alternative materials & new methods... etc

[williwaw]

A nice discussion is going in a parallel thread regarding alternative lams materiels where carbon or glass is typically used on the back or the belly.  https://www.tradgang.com/tgsmf/index.php?topic=174583.0

Foam is mentioned as an alternative to wood for cores, but my understanding is that its primary benefit is temperature and moisture stability. Arrow speed improvements attributed to core selection are said to be nominal. 

Some comments suggest presently used glass and carbon lams are not utilized as fully as they might be for performance gains.   Are there better core materiel's out there to build with?  Can anyone share their their understanding of what materiel properties would be required to make a better core for a faster bow? Or maybe reference or comment on any previous development attempts?

[Crooked Stic]

First thing is good design. I have never tried it but I see several people mention walnut edge grain. Have used Yew edge grain it is pretty stiff. The old standby Elm edge grain.
I think the actionboo is used because it is real consistant and pretty decent core.

[Longcruise]

Ive had this wood on my mind for a while.  Paulownia.

From the wood database:

  Comments: The other Balsa. Paulownia is used in applications where a lightweight (yet proportionately strong) wood is needed. It’s widely used in Japan for construction of the koto (a stringed musical instrument), as well as other household items, where the wood is referred to as Kiri. Paulownia is one of the fastest growing trees in the world, capable of growth rates of well over seven feet per year as a seedling! But while it’s highly appreciated and cultivated in Asia, Paulownia has come to be considered an invasive species in the United States.

Paulownia was named after Queen Anna Pavlovna of Russia (1795-1865), and is sometimes called Royal Paulownia or Princess Tree.

I might track some down and try it.  The more I figure out about this bowyering thing the less im focused on the search for the ideal core wood.  The amount of weight saving from core to core doesn't seem to have much bearing on performance.   This was brought home to me when I did an experiment with a 66" ASL.   I chronographed the bow and then continued to check speeds as I added more and more weight to the tips.  I would have to check my notes for sure, but I think it got up there to more than an ounce on each tip.  The loss of speed was way less than i expected.  Since then I don't give hardly any thought to the weight of tip overlays!   

So, my conclusion was that the effect of weight is the most noticeable at the nocking point and progressively less noticeable as it moves out the string to the nocks and then continues down the limb to the fades.

That area from nocks to fades is the area that is influenced by the weight of the core material.  And based on my observations,  it is the least important area to try to save weight.  That's what has gotten me off the search for lighter core woods.

But none of that addresses the possible return rates of the various core materials and maybe it's inconsequential when dealing with the performance of the most common and proven core woods.   Most of the work is taking place in the first .050 to  .100 of the back and belly surfaces so, how important are the return characteristics of the wood or whatever that is making up the rest of the limb?

It's interesting to see the loyalty that many archers have for the various core materials.   Every possible core has a following and many professional bowyers seems to represent that certain cores are superior.  That's smart marketing.

It might be worth paying more attention to the weight of the string serving.

[Shredd]

  I'll say it again... Your best bet for a fast bow is a recipe with a great bow design... With that and standard wood core and glass you can reach speeds of 186 to 193 @10gpp and possibly faster...  After that and you still want to increase speed try tapering your glass and trying lighter core materials...  To me it does not make sense to go with exotic materials and/or tapered glass on an inefficient design...  Plus straying from the standard layup could be opening up another can of worms...  There could be an exception or you could get lucky but this is how it usually works...  You spend months and go through about 15 to 20 bows to widdle down a very efficient recipe to get you 186 fps, now you decide to taper the glass and go with a lighter core...  You get all excited...  You are gonna break that 190 mark...  Guess what??  Your bow shoots 180 fps... Why?? Because you changed the recipe...  Now you have to start all over again... Maybe not go through as many bows as last time because you have most of the kinks ironed out but you will probably have to make another 5 to 10 bows just to find out you broke even or gained 2 fps...  You may gain 4 to possibly even 6fps but I doubt more than that...  But then I have not gone to that extreme yet so I don't truly know...  Then there is the possibility of only gaining 1 to 3fps if your design is only shooting 175 fps to begin with...  A lot of trouble and less stout bow for 1 to 3 fps... Better to perfect your design with standard lay up before you start getting funky...

  If you are gonna go for a lighter core I suggest a nice piece of Douglas Fir for the whole limb in a bow under 35# and a maple/fir spliced core for a  heavier bow...  To go much lighter than fir I believe you are taking chances...  Kenny has a cool way of splicing a core lam, I forgot what he told me... Maybe he will share that with us...  I would like to hear it again to take note of it...

[Shredd]

  In reference to Longcruise's post...

   I have talked to bowyers that swear that certain wood cores shoot faster and smoother and talked to other bowyers that say the core does not really matter and seen no difference in performance between different woods...

[Longcruise]

Yup.  There are endless internet conversations on the topic but no supporting evidence that i know of.

Smooth???  What is "Smooth"?  You nail the answer with your reflections on design versus material performance.

[williwaw]

Kenny has a cool way of splicing a core lam, I forgot what he told me... Maybe he will share that with us...  I would like to hear it again to take note of it...

hopefully he can.

Tapering glass is worth a thought.  How much of a taper have you experimented with?  I hope I am not asking about something that has been covered in previous threads.  Have you seen much written about this online elsewhere?

thanks

[Shredd]

   As I said I have not gone to that extreme so I have not tapered glass yet... 

   Just a note... I have hit 193 fps with standard lay up...  If I get to 196 and I feel that I have hit the wall, that will be one of the few times that I might go exotic just to break 200 and just to say I did it...   Anything over 184 is plenty fast enough and really no need to go much faster unless you got reasons to...  I got mine...   

[kennym]

I tapered glass on one bow, didn't seem to make a diff, then it was pointed out that you are cutting glass fibers on the tapered side ...

The only cool spliced lam I can think of was one I made with maple and walnut using tapered lams , seems like about .004 or .005 " per inch .

Thick end of maple to riser and thick end of walnut to tips.  Hoping for a lam that was lighter at tip end.  Wasn't my idea tho, read it somewhere.

Thad Soy got that bow in a swap and told me later it was the fastest one he had. I think he was just being nice tho.

As for core materials, here is a test I did long ago...

http://www.tradgang.com/tgsmf/index.php?topic=143549.msg2519680#msg2519680

[Roy from Pa]

I've found 1/4 sawn elm to be the best for my BBO bows.

Not speed bows but one that I made for fujimo hit 175 fps, not bad for wood and boo.

[Flem]

I've just been reading about foam cores. Fascinating stuff. There are quite a few patents regarding the material. Here is a excerpt from a Hoyt patent, circa 1987;

 "It has been found that a substantial reduction in bow limb inertia resulting in a substantial increase in arrow velocity is achieved by reducing the weight of the core strip. Applicants have substantially reduced the weight of the core strip while retaining adequate physical properties for the purpose by constructing the core of a material known as "syntactic foam" which consists of a plurality of hollow micro spheres of less than 100 microns in diameter in a matrix of hard synthetic resin. The relative volume of hollow spheres is such as to attain a density of the "syntactic material" which is substantially less than any solid or composite hardwood core.

It was also found that in addition to reducing the weight of the core strip and therefore the inertia of the bow limb in this manner, that the hollow micro spheres in the core material also function as microscopic shock absorbers to dissipate energy of impact and therefore the syntactic material has a relatively high resistance to impact which renders the material peculiarly suitable to bow limb construction. Archery bow limbs in normal usage are subjected to relatively high impact stress every time an arrow is shot and the bow limbs approach a braced position.

In the case of heavier hunting bows it is contemplated employing, in addition to the hollow micro spheres, reinforcing fibres for further enhancing the physical properties of the syntactic material while maintaining a density substantially below that of any solid or laminated hardwood. Moreover, when molding the cores the rolling action of the spheres helps distribute evenly the hollow micro spheres and fibres in the very thin tip ends of the tapered cores."

[mmattockx]

I've just been reading about foam cores.

The fancy target limbs use foam cores these days. They claim better performance, but I haven't seen any testing that confirmed that. They should offer the ultimate in consistency for production manufacturing, though.

Applicants have substantially reduced the weight of the core strip while retaining adequate physical properties for the purpose by constructing the core of a material known as "syntactic foam" which consists of a plurality of hollow micro spheres of less than 100 microns in diameter in a matrix of hard synthetic resin. The relative volume of hollow spheres is such as to attain a density of the "syntactic material" which is substantially less than any solid or composite hardwood core.

I've never seen or handled the foam, but I have seen comments from bowyers that the foam they used is pretty much the same density as maple. I assume there are many different densities available if you can find them, but have never looked. It's good to have the correct name for the foam, I had looked for it but had little luck without knowing what its trade name is.


Mark

[Roy from Pa]

I had a pair of limbs for my ILF bow that were carbon limbs with foam core.

They were noisy and the speed did not impress me at all.

Sold them.

[Shredd]

Thanks for sharing again Kenny...

[mmattockx]

http://www.tradgang.com/tgsmf/index.php?topic=143549.msg2519680#msg2519680

Just got through this thread. What a great amount of info, thanks for all your work on that one Kenny.

I had a pair of limbs for my ILF bow that were carbon limbs with foam core.

They were noisy and the speed did not impress me at all.

Sold them.

Were they noticeably lighter than wood core limbs? I think they are mostly a marketing exercise and maybe an improvement from the manufacturing side, but no real improvement in terms of performance.


Mark

[Flem]

Kenny, can you tell us about Loren Piper and "Pipers Bowtuff"

[Roy from Pa]

Physical weight wise, not much difference than my other wood core limbs.

Both my limbs and the carbon limbs were the same exact draw weight.

The Bear archery glass with wood core was noticeably faster.

[kennym]

Kenny, can you tell us about Loren Piper and "Pipers Bowtuff"

If memory serves me correctly, that is the guy who made his own glass and was making solid glass limbs?

He wanted me to be a dealer for it, but never sent me the sample to test, then he kinda disappeared...

[Longcruise]

I recall the failure of foam described as being dramatic with an explosion of foam bits.  Belker used to sell it  but he got out of bowyer supply with the change to Bivouac.

[williwaw]

Thanks for all the replies. Quite a bit to digest, especially the earlier testing by KennyM.
As with most tech developments, improvements come slowly and incrementally. One in a while a game changer comes along, as we have seen happen a few times with the wheelbows.

A bit about Fred Bear copied from the 3rivers website.

He found that the fiberglass, currently in a crisscross pattern, worked great on the back of the bow, but did not work well on the belly. This prompted Bear to begin manufacturing bows with fiberglass laminated backs and aluminum bellies. Interestingly, the aluminum was scrapped from B-17 bomber airplanes of WWII.

However, Bear found that the aluminum caused too much handshock when shot and there were also a large number of bows returned because of delaminating, which was caused by the large amount of shock. This warranty problem caused a substantial strain on the company’s finances; nonetheless, Bear insisted that all bows be replaced if returned broken.

This prompted Bear to begin developing a unidirectional fiberglass and, in 1951, the aluminum belly bows were discontinued entirely.

Two years later, in 1953, Bear patented the working recurve limb, which is the design that almost all modern recurves use today. The next year Bear began marketing their new fiberglass working recurve – the Kodiak II.

If Fred were still with us, would he think 250 FPS @ 10 GGP  is doable?