Speed of cast vs draw weight?

[DC]

Wood is normally able to stretch further than it can compress.

 Source?

Common sense matey

  Unfortunately it's false. 

Before I start making popcorn are you guys talking strength or distance?

[Badger]

Strong in tension simply means it is harder to bend and resist breaking. Elasticity is another thing all together. Wood does not stretch very much at all, nearly all the bend is because of compression being elastic. That is why when you heat bend something you strap the back so it cannot stretch and break

[PatM]

Wood is normally able to stretch further than it can compress.

 Source?

Common sense matey

  Unfortunately it's false. 

Before I start making popcorn are you guys talking strength or distance?

  It can only mean distance when worded like that. 

[willie]

  It can only mean distance when worded like that. 

@Patm, bownarra

there's lots of tests results out there from folks who like to break boards, but of course as bowyers we are more concerned with set taking.

do you have a source for "distance" or elongation before set in tension of any species?

[PatM]

It is known that wood breaks when stretched a minimal amount.  The elongation distance is very short before that happens.  Tensile "set"  is likely not an issue at all with wood bows in most cases. 

 That's likely why tensile members in wood buildings are replaced by steel.

[willie]

That's likely why tensile members in wood buildings are replaced by steel.

My understanding of why wood is not often used as a tensile member in wood buildings is because of a limitation in the practicality of making adequate mechanical connections in the field. Tension shears the wood along the grain at a connector, an example being a bolt in the end of a board pulling out the end. Actually wood is used quite a bit in tension in wood truss designs, but requires large carefully glued gussets or properly sized nailplates.?

Please consider this quote from the flight bow section.

Q.  Are record quality bows pretty much all Osage and Yew? What would be the top five?
A.  Hickory for self bows, Ipe backed with hickory or bamboo is at the top for backed and multi-lam bows.

Do you think the hickory backing on an ipe backed with hickory is stretching further than the back on a
hickory selfbow? what about the bamboo? could the advantage of a multilam be that the bamboo is stretching more and storing more energy than the ipe belly?

Tensile "set"  is likely not an issue at all with wood bows in most cases.

If that is true, we should be looking into constructing better wood backings

[Woody roberts]

Got the Ash pyramid bow built today. 67-1/2” N to N. 40 lb at 26”. Thinking about heat treating the belly. What do you all think.

Ive only shot 4 arrows so far. I thought it might be better to heat treat before it picked up anymore string follow.

Any advice appreciated.

[PatM]

[quote author=willie link=topic=68728.msg964764#msg964764

Do you think the hickory backing on an ipe backed with hickory is stretching further than the back on a
hickory selfbow? what about the bamboo? could the advantage of a multilam be that the bamboo is stretching more and storing more energy than the ipe belly?

Tensile "set"  is likely not an issue at all with wood bows in most cases.

If that is true, we should be looking into constructing better wood backings
[/quote]

 Even if it does, it still can only stretch a tiny amount or it will break.  The amount of "working" stretch  has to be tiny.   

 I'm not sure what you mean by "constructing"  a better wood backing.  We don't do that.   We just harvest what nature made.

[Yooper Bowyer]

It seems this topic has shifted and developed quickly:)  Any engineers here with input on the mechanical properties of wood, or even just the terminology?


A moderate heat tempering never hurt anything except glue lines -- Just be careful not to let the wood get black.

Post photos when your done!

[willie]

Got the Ash pyramid bow built today. 67-1/2” N to N. 40 lb at 26”. Thinking about heat treating the belly. What do you all think.

Ive only shot 4 arrows so far. I thought it might be better to heat treat before it picked up anymore string follow.

Any advice appreciated.

Woody, do you know the cause of the string follow? hope the site will let you post some pics soon, and please let us know if going off track in your thread is offensive. Sometimes discussions just kinda evolve in strange places.

[willie]

Any engineers here with input on the mechanical properties of wood, or even just the terminology?

yes, and sometimes the terminology get difficult, as folks here come from many different backgrounds, but you should ask technical questions if woody is ok with it.

[Woody roberts]

I don’t mind the thread straying at all. I’m taking it all in and trying to learn.
Ive decided against heat treating the bow for now. Ive put close to 100 arrows through it and is very smooth and accurate. Only getting 125 fps with 550 gr arrows. I would like to have more speed but I’m confident I can kill a deer with either of my 2 bows I have.
Ive built six in the last 2 weeks and see no reason to stop. Only 3 have broke so far. I have a bear reflex and a bear recurve but no interest in hunting with a bow I didn’t build myself.

Ive knaped points before and I know where a good patch of river cane is so that will be next. Ive always been an avid hunter but since the kids are all out of the house I only need a couple deer a year. Most of my deer the last few years have been taken with a 45 colt revolver. I like to hunt close.
Thanks guys. Woody

[bownarra]

As I've mentioned a few times before.....
Take a bow and draw it far enough to take a few inches of set.
Cut that bow along the nuetral plane.
Take a look at the back and belly pieces and the shape they now are when 'released' from each other.
Doing this will greatly help you when it comes to making better bows
Pat there are many reasons why steel beams are used in construction over wood. Before we start going down a pointless rabbit hole  - are they using pristine split 'staves' in construction.....no.....can you compare apples and oranges.....
I did study mechanical engineering for a few years if you want to dicuss buildings etc but they have very little to do with bow making in the real world.
Theory and numbers on sheets are useful to a point but you have to have a greater knowledge to see how said numbers fit into the bigger picture or else you will end up with a view point that is limited at best.

[PatM]

  Your description  proves the error.    The belly shortens. 

[willie]

Your description  proves the error.

Tensile "set"  is likely not an issue at all with wood bows in most cases.

PatM. I think you are being too dismissive of the back being a working part of the limb.

granted, the back does not stretch as much as the belly compresses when a bow is drawn, but if (roughly speaking), wood is twice as strong in tension than in compression, the back is still stretching 1/2 as much as the belly is being compressed. Considered as a whole, the back contributes 1/3 of the deformation that stores the draws energy. Being that the deformation in the back is in a materiel that is twice as strong, it is worth considering.

The fact that set is not observed in the back, could be a good thing worth noting.