Face or back

[EvilDogBeast]

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?

[EvilDogBeast]

*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?

[Shredd]

  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...

[EvilDogBeast]

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.

[Longcruise]

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.

[Longcruise]

*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%

[williwaw]

  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?

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.

[williwaw]

*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

[Longcruise]

  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.

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.

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.

[williwaw]

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.

[williwaw]

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
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?

[Stagmitis]

Hey longcruise thats an awesome test!!!  Momentum factor? I would love to know what the speeds were w/10-9 gpp for that bow.

[Bvas]

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?

[Longcruise]

Stag, I no longer have that bow and never tested it with lighter arrows.   I wanted to do it with a recurve but the only one I had at the time was a vintage Necedah and didn't want to risk damage.

Bvas, i think i get what you are saying but.....I'm not sure.

[Shredd]

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...

[Shredd]

  Cruiser...  Looking forward to seeing the test on that bow...  Something tells me that the inside glass on the belly is doing very little but making the limb heavier...

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...

[Shredd]

I did a little homework for you guys hooked on Carbon...  Here is a quote from a guy with a very successful well known company that uses Carbon Fiber in his bows... I am not mentioning his name because I don't know if he wants to be quoted and I did not ask...  I was very surprised by his answer and he is usually long winded, maybe he did not have time to talk...  You can read into it what you want... I would consider him one of the top 10 guys who work with Carbon...

   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.

[Bowjunkie]

"the feeling you get". That's hilarious.     

[Shredd]

Sounds funny and I was surprised but I don't think it should be taken lightly from a man of his experience... What I think he meant is after you been experimenting so long with so many designs you kinda know things (Feeling You Get) and round off a figure of how many extra fps you can get using C/F... There may not be an exact number... One design can get you 3fps and another can get you 5 fps... So it is the experience of knowing how to create a good design that works with the carbon that gives you good results...

   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"...

[williwaw]

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.