Fancy Yew 55" // 35# @ 25"

[DC]

Very novel idea and well executed. It must be a bear to brace. Nice bend. For future reference "V" joints on the tips are very easy to do. The wood is thin enough to flex a bit so a good glue line just happens

[simson]

Really nice work, but if you have no string lift off, that epoxi thing only adds mass and makes your bow slow.
I admire the idea and like experimenting also.

[simk]

Simson, thanx for making that clear - i'm not completly through with bow mechanics so it was try and error.

so this epoxy thing has zero effect on stacking as long as the string doesent lift???

ok. what if i tune it a liitle bit and bevel and round more from the bottom? ther's still room for doing that i think.

while building i often thought about the relation between the exact shape of this epoxi thing and draw curve. i was even close to ask here at pa...should have done that.

cheers

[simson]

Simson, thanx for making that clear - i'm not completly through with bow mechanics so it was try and error.

so this epoxy thing has zero effect on stacking as long as the string doesent lift???

.......

Yes no effect, you can see the string is just at the end of the yew limb. As said that epoxi is just additional mass at the most critical point - at the end of the limb= end of the lever.
You should think over the mechanics of a recurve bow. There are a lot of parameters that influences the efficiency.
Here is a very good article: https://www.bio.vu.nl/thb/users/kooi/thesis.pdf

If you don't believe me:
Measure the speed now and compare with cut of epoxi. I'm absolute sure you will see a great influence of the lighter lever (= limb).

[backtowood B2W]

Nice experiment! Looks like the stick they use in China for transporting two buckets of water!

PS: yes im in! Going to write you a pm!

[simk]

Thanx +1 Simson - the bow is now temporary stored in the hall of shame  maybe I will do as you suggested...cut it off and measure speed before and after.

Thanx + 2 Simson for the link - very very scientific, almost rocket scienece from my point of view - maybe something for the upcoming long and dark winter evenings.

Allow me one more question: With the shown draw of 26" the string angle is almost 90 dergee. Would there be a positive effect of this epoxy thing if drawn further??? Del?

bttw: Maybe I could sell it in china for good money? Looking forward to hear from you.

Cheers

[Del the cat]

If drawn another say 3" the string would lift off and effectively lengthen, lowering the draw weight like the "let off" on a compound.
Imagine you bound the string so that it couldn't lift, if you draw another 3" the tips would pull back say another 1". If the string is allowed to unwind off the epoxy that will let the string come back further... so for your 3" of extra draw the tips would only be coming back maybe 0.75" .
So what does that mean?
At 3" extra draw, as the sting unwinds the pounds per inch of draw weigh is less (let off) and there is less strain on the bow that there would have been without the epoxy cams.
Another way to look at it.... you are suddenly putting an extra few inches of slack into the string, so it draws further.
In terms of performance, this will give a slightly more gentle acceleration over the first few inches of the loose, which should give less arrow flex and less wasted energy.
All the above is just my understanding of it, I'm happy to be shown to be wrong... terms and conditions apply etc etc
Del

[simk]

Sound's interesting del  Maybe I'll mount my fullface helmet and draw it to 29" (and take a lot of set... )

I was also thinking about changing tiller and let it bend more on the outers so that the "let off" effect will begin on earlier draw - but this will probably cost me draw weight.

Cheers

[bjrogg]

Smik I wouldn't change your tiller. It looks great. Just the shape of your tips. They need a bit more radius or less angle to let the string come off before full draw. I personally like a fairly gentle curve that increases the amount of string that is let off as the last few inches of draw are drawn. I wouldn't put that bow in the hall of shame. It's a interesting idea. Just might have to tweak it a little. Hope to see it again.
Bjrogg

[simk]

Hello bj

This option I was also evaluating when falling asleep yesterday (-; The problem is, that the tips are fairly reduced with the hole so that I'm getting into statical problems with further reducing to a bigger curve. So I thought to just deepen the middle groove for the string what will virtually shorten the bow and get that better radius so that the string lfts off earlier  - as you suggested!

That might be the plan now. My update will follow.

Thanx 2 all. You are so helpful!!!!!!

Cheers

   

[bjrogg]

Smik, just throwing this out there. Could you add more epoxy mix to change angle of tips. Maybe cut some off and add some on. Not sure just a thought.
Bjrogg

[Hawkdancer]

It appears that you cast the epoxy as a block right onto the tip and then shaped it by hand, from a pattern, maybe?  Very unique idea!  Nothing wrong with a short(er) 26" draw length, either!  Nice bow!
Hawkdancer

[simson]

Just had another look at your construction.
If you like to do another experiment, think of this:

What about glueing on that epoxi thing on the belly (not on the back ), making just a Quarter of a circle. Limbs more or less straight at brace. When drawing the bow the string unrolls from the cams. Just an idea ...

[simk]

another good idea bj. I'll give her some time now to decide on how to become a working bow. She'll be back 

Hawk: Just place the stick in a cup/form filled with epoxy, place the stick in it and let it react. Where you don't want the epoxy to stick put some wax or grease first. If you plan simple nocks wax the tip and the sand it down then. The epoxy will only stick where you want it. For UV-protection you should lack the epoxy (pic).

Simson: That sounds interesting. Still hard to imagine...my inner eye somhow doesent work with your description. If you do you suggest some kind of deflex-construction @ the fades wouldn't this lead to a very low initial draw weight? Of course it's to consider also that it's tillerd out with 2" of reflex. I'm still lookin' for the best solution and I'm open for experimental ideas. Maybe you could try to explain again or draw on your weiss-beermat for me 

Any design-suggestions welcome for those epoxy things!!!!!

Cheers

[upstatenybowyer]

This is a great looking bow and cool ideas with the tips. Reading everyone's responses has been educational as well. Thanks for posting this simk!