Very interesting set up jig for your glue ups. Looks adjustable and sturdy. I like it!
Thanks, Dave. The spine is a 4"x3"x~5/16" steel angle that I inherited with our acreage. I was looking for a way to be able to do glue ups with different reflex, deflex, etc. and came up with clamping blocks to the angle to allow for almost infinite adjustability. It allows me to define the amount of reflex, where the reflex is placed on the limb, the bend radius for the reflex, etc. and keep everything square and straight while doing it.
thanks for the detail pics on the fade pieces. As I thought, the power lam helps distribute the load better over the fade area.
Yes, the power lam helps control the bending out of the fades and keeps the center section stiff enough to not pop the handle off. One of the best tweaks to the basic constant limb thickness pyramid design is a bit of thickness taper in the first 2-3" of limb off the ends of the fades instead of a constant thickness from fade end to limb tip. It smooths the stresses in the transition area from fade onto the meat of the limb nicely. I won't take credit for this idea, I saw it mentioned by badger and when I checked it out in the software it looked like a significant improvement. That badger guy knows his stuff!
Curious about the perry part of the experiment. Did you collect force draw data when the bow was fresh off the form?
My guess is that if there was a measureable benefit to the pre stressing of the lams before glue-up, then there might be a higher string tension at brace and early draw weight, (when compared to a non perry reflexed of the same design).
since you dont mention a control bow for comparision, would you comment if the bow has lost any draw weight, or specifically, any early draw weight, in the few years of use?
My thought is that if the bow, fresh off the glueup, has internal stresses even when unstrung, then
perhaps over time the wood might creep back towards an unstressed condition similar to the way a thin board leaned up against the wall will take a permanent set or "belly" over time.
I didn't do an F/D curve because my scale isn't precise enough to get good numbers. The bow did end up quite a bit heavier than I expected based on my calculations, which I attribute to the Perry reflex in the glue ups. Going from memory, the upper range of calculated draw weight was ~45lb@28" and the bow was right around 50lb instead, which is a significant miss considering I measured the elastic modulus of the wood used in the limbs and should have been much closer than that 10% difference. Because I had never done this before and there was no guidance for this sort of thing online or in books, I was guessing on how much weight I would gain with the pre-stressed glue up and it appears I underestimated the effect.
The reflex did pull out during shooting in (the limbs are straight, nocks basically right in line with the grip instead of 1/2"+ ahead), so it definitely relaxed some from glue up to being shot in. I can't tell if it is the wood or the TB3 glue that let the reflex go. TB3 doesn't cure completely hard like epoxy, so there may have been some creep on the glue lines. I designed the bow to have stresses low enough that set shouldn't have been much of an issue. As I said, the next one will use smooth on for the laminating and I know it cures hard and won't creep over time.
I know lots of guys here are skeptical of being able to design and predict bow behaviour on paper, but I designed this and built it directly according to my calculations, glued it up, profiled it and worked it out to full draw without any tillering at all. The bend you see is how it came off the form, after cutting the back profile in according to my design. I missed on draw weight because it was the first try, but I will get closer the next time and should continue improving with each subsequent bow I build this way. Wood is a predictable structural material and can be used as such with the right approach. It's just a different way to skin this cat.
Mark
