Linen backing raising draw weight?

[toomanyknots]

Ya, before you say no, I made two bows. Both red oak. Same exact dimensions. One unbacked, one backed with linen. The unbacked one came out at 45# at 26". The linen backed came out at 65# at 26". Big difference. I thought that I've read on some threads that linen backing won't affect weight or tiller?

[NTProf]

Did you check the draw weight before you backed it to see if it actually gained weight? I am not saying it didn't, but the difference may have been in the wood's density or something? I don't know. I have backed bows with linen after I tillered them, and the weight did not change. But that is just my experience.

[sailordad]

also check the limb thickness with a dial or better yet digital caliper
i'll bet the heavier bow has a little thicker limbs too,especialy if all other demensions are equal

[toomanyknots]

Dimensions are exact to a 32nd of an inch. (way it looks on the tape anyway, I don't have access to either a dial or a caliper or I definitely would check it.) I use a jig for consistent thickness and a "jig" of sorts, if you can call it that, for width. Both pieces of wood looked identical, same thickness of rings, same color, exc...

"I have backed bows with linen after I tillered them, and the weight did not change. But that is just my experience."

Ya, I can second that. I just linen backed a "ambush style" bow after tillering, and it did not raise the weight. (I think, it was supposed to come out at 55#, and came out at 55# anyway, but I didn't weight it before I backed it). This time applied the backing before bending it at all. I think that just how the belly is said to compress and get set, and in effect become permanently compressed, I bet you the back of the wood also gets permanently stretched out a bit. So maybe the linen stopped it from stretching, and forced all the bend to be compression, thus raising the weight from forcing the belly to compress more than it would normally?

[JW_Halverson]

1/32 is over 31 thousandths of an inch which sounds even less critical, but in tillering, each scrape of a good blade takes off just a couple thousandths.  And how many of us have had a tiller go off because of just a few too many licks scraping, huh? 

Yeah, I use a dial caliper when roughing in the limbs.  I hate working with fractions, they make me fractious! I too used to think same dimensions made same draw weight bows, especially when I was working with dimensional hickory lumber.  Fact is, some pieces of wood are more dense than others and some pieces even from the same tree are better than others.  Every bow is a puzzle unto itself.

The real test is to make the bow, finish it out, check the draw weight, shoot it in for a few hundred arrows, check weight again...and then back it with linen and check your draw weight. 

[mspink]

As JW said, all it was is the difference in densities of the wood,. Ive mad a lot of red oak bows and found that if you take a heavy thich ringed board and a thin ringed red oak, that is less dense, cut to the same dimensions, when done the thick ringed bow will be heavier everytime. Other species as well. More dense = heavier bows if made correctly.

[NTD]

Yep unless you make a bow of a certain weight and THEN back it, it's all speculation....

[toomanyknots]

"Yep unless you make a bow of a certain weight and THEN back it, it's all speculation...."

I guess, but isn't 20#s a bit of a big difference for just density? Doesn't it make sence that not allowing the back to stretch would make the belly have to do all the work to bend, compressing the belly more then it normally is, thus making it a heavier bow? I think if I tillered and then backed it it would not have any difference since the back was already stretched out. Since linen is in fact doing like 0% work anyway.

"Ive mad a lot of red oak bows and found that if you take a heavy thich ringed board and a thin ringed red oak, that is less dense, cut to the same dimensions, when done the thick ringed bow will be heavier everytime."

You have got a difference bigger than 5# for the same dimensions? Cause I havent? I sure have not got a 20# difference.

[NTD]

"I think if I tillered and then backed it it would have not difference since the back was already stretched out. Since linen is in fact doing like 0% work anyway"

Have you read the TBB's yet?  The back is already stretched out?  No!  The back stretches when the bow is bent.  So unless you applied the linen while the bow was at full draw the the linen would still be taking tension forces.

In the 2 different bows you have of the same dimension, where they taken from different boards?  There can be density differences, MC differences too.  What about ring size? How comparable are they?  When you add up density, MC, and the fact that miniscule amounts of thickness variation can affect draw weight it's likely it's not the linen.

Now, that being said I would encourage you to experiement more.  But just make sure you stay to the scientific method as much as possible, otherwise any conclusions you make are nebulous at best.  I would say make the bows from the same board.  Measure MC's and use a digital caliper to ensure thickness measurements are the same.  I'm all for you rocking the bow making world and would love to see you change long held assumptions but if that's your goal there must be integrity in testing.

[toomanyknots]

"The back is already stretched out?  No!  The back stretches when the bow is bent."

The belly in an all wood bow is not the only place that does work, as you know, so why would it be the only place that takes set. What you under look is that after tillering the back HAS stretched a bit, into "tension" set, as the belly has crushed into "compression" set. Why would you think the back wouldn't stretch?

"Have you read the TBB's yet?"

Yes, but that doesn't have anything to do with what I'm saying. I think you just don't understand what I'm saying.

"There can be density differences, MC differences too.  What about ring size? How comparable are they?"

See my second post. Also, can anyone attest to having a bow with the same wood and dimensions come out any different than around 5#s?

"Now, that being said I would encourage you to experiement more.  But just make sure you stay to the scientific method as much as possible, otherwise any conclusions you make are nebulous at best. "

lol I know, I know, I really just thought this was crazy and should share it with yall. So ther ya go.



 

[NTD]

"The belly in an all wood would is not the only place that does work, as you know, so why would it be the onlyplace that takes set. What you under look is that after tillering the back HAS stretched a bit, into "tension" set, as the belly has crushed into "compression" set. Why would you think the back wouldn't stretch?"

Do you build a lot of bows that take a lot of set?  Sure the back retains SOME memory.  But by your argument if I tiller a bow and THEN back it with a slat of wood without inducing reflex I won't raise draw weight because the back is already stretched.  That is what you are essentially saying.  That linen adds weight but only on a pretillerd bow.   See what I"M saying?

"Yes, but that doesn't have anything to do with what I'm saying. I think you just don't understand what I'm saying."

The TBB's cover everything that you have brought.  How wood works and takes strain, how backings affect performance, how recurves work.  Unfortunately for a dunce like me it took Many Many Many readings to adbsorb a fraction of the information they contain.

It IS crazy and thank you for sharing.  Now we can try to figure out WHY it's doing it.

[dragonman]

I have made ash bows taken from right next to each other in the tree ,made identical limbs as measured with a digital vernier and had more than 5# difference,I have measured limbs on the same bow with digital calipers extremely accurately to see if I can avoid set and still one limb is well out. Wood is very variable over small distances within one tree, it appears, to me anyway...... I only made one linen backed bow, TBB said it makes bows unbreakable...mine exploded and clean snapped accross the linen back.!!!

[adb]

Wood is a natural material, and 2 staves, even from the same tree, with the same dimensions, will NOT make the same bow. Linen backing, unlike sinew, does not add draw weight. Same as rawhide. It only provides insurance against breaking.

[oat]

How could you know that the DW increase is not the result of glue/back wood composite  which could move the normal plane a bit to the back and then you have a bit more belly to do more work.

[Pappy]

I have had Osage/Hickory and especially Hackberry out of sister stave come out with way different weights at the same dimension's .That is why I always leave them thick when I rough them out before starting the tiller process. Never used Lenin so just guessing,but I would say
no.
   Pappy