backing a bow

[critman]

How much draw weight is added when you back a bow with bamboo?  How about 'glass? Want to back a bow and not sure which to use.

[macbow]

I'll assume your talking about a all wood bow.
To get to the answer we'll need the type of wood.
Both bamboo and glass when used as backing increase the tension on the back a lot.
Thickness of both will effect the weight gain.
If the wood used was low in compression then it would not take the heavy compression backing and would be too weak in compression and fail.

Wood like oak is low in compression.
Osage is good in compression.

As far as how much weight. Say the bamboo was 1/8 inch or less. And the bow about 3/8 then it would add at least 30 to 40 % . This is a guess.  I'm sure there is written data somewhere.

If you add some data some of these guys will probable have some experience.

[Bowjunkie]

Macbow... you mean good in or low in tension resistance and compression resistance dontcha?

A bamboo or glass back doesn't increase tension on a bow, for instance, instead, it has an increased resistance to it.

In fact, instead, if anything, a backing with a higher resistance to tension forces can exert more compression force per inch on the belly... that's one reason why we trap bows when we apply bamboo backing and such.

[John Scifres]

Kinda hard for me to look at it like that.  Backing a bow doesn't add weight unless you are just trying to apply a bandaid to one that missed weight.  If that is the case, I would prefer to just start a new bow.  Good backing is expensive in both time and money and deserves a new effort.

Look at it from the beginning as part of the design.

[macbow]

My main point is adding a,strong backing could over power the belly.
Be interesting to add a piece of bamboo after measuring a slat then measure after adding it.
John it's hard for me,to imagine it wouldn't add pull weight.

I totally agree it would be better to start over.

[Roy from Pa]

John how can backing a bow with a material like boo or hickory not add weight? Now backing with paper or a cloth, then yes it wouldn't add weight.

Crit what's ya trying to build? What type of wood, etc?

[John Scifres]

My first post was not well stated.  My assumptions are as follow.  Critman made a selfbow.  He missed weight.  He wants to turn a selfbow into a composite bow.  I would not do that.  Especially with bamboo which, when done correctly, is more work than it would be worth as a bandaid.

Instead, start fresh.  Do some research and make that work worth it.  And maximize bamboo's awesome potential.

Now if my assumptions are incorrect then critman is asking something different than how much weight does a backing add.  Then he is asking how do you make a backed bow.  In that case, a backing doesn't ADD anything.  It is part of the design.

Reread the question critman posted.  It just doesn't make sense to me.  You don't back a bow to add draw weight.  Except as a bandaid.  In that case, just start over.  Your results will be better.

[Roy from Pa]

Agreed John, I would never back a bow to gain weight either. I think he is just looking for info on the effect of backing a bow as to would it gain weight.

[critman]

John, and others: what I am currently working on is bows for youngsters. Several have seen the bow I made for myself and really want me to make them one. I figure it will be very good experience. What I have built are board bows from red oak. Since I'm building low poundage (probably 20-25#) bows could I use something like poplar and back it? I have to keep cost in mind so I was thinking on maybe linen or something just to help keep it from breaking if someone's big brother decides to show how strong he is. What are some other choices to back with other than boo or 'glass that look good, is readily available, inexspensive and will do the job? Is poplar strong enough wood for kid's bows? Have seen some bad reviews on it but that was for adult bows (50# and up). Even though they are for kids I treat each one like it is mine and take the time and details to produce a quality, good looking bow. Otherwise, what's the use?  Oh yeah, I throw in some arrows made from good dowels. Can't have a bow and nothing to shoot!  Thanks for all the good advice and keep it coming. Glued up 2 more bows this evening. Looking foward to morning, got another red oak board and now my Mom want's one! Gotta love it.
Critman

[critman]

That should be "inexpensive" :-)

[John Scifres]

If you are set on composite bows, the best choice would be something like this:  http://www.stickbow.com/FEATURES/SELFBOWS/beginnings.CFM

If you want something that is bombproof, go with rattan:  http://bowyersedge.com/kidsbows.html

I have been involved in several kids bows builds and it is very rewarding.  Please feel free to ask specific questions.  Thanks.

[deceneus]

Linen backing is cheap and effective, it prevents rising of splinters without to increase the draw weight.I made a 57# board bow using cumaru wood and backed it with linen and it works smooth. For kids bows linen backing is bulletproof.

[LittleBen]

Yeah I think John is onto it there. If it were me I'd probably be making a bunch of hickory backed hickory. It'd take alot of punishment, and hickory is cheap if you've got a lumber mill somewhere