Stress and performance

[Selfbowman]

Kidder has a good topic here . Lots of folks looking. Good design yields good bows. Yes that was an exceptional piece of Osage I have one maybe two staves that I think are from the same tree. I save those because I’m still learning this skill and keep getting better. Yes I did a computer  design bow. The stave was excellent! But still a stave. I ironed it out as best I could. Clamped it to the caul and dry heated it to its design. The dimensions came in with in 5-15 thousands every two inches. Lots of hand sanding. The bow was designed at fifty pounds. It came in at around 40#. It could have been less dense than the data used to design. Moisture content etc.  But I learned to watch for thickness change in the design. So if you take into consideration the mass placement in those areas it will gvie you new possibilities. Now Alan also gave me three bend designs from the same computer design. Brace , half draw, and full draw. I know Marc has built from computer design and had success. I will also say this was my first try. So a lot of the draw weight difference could have been on me.i never really got to test the design. Now I’m rambling.🤠

[willie]

The bow was designed at fifty pounds. It came in at around 40#. It could have been less dense than the data used to design............ So a lot of the draw weight difference could have been on me...............i never really got to test the design

coming in at 40 could have been from presuming a general strength value  for the species instead of  doing a bend test on a sample from the same stave? (thats rather simple to do actually, and  I wouldnt put that on the bowyer's skill if the preliminary test was not done)

I am more curious about how much additional tillering you had to do after the bow was constructed to thickness.   
did you have to make much adjustment to get it bending like the three plots alan supplied?
predicting the desired finished bend profile with a reflex/deflex design should be something a program should be capable of doing

[Greg]

Loving this topic. Following along trying to learn. Some of it is way over my head

[Selfbowman]

It was a reflex deflex design.Best I can remember the bow reacted good to the end bend design. I don’t recommend this with a selfbow unless you want to make the bow build a long slow build. Now made from different laminators it would be much easier. Interesting build though. And yes using the dimensions as a guide decreasing the thickness as the design shows starting the tiller at the fades may be a better outcome. Don’t know for sure . I haven’t tried it that way .

[mmattockx]

I don’t recommend this with a selfbow unless you want to make the bow build a long slow build. Now made from different laminators it would be much easier.

I agree, Arvin. I made one maple pyramid from a board using software calculated dimensions and it was a significant nuisance to keep measuring thickness with calipers and slowly sneaking up on the final dimensions while tying to keep everything even and correct. Switching to a multi-lam bow design was much, much more straightforward and I had better control of the important dimensions.


Mark