 02, 2021, 01:55:20 PM
Chris, I have been trying to figure out how to incorporate pre-preg into a lay-up. Then I re-read your post.
So you cure it first, then incorporate it into a lay-up?
:banghead:
What would be the advantage of prepreg over hexcell?
Post by: williwaw on February 03, 2021, 12:50:06 AM
Here's a question that I've been trying to muddle through on my own. I'm not going to throw my opinion out there because I'm more interested in the opinions of our esteemed conclave of Bowyers.
This is in regard to glass/wood lam bows.
Which side of the bow should be optimized for to obtain highest performance? IOW is it better to have more tension than compression or vice versa. Or, should the two be in perfect balance?
What do you think and why?
upon giving the original question some thought and research, perhaps one should minimize the amount of glass used, ie as little as necessary, which might be a different amount for the face or back.
https://www.tradgang.com/tgsmf/index.php?topic=156814.msg2706768#msg2706768 (https://www.tradgang.com/tgsmf/index.php?topic=156814.msg2706768#msg2706768)
Quote
I asked the same question to Bingham Projects a little while ago because I was unsure about it and am planning to build a glass lam recurve.
Here is the response I got from them copy/pasted:
"Thanks for your e-mail. For a given limb thickness, there is no difference in draw weight with different thickness of glass. If the total limb thickness is the same, the weight will be the same. The best way to most closely hit draw weights is to use a micrometer to measure your limb thickness. If you measure to .001”, then your weights will be pretty consistent. It will never be 100%. There are always those bows that surprise you but the vast majority will be pretty consistent."
https://www.tradgang.com/tgsmf/index.php?topic=147846.msg2573501#msg2573501
Post by: Mad Max on February 03, 2021, 08:55:57 AM
Why doesn’t someone build a relatively simple bow. Perfectly flat limbs, with a perfectly centered riser. .040 glass one side, .030 other. Cut string grooves so bow can be strung and drawn either direction.
And before anyone says it........I have time to think about, not to do it.
Bvas is the smartest one here :jumper: :jumper: :jumper: :jumper: :jumper: :jumper: :jumper: :jumper: :jumper: :jumper: :jumper: :jumper:
Post by: Roy from Pa on February 03, 2021, 09:11:43 AM
LMFAO
:knothead:
:wavey:
Post by: Flem on February 03, 2021, 10:31:37 AM
Chris, I have been trying to figure out how to incorporate pre-preg into a lay-up. Then I re-read your post.
So you cure it first, then incorporate it into a lay-up?
:banghead:
What would be the advantage of prepreg over hexcell?
Mike are you referring to Hexel honeycomb? Maybe Chris can shed some light. I don't know about pre-preg because I don't have the facilities to pressure cure the stuff at elevated temperatures for hours.
Post by: mmattockx on February 03, 2021, 11:02:04 AM
upon giving the original question some thought and research, perhaps one should minimize the amount of glass used, ie as little as necessary, which might be a different amount for the face or back.
Yes! This is why I asked about using different lam thickness a while back. The back should need less glass to carry the loads than the belly and you always want to minimize the limb weight. Since glass is approximately twice the weight of wood, using the smallest amount of it possible seems like a very good idea.
One other thing to consider (Alan Case has mentioned this) is the strains on the core wood. Thicker glass lowers the strain on the core, while thinner glass increases it. So going too thin on the glass can cause problems with set.
Like almost every real world design problem, there are a bunch of competing factors to balance off and a careful compromise is required to maximize performance with longevity.
Brads suggestion is a good one, but it only addresses a small segment of the question.
I would like someone to explain what they expect that experimental bow to demonstrate? Unless it is heavily strained to near failure I wouldn't expect it to shoot any differently either way. I'm willing to make one but it will be a while before I am set up to do that.
Do we really need a composite with 120,000psi compressive strength when a couple of classic woods like Osage and Yew, proven over thousands of years, come in at around 1/10 of that strength?
Do we NEED it? Of course not. Yew, osage, ipe and the various junipers are all great bow woods that perform extremely well. But glass bows can be strained to significantly higher levels than any wood can be. This allows different limb profiles and a bit higher performance than wood bows with greater consistency and reliability and less tillering skill required to get there.
Mark
Post by: EvilDogBeast on February 03, 2021, 11:16:41 AM
What would be the advantage of prepreg over hexcell?
Sorry I missed this yesterday. I'm not sure what hexcell is. The career field is littered with trade names, do you have a picture or a description of what it is?
Post by: Flem on February 03, 2021, 11:20:46 AM
"Yes! This is why I asked about using different lam thickness a while back. The back should need less glass to carry the loads than the belly and you always want to minimize the limb weight. Since glass is approximately twice the weight of wood, using the smallest amount of it possible seems like a very good idea."
"Do we NEED it? Of course not. Yew, osage, ipe and the various junipers are all great bow woods that perform extremely well. But glass bows can be strained to significantly higher levels than any wood can be. This allows different limb profiles and a bit higher performance than wood bows with greater consistency and reliability and less tillering skill required to get there."
Mixed messages
Post by: mmattockx on February 03, 2021, 11:40:16 AM
Mixed messages
Can you explain what is mixed?
Mark
Post by: Flem on February 03, 2021, 11:51:04 AM
Post by: mmattockx on February 03, 2021, 12:48:21 PM
Sure, so if using the "smallest amount of it (glass) possible" equates to no more than necessary, then the excessive strain which can be sustained is rendered moot.
Hmmm, how to explain?
Many glass bows are very overbuilt, that would be where using less glass would have a benefit. It would be optimizing the amount of glass needed for that particular design.
On the other side of things, you can design far more extreme bows using glass than with wood, which is where the ability to survive higher strains can be used.
Mark
Post by: Longcruise on February 03, 2021, 01:08:03 PM
Mike are you referring to Hexel honeycomb? Maybe Chris can shed some light. I don't know about pre-preg because I don't have the facilities to pressure cure the stuff at elevated temperatures for hours.
No I was referring to the 45/45 weave that you illustrated from envision composites.
Managing set in wood/glass ASLs is what got me thinking about the "face/back" question. With thick cores, I think the use of glass thicknesses that are are appropriate for given bow weights in r/d and rc bows is reducing the glass wood ratio to a point where set becomes inevitable. You will see it on many if not all "hill style" bows. Sometimes it's a smooth arc resulting in a string follow effect and often it's abrupt in the face area.
It's not that they aren't good bows, but any time the bow gives up preload to set it results in a loss of efficiency.
I have an unfinished bow on the bench in which the belly glass is enhanced for a kinda unscientific test of the concept. We'll see, but about the only thing that can be actually measured with certainty is the change in profile.
Post by: Mad Max on February 03, 2021, 02:31:23 PM
Remind me not to click on this topic again :laughing:
Post by: Roy from Pa on February 03, 2021, 02:49:02 PM
Post by: EvilDogBeast on February 03, 2021, 04:29:48 PM
Managing set in wood/glass ASLs is what got me thinking about the "face/back" question. With thick cores, I think the use of glass thicknesses that are are appropriate for given bow weights in r/d and rc bows is reducing the glass wood ratio to a point where set becomes inevitable. You will see it on many if not all "hill style" bows. Sometimes it's a smooth arc resulting in a string follow effect and often it's abrupt in the face area.
Based on this information, the real answer we are looking for is probably thicker glass or graphite on the belly to prevent the high compression. In a nod to Shredd, perhaps it could also be attacked from a design perspective by designing a trapezoidal limb to mimic a D-shaped cross-section?
Post by: EvilDogBeast on February 03, 2021, 04:43:22 PM
I am not very familiar with the construction of ASL's, could I get the stack dimensions for one you know took set please?
Post by: Shredd on February 03, 2021, 05:23:56 PM
Since you are on the subject of limb weight, I have always wondered how much weight you would have to lose in the limb to gain 5 fps... Do you guys have any idea?? Is there a way of calculating that??
Well I figure if I can't get into this conversation maybe I use use your brains to help me out calculating this this problem...
Post by: EvilDogBeast on February 03, 2021, 05:43:32 PM
My apologies for being a jerk. I in no way meant you shouldn't be included in this conversation. Please excuse me if I came across that way. I think you bring a lot to the table and hope you jump back into the fray.
Post by: Longcruise on February 03, 2021, 05:49:18 PM
Managing set in wood/glass ASLs is what got me thinking about the "face/back" question. With thick cores, I think the use of glass thicknesses that are are appropriate for given bow weights in r/d and rc bows is reducing the glass wood ratio to a point where set becomes inevitable. You will see it on many if not all "hill style" bows. Sometimes it's a smooth arc resulting in a string follow effect and often it's abrupt in the face area.
Based on this information, the real answer we are looking for is probably thicker glass or graphite on the belly to prevent the high compression. In a nod to Shredd, perhaps it could also be attacked from a design perspective by designing a trapezoidal limb to mimic a D-shaped cross-section?
Yes, trapping the back would reduce the tension and give the some relief to the belly.
Another tbing I'm thinking is increased thickness taper with a stout and fairly long tip wedge. There migh be unforseen (at least by me) consequences for that one. Also, there's a point where an ASL can start getting sluggish when there is too much taper allowing the limbs to come around to far. It may not stack due to length NtN but the limbs still have a longer hike to brace.
I'm also looking at using stabilcore under the face glass. Not for stability but to reinforce the glass. I also have some carbon weave that is planned to stabilize some sorta radical hooks on a recurve that might work.
Lastly, there is just putting more glass on the face. Below is my first attempt at that. This is a 68" ASL with 1 1/8" fades and. 042 back glass and .070 belly side. The stack is. 412 so the glass ratio is 27%. Still under construction so no testing yet.
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Post by: Longcruise on February 03, 2021, 05:55:33 PM
*Prevent high compression from damaging the core.
I am not very familiar with the construction of ASL's, could I get the stack dimensions for one you know took set please?
This one didn't take too much set and possibly because it had a .005 taper rate but it did take some.
69" NtN
15" riser
Stack .473
.040 glass front and back
Glass ratio 16.9%
Post by: williwaw on February 03, 2021, 05:59:26 PM
Just a heads up... There is a topic on the Bowyers Corner on FB right now with carbon fiber... A few of the guys that have worked with it are on there... Might be worth a look for you all...
Since you are on the subject of limb weight, I have always wondered how much weight you would have to lose in the limb to gain 5 fps... Do you guys have any idea?? Is there a way of calculating that??
Well I figure if I can't get into this conversation maybe I use use your brains to help me out calculating this this problem...
what's FB? :dunno:
why dont you tape something around your limbs until you loose 5 fps? the weight might not be good for calculating a speed change for all possible arrow weights, but could be close enough at your particular gpp.
Post by: williwaw on February 03, 2021, 06:06:26 PM
*Prevent high compression from damaging the core.
I am not very familiar with the construction of ASL's, could I get the stack dimensions for one you know took set please?
This one didn't take too much set and possibly because it had a .005 taper rate but it did take some.
69" NtN
15" riser
Stack .473
.040 glass front and back
Glass ratio 16.9%
I guess I am in the same boat with EDB, that is not knowing much about ASL's. Can you post a full draw pic of it on the tiller tree?
thanks
Post by: Longcruise on February 03, 2021, 06:17:19 PM
Just a heads up... There is a topic on the Bowyers Corner on FB right now with carbon fiber... A few of the guys that have worked with it are on there... Might be worth a look for you all...
Since you are on the subject of limb weight, I have always wondered how much weight you would have to lose in the limb to gain 5 fps... Do you guys have any idea?? Is there a way of calculating that??
Well I figure if I can't get into this conversation maybe I use use your brains to help me out calculating this this problem...
I'm not much on calculating. That's for smarter people than me and some of them are right here on this topic. I include yourself in that group. If I'm wrong, you have tricked me with your persistance. :biglaugh:
However, I did do an experiment with weights on the limb tips of a 66" ASL. The results were surprising to me. I thought my added weights would have much greater effect on the arrow speed.
Something to think about here though is that first of all the results of adding weight to the tips of limbs is probably going to vary a whole lot with design. I think if this were done with a high performance recurve or a flight bow the effects would be way more pronounced. The other thing is that the weight of the whole shot moving forward has a different effect on performance depending on the location of the weight. If we start at the nocking point of the string and progress to the limb tip and then down the limb to the fades, I'm pretty sure the addition of weight will have a decreasing effect on performance (speed) as that progression is followed. Adding weight to the limb two inches beyond the fades might not even be noticeable.
Anyway, I added equal amounts of weight to the tips of this bow and chronographed it with increasing weight added to the tips.
There's a few pictures here too. Copied and pasted from the notes I took the day of the experiment.
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Bow:
ASL 66” NTN
Slight string follow
44# @ 28”
This bow has no tip overlays and pin nocks
Weight was progressively added to both bow tips and the arrow speed checked with a chronograph. The weight was added by taping quarters to the tips of the bow. Each quarter weighs approx 87 grains.
All shots are with the same arrow. The arrow weight is about 625 grains. I didn't weigh the specific arrow used but that is in the range of that set of arrows.
First, four shots with no weight to establish a base line
141.8
139.9
137.3
139.5
Avg 139.6
Next four shots were with one quarter taped to each tip of the bow, so 87 grains of additional tip weight.
137.2
139.8
139.6
138.2
Avg 138.2 Equals 1.4 fps slower than unweighted tips
That resulted in such a minor speed difference that I went next to three quarters on each tip for a total of 261 grains of added weight.
138.7
137.9
138.7
137.8
Avg 138.2 This is identical to the speed with only one quarter on each tip. This is probably explained by the statistical margin of error.
The next increment was four quarters on each tip for a total of 348 grains of added weight on each tip.
137.0
135.5
135.8
137.0
Avg 136.3 Now, we have arrived at a speed loss of 3.3 fps.
And finally, six quarters were added to each bow tip for a total weight of 522 grains of added weight on each tip. This is in excess of one ounce per tip with one ounce equaling 437.5 grains.
134.1
130.4
134.4
135.6
Avg 133.6 this is a total of 6 fps loss of speed with the 522 grains added to each tip.
Post by: williwaw on February 03, 2021, 06:20:10 PM
Do we really need a composite with 120,000psi compressive strength when a couple of classic woods like Osage and Yew, proven over thousands of years, come in at around 1/10 of that strength?
I think osage and yew are proven superior to other bow woods because of their elasticity. Of course, glass is better still in that regard, but like you mention, is too strong. A solid glass bow, if I remember correctly, build to typical draw weights in normal bow ntn lengths, could be built a 1/2" wide, maybe having stability issues caused by being too narrow. Consider a materiel with the stiffness of something like ipe, yielding a bow of quite pleasing widths and thicknesses.
Post by: williwaw on February 03, 2021, 06:56:13 PM
Do the materials we use store more energy and return to their resting position faster, when in tension or compression?
For linear elastic materials they will store the same energy either way. I don't know if our composite lams behave close enough to linear elastic or not for that to work. Gordon's published info says their lams have the same elastic modulus in both tension and compression, which indicates they are very close to linear elastic behaviour.
Also worth noting is that Gordon's lists the tensile strength of the ULS lams as 152,000psi and the compressive strength as 119,000psi. The UL lams have a tensile strength of 152,000psi and a compressive strength of 111,000psi.
the AIAA generic data posted in the table at
https://www.tradgang.com/tgsmf/index.php?topic=174583.msg2947233#msg2947233 (https://www.tradgang.com/tgsmf/index.php?topic=174583.msg2947233#msg2947233)
shows similar tensile values, but significantly lower compressive values. (compressive being only 56% of tensile). And a compressive MOE at 80% of tensile.
The above cited strength values being max of course. Have you run across any working stress recommendations for unidirectional gordon composites that could establish a reasonable safety margin for bow building?
Post by: Stagmitis on February 03, 2021, 09:11:27 PM
Post by: Bvas on February 03, 2021, 10:20:21 PM
Hey longcruise thats an awesome test!!! Momentum factor?I have wondered about this test ever since Mike posted it. Could the additional tip weights stop/reduce the string travel beyond brace?
Post by: Longcruise on February 04, 2021, 09:39:44 AM
Bvas, i think i get what you are saying but.....I'm not sure.
Post by: Shredd on February 04, 2021, 11:23:07 AM
Rich,
My apologies for being a jerk. I in no way meant you shouldn't be included in this conversation. Please excuse me if I came across that way. I think you bring a lot to the table and hope you jump back into the fray.
I must have passed over that post... :) I did not take anything that way... What I meant by not into the conversation I meant that I (personally) am not into it.... Meaning it's not my bag... But it does not mean that I can't sit on the sidelines and maybe learn something from you guys... We all have something to offer and I figure that since these guys are good with numbers and such that they could figure out some kind of formula...
Post by: Shredd on February 04, 2021, 12:15:03 PM
Willi... FB stands for Face Book... Carbon failure and comments from the experts... Good stuff to learn if you are into carbon...
Cruiser... Persistance, Yes... A little bit of smarts, but mostly pure hard headed stubbornness and the fact that there were guys out there building bows over 180 fps and my attitude was, why can't I...
Cruiser... Stag had a big point... Testing at 9 to 10 gpp... I am sure there is a curve here just like most things that are dynamic... A 44# bow with a 625 gr. arrow you are pretty much bottoming out the performance of that bow... Meaning you probably won't see as much of a change in arrow speeds between two different weight arrows as you would with a lot lighter arrows...
If memory serves me correctly I did the same experiment with pennies... The bow was probably shooting around 180 fps and I was probably shooting 10 gpp as I usually do and 2 pennys would cost you 5 fps... Big difference from your experiment... But I don't remember if it was two pennys on one limb or one penny on each limb... I might have written it down somewhere and the experiment is on the trad archer forum if anyone wants to look it up...
Just as there was a curve in this coin experiment there probably is also a curve in adding weight to the limbs vs removing weight... And like you said this weight is only concentrated at the tips and not through out the limb... Adding weight is easy but taking it off is more entailed and taking the weight off may not be the same results as adding it on... We can possibly get a guesstimate from the coin thing but that's about it...
Post by: Shredd on February 04, 2021, 12:31:43 PM
Me - I asked you the other day how many fps does Carbon fiber add to a bow... I believe you said around 5 fps... I am assuming that is with well designed and efficient limbs that are already shooting 185 fps with glass... What if you add CF to a bow that shoots 170 fps?? Will you still get 5 fps or more like 2 to 3 fps faster?? Do you owe the speed to higher stress of the carbon or the weight loss in the limb??? Or a combo of both...
Bowyer - The 5fps is the feeling you get after lots of playing. Lots of feedback, and changing many designs.
Post by: Bowjunkie on February 04, 2021, 12:38:45 PM
Post by: Shredd on February 04, 2021, 12:52:24 PM
At least that's what it sounds like to me because this guy would not just haphazardly say "the feeling you get" meaning he's not sure of himself... This feeling only comes with experience and doing much research...
Kama'aina - Hawaiian - "One who knows"...
Post by: williwaw on February 05, 2021, 03:03:51 AM
Managing set in wood/glass ASLs is what got me thinking about the "face/back" question. With thick cores, I think the use of glass thicknesses that are are appropriate for given bow weights in r/d and rc bows is reducing the glass wood ratio to a point where set becomes inevitable. You will see it on many if not all "hill style" bows. Sometimes it's a smooth arc resulting in a string follow effect and often it's abrupt in the face area.
Based on this information, the real answer we are looking for is probably thicker glass or graphite on the belly to prevent the high compression. In a nod to Shredd, perhaps it could also be attacked from a design perspective by designing a trapezoidal limb to mimic a D-shaped cross-section?
Set could be alleviated by having the proper width taper for the chosen thickness taper.
Post by: Flem on February 05, 2021, 08:15:24 AM
Mike, are you going to pre-impregnate and cook your bi-axial fabric before lay-up?
Post by: Roy from Pa on February 05, 2021, 08:21:34 AM
Some of us weirdos actually design/build our bows so they have a tiny bit of string follow :say what:
A little string follow yields a quiet smooth shooting bow, especially with a long bow!
Post by: Longcruise on February 05, 2021, 09:18:57 AM
Managing set in wood/glass ASLs is what got me thinking about the "face/back" question. With thick cores, I think the use of glass thicknesses that are are appropriate for given bow weights in r/d and rc bows is reducing the glass wood ratio to a point where set becomes inevitable. You will see it on many if not all "hill style" bows. Sometimes it's a smooth arc resulting in a string follow effect and often it's abrupt in the face area.
Based on this information, the real answer we are looking for is probably thicker glass or graphite on the belly to prevent the high compression. In a nod to Shredd, perhaps it could also be attacked from a design perspective by designing a trapezoidal limb to mimic a D-shaped cross-section?
Set could be alleviated by having the proper width taper for the chosen thickness taper.
Yes, that is an important consideration.
Post by: Longcruise on February 05, 2021, 09:24:53 AM
Some of us weirdos actually design/build our bows so they have a tiny bit of string follow :saywhat:
Mike, are you going to pre-impregnate and cook your bi-axial fabric before lay-up?
I'm thinking about that and can't quite make up my mind. My small test hasn't been examined yet but so far I think it can be layed up the same way as stabilcore if the glue is thin enough.
I squeezed the test strip together in a foodsaver bag and left it on a floor heat vent yesterday afternoon. I'll give it a few more hours. :)
Post by: Longcruise on February 05, 2021, 09:33:57 AM
Some of us weirdos actually design/build our bows so they have a tiny bit of string follow :say what:
A little string follow yields a quiet smooth shooting bow, especially with a long bow!
Won't argue with that but OTOH, if I want string follow I'd rather put it there intentionally.
This playing with the bi ax is not primarily to deal with the "face back" question. It's just come up coincidentally as a possible approach. The bi-ax is going into the swap bow for stability since, so far it has some serious hooks....... Unless I decide to completely change to another style. :)
Post by: Longcruise on February 05, 2021, 11:25:31 AM
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Post by: EvilDogBeast on February 05, 2021, 11:37:02 AM
Post by: Longcruise on February 05, 2021, 12:46:38 PM
Post by: EvilDogBeast on February 05, 2021, 12:59:33 PM
Post by: Longcruise on February 05, 2021, 01:16:28 PM
Sounds good, I'll have it up in about an hour!
Thanks. I'm about to head out for a long walk. Getting bow shop fever. :)
Post by: EvilDogBeast on February 05, 2021, 01:58:01 PM
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Post by: EvilDogBeast on February 05, 2021, 02:01:45 PM
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Post by: williwaw on February 05, 2021, 03:15:58 PM
if I want string follow I'd rather put it there intentionally.Intentional means to deflex the limb on the form rather than have the bow take set after being drawn? The object being to create a lower string tension at brace possibly?
My suggestion about proper limb taper was to prevent set/damage being taken at the fades. Isn't set at the fades what causes excessive handshock?
Post by: Flem on February 05, 2021, 05:21:03 PM
Mike, I think I would look for a epoxy with a viscosity rating of 600 CPS or less. The fabric will wet out a lot easier and you are less likely to end up with excess resin content, especially if not pressing or vacuuming the lam while curing.
Post by: EvilDogBeast on February 05, 2021, 05:44:11 PM
Post by: Longcruise on February 05, 2021, 05:45:22 PM
if I want string follow I'd rather put it there intentionally.Intentional means to deflex the limb on the form rather than have the bow take set after being drawn? The object being to create a lower string tension at brace possibly?
My suggestion about proper limb taper was to prevent set/damage being taken at the fades. Isn't set at the fades what causes excessive handshock?
Yes, that's how "string follow" is induced when it's intentional. Many ASL stle bows that are layed up flat take on the string follow with use just as a self bow does.
I don't think hand shock is related to set at the fades. One of my bows is built with an arc of reflex in the outer 24 inches of the limbs. It was originally destined to be a wide pyramid bow with. O02 total taper. 68" NtN. There was a huge bit of squiggle in the form and it ended up being 1 1/8" at the fades. :o. It took some set at the fades but it doesn't have hand shock. It's actually a pretty good bow. It was meant to be 55# but ended up at 43#. DFC is a plumb straight line, whereas a string follow bow tends to have a bit of perch belly in the DFC.
I think hand shock is from an incorrect grip (chockin the chicken) and/or poor tillering.
Post by: Longcruise on February 05, 2021, 05:57:33 PM
Flem, I didn't wait for it to cure. It keeps that greenish tint enough that I wouldn't use it on a bow with clear glass. It's a shame though because it's a really strong resin. Nearly double the shear strength of EA 40.
I see what you did there and it makes sense. I would prefer to stay with EA40 since it is well proven and that approach looks like it would work. I'm going to do a run like that with EA40 and see how it works out.
I did another test strip like the last one with some epoxy that is a bit thinner than EA40. It’s the stuff that is sold in the hobby stores usually packaged under the store name. It’s 15 minute stuff so it didn't take long. Still a bit of air bubbling.
Flem, I agree on the thinner stuff and maybe I'll go against the tech support advice and try the epic with the EA40 or maybe use Epoximite if you think it will hold up in a bow.
Post by: EvilDogBeast on February 05, 2021, 06:04:15 PM
Post by: williwaw on February 05, 2021, 06:22:18 PM
if I want string follow I'd rather put it there intentionally.Intentional means to deflex the limb on the form rather than have the bow take set after being drawn? The object being to create a lower string tension at brace possibly?
My suggestion about proper limb taper was to prevent set/damage being taken at the fades. Isn't set at the fades what causes excessive handshock?
Yes, that's how "string follow" is induced when it's intentional. Many ASL stle bows that are layed up flat take on the string follow with use just as a self bow does.
I don't think hand shock is related to set at the fades. One of my bows.....
I think hand shock is from an incorrect grip (chockin the chicken) and/or poor tillering.
Coming from a wood bow background, its common to discuss tillering and limb design alongside full draw pics illustrating the final bend. It's been difficult for me to understand some of the pros and cons of ASL design, as I have seen very few pics on the tiller tree.
Did your 68" bow carry it's bend all the way out into the tips? A 20" stiff handle?
Is there room in this thread for example pics of poorly
Post by: Longcruise on February 05, 2021, 06:55:18 PM
Post by: Flem on February 05, 2021, 07:18:11 PM
give out. They are not inclined to admit anything will work. They were dubious about me using Epoxamite as an adhesive. They told Big Jim they would not recommend using dye in their epoxy without testing first. They sell dye to use in their epoxy's! And then they told you the thinner "might' weaken the epoxy. If it does, what it amounts to is irrelevant.
I use Epoximite exclusively for lams and glueing up bows. I have used both the Epic thinner and the flexiblizer with success. You have to make some adjustments from using EA-40. It's not a gap filler, so lams need to be ground finer and you need pressure distributed evenly over the entire blank during glue up. Might not be appropriate for clamping or wrapping methods.
Post by: williwaw on February 05, 2021, 07:54:17 PM
Let's go ahead and post them up.Thanks
Quote
Flem, I agree on the thinner stuff and maybe I'll go against the tech support advice and try the epic with the EA40 or maybe use Epoximite if you think it will hold up in a bow.
smooth-on does not seem to have technical spec sheets for their products on their web site. I use system three, and will compare in principle.
Straight resin has the highest strengths. it is usually supplied in viscosities suitable for laminating fabrics. additives such as fumed silica can be added to prevent runout when the resin is used for an adhesive or for overhead fabric layups. Fumed silica may well be what gives Ea-40 it's extra body . If so, then adding a thinner to Ea-40 would be conbining two additives at cross purposes. Any/all additives weaken strength of straight resin, although they can improve other specific qualities.
Flem mentions closer control of gaps as a option to needing a thicker product. Avoiding vertical joints when curing may also help if you wish to work with a thinner mix. I also use heat and cold to good effect when using laminating resin as an adhesive and add minimal amounts of fumed silica when neccesary.
Post by: Roy from Pa on February 05, 2021, 08:20:06 PM
That says it all, hand shock comes from poorly tillered bows.
I tiller for equal limb timing and there is no hand shock in them.
Post by: williwaw on February 05, 2021, 09:00:33 PM
poorly tillered/shocky bows and full draw pics of bows that get it right
That says it all, hand shock comes from poorly tillered bows.
I tiller for equal limb timing and there is no hand shock in them.
Lol, my bad. I meant poorly designed instead of poorly tillered. went back and changed that, thanks.
I have read the hill style or asl has inherent handshock. Is this a myth or are there design challenges to making a damp in the hand bow? Of course any bow can be tillered poorly with unequal limbs. I was hoping for pics of asl's of varying designs, to better understand the issues of building a pyramid bow with glass.
Post by: onetone on February 05, 2021, 10:18:32 PM
Post by: EvilDogBeast on February 05, 2021, 10:39:12 PM
On the topic of ASL's and set: It seems most are built with two or three very thick core laminations tops. Would a higher number of thinner laminations reduce set?
Post by: Stagmitis on February 06, 2021, 04:25:33 PM
But Carbon and Woven glass on the back does to a degree. Shredd noted that linear glass stretches when applied to the back and I am tending to beleive that. The odd thing with a hill bow is that it will take a set (Lose preload,backset) when strung and shot even for a short period of time. However once unstrung and at rest for a short period it recovers what was lost. I have to think the back material dictates that not the belly.
Flem have fun with this one:
https://www.sakimarchery.com/en/diy-bows/195-2476-still-tech-laminations-.html?fbclid=IwAR09ibtjU8Coj0IGMvJ2fdNO6LH1KgpFEpL_khv_OUDTpJ4-Y9juafgS85I#/241-larghezza-45_millimetri/243-length-920_millimetri/244-finish_color-red_kevlar
Post by: Longcruise on February 06, 2021, 05:03:15 PM
Looks like air in there but it's tape residue.
Post by: Stagmitis on February 06, 2021, 05:29:20 PM
However smooth-on is not as strong (doesnt provide the stiffness) and is more viscous than other thinner laminating epoxies. So I prefer a pre-preg
(
Post by: Longcruise on February 06, 2021, 05:44:49 PM
Loncruise I have done it both ways with smooth-on and found that heating both parts before mixing together helps alot with wet-out and eliminates air bubbles-I use a roller
However smooth-on is not as strong (doesnt provide the stiffness) and is more viscous than other thinner laminating epoxies. So I prefer a pre-preg
I'm leaning toward pre- preg if only to allow knowing exactly what will be inside the bow.
Also thinking Huntsman glue because it is said to be thinner.
Anyone have experience with EA40 and Huntsman who can describe the difference in viscosity??
Post by: alaninoz on February 15, 2021, 03:42:03 AM
Post by: Flem on February 15, 2021, 10:34:07 AM
Post by: Roy from Pa on February 15, 2021, 10:56:19 AM
:thumbsup: Discourse is a good thing!
Depends on the opponent:)
Just sayen...
Post by: Shredd on February 15, 2021, 11:44:19 AM
Well Buddy... Did you find out which side of the bow should be optimized?? Or summarize your findings from all this... Curious what you are thinking...
Post by: Longcruise on February 15, 2021, 03:12:04 PM
The thread went off in different tangents... Which can usually happen and good can come from it... The most important thing is whether Longcruise got his questions answer to his liking...
Well Buddy... Did you find out which side of the bow should be optimized?? Or summarize your findings from all this... Curious what you are thinking...
As was said, the topic took off in several directions. Not a bad thing at all.
So the original question addressed which side of the bow should be the more heavily reinforced for best performance and retention of form. There seems to be a consensus that performance is more related to tension (the back) as opposed to the belly (compression).
I was/am more interested in retaining form or IOW, preventing set in an ASL build.
Still wondering why tension is thought to be a greater contributor to performance than compression. Indeed, if one is pulling (tension) then the other is pushing (compression) is it not? Both wood and glass are typically stronger in tension than compression so what is the best way to make both do equal work?
Post by: Mad Max on February 15, 2021, 06:37:04 PM
Put masking tape on the back when braced, then un brace, wrinkled
Post by: Roy from Pa on February 15, 2021, 07:47:33 PM
Post by: Mad Max on February 15, 2021, 07:51:39 PM
whats dat :biglaugh:
Post by: Roy from Pa on February 15, 2021, 07:52:50 PM
:laughing:
Post by: williwaw on February 15, 2021, 08:07:23 PM
I was/am more interested in retaining form or IOW, preventing set in an ASL build.
Still wondering why tension is thought to be a greater contributor to performance than compression. Indeed, if one is pulling (tension) then the other is pushing (compression) is it not? Both wood and glass are typically stronger in tension than compression so what is the best way to make both do equal work?
the takeaway i am getting from this discussion is...... if you can strain the back harder, it is storing more work. Set most likely comes from the belly side core, as wood is susceptible to compression damage sooner.