Twill Thrill

[Kirkll]

About a month ago i got some of this China Twill carbon and wanted to give it a go... First i tried it in the core to help stabilize a lighter draw weight bow instead of using stable core. I must admit, it did a little better job adding torsional strength. It was noticeable, but nothing to get excited about.

Well i thought i'd do an experiment on some ILF limbs. I wanted a set of long limbs (25") that would draw 42 @ 30"  using my static tip SS forms. I typically run an .001 FT on these limbs, but the lighter weight limbs always get real squirrely and have real poor torsional stability or strength. So i run a par instead of the .001 to help keep some more limb thickness at the base of the curl to help stabilize things better... Typically once i get below .190 thickness at the base of the curl its wanting to go sideways pretty easily...

So i decided to to a test.... I built a set at .185 stack with a par. I used a maple belly lam, and an .044 action bamboo lam towards the back. i used .040 black glass on the belly, and a layer of stable core  at .015 and this .015 Twill carbon on the back. I figured for a light draw weight bow , i'm still going to have .030 composite backing, so it should be plenty strong....

What happened when i strung this up was nothing short of amazing... First thing i checked was torsional strength at my standard width profile. When i tried to twist it with my hand it was like i was trying to twist a 60 pound limb.... I thought to myself Aw Chit!  i missed this draw weight by 12-15 pounds!  Then i drew the bow slowly watching the tracking, and this thing came back like butter and perfectly perfectly straight... no adjustment needed either.... I was shocked!  She weighs in at 40 @ 30" and every bit as torsionally stable as a 50-60 pound glass bow..... Incredible difference. 

The combination of the Twill right over the stable core makes it feel like a double carbon bow with carbon on the belly side too.  This is going to be a great combo with a glass belly to adjust tiller and draw weight a few pounds....

I just had to share this with you guys. I'm not easily impressed after all these years of building bows, but i'm absolutely thrilled with the results.

I pretty much gave up building carbon limbs years ago. But i'll be buying more of this stuff and use it for backing. I can easily get lower draw weight target limbs stable with this combo...
 (some photos)

https://photos.app.goo.gl/E3qrHpPYmnAjGcuH7
Kirk

[Mad Max]

Nice call on that one

[Mad Max]

I got one of these from Mark a few years ago.
I want to make one some day.
57" NTN 12" levers

[B-JS]

I'll never understand why placing stabilcore or carbon in the center of a bow should give more than a nice black line.
If i use 45/45 Carbon, i place IT as far on the outside of the Stack as possible to get the most Out of IT.
If i use Veneer and clear Glass, it's under the Veneer.
But for max effect IT needs to be on the outside in Back and Belly.

[Kirkll]

I'll never understand why placing stabilcore or carbon in the center of a bow should give more than a nice black line.
If i use 45/45 Carbon, i place IT as far on the outside of the Stack as possible to get the most Out of IT.
If i use Veneer and clear Glass, it's under the Veneer.
But for max effect IT needs to be on the outside in Back and Belly.

Absolutely correct…. There have been some in depth debates regarding how the core works in a bow limb. The tension, compression , and location of the neutral plane all a part of it… but….

I’ve been using the stable core in my recurve limbs for years now, and it definitely adds more torsional strength to low poundage recurves in various degrees,  regardless of whether it’s towards the back, or the belly. The best results were using .030 glass with the stable core just under the glass both belly and back.

The problem with that approach was that using that much composite material belly and back on ultra light draw weight RC limbs didn’t leave you much core material at all….

The use of this .015 Twill carbon right over the .015 stable core just on the back of the limbs made a HUGE difference in lateral stability, but it didn’t add a lot of extra draw weight like using thicker pre preg carbon lay ups I’ve used in the past. I don’t think the twill weave is as strong as the conventional one over , one under bias weave carbon… but the 45/45 direction on the Twill still has good twist strength.

This might be a great thing to consider when building something seriously radical in design…..  I will be using this combo more on some heavier draw weights with a thicker core in the future. I believe this could bump performance levels considerably just in limb mass weight reduction.

Kirk

[Crooked Stic]

I am not at all surprised Kirk. But never thought of adding stablecore for the extra composite.  The high dollar stuff 45/45 from Rosewood does good but too many $$$.

[B-JS]

I use 45/45 under the Glass or under the Veneer for several Years now.
Best Option for low poundage.
My weave is just about 0,25mm thick in the Stack.
Thats 0.01"?
If i need some SERIOUS torsional stability for extreme Recurves, i use 0.02 45/45 Carbon on top of Glass or Carbon with that much 45/45 in it.

And yes...
Stabilcore adds a bit stability.
But it's just black 90/0 glass and absolutely ridiculously pricy for what IT IS.
Real 45/45 Carbon weave costs less and does way more.
So why by that stuff?

[Longcruise]

Kirk, I'm still not clear on exactly what your layup is on the back of the subject bow. ??

[Kirkll]

Actually the stable core isn’t that expensive at all if you buy it in large quantity rolls directly from Custom King, or in your case buy it from Bear Paw over there in Germany.

I like it because it’s vey light weight and thin material. Used together with a thin 45/45 carbon weave makes a pretty impressive matrix.  This thin twill carbon we got from China was pretty cost effective compared to most other carbon I’ve purchased over the years…. But it makes me want to go back to my old carbon supplier and see what it would cost to lay up this twill weave locally now. I’ve never played with this before….    Kirk

The pre preg Carbon fiber panels can be laid up in custom thickness and have various different combinations of uni added for extra zip for higher performance. But nothing beats that 45/45 weave for torsional stability right on the back of the limb….

Well that’s not true… putting it both belly and back is the strongest combo, but it’s very difficult to keep the belly side carbon from shearing the belly side core material on RC limbs that have a short working limb. The things are time bombs waiting to fail….it’s not a matter of If they will fail…. It’s just when… look at all the border bombs out there….  I’m done with playing with belly carbon bows. Have been for years.

[Kirkll]

Kirk, I'm still not clear on exactly what your layup is on the back of the subject bow. ??

I just used the .015 Twill carbon directly on the back right over one layer of stabile core. Gives you an .030 backing …. Ultra light in mass weight, and made that  light weight limb feel like a 50-60# limb in torsional strength… I kid you not…. Kirk

[B-JS]

Morrison MAX 6 are Carbon Back and Belly Glass with Carbon on top.
Don't hear much of them failing.

Border goes full Carbon.
Most of the Border got killed by Low GPP.
They Store a shitload of Force but are still Shot with 7-8gpp to max drawforce.
That compares to about 3-4gpp with a conventional limb.

I build 60-64" Hybrid Longbows with a lot of preload with full Carbon since 2 Years.
I had ONE fail since. And this one was 90#.
As long as i keep it below 50# they are safe.

I'm just not a fan of stabilcore.
And PB just went nuts with their prices.

Try to get some .02 45/55 Carbon layed Up locally und use IT in Back and Belly.
I'm a fan of local supplies.
Still working on the perfekt Carbon Made in Germany for my bowyer buddy and me.
Won't be cheap, but will do exactly, what WE want IT to do.

[Crooked Stic]

I have two curves with .020 45/45 (high dollar stuff) over glass frt And belly. That seem to be holding up real well.

[Longcruise]

Are you guys using pre preg or "cloth" mat?

[Kirkll]

You guys that want to play with carbon on the belly of a limb. Have at it!.... Been there, done that, spent thousands of dollars building prototypes. Sure... It can be done, and has been done, and i've done it myself successfully.

But for a small time bowyer that cannot buy carbon in large quantities, and do not build 100's of bows per year, it's too darn expensive to try and hit exact draw weights for a custom orders.... That and the longevity is always in question. They are just not as durable as glass bows...

I just wanted to share this experiment with you using this thin twill carbon over stable core. Great combo for ultra light RC limbs. It would probably work the same over thin glass too, or maybe use some of that core tough glass that Binghams sold for years under the carbon. grind it to.020 .

Kirk