Bamboo backing

[Badger]

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.

  I have had a lot of failures from Franks Bamboo as well. I used to buy 100 at a time but now if I do go there I hand select a few. He has trouble with mold. I only live a few miles away so it is easy for me to drive over there and hand pick.

[Eric Krewson]

My last bundle arrived soaking wet and covered with heavy mold, I threw it all away. I found a place to cut locally and never looked back, wonderful stuff.

[mmattockx]

How are you measuring the properties?   Few people have access to testing equipment.

The only one that is really critical is the modulus of elasticity (Young's modulus, MOE). That I measure with a bend test, which gets me within ~5% accuracy. The TBB bend test offers good info in the modulus of rupture and set strain, but those are not nearly as critical if you are designing to minimize set and not for the absolute maximum you can squeeze out of the wood.

The 5% accuracy is good enough to design the bow and get a set of dimensions to work to, then I use the measured draw weight at short draw lengths (16-18") to tweak the MOE to get the calculations and measured numbers to match and fine tune the final tiller and draw weight.

My hats off to you guys who get into the intricacies of stress of this and that but my point is 99.5% of us cut a stave, make a bow and shoot it, period. We don't even think about the technical side and still make great bows.

Taking a stave and making it into a bow by eye has worked for 10,000 years. Some of us just like the more complicated way to the same end point. 

We don't have to pick one side or another.  Someone who is drawn to wooden bows and primitive archery because of science/engineering/interest in the materials and their properties may learn to appreciate the artistic side.

There is definitely room for everybody here (or should be). I appreciate the artistic side, I just have no artistic ability so I have to make it work from the technician side of the equation.


Mark

[willie]

How are you measuring the properties?   Few people have access to testing equipment.

The only one that is really critical is the modulus of elasticity (Young's modulus, MOE). That I measure with a bend test, which gets me within ~5% accuracy. The TBB bend test offers good info in the modulus of rupture and set strain, but those are not nearly as critical if you are designing to minimize set and not for the absolute maximum you can squeeze out of the wood.

The 5% accuracy is good enough to design the bow and get a set of dimensions to work to, then I use the measured draw weight at short draw lengths (16-18") to tweak the MOE to get the calculations and measured numbers to match and fine tune the final tiller and draw weight.

Mark

Mark,
do you think a arrow spine tester is good enough to test bow wood for stiffness?

[PatM]

That's only  one variable which won't tell you much about the potential as bow material.

[Allyn T]

My main interest is self bows, I really don't plan on even making a backed bow but I like the technical side for discussions. As far as artistry goes I enjoy carving wood and make wooden rings and other jewelry for my wife. I don't measure anything and just eyeball it. Besides measuring out my starting dimensions on my bow I haven't measured anything or done any bend test and I don't plan too. I really just like talking about the technical stuff, I hope I haven't offended any of you artist out there but it's just about kicking ideas around.

[mmattockx]

Mark,
do you think a arrow spine tester is good enough to test bow wood for stiffness?

I have never used one, so I can't say. If it will get as close as my 5% accuracy with a home brewed bend tester then it probably will work. The biggest determinant of accuracy is being able to accurately cut/grind and then measure the thickness of the bend test sample. Bending stiffness is proportional to the third power of the thickness, so small errors in thickness magnify greatly. You also want fairly large deflections so that they are easy to measure accurately without lab quality instruments.

That's only  one variable which won't tell you much about the potential as bow material.

I agree, it means almost nothing in assessing a new wood for bow use. I need the MOE to calculate limb thickness for the target draw weight, nothing else.


Mark

[Flntknp17]

I should have specified, I am a terrible artist.  My bows won't ever win any contest on aesthetics.  I just love making bows so I can study how they work and how different materials work in a dynamic manner.  I totally appreciate those of you who make beautiful bows because I can make bow that shoots well, but it won't ever be pretty because that just isn't a skill set I have.

Matt

[Allyn T]

Nothing wrong with that function is really the most important part, I started down this rabbit hole strictly to make a hunting bow and now I'm fully engrossed. I have a feeling my finish work will be subpar

[Eric Krewson]

Making a nice looking bow is easy if you keep the flow in mind, no abrupt angles, make one part flow into another, plus you can never over sand a bow with 400 grit paper followed by steel wool. Ideally there should be no tool marks showing anywhere.

I use a small orbital sander for final tillering, this is great for getting rid of tool marks and any washboard on your limbs or in the fades from scraping.

Flow;

[Allyn T]

Eric what is you finish routine, as far as sand grit and how many times you move up grit count?

[Eric Krewson]

All I have is 220 and 400 grit. First I take the bow out in the light of the setting sun with a scraper, every tool mark on the bow will become visible in this light. I use a card scraper and remove any tool marks I find.  I sand the whole bow with 220, give it few minutes with 400 and switch to a green scotch bright pad for that last push for perfection. Next I put on one coat of finish and inspect the bow for any tool marks I might have missed, If I find any I scrape them off, sand the spot and proceed with the multiple coats I always put on for a finish.

[Allyn T]

So you like the green pad over 0000 wool steel wool

[Eric Krewson]

Steel wool is OK, it works a little better than a scotch bright pad but leaves those little bits of steel on the surface.

[PatM]

I use the automotive synthetic steel wool pads.  They come in finer grades than just plain Scotch-Brite.