DR bowform limb shape.

[Buemaker]

I have been using a true circle, how have you shaped your bowform?

[Mad Max]

I have too.

Some say you use this theory
https://www.elegantthemes.com/blog/design/the-golden-ratio-the-ultimate-guide-to-understanding-and-using-it

[Kirkll]

i'm an elliptical kinda guy myself... with a few flat spots thrown in just for sport.

[mmattockx]

I have been using a true circle, how have you shaped your bowform?

Excellent question, perhaps without a discrete answer. I suspect the optimal way to do it is to start with your desired limb bend at full draw or maybe brace and then work back to what it looks like unstrung. That should be technically possible, but would be a very challenging thing to calculate out. The number of variables that interplay here is large and you need to get them all working together to get a great result, so it is a big thing to try and solve.

I haven't done my own FG bow form yet but I have also been using circles for my wood lam bow layouts, because they are easy to work with and seem to work well when you get everything else correct.

i'm an elliptical kinda guy myself... with a few flat spots thrown in just for sport.

How did you go about improving your bow designs? Did you pick a form shape, then play with lam details (FG thickness, taper, etc.) and back profile or stick to a basic set of lam details and try different forms to see what happened?


Mark

[kennym]

About all I can tell you is I started with a true radius and it was good, but then testing I added an inch more reflex in outer half and it made 5 lbs and 5 FPS with same stack
…

[Kirkll]

Quote from: Kirkll on April 08, 2024, 07:56:41 PM
i'm an elliptical kinda guy myself... with a few flat spots thrown in just for sport.

How did you go about improving your bow designs? Did you pick a form shape, then play with lam details (FG thickness, taper, etc.) and back profile or stick to a basic set of lam details and try different forms to see what happened?

You have most likely heard the old expression. "It's all been done before" or "There is no sense reinventing the wheel" As far as bows and limb designs go, both of these statements are probably true.... What i did was study a bunch of different limb designs that have been developed over the years, and picked something i liked the looks of . One of my favorite limb designs was the Sovern Balistic for example....  Then i got a hand full of finish nails, a piece of 1.5" wide fiberglass, or a formica strip, and a piece of 1/4'' plywood  on my bench.  i call this "Carpenter Cad" .... Once ya get a good looking shape, mark it on the plywood, cut it out, and use it as a pattern...

When building the form i always use a 3' LVL now, or 6' for a one piece. And keep it full thickness even if i plan on using 1.5" glass.  Running those LVL through a thickness planer causes them to warp every time for some reason.

The extra length in the form allows you to shift your stops on way or another. i typically use 30" stock in my TD form  and 68" - 70" on the one piece..... Then it's always been trial and error shifting the wedges and tinkering with taper rates to get what you are looking for. Not necessarily errors..... Just some come out better than others with different characteristics.  different limb designs bend in different locations, and store energy differently. then there is the pre load you put into the limbs which is a combination of limb pad angles, string lengths, and working limb lengths and location which all can be manipulated...

Quite often a computer generated scientific approach to what shape stores the most energy and should generate the highest performance is quite different than reality, and you end up fighting stability issues. Then there are all the different materials that are used to mitigate design parameters....... it's one great big giant rabbit hole is what it is.  As long as ya enjoy hunting rabbits, it can be very entertaining.   

[Bryan Adolphe]

Haha i’m definitely down that rabbit hole! Kirk thankyou again  for all your help tips and tricks ect I’ve learned a lot. I’ve built three forms for his design on my sixth set of limbs almost happy ! Had some new Glass show up yesterday from Kenny so I can continue on. Definitely true about the LVL‘s I won’t be planing down anymore.

[rmorris]

Are you plaining down both side’s equally or just one side?

[Bryan Adolphe]

I was doing both sides pretty equal then sealing, imo i do think its best to leave them full width and the factory finish left on, depending on how you go about it a little bit of work with the router both sides whether you use tywraps or washers or both and you’re good to go.

[rmorris]

Very interesting. Currious if it could be humidity difference.

[Kirkll]

Very interesting. Currious if it could be humidity difference.

The LVL material just doesn’t do well taking that original factory finish off. I don’t think the humidity would make that much difference…. It’s just not a big deal to use it full thickness.   

[Susquehannariverarcher]

When using lvl that is original thickness do you need to router the edges of your form so that the glass is on something that's 1.5"?

[Bryan Adolphe]

When using lvl that is original thickness do you need to router the edges of your form so that the glass is on something that's 1.5"?

I routed areas where I drilled for ties on both sides of the form. You could easily install washers there to keep everything centred at an inch and a half.

[Bryan Adolphe]

I have been using a true circle, how have you shaped your bowform?

  Apologies Bue for being way of topic  I didn’t mean. 🙂