Post by: Flem on January 06, 2021, 03:10:26 PM
[ You are not allowed to view attachments ]
[ You are not allowed to view attachments ]
[ You are not allowed to view attachments ]
I'm thinking of wrapping the carbon fiber with this 1.4oz plain weave fiberglass cloth, making a torsion box construction, which I hope would help stabilize the carbon fibers and hopefully add some elasticity to the matrix.
My issue is that I have no means to do any comparative testing to see how it performs against a fiberglass laminate. The only tool at my disposal is a home made tensiometer I made for lacing up bike wheels.
[ You are not allowed to view attachments ]
But since its not calibrated to any know scale, its only a reference tool. Plus to use it I would have to cut it and a fiberglass laminate into 3/8"X 12" sections and still it would only be a comparative exercise.
So my question, is there any body here who has access to lab equipment that could be used to get some meaningful numbers? Otherwise its just a subjective exercise. I know a couple of you out there have alluded to a materials background and if you are willing to do some testing, I would be happy to pay shipping and any other associated costs.
Post by: williwaw on January 06, 2021, 03:32:40 PM
please describe your proposed layup in a bit more detail. Dimensions of the torsion box?
Post by: Roy from Pa on January 06, 2021, 04:27:51 PM
Post by: Shredd on January 06, 2021, 04:55:25 PM
Post by: Flem on January 06, 2021, 05:47:52 PM
.050 X 1.75" X 72" I would do a vacuum infusion to minimize excess resin and should be able to get at least a 60/40 fiber to resin ratio. But it's a lot of work for nothing if I can't get it tested and compare it to Gordons or Bearpaw.
Post by: Mad Max on January 06, 2021, 07:14:50 PM
would a guitar tuner work :dunno:
Post by: williwaw on January 06, 2021, 08:18:25 PM
you could make form by routing a wide shallow groove in a board, and then sawing/sanding the board away. the torsional box you mentioned is the part I do not visualize well.
what do you want tested? the stiffness of the lam?
Post by: Flem on January 06, 2021, 08:38:41 PM
for a lam of .050 X 1.75" X 72" , I think the glass cloth will be extra baggage.
you could make form by routing a wide shallow groove in a board, and then sawing/sanding the board away. the torsional box you mentioned is the part I do not visualize well.
what do you want tested? the stiffness of the lam?
Go for it
Post by: Flem on January 06, 2021, 09:26:31 PM
Post by: williwaw on January 06, 2021, 11:10:01 PM
Quote
Sorry Willie, that was rude.I thought so too, and was reading
https://www.tradgang.com/tgsmf/index.php?topic=161214.msg2791972#msg2791972 (https://www.tradgang.com/tgsmf/index.php?topic=161214.msg2791972#msg2791972)
when I saw your most recent post. Apology accepted.
Quote
As far as testing goes, I am interested in all the same data that fiberglass lams are tested for.
testing for stiffness would be the most useful, seeing how bow designs typically don't push the limits for ultimate strength. For the cost of shipping, you could buy something like this
https://www.amazon.com/uxcell-Thickness-0-20mm-Measuring-Silver/dp/B07JB1CV8G/ (https://www.amazon.com/uxcell-Thickness-0-20mm-Measuring-Silver/dp/B07JB1CV8G/)
if you have a caliper to measure the thickness of your lam, you could probably get by using an arrow spine tester to measure deflection.
Hopefully others can weigh in with other things to test for.
Post by: Flem on January 07, 2021, 12:22:38 AM
Not that I blame you, I deserved it. :saywhat:
Post by: Shredd on January 07, 2021, 09:13:41 AM
Number one... Unless you are doing something that is unique and different I suggest to go buy some lams...
Two... I hear nightmares about carbon... I also hear it only buys you 2 to 4 fps, so if you don't have a maxed out efficient design that's shooting 190+ fps and you want ultimate or record speed I may opt to use carbon, otherwise I don't see the purpose of using it in the working portion of the limb... Now using it to lighten up and stiffen up the last 5 to 6" of limb is a different story... Trick is how to pull that off... Carbon is brittle and used to make things stiff and non-bending... Glass is tough and handles bending well... I personally think you need to use each material where they are needed most and work the best...
If you op to go through with this...
The tow must be all straight with no twists in it to give you a better quality product... To make all the fibers evenly tensioned will be a challenge and almost impossible at this scale but may not be totally necessary to give you a decent lam... Using woven glass may not be wise... I has different properties than carbon, especially the fact that it is woven vs the straight fibers of carbon... You may find that the woven glass may/will turn white when flexed to a certain point because either the glass or resin is fracturing or separating from each other... It may work well in other applications where it is stiff or with very little bend... It may work on the underside of carbon just as the scrim in a glass lam... Or I could be totally wrong and the stiffness of carbon could totally override the properties of the glass and keep it from fracturing... If you are shooting for a certain thickness I would add an extra .005 to .010" more material to be sanded off to get rid of irregularities on the surface...
Post by: Flem on January 07, 2021, 10:42:04 AM
This is test, only a test and it might not even happen if I can't find someone with access to lab equipment to verify the result. But I might just do it in any case, just for fun. :goldtooth:
Post by: Flem on January 07, 2021, 11:14:43 AM
Post by: Roy from Pa on January 07, 2021, 11:22:19 AM
Post by: Shredd on January 07, 2021, 11:45:21 AM
Good Luck... Enjoy your adventure...
Post by: Longcruise on January 07, 2021, 11:55:09 AM
Here's uni d Carbon.
https://binghamprojects.com/store/carbon-unidirectional-glass/
Post by: Flem on January 07, 2021, 12:20:52 PM
Post by: Mad Max on January 07, 2021, 12:31:19 PM
you may find him on a flight bow forum, I think he broke a record this year wif a foot bow. :thumbsup:
Post by: Mark R on January 07, 2021, 12:39:45 PM
Post by: Flem on January 07, 2021, 12:55:22 PM
Post by: Roy from Pa on January 07, 2021, 01:11:46 PM
Quote
My motivation is curiosity and to see how it would compare to a fiberglass lam. I like to push boundaries, never been one to accept the status quo
Noooo, say it isn't so:)
Post by: Flem on January 07, 2021, 01:32:49 PM
Post by: williwaw on January 07, 2021, 03:51:58 PM
Post by: Flem on January 07, 2021, 04:10:02 PM
Post by: williwaw on January 07, 2021, 04:43:55 PM
Quote
just getting the slack out,seems like a good idea for consistency.
silk was once used as a backing by hickman, before glass. it was prestretched before gluup, but of course it's quite stretchable compared to carbon
Post by: flyonline on January 07, 2021, 10:37:08 PM
have you looked at the uni-directional fabrics? They come in a fair range of weights and tow count and might make it easier to get a nice straight layup. The stuff I had was backed with scrim to hold it together, but I was doing foot wide wet layups. There is uni tapes but the one's I've seen all have scrim which I'm guessing won't be what you want.
How are you pre-tensioning your glass now? I know someone who has done this (CF not glass) and from memory he was using a bar type clamp to hold each end then tension by pulling the clamps apart over some kind of form. Don't think he was getting any arching either.
Steve
Post by: zhangkeyang on January 08, 2021, 07:55:58 AM
Post by: Stagmitis on January 08, 2021, 10:34:58 AM
Post by: Flem on January 08, 2021, 11:18:42 AM
Charles, I have used my tensiometer to measure deflection with homemade glass composites and checked them against Gordon's. Gordons is stiffer, or should I say it has a higher MOE. But it would be nice to have more info and some real numbers for comparison. If you look at property charts for manufactures laminates their is a lot of info that I have no ability to acquire at home. Tensile modulus and strength, flexural modulus and strength, compressive modulus and strength and shear modulus and strength. I'm just a goofball grunting around in my cave with sticks and stones for equipment.
Post by: avcase on January 08, 2021, 01:13:54 PM
There are a couple of different ways to obtain the Elastic Modulus. The easiest method is to use a 3-point bending method with a dial indicator to measure deflection under a known weight applied at the center of the sample. It is hard to tell for sure, but it looks like your device pictured on the previous page might work in a similar way. The rest of the info required is the span between supports, sample thickness, and width.
Elastic Modulus = (deflection/load)*(span^3)/(48*I)
I = sample_width * (sample_height^3)
I have a spreadsheet that I can share which does this and other calculations. I also measure the mass of the sample in order to see the stiffness or elastic modulus to mass ratio.
Another small detail. I removed the return spring from my dial indicator. The return spring in skews the results because it is counteracting some of the applied load by a varying amount depending on the amount of deflection of the sample. My simple test results agree very well with the Bingham specs for their glass and carbon. The Bearpaw samples were much less consistent.
I also have also found it useful to test composite sample layups and compare the results to those I calculated.
Measuring the strength properties is the other important property, but this is not as simple a process.
I find that the slightest misalignment of carbon fibers makes a big difference in the stiffness of the carbon layup. This is why a layup using woven carbon fiber cloth has just a fraction of the bending Modulus of unidirectional.
I hope this helps.
Alan
Post by: Longcruise on January 08, 2021, 02:05:47 PM
Post by: williwaw on January 08, 2021, 05:41:04 PM
Quote
If you look at property charts for manufactures laminates their is a lot of info that I have no ability to acquire at home.True, but do you need all the data?
the flexural modulus (which is what Alans formula will give), seems to be an average of the tensile and compressive, and would be adequate if you were to use your lams on both back and front of the bow.
In a case where your limb design utilizes your lam on only one face, you could make an adjustment up or down from the results obtained from the beam (flexural modulus) test described by Alan.
Post by: Flem on January 08, 2021, 06:03:08 PM
Post by: williwaw on January 08, 2021, 07:03:34 PM
the math is fairly straightforeward, and I expect someone on the forum could help, given the needed dimensions.
Are you hoping to crunch numbers so that you can eventually calculate a stack height with your custom lam?
Post by: avcase on January 09, 2021, 01:11:51 AM
Do you have some specs on the carbon fiber that you are using?
If the fibers in your layup are well distributed and aligned, and you know the percentage of fiber by weight, then we can calculate a pretty decent estimate of the mechanical properties.
Will it be useful? It depends on how you use the info. I find it useful.
Alan
Post by: Flem on January 09, 2021, 01:21:04 PM
I can calculate the mass and volume of the materials and I can create a static loading and measuring device, but building something that could take the material thru its elastic range into deformation, to failure, is way beyond my current ability. To me that the most useful information, we as bowyers could possibly put to use.
Post by: williwaw on January 10, 2021, 09:09:25 PM
Quote
but building something that could take the material thru its elastic range into deformation, to failure, is way beyond my current ability.
If wood is part of your design, them I would think set taking would be where your your concerns for deformation would be prudent. A bow design that pushes carbon to stresses outside it's elastic range, or even plain glass, for that matter, would be a radical departure from most bow designs.
Post by: Flem on January 11, 2021, 12:07:04 AM
Post by: williwaw on January 11, 2021, 12:59:49 AM
Post by: Flem on January 11, 2021, 12:01:07 PM
I guess I do not understand what kind of improvement you hope to bring to your design. You only work with one? which is it, btw?
Nothing here to understand, I'm not tweaking the design. Hill style is my boy bow crush.
I could be wrong but I only see two methods to increase performance. One is thru design, the other is optimizing material selection and orientation. Most focus on tweaking their design, but since thats not an option for me, I'm a material tweaker.
So I have finally come up with some specs for the hypothetical composite. Don't know if its enough, but here is what I have;
Total volume: 103.2cc
Weight of reinforcement: 189.5g
Specific gravity of resin: 1.1g/cc
Since this composite does not yet exist, I don't have a percentage ratio of fiber to resin.
The carbon tow is 24k, 1.8g/cc and I will use approx. 115.2 metres. Don't know how to calculate that as volume. All usage numbers are estimates.
The other thing that I question is how can the mechanical properties be calculated on a material that is progressively loaded? Seems any equation would only yield a linear answer? Unless I am way off in assuming a bow and it's components are considered elastic materials.
Post by: mmattockx on January 11, 2021, 12:46:16 PM
I could be wrong but I only see two methods to increase performance. One is thru design, the other is optimizing material selection and orientation. Most focus on tweaking their design, but since thats not an option for me, I'm a material tweaker.
Just a dumb question. Does your self imposed bow design restriction preclude adding reflex and the like, as long as the bow looks/bends like a Hill when braced?
Have you found a limitation in the commercial materials that you are trying to avoid or is this an experiment to see if carbon will offer anything extra?
The other thing that I question is how can the mechanical properties be calculated on a material that is progressively loaded? Seems any equation would only yield a linear answer? Unless I am way off in assuming a bow and it's components are not considered elastic materials.
Material properties seldom change due to the loading. Bow materials are most definitely linear elastic materials.
Mark
Post by: Flem on January 11, 2021, 01:04:01 PM
Thats where I disagree. Linear=non yielding, non-linear=yielding.
Post by: mmattockx on January 11, 2021, 02:15:40 PM
Thats where I disagree. Linear=non yielding, non-linear=yielding.
That's correct. Bow materials don't really yield as such in our application, but wood will take some set on the compression side which is similar to yield.
Mark
Post by: avcase on January 11, 2021, 02:47:46 PM
Nothing here to understand, I'm not tweaking the design. Hill style is my boy bow crush.
I could be wrong but I only see two methods to increase performance. One is thru design, the other is optimizing material selection and orientation. Most focus on tweaking their design, but since thats not an option for me, I'm a material tweaker.
So I have finally come up with some specs for the hypothetical composite. Don't know if its enough, but here is what I have;
Total volume: 103.2cc
Weight of reinforcement: 189.5g
Specific gravity of resin: 1.1g/cc
Since this composite does not yet exist, I don't have a percentage ratio of fiber to resin.
The carbon tow is 24k, 1.8g/cc and I will use approx. 115.2 metres. Don't know how to calculate that as volume. All usage numbers are estimates.
The other thing that I question is how can the mechanical properties be calculated on a material that is progressively loaded? Seems any equation would only yield a linear answer? Unless I am way off in assuming a bow and it's components are considered elastic materials.
Flem,
What is still needed to calculate an estimate are the specs for the carbon fiber you are using. There is a wide range of mechanical properties for carbon fiber. The 24k only states the number of fibers present in your TOW material. The volume of carbon isn’t important. The percentage by weight of carbon and epoxy is important.
You don’t want the materials to operate outside their linear or elastic range. If the materials are yielding during normal use, then the bow is not going to last very long. I even make an effort not to exceed the linear range for the wood core of the bow.
Are you not able to obtain Gordon’s GC-70-UCL for a backing material? I recently bought and used this for a back on a longbow design.
Alan
Post by: mmattockx on January 11, 2021, 05:04:57 PM
Are you not able to obtain Gordon’s GC-70-UCL for a backing material? I recently bought and used this for a back on a longbow design.
Alan,
A while back you told me that fibreglass stores energy better than carbon does. If that is correct, what do you gain by using carbon in your flight bows? Is this just a weight issue or something else? It's not like we approach the material limits of either in a hand drawn bow.
Hopefully this is just a continuation of OP's desire to try carbon lams as an upgrade and not a hijack...
Mark
Post by: Flem on January 11, 2021, 05:22:39 PM
I did do some digging and found the specs for the carbon
T800S R1_04132018.pdfThe only reason I'm obsessed with the volume is because I don't have the resin weight, nor do I have a total weight for the unborn composite. I do know the total volume and the weight of one component.
See my conundrum?
Post by: Mad Max on January 11, 2021, 06:18:03 PM
mmattockx, what did you do for a living? If I may ask :)
Post by: avcase on January 11, 2021, 06:42:57 PM
I've never seen UCL or even ULZ for retail sale. I would not even know what to expect for cost.
I did do some digging and found the specs for the carbon
The only reason I'm obsessed with the volume is because I don't have the resin weight, nor do I have a total weight for the unborn composite. I do know the total volume and the weight of one component.
See my conundrum?
I suppose it depends on how you make the laminate. I assume you would lay it up, and then you would need to grind it to a thickness and width. Am I correct? In this case, you won’t know how much fiber is still present in the same. So I would take the finished sample and precisely measure the thickness, width, length, and mass. Do a deflection test if you can, and then take a propane torch and burn away all the resin until just the carbon fiber remains. Precisely weigh remaining carbon fiber. This will give a good idea of the fiber to resin ratio by weight.
Alan
Post by: Flem on January 11, 2021, 08:32:19 PM
"So my question, is there any body here who has access to lab equipment that could be used to get some meaningful numbers? Otherwise its just a subjective exercise. I know a couple of you out there have alluded to a materials background and if you are willing to do some testing, I would be happy to pay shipping and any other associated costs."
Call me greedy, but I am going to want more and diverse data if I am putting in the effort to make and or deconstruct this composite.
Post by: mmattockx on January 11, 2021, 11:29:02 PM
mmattockx, what did you do for a living? If I may ask :)
I am a mechanical engineer. Do most of my work in oilfield equipment and structures design/analysis/rating/certification.
Mark
Post by: Mad Max on January 12, 2021, 07:01:18 AM
Post by: Stagmitis on January 12, 2021, 08:12:58 PM
Post by: Mad Max on January 12, 2021, 08:49:08 PM
Alan
sounds like a plan to me :thumbsup:
Post by: Flem on January 12, 2021, 11:19:18 PM
Just for the back, I've got something else in mind for the belly.........
Post by: avcase on January 13, 2021, 01:09:44 AM
Sound like a toxic fiesta burning all that epoxy. I'd like to know who has done that and how much residue was left on the fiber. That and you still won't have squat for stats for your effort. I'm not doing all that just to fill some numbers in an equation!
Just for the back, I've got something else in mind for the belly.........
Flem,
Burning away the resin to inspect and measure the fiber content is a pretty standard inspection procedure. Just don’t do it inside or in a poorly ventilated area! The resin burns away leaving clean fibers behind.
Otherwise, I’m running out of ideas for you. If your goal is to compare your layup to the Gordon Composite spec, then you have to test it and measure the mechanical properties. Companies that manufacture composites and maintain their quality invest a lot of time and resources in this.
There is yet another method, but it involves measuring natural vibration frequencies and it still requires you to precisely measure the length, width, thickness, and mass of the sample.
You can also not worry about it. Just make carbon laminates as best you can and use them. Don’t worry about how it compares to anything else. Do it by feel. Flex the pieces you make. Destroy a few pieces and observe how they fail. Build bows. Make adjustments to your process and do it again.
Alan
Post by: Shredd on January 13, 2021, 12:25:03 PM
Flem,
You can also not worry about it. Just make carbon laminates as best you can and use them. Don’t worry about how it compares to anything else. Do it by feel. Flex the pieces you make. Destroy a few pieces and observe how they fail. Build bows. Make adjustments to your process and do it again.
Alan
[/quote]
:thumbsup: :thumbsup:
Great idea on burning off the resin... Never heard of that... Simple but accurate... Thanks for sharing...
Post by: Flem on January 13, 2021, 01:49:05 PM
And besides, I have had a generous offer to have my composite tested by a University testing lab manager! Now I'm going to have to get off my a$$ and actually make this material.
Post by: Mad Max on January 13, 2021, 02:16:23 PM
you got nuffin else to do :tongue: :laughing:
Post by: Roy from Pa on January 13, 2021, 02:31:37 PM
Post by: Flem on January 13, 2021, 03:26:59 PM
wasting time?
you got nuffin else to do :tongue: :laughing:
No comment
Long as yer having fun Flem, that's all that matters.
I don't have the attention span to do many things thats are not fun
Post by: Roy from Pa on January 13, 2021, 03:46:29 PM
Post by: Mad Max on January 13, 2021, 04:26:21 PM
:laughing: ;)
Post by: avcase on January 13, 2021, 05:39:32 PM
Alan,
A while back you told me that fibreglass stores energy better than carbon does. If that is correct, what do you gain by using carbon in your flight bows? Is this just a weight issue or something else? It's not like we approach the material limits of either in a hand drawn bow.
Hopefully this is just a continuation of OP's desire to try carbon lams as an upgrade and not a hijack...
Mark
Mark,
Unidirectional glass stores more energy in bending for a given weight of material than unidirectional carbon fiber. This is because glass can take much higher strain in bending than carbon. Unidirectional carbon is much stiffer, but cannot handle as much deformation. This is especially true in compression.
Unidirectional carbon is superior to glass as a structural material, where it isn’t subjected to large amounts of bending. Unidirectional carbon also works pretty well as a backing in long limbed bow designs because it still has pretty decent tensile strength.
I do design my flight bows to take full advantage of glass. This is helped by the freedom to use high draw weight and short draw length designs. Heavy weight crossbow limbs and compound bow limbs are other good examples where glass can be used to its true potential. In contrast, it is much harder to take full advantage of the properties of glass in bows that require relatively low draw weight and long draw lengths (typical of most target and hunting bows).
Alan
Post by: avcase on January 13, 2021, 05:42:13 PM
And besides, I have had a generous offer to have my composite tested by a University testing lab manager! Now I'm going to have to get off my a$$ and actually make this material.
Great! I look forward to the find out how it turns out for you.
Post by: Longcruise on January 13, 2021, 05:49:53 PM
Quote
Just for the back, I've got something else in mind for the belly.
I'm interested in this aspect. I think it is more important to an ASL design than some others.
Post by: Shredd on January 13, 2021, 08:12:13 PM
Take us with a grain of salt Flem... You know us men, we like to give advice and offer our opinions whether you like it or not... ;) :)
Post by: Roy from Pa on January 13, 2021, 08:38:50 PM
Post by: onetone on January 13, 2021, 10:09:41 PM
Post by: Flem on January 14, 2021, 12:33:21 AM
@FlemQuoteJust for the back, I've got something else in mind for the belly.
I'm interested in this aspect. I think it is more important to an ASL design than some others.
Figured I was not the only one thinking about this. I'm just going to throw this out and see what you all think. So I'm thinking the laminate we put on the belly side is not optimal. We use a laminate that was obviously designed to placed on the bow's back. It's reinforced with unidirectional fibers that have one purpose. So why do we use the same laminate on the belly? Why not use a laminate designed to resist the compressive forces. I have been planning on doing some experimenting with epoxy and hollow glass microspheres. 3M makes some with 27,000psi crush strength. The epoxy I will use is 26,000psi. The density of the microspheres is 0.6 g/cc, the epoxy is 1.1 g/cc. Big potential for weight savings for no loss in strength. Plus I have been reading documents on testing of various composites and the addition of hollow glass microspheres has been shown to increase the modulus of resistance, so the theoretical laminate should be able to absorb and release more energy. I still need to do a bit more research to confirm and would like to see MOResistance specs for epoxy. I am still debating whether or not to add a .002 biaxial layer of glass for a bit more structural integrity and if the addition of more elastic epoxy is necessary, also the percentage of HGM to use in the matrix. I'd like to hear anybody's ideas, just remember I'm trying to move this idea forward, not stalling out or going backwards.
Post by: onetone on January 14, 2021, 01:23:56 AM
Post by: williwaw on January 14, 2021, 01:28:43 AM
Hi Flem
cooking your own belly stuff. nice!
Quote
I have been reading documents on testing of various composites and the addition of hollow glass microspheres has been shown to increase the modulus of resistance
Are these documents something you could link to online? I'm not familiar with a resistance modulus. Probably shouldn't comment before reading up some.
Post by: avcase on January 14, 2021, 01:52:14 AM
AVCase: It seems to me that both glass and carbon fibers are only marginally flexible, compressible or elastic. So is true that the matrix binding such fibers, like epoxy, is where the stretching, compressing and recovery happens? Would appreciate hearing your work thoughts.
The tensile and compressive strength comes from the fibers. They are like thousands of tiny columns. If the epoxy matrix wasn’t there, then those columns would buckle with hardly any compressive stress at all. The epoxy just keeps the fibers aligned and together, and helps prevent buckling under compression. It doesn’t contribute much otherwise, and just goes along for the ride. This is why composite manufacturers try to maximize the percentage of fiber in a composite.
The epoxy matrix plays a bigger role in the mechanical properties where the fibers are woven or short random fibers. This is because the fiber is being pulled and pushed at angles to the epoxy matrix, like pulling a rope sideways through jello. This is also why woven composites are much less stiff compared to unidirectional composites.
Alan
Post by: Buemaker on January 14, 2021, 07:58:29 AM
Post by: onetone on January 14, 2021, 09:49:56 AM
Post by: mmattockx on January 14, 2021, 11:19:57 AM
AVCase: It seems to me that both glass and carbon fibers are only marginally flexible, compressible or elastic. So is true that the matrix binding such fibers, like epoxy, is where the stretching, compressing and recovery happens? Would appreciate hearing your work thoughts.
Alan has already answered the question about what carries the load in an epoxy/fibre composite, but he didn't comment on the 'marginally flexible' part.
Fibreglass is quite flexible/elastic in that it will survive ~5% strain before failure in a tensile test (for bare S glass fibres). As a reference, most carbon steel begins yielding at around 0.2% strain, so fibreglass will stretch 25 times more than steel will before failing. Gordon's claim a maximum tensile strain limit of 2.5% for their S glass lams, so it is a fair bit lower in the epoxy/fibre matrix.
Carbon fibres are much stiffer than fibreglass fibres, but the difference is less in the epoxy matrix. Gordon's claims a flexural modulus for their carbon lams that is 13% higher than their S glass lams. The maximum tensile strain for the carbon lams is 3.3%.
Mark
Post by: Shredd on January 14, 2021, 11:59:50 AM
Post by: Flem on January 14, 2021, 01:34:20 PM
Flem... Are you planning on using the microspheres as a core or as a lam..?? What you wrote sounded like you were gonna use it as a lam... If so I feel it would be a complete failure...
Please elaborate
Post by: Bow-n-Head on January 14, 2021, 02:14:39 PM
Post by: avcase on January 14, 2021, 04:22:06 PM
Figured I was not the only one thinking about this. I'm just going to throw this out and see what you all think. So I'm thinking the laminate we put on the belly side is not optimal. We use a laminate that was obviously designed to placed on the bow's back. It's reinforced with unidirectional fibers that have one purpose. So why do we use the same laminate on the belly? Why not use a laminate designed to resist the compressive forces. I have been planning on doing some experimenting with epoxy and hollow glass microspheres. 3M makes some with 27,000psi crush strength. The epoxy I will use is 26,000psi. The density of the microspheres is 0.6 g/cc, the epoxy is 1.1 g/cc. Big potential for weight savings for no loss in strength. Plus I have been reading documents on testing of various composites and the addition of hollow glass microspheres has been shown to increase the modulus of resistance, so the theoretical laminate should be able to absorb and release more energy. I still need to do a bit more research to confirm and would like to see MOResistance specs for epoxy. I am still debating whether or not to add a .002 biaxial layer of glass for a bit more structural integrity and if the addition of more elastic epoxy is necessary, also the percentage of HGM to use in the matrix. I'd like to hear anybody's ideas, just remember I'm trying to move this idea forward, not stalling out or going backwards.
Flem,
What is the best way to make a composite for best compression strength? Maybe another example might help. A solid Steel column has very high compression strength, right? Now picture making an equivalent steel column out of many spaghetti-like strands of thin steel wire and put a compressive load on it. Even though an equivalent cross-section of wire is just as strong in compression as the solid column, it won’t support much weight at all because all the little strands buckle under load. But then take some super strong thread and tightly bind this bundle together so that it can’t buckle so easily, and put a compressive load on it. It will behave totally different. It will be able withstand a very high compressive load and will act more like the solid steel column. For composites, the epoxy is what is tightly binding these little thin columns together and preventing them from buckling.
Now add micro balloons to this bundle. What do you think will happen? In the example of the thin steel wires bound together, it will be like mixing marbles between the wires before they are bound together. This creates little voids and misalignments of the wires, which does two things. First, there will be fewer wires to resist the compression that can fit in the same space. Second, it can cause little misalignments and kinks in the wire bundle, which makes the bundle more susceptible to buckling under compression.
27,000 psi crush strength in not even close to the compression strength of a composite with unidirectional fibers reinforcing it. Unidirectional Glass or carbon composite materials have a typical compression strength of around 150,000-160,000 psi.
The strength of the epoxy is not a major factor. The elastic modulus of the epoxy is relatively low, so it just goes along for the ride when compressed or pulled in tension. In the example of the steel column, it is more like binding together the steel spaghetti column in a matrix of rubber.
Alan
Post by: Flem on January 14, 2021, 05:40:11 PM
Ray, I get most of my fabric from Fiberlay, but thats if Im near a store. There are a lot of retailers with great selections on line. If I need to mail order, I use Composite Envisions. They have the most extensive selection of fabrics I have seen to date.
Post by: Shredd on January 14, 2021, 05:51:27 PM
Post by: mmattockx on January 14, 2021, 06:23:40 PM
The composite I have in mind contains no longitudinal reinforcement. My idea is to reduce the mass, since all that unidirectional fiber is overkill on the belly of a bow.
The fibres are what carry all the load, on both the back and belly. They aren't overkill, they are the only way lams can work.
Mark
Post by: Flem on January 14, 2021, 06:51:54 PM
I did mention I was considering a thin biaxial layer for structure. Think elastic concrete.
So if someone has tried this and it failed, details please. Otherwise I might just try it. Unlike the other composite I need to make, this would be a piece of cake and inexpensive.
Post by: williwaw on January 14, 2021, 06:59:41 PM
Heavy weight crossbow limbs and compound bow limbs are other good examples where glass can be used to its true potential. In contrast, it is much harder to take full advantage of the properties of glass in bows that require relatively low draw weight and long draw lengths (typical of most target and hunting bows).
Alan
Quote
Microspheres with epoxy is pretty much only good as a filler or core material...
but wouldn't innovation in core materiels be just as important as innovation with front or back lams? especially if glass or carbon is not being used to its full potential?
Post by: williwaw on January 14, 2021, 07:06:26 PM
Quote
Think elastic concrete.
microballons in laminating resin gets quite runny, and some cabosil (fumed silica) in the mix would be useful to stiffen the uncured mixture. Maybe even stiffen the cured mixture. Think of the sand needed in addition to the larger aggregates to make good concrete
Post by: onetone on January 14, 2021, 08:09:21 PM
Post by: Shredd on January 14, 2021, 08:14:07 PM
Post by: avcase on January 14, 2021, 08:18:55 PM
You guys sound like the voice of experience. Did somebody try this? What ratio of spheres to resin was used? What was the composite intended for? I got questions?
I did mention I was considering a thin biaxial layer for structure. Think elastic concrete.
So if someone has tried this and it failed, details please. Otherwise I might just try it. Unlike the other composite I need to make, this would be a piece of cake and inexpensive.
Yes, there is test results available that document the mechanical properties of epoxy filled with a range of 3M glass microballoon sizes, wall thicknesses, and volume ratios of micro balloons to epoxy. The tensile strength, compression strength, and elastic modulus all suffer in relation to increasing percentage of microballons. Density gets a little better with higher volume of micro balloons, but it is not enough to offset many of the downsides. As mentioned above, this is the recipe for the syntactic foams used in some bow limb cores.
I agree with Shredd’s comments above. My bet is you are better off using a piece of straight grained wood for a back, belly, or core laminate. It makes sense to me to me using syntactic foam cores in things like surfboards because it isn’t going to rot out if some moisture happens to seep in.
Alan
Post by: Flem on January 14, 2021, 11:01:54 PM
Density should decrease as the volume of microballons increased. HGM .06 g/cc , epoxy 1.1g/cc
and the addition of HGM to epoxy with not render it porous. Its used in flotation applications! Neither glass nor epoxy are subject to rot from water contact.
Post by: mmattockx on January 14, 2021, 11:20:35 PM
Has anybody done that? Can anyone say that the amount of compressive force incurred drawing a bow, exceeds the limits of epoxy or Hollow glass microballons?
Yes, both Alan and I can confirm that the compressive stresses on the belly will very significantly exceed the strength of your epoxy (I believe you stated it is ~26,000psi?). Bending stresses can run upwards of 50,000-60,000psi depending on the design.
Mark
Post by: Shredd on January 15, 2021, 12:21:26 AM
Post by: Flem on January 15, 2021, 10:11:42 AM
Has anybody done that? Can anyone say that the amount of compressive force incurred drawing a bow, exceeds the limits of epoxy or Hollow glass microballons?
Yes, both Alan and I can confirm that the compressive stresses on the belly will very significantly exceed the strength of your epoxy (I believe you stated it is ~26,000psi?). Bending stresses can run upwards of 50,000-60,000psi depending on the design.
Mark
Thats too vague a statement. Do you have some figures to validate that statement. "Can run upwards" leaves a lot to the imagination. Whats typical? Specifically which stresses are you referring too?
And what design are you correlating those "figures" too?
Rich, I am not building that bow. Not sure how you came to that conclusion. I am getting ready to experiment with composites. One is the carbon/epoxy "lam" the other is the minimally reinforced epoxy composite "lam"with HGM used as a yet undetermined amount of filler. I would not call what I am planning syntactic foam. I'm not trying to make a floating bow. I'm not attempting to make any core material. All I can tell you is that ultimately if I use any of these test composites, they will go into making a straight limb, slight string follow ASL.
Post by: Roy from Pa on January 15, 2021, 10:25:46 AM
Just sayen:)
Post by: mmattockx on January 15, 2021, 10:36:20 AM
Thats too vague a statement. Do you have some figures to validate that statement. "Can run upwards" leaves a lot to the imagination. Whats typical? Specifically which stresses are you referring too?
And what design are you correlating those "figures" too?
It depends entirely on the design, they vary from soup to nuts depending on the details. The stresses I am referring to are the bending stresses seen on the belly and back surfaces of the limb. Typical is pretty hard to define because there are so many different designs possible.
The red oak lam bow I am working on now has maximum stresses in the low 16,000psi range because red oak can't take much more. My maple pyramid bow I posted a week or so back has maximum stresses of ~18,000psi because it is shorter than the oak bow. I have a 61" lever bow designed for FG lams that has a maximum stress of ~54,000psi. From the modeling I have done of 'typical' FG recurve designs the stresses are never much less than 50,000psi.
If you want another reference point, ask Alan what the stresses are in the foot bow he built and shot this year to shoot an arrow 1600+yds.
If you want to know what your Hill style bows run PM me the specs and I will analyze it and let you know.
Mark
Post by: Flem on January 15, 2021, 01:08:58 PM
Post by: mmattockx on January 15, 2021, 03:00:07 PM
Which I why I question the efficacy of modeling.
You're welcome to question it all you like, but I use it every day to design and analyze much more complicated structures than a bow.
I would be interested to know if anyone has designed and calculated the properties of a hypothetical bow, built the bow and then checked the accuracy against test data of same bow in a laboratory?
My maple pyramid was designed using software. I simply cut the board to the dimensions predicted by the software. It was accurate to under 1% in terms of predicting weight, which means that the stresses are predicted to the same accuracy. If you don't believe me, ask Alan Case about his bows.
Just because you don't like the answers it gives doesn't mean it is faulty or invalid.
Mark
Post by: avcase on January 15, 2021, 03:23:34 PM
I would be interested to know if anyone has designed and calculated the properties of a hypothetical bow, built the bow and then checked the accuracy against test data of same bow in a laboratory?
Yes, every bow I build.
You might be able to get a workable bow with your micro-balloon belly strip. After all, you can make a bow out of concrete with the right dimensions. It may not be much fun to shoot or carry around, but it can be done. The elastic modulus of the no-glass-fiber material you described will be very low, kind of like putting a piece of taffy on the bow belly. Probably a best-case result will give you something like a piece of PVC for the belly lam of your bow (best case). It will require much more than typical stack thickness to achieve draw weight.
Good luck. Make your material, use it on a bow, and let us know how it goes.
Alan
Post by: Flem on January 15, 2021, 04:14:09 PM
Would you not like to address my assumption that if we were exceeding the elastic limit of the epoxy in the composite, that we would be seeing signs of plastic deformation?
This is the bow you are referring to?
“Thanks. It had quite a saga and it is likely a miracle it became a bow at all. There was a pin knot on the back that concerned me, so I initially backed it with cotton fabric and TBIII. The rest of the board was nice, straight grain and I wouldn't have backed it except for that knot.
Got it worked in some on the tree and then decided to heat treat the belly and put a touch of reflex into it. During heat treating I scorched the edges of the backing a bit in a couple spots. I didn't trust it after that, so I sanded it off (sanding all that off by hand was certainly penance for being a muppet with the heat gun...) and put a small patch of vectran fibres over the pin knot and left the rest of it unbacked. It was OK after that and I finished tillering it out to 28". First crisis averted...
Similar to Roy's recent BBO build along, a knot had appeared on the belly side of the lower limb when I was removing wood at the beginning. It was small and didn't transfer through to the back, so I soaked it with CA and carried on. After a few hundred shots that spot started hinging. So I rasped off some of the belly wood at the hinge and glued a patch over the knot area. I didn't pull it back perfectly flat when I glued the patch on and you can still see where the hinge was on the limb, but the patch has held for 1000+ shots now and nothing has moved, so it is hopefully going to stay that way.”
How is it possible to account for all that modification?
Do you have an example other than your Maple bow, one with fiberglass that you have done the same design and testing procedures?
I would be interested to know if anyone has designed and calculated the properties of a hypothetical bow, built the bow and then checked the accuracy against test data of same bow in a laboratory?
Yes, every bow I build.
You might be able to get a workable bow with your micro-balloon belly strip. After all, you can make a bow out of concrete with the right dimensions. It may not be much fun to shoot or carry around, but it can be done. The elastic modulus of the no-glass-fiber material you described will be very low, kind of like putting a piece of taffy on the bow belly. Probably a best-case result will give you something like a piece of PVC for the belly lam of your bow (best case). It will require much more than typical stack thickness to achieve draw weight.
Good luck. Make your material, use it on a bow, and let us know how it goes.
Alan
Sound like you have access to a lab?
And thanks, I think I will just to spite you guy's :tongue:
Post by: mmattockx on January 15, 2021, 05:22:40 PM
Would you not like to address my assumption that if we were exceeding the elastic limit of the epoxy in the composite, that we would be seeing signs of plastic deformation?
I missed this in the exchanges. Are you referring to the epoxy that is holding the unidirectional lams together? If the modulus of elasticity of the epoxy is much less than the fibres then the epoxy will just follow the deflections and the load will be carried by the fibres. A typical recurve bow will not induce more than about 1% of strain in the limbs. I expect that is significantly less than the strain limit of the epoxy. If you have the material properties info for your epoxy we could see what it will be.
I think I understand now where you are coming from on this. When I say a bow has maximum stresses of 50,000psi on the limb surfaces that does not mean all of the material in the lams will see 50,000psi. They all see the same amount of deflection, but that does not equal to the same amount of stress. Stress is calculated by multiplying the deflection (the strain) by the modulus of elasticity of the material. A stiffer material (higher MOE) will see higher stresses than a less stiff material for the same amount of deflection. Because the fibres are hugely stiffer than the epoxy (probably a couple orders of magnitude) they end up carrying all the load and having the high stresses while the epoxy is doing almost nothing aside from holding the fibres in place in the lam.
This is the bow you are referring to?
Yep, that's the one. The 1% accuracy and weight I referred to were measured before I screwed it up with my heat treating attempt and the hinge started to appear. Stresses won't be a lot different now but the light heating and bit of reflex added (and then lost) likely changed the starting point a bit.
Do you have an example other than your Maple bow, one with fiberglass that you have done the same design and testing procedures?
Nope, I haven't done a FG bow yet. If Kenny is on it then I should have a bow kit and extra materials in the mail today sometime.
And thanks, I think I will just to spite you guy's :tongue:
I look forward to it, experiments are always cool to see. My red oak lam bow is nothing but an experiment in Perry reflex along with a different style of form and slightly unusual construction method. As you have read, there have been some speed bumps on the trip so far but I am learning a bunch and that is mostly the point.
Neither Alan nor myself are trying to be difficult about this, it is the reality of the situation that we understand as engineers. You can be skeptical about our methods, but if our understanding of the physical world was significantly incorrect buildings would be falling over on a daily basis and machines would almost never work properly.
Mark
Post by: kennym on January 15, 2021, 05:35:21 PM
On it! Went this morn...
Post by: Roy from Pa on January 15, 2021, 06:03:48 PM
Thanks
Post by: williwaw on January 15, 2021, 06:33:55 PM
Quote
If you have ever physically bent a piece of bo-tuff or other laminate, you will find that the epoxy will start to fracture long before the composite its self will fail.
this happens in composites when the bends are so extreme, that the fibers slip away from the epoxy. values for shear with e glass in epoxy can be seen in the bottom rows.
Post by: Shredd on January 16, 2021, 12:36:53 AM
Guys, let's not let things get out of hand in here, please....
Thanks
:laughing: :biglaugh: :laughing: Too Late, Roy... Let them talk... It aint hurting nuthin... Yah can't build a bow unless yah gots lots of numbers...
Post by: Roy from Pa on January 16, 2021, 05:16:07 AM
I had to edit a post to bring a comment into compliance.
Quote
Yah can't build a bow unless yah gots lots of numbers...
Ya but them decimal things ole Kenny throws out just mess up my boo layouts:)
Post by: Mad Max on January 16, 2021, 10:14:07 AM
just sayin :tongue:
I think it's good to challenge each other but I don't think we ever agree on 1 answer :dunno:
I'm not a tech. guy like some of you, NOT roy :tongue: but using thicker glass on the belly (stronger bellys) as alot of people have said before on other threads should work better. Not on the subject anyhow?
Post by: Shredd on January 16, 2021, 11:36:10 AM
Now it seems to be your turn Flem... I was being facetious when I told Roy to keep letting you guys talk numbers... Here is my question... Are you gonna build a paper bow or a real one?? I am not trying to be a jerk here... I am just being real, straight up, man to man and also dying to see what you are gonna come up with... I'll bet I could build a bow with a formica back and belly that will blow the socks off of what you propose to do and I don't need numbers to figure it out... I figure I could realistically hit 165 to 175 fps... So here is my challenge for you... You build your carbon backed bow with a syntactic foam belly and if it hits 176 fps @ 10gpp I will build a formica bow to try to beat it... I think you would be lucky to get 140 to 150 fps out of your bow but I think it will not even hold together and there are a few other guys on here that think the same way... Prove us wrong... You could spend a year talking numbers... But the proof is only gonna be in the Pudding... :thumbsup:
What say you Brudder??
Post by: Roy from Pa on January 16, 2021, 11:54:18 AM
He calls me all the time for bow building advice...
LOL
Ok Flemmy, I agree wif Shreddy.
It's time to get this project on the road and see how it turns out.
:campfire: :wavey:
Post by: Shredd on January 16, 2021, 12:02:33 PM
Post by: Roy from Pa on January 16, 2021, 12:03:27 PM
Post by: Mad Max on January 16, 2021, 12:30:50 PM
I = sample_width * (sample_height^3)
Tech. Is this English :laughing:
I go by the seat of my pants
Post by: mmattockx on January 16, 2021, 12:57:18 PM
I'll bet I could build a bow with a formica back and belly that will blow the socks off of what you propose to do and I don't need numbers to figure it out... I figure I could realistically hit 165 to 175 fps...
This is getting good now. I think you would find formica too brittle for a back, but there is only one way to find out. I look forward to that build along thread!
I = sample_width * (sample_height^3)
You need a 1/12 in there... :biglaugh:
Seat of the pants is a very time honoured tradition, nothing wrong with it. Just put some safety glasses on before putting the bow on the tree. :o
Mark
Post by: Shredd on January 16, 2021, 01:03:42 PM
Post by: Shredd on January 16, 2021, 01:15:26 PM
Now, I don't wanna see any damn numbers on formica... :biglaugh: Just take the chit in your hands and bend it, pull on it, twist it and break it and then do the same to the same size piece of wood... ;)
Post by: Longcruise on January 16, 2021, 01:31:48 PM
Post by: mmattockx on January 16, 2021, 01:43:15 PM
Just take the chit in your hands and bend it, pull on it, twist it and break it and then do the same to the same size piece of wood... ;)
I agree it is stiffer than wood, but it has always seemed brittle to me. Glass (window glass, that is) is high strength and hard, but it is also brittle and fails easily in tension. My impression of formica is similar.
Build a bow and prove me wrong, I would love to see a formica lam bow.
Mark
Post by: Mad Max on January 16, 2021, 01:57:00 PM
Mattock... Think on this... What's tougher... A .040" piece of maple or formica... Now take a simple unbacked board bow vs. one backed with formica...
Now, I don't wanna see any damn numbers on formica... :biglaugh: Just take the chit in your hands and bend it, pull on it, twist it and break it and then do the same to the same size piece of wood... ;)
x2 :tongue:
I did Tool and Die/Machine work for 30 years and Fabrication too.
I always new what size bolt, Tool steel thickness, or square tubing, angle Iron, ect. to use wif out any equation ;)
First thing I learned in the Machine shop was the KISS factor and Nothing Ventured Nothing gained and read My signature below :thumbsup:
Post by: Shredd on January 16, 2021, 02:03:19 PM
I always wanted to do a build video on it to share with all those wanna-be bow makers that watch you tube... It's a great way to build a decent bow for cheap and get most of your supplys from home depot or cut-offs from a counter top shop...
Post by: Flem on January 16, 2021, 02:11:34 PM
I can tell you what inspired me to consider alternatives to the current offerings, specifically the belly lam. Unfortunately I do not have any figures to share, guys like me count with our fingers and toes. But I have done some bend tests with both Gordon's and homemade. I clamp a 1.5" X 17" X .050" piece to my bench and start bending. I do stop incrementally to do a visual inspection with magnification and also check it on a surface plate, but I only have feelers down to .001".
Initially I had a pulley system with a scale attached to the unclamped end, but abandoned that right away because I was able to bend the sample way past the capabilities of my very primitive test set up. The first time I did this, I would unclamp the sample and do the visual and flatness inspection every 20deg or so. That was a Pia unclamping and re-clamping Now I just bent them to about 120deg before I start checking.
The first detectable sign of failure, which is consistent for all samples I have tested, is the surface epoxy will start to fret. It always happens first, on the tension side. The next stage is an increase in the fretting that causes distortion I can can measure (>.001). The next stage is where my tests shortcoming really shows. I can’t say that one or the other happens first, but it appears the the epoxy under compression does not start to distort before the lamination is fracturing on the tension side. Considering how far I had to bend the sample before it was obviously outside its elastic range and I could cause any discernible damage, I concluded that what we are using is likely severe overkill for its intended purpose. And that epoxy is stronger in resisting compressive forces than tensile ones. So the main problem I am having is reconciling you guys telling me it won’t work on paper, with how I am interpreting my crude test data. This created some curiosity, but the curiosity does not stem from a desire for speed or to create something or unique. In the case of the carbon lam, I am curious if I can make a decent version. Not planning on becoming the competition, but seeing how they are unavailable in a retail setting, I could not buy and try one if I wanted to. The other lam, I basing my curiosity on my bend test.…. I still have not see any evidence that the version I am thinking of making, is certain to fail or underperform.
I am definetly going to make both these experimental composites.
I’ve got nothing to loose and I will certainly report any success or failure.
The failure part will be easy. The success, if any will be a hard sell without real world numbers. I will try not to overextend the offer I received for testing.
Rich, now that you have thrown down the gauntlet, I’m just going to capitulate from the get go. I will never build a faster bow than you and so I don’t intend to try.
Post by: Mad Max on January 16, 2021, 03:24:56 PM
Ha ha ha ha... Mattox... That is the funniest thing I heard all week... You, build the bow and prove me wrong... :thumbsup: I already said that I did mock ups with it and I know how tuff it is... I don't wish to take the time to prove something that I already know... However I may do one in the future just for fun...
I always wanted to do a build video on it to share with all those wanna-be bow makers that watch you tube... It's a great way to build a decent bow for cheap and get most of your supplys from home depot or cut-offs from a counter top shop...
Look at where he lives, may not be alot to choose from or shipping eats him up shredd
Post by: Shredd on January 16, 2021, 05:41:01 PM
Post by: Mad Max on January 16, 2021, 06:33:15 PM
No Osage in other country's, mostly
Post by: onetone on January 16, 2021, 06:38:29 PM
Post by: flyonline on January 16, 2021, 07:16:07 PM
Steve, uni fabrics would no doubt work, just not for what I am doing. Mine is not an open lay-up, so clamps are not an option. I have been trying to as closely as possible mimic the process used by manufactures, pultrusion, to make my composites. The main issues with an open lay-up are fabric saturation, surface finish and excess resin content, which is why I have started doing a resin infusion process. Do a search on that subject and you will see what I mean.
I'm aware how infusion works, and even tried a couple of crude experiments myself but I don't see why you couldn't use uni fabric, or use clamps to tension the carbon. It would be a fair whack of work and you'd have to build a specific mold and the way I was thinking there would be a lot of waste.
Quote from: Flem
I'd like to hear anybody's ideasHave you come across foaming agents for resin? I know guys have used it to build RC gliders to reduce resin weights (e.g. https://www.rcgroups.com/forums/showthread.php?1842115-Foaming-agent-epoxy (https://www.rcgroups.com/forums/showthread.php?1842115-Foaming-agent-epoxy)), I understand you need to be careful with heat though :laughing:
Post by: mmattockx on January 16, 2021, 07:27:18 PM
Ha ha ha ha... Mattox... That is the funniest thing I heard all week... You, build the bow and prove me wrong... :thumbsup: I already said that I did mock ups with it and I know how tuff it is...
In my world doing a mock up isn't the same as making the bow. I wasn't looking for a fight, I would genuinely like to see that. Cheap and effective are always a good thing in my book. Any info on calculating stack for one of these?
Look at where he lives, may not be alot to choose from or shipping eats him up shredd
This is true. Good bow wood is very thin on the ground here. I like working with wood but may eventually end up doing a lot of fibreglass bows just because the wood I have available is not great. If I had good supplies of osage, yew or juniper I probably wouldn't worry much about fibreglass but that isn't the case.
Yeah... That's a wee bit up there, isn't it... Well you are welcome for a visit in sunny Florida to escape some of that winter... I'll even spot you a few strips of formica... :)
Someday, who knows? It could be a formica bow building retreat. :biglaugh:
Mark
Post by: Shredd on January 16, 2021, 07:45:51 PM
Got no idea on stack... No fight here... You might have read me wrong...
I have used it instead of glass to see what the springback would be on an experimental prestress limb project... I had to really stress that limb to break it... Way more than wood would have handled...
Post by: Flem on January 17, 2021, 11:59:11 AM
I've seen foaming agents, but I'm thinking they will weaken the matrix. Right now I am having a hard time sourcing the hollow glass spheres I want. All I can find for sale are the ones with low crushing strength.
The ones with a crushing strength of 18,000psi or higher are not readily available.
Post by: Shredd on January 17, 2021, 12:23:53 PM
Post by: Flem on January 17, 2021, 12:38:27 PM
They are available... I found it before...
Care to share where you found them and if they are still available from your source?
Post by: Shredd on January 17, 2021, 02:27:40 PM
Post by: Flem on January 17, 2021, 03:39:14 PM
Thats like comparing Balsa wood to Ebony and thats not even accurate because Balsa is closer to S32 and no wood comes close to 27,000 psi crush strength.
Post by: Shredd on January 17, 2021, 07:48:17 PM
https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Glass-Bubbles-HGS19K46/?N=5002385+8745513+3292737335&preselect=8710783&rt=rud v
Post by: Flem on January 18, 2021, 10:38:59 AM
3M does not sell in small quantities to you and me. Maybe if you were looking for a semi load...
Post by: Shredd on January 18, 2021, 11:05:25 AM
Post by: Flem on January 18, 2021, 11:12:10 AM
Calling might be a good idea :thumbsup:
Post by: williwaw on January 18, 2021, 03:49:11 PM
Quote
I am definetly going to make both these experimental composites.
are the bubbles you are trying to source for the lam experiment or the core experiment? The stresses would not be as extreme for a core materiel.
Post by: Flem on January 18, 2021, 08:00:04 PM
Post by: Stagmitis on January 19, 2021, 06:32:50 PM
Whatcha think Shreddy? You can see the dark area on the belly lam compared to the back glass.....
Post by: Shredd on January 19, 2021, 06:36:20 PM
Post by: Stagmitis on January 19, 2021, 08:23:45 PM
[ You are not allowed to view attachments ]
Post by: Flem on January 19, 2021, 08:42:17 PM
What is the belly lam, Charles?
Post by: Stagmitis on January 19, 2021, 08:56:56 PM
Post by: williwaw on January 20, 2021, 01:06:39 AM
1971 Cravotta Brothers Black Hawk Catalog
http://nebula.wsimg.com/068e3a4a4372b21d6830b74cb42154a7?AccessKeyId=A203C91555201A4407B4&disposition=0&alloworigin=1 (http://nebula.wsimg.com/068e3a4a4372b21d6830b74cb42154a7?AccessKeyId=A203C91555201A4407B4&disposition=0&alloworigin=1)
Post by: Roy from Pa on January 20, 2021, 06:14:24 AM
That brings back memories, there shop was about 10 miles from me.
Post by: Flem on January 20, 2021, 08:39:26 AM
I was wondering what the dark area material is?
Post by: Stagmitis on January 20, 2021, 08:47:52 AM
Post by: Stagmitis on January 20, 2021, 08:51:29 AM
Post by: Mad Max on January 20, 2021, 09:11:32 AM
Post by: Flem on January 20, 2021, 09:17:38 AM
Post by: Mad Max on January 20, 2021, 09:33:03 AM
Flem, Its the brown craft paper underneath the decorative one on the face.
what is the craft paper for?
Post by: Stagmitis on January 20, 2021, 09:54:02 AM
Flem I know it looks thick but I think its the angle of the handle. Probably .50 or less. I can see the engineered paper layers if I look close. Darn thing even has a maple power lam extending about 5" past the fades Lol.
Post by: Mad Max on January 20, 2021, 09:57:31 AM
:readit:
(https://i.imgur.com/4sSs2Wp.jpg)
Post by: Flem on January 20, 2021, 10:06:48 AM
Now who would do something crazy like that. Like to see the numbers on that stuff. Wonder if the cognoscenti would approve :goldtooth:
Post by: Mad Max on January 20, 2021, 10:10:39 AM
Post by: Mad Max on January 20, 2021, 10:19:03 AM
They are not saying back and belly.
They are saying back and facing.
(https://i.imgur.com/fSA5eSO.jpg)
Post by: Flem on January 20, 2021, 10:41:24 AM
Post by: Stagmitis on January 20, 2021, 10:54:13 AM
Post by: Flem on January 20, 2021, 11:18:53 AM
Post by: williwaw on January 20, 2021, 03:32:23 PM
Flem, I read some where you have noticed density of laminates (glass/resin ratios) make a difference. Can you share more of your observations? Is it just the belly lams that it makes a difference on?
Post by: Roy from Pa on January 20, 2021, 03:45:56 PM
Flem, stop using those words I gotta look up.
LOL
Post by: kennym on January 20, 2021, 03:53:58 PM
Post by: Roy from Pa on January 20, 2021, 04:41:32 PM
Post by: Flem on January 20, 2021, 05:57:53 PM
Post by: avcase on January 20, 2021, 06:22:53 PM
you will have to find that out by trying, I suppose. It would be interesting to compare the density of formica to glass.
Flem, I read some where you have noticed density of laminates (glass/resin ratios) make a difference. Can you share more of your observations? Is it just the belly lams that it makes a difference on?
My father made me a laminated ash bow with Formica on the back and belly when I was a child. I still have that bow. For what it is worth, here is a quick comparison of mechanical properties. In terms of material properties, Formica is not much different than some of the high density tropical timber used to make bows.
Unidirectional
Glass Formica
Density 117.5 lb/ft^3. 84.3 lb/ft^3
Flexural Modulus 6.0 Mpsi 1.9 Mpsi
Flexural Stress. 111 ksi. 21.2 ksi
Post by: Stagmitis on January 20, 2021, 07:39:41 PM
I wouldnt discount the binghams carbon core. I would bet its one in the same as a carbon backing just sanded on both sides.
One of the best carbon backs I made for my hills started with .30 linear carbon whittled down in thickness and backed on both sides with S2.
Post by: Flem on January 21, 2021, 09:05:36 AM
Willie, If I we are talking about the same post I made, I had observed that Gordon's is stiffer than my homemade laminate using my tensiometer. But my observation about Gordon's resin to fiber ratio was WAY wrong. I read the description to suit my theory. Sometimes we need to carefully read all the information being presented before we respond with what we think we know is set in stone. Guilty here.
I'm going to start calling you the Gopher, you do some digging! :saywhat:
Charles, you got some crazy ideas ;).
I was wondering about that carbon also. I was thinking maybe it was material that had surface blemishes and they did not want to bin the stuff.
What was the total thickness of the carbon/S2 back? That sounds strangely familiar........
Post by: Stagmitis on January 21, 2021, 09:47:09 AM
Post by: williwaw on January 21, 2021, 03:36:59 PM
From reply 81
Quote
all that unidirectional fiber is overkill on the belly of a bowand from reply 70
Quote
I'm thinking the laminate we put on the belly side is not optimal. We use a laminate that was obviously designed to placed on the bow's back
Please allow me rephrase my question a bit.
What observations of your finished bows support these theories?
Post by: Flem on January 21, 2021, 04:09:39 PM
Post by: avcase on January 21, 2021, 06:07:25 PM
I wouldnt discount the binghams carbon core. I would bet its one in the same as a carbon backing just sanded on both sides.
Yes, this carbon is the same. I’m using Gordon’s .030” unidirectional carbon as a backing strip on a 120#@30” deflex-reflex longbow for the US Flight Championships this coming September. These are just one-off bows, yet designed to be durable enough to serve equally well as the regular hunting and stump shooting bow when not used for flight.
I wish I could find a source to get this carbon in .050” thickness.
Alan
Post by: Longcruise on January 21, 2021, 06:42:30 PM
Post by: Stagmitis on January 21, 2021, 06:47:42 PM
Post by: Stagmitis on January 21, 2021, 06:49:38 PM
Post by: onetone on January 21, 2021, 07:21:43 PM
Post by: williwaw on January 21, 2021, 08:25:41 PM
I’m using Gordon’s .030” unidirectional carbon as a backing strip.....I wish I could find a source to get this carbon in .050” thickness.
Alan
With .050 carbon on the back, how much strain do you calculate will be on the belly?
Post by: Flem on January 24, 2021, 10:31:27 AM
Alan"
I have been holding out, hoping you would share your source. But it would seem from your last post that this source has disappeared?
Post by: avcase on January 24, 2021, 02:13:05 PM
I have been holding out, hoping you would share your source. But it would seem from your last post that this source has disappeared?
I am using the unidirectional carbon that Bingham’s sells. It is the same as the Gordon’s unidirectional carbon that I bought in previous years for backings.
Post by: Flem on January 24, 2021, 04:34:25 PM
As long as you don't tell anybody where you got it.