Bamboo backing

[Allyn T]

I was reading about Perry reflex in the archives and it seems like a back that is less strong than the belly works best so why do people use bamboo backings at all if it's so strong? Wouldn't it always overpower the belly and create more set even if you can't see the set?

[Pat B]

A lot depends on the belly wood used. Typically compression strong woods like osage, ipe or yew are used for boo backings with very good results.

[Dances with squirrels]

How could I not see the set?

Bamboo works great with strong woods like Pat said. It's always my first choice for backing, and osage is always my first choice for the belly, and core if a trilam.

If I make a bow with cherry, walnut, maple, or other wood that's weaker in compression resistance, THAT'S when I use a weaker backing piece, and make it correspondingly thinner... but honestly, I don't know whether I'll ever do that again. I have plenty of osage and bamboo and they make a much better bow in my preferred aestetic and design specs.

[mmattockx]

I was reading about Perry reflex in the archives and it seems like a back that is less strong than the belly works best so why do people use bamboo backings at all if it's so strong? Wouldn't it always overpower the belly and create more set even if you can't see the set?

Because is it available, it is near bombproof when done properly (safety counts, back failures are bow explosions) and you can somewhat balance the back stiffness to the belly by making the bamboo much thinner than the belly lam. As Pat says, often lam bows are made with belly woods that are very similar in strength and stiffness to bamboo, which gives superb performance.

It is stiffness that matters for balancing the back and belly, not ultimate strength. The only natural material that is less stiff than wood but able to survive more strain is sinew and that is a lot of work to use. Gluing up a lam bow with bamboo is way less work and performs very well when done properly.


Mark

[Allyn T]

How could I not see the set?

Because the backing pulls the bow back after unstrung even if the belly cells are mush.

[Eric Krewson]

The thickness of the bamboo has a lot to do with it, I see a lot of bows backed with too thick bamboo. I make my bamboo 1/16" thick on every edge, this is great backing for questionable staves, heat treat the belly and you will have a rocket launcher.

I know a guy who makes bamboo backed ERC bows with flipped tips, they don't fail on him, he sells them commercially.

He is quite a bow maker, told me he made up tp 75 bows a month and worked 7-12s on them.

 

[Allyn T]

Jesus that's a lot of bows

[bownarra]

Bamboo thickness (in bow making terms) has nothing to do with its resistance to being streched.....
It is the outer surface that is doing the vast majority of the work. Same as the belly.
Backings should be trapped to make them suitable for less compression resistant woods - not thinned. You can not make bamboo thin enough to lower its stretch resistance and still be suitable for a bow backing. This is one of the most commonly mentioned misconceptions in bow making
Why do you think bamboos outer fibers become somehow 'weaker' when the backing is 1/16th thick as oppossed to 1/8ths?
I've experimented with many different thicknesses for boo backings and it don't make any difference to set.
Has anybody made a bow pulled it too far to induce set, then cut the bow in half along the nuetral plane? Doing so will prove what i'm saying if anybody wants to experiment

[willie]

You can not make bamboo thin enough to lower its stretch resistance and still be suitable for a bow backing. This is one of the most commonly mentioned misconceptions in bow making

unsuitable in what way?

[PatM]

Mike means that in order to make it thin enough to reduce its stretch resistance it would have to be reduced to dust.

[Allyn T]

What happened if you reduce the bamboo on top, take off the hard putter layer? Then the tension would be carried by the slightly softer inner fibers, would that help?

[Eric Krewson]

I have made a lot of bamboo backed bows, at least 50, back when I was selling bows that is what most people shooting tournaments wanted because of the increased performance. Back then they were allowed in the selfbow class, no so today.

If the bamboo was thick I would have what I called an osage belly bamboo bow, all of which were under performers because the bamboo was doing all the work and bamboo by itself is not a great bow wood/grass.

For me bamboo was merely a backing, a thin strip glued in a reflex and tillered to perfection made for a nice performer with "0" set if I glued in 2 1/2" of reflex on my form. I found a formula that worked for me, every one of my BBOs was exactly like all the the others.

One can argue about this and that as far different qualities of a bow components is concerned until you are blue in the face, neutral plane, compression resistance and all are not on my radar. I just make bows, and pretty good ones at that.

I do get a chuckle out of some of the "facts" put out here at times. The most recent one was a bunch of guys telling a newbie that his osage had too many run outs and even backed with bamboo it was sure to fail.

Well, well, I reserved my tight ring twisty osage for bamboo backed bows, and never had a failure, the bamboo did it's job.

Here is a typical example, this bow, or one just like it, won a national championship in the hands of a very skilled lady archer. It took about 10 years and hundreds of thousands of arrows before it lost tiller, got mushy and had to be was retired.

[Eric Krewson]

To be perfectly honest I did have failures in my bamboo bows on occasion, it was always the bamboo that would raise splinters never a core wood problem.

I once bought a 25 slat bundle of beautiful bamboo from Frank's in California, every bow I mde with this bamboo failed, all bamboo failures. I had to replace 5 or 6 failed bows before I wised up and burned the rest of the slats.

[mmattockx]

Bamboo thickness (in bow making terms) has nothing to do with its resistance to being streched.....

A piece of bamboo that is half as thick is also half as stiff, regardless of what you think of it. That is basic mechanics of materials stuff. In bending on a lam bow it will be a bit more than half as stiff. Yes, the outer fibres do more work, but the inner ones on a thin backing piece are also doing significant work as well. The strain/stress/energy storage does not go from everything to nothing in one very thin layer, it is linear from maximum at the outer surface to zero at the neutral axis.

The thinner boo also shifts the neutral axis less than a thicker piece does, reducing the extra load on the belly wood from the NA shift.

I believe your experience that says you can't thin the boo enough to completely balance it, but thicker is always going to be worse than thinner. Seems completely reasonable to me that trapping the back may also be necessary depending on the woods being used.


Mark

[Allyn T]

I know bamboo isn't wood but does it's strength correlate, so half as thick would be 8x less stuff. Even if that is the case does that not matter since it is a backing and won't be under compression anyway