Trapping bamboo backing?

[Lee Lobbestael]

Is it possible to trap bamboo backing? I mean sand the back completely flat? The reason I ask is because awhile ago I glued up a bamboo backed red oak and some fellas on here expressed some concern over the wood combination. They mentioned making the bamboo as thin as possible. Well the backing strip on there was looking kinda thick and the rounded back seemed like it would concentrate strain in the center of the limb causing chrysals on the red oak belly. so I was wondering if I would be able to save it by sanding the back thinner and flatter

[Pat B]

Trapping is not flattening the back but beveling the edges to narrow the crown of the boo. You can trap boo without any worries but if you flatten it it won't last. By trapping you will reduce the tension stresses making it less apt to overpower the belly. Red oak is not a good candidate for a boo backing in the first place. I know some have successfully made boo backed red oak but there are better options like hickory or maple that won't overpower the belly.

[Bowjunkie]

No, don't work the surface of the bamboo down to thin it. It needs to be thinned from the inside prior to glue up. The bamboo gets progressively less dense, less powerful, and less resilient from the outside in. In other words, it's stronger nearest the outside, and if you thin it from the outside, it will be useless as a backing and fail when you bend it.

How thick is the bamboo?

Unless the bamboo and/or the oak was thick enough to carefully saw off and reuse, I would just trap it and make the bow.

[Lee Lobbestael]

oh ok will someone explain trapping to me then? Whatabout if you backed it with heavy paper or rawhide?

[Pat B]

Trapping is when you make the cross section of the limbs in a trapizoidal shape. In this case the back would be narrower than the belly reducing the tension of the back as it relates to the belly.
  I don't think the make up of boo would allow you to use it as a backing if the top is removed and I don't think a cloth or paper backing would be strong enough to support it. IMO a better option would be to add thin lams to the belly and leave the boo as is or add a hickory or other wood backing over the decrowned boo.

[Jermcramp1]

_____
/_____\\ sort of...

if the back is up and the belly

down

[Bowjunkie]

Keep in mind, even though we CALL it 'trapping'(trapezoidal), essentially it only means that the width across the back is narrowed to be less than the width across the belly. That said, the lines comprising the trapezoid aren't necessarily straight/flat as they are in a true trapezoid. The bamboo has a slight curve to it and that's fine. Some folks make bows with flat bellies, but the belly of my bows are all radiused, or convex shaped and all 'corners' are considerably rounded off. If you were to look at one of my bamboo backed bow's 'trapped limbs' in cross-section, at about midlimb, they may look something like this.

 


That said, THAT shape morphs into different things as it nears the tips, or the other way toward the dips... becoming more oval, elliptical, round, etc.

[Bowjunkie]

My paint/image skills are pretty sad. LOL.

That thing's probably not proportionately correct. My bottom corners are actually rounded more than that, the sides aren't that straight, etc... but hopefully you get the jist of it.