That’s a good looking bend to those limbs Max.
How you guys pull that off with an .002 forward taper without them going sideways amazes me. I’ve never had much luck with a fast taper on a recurve limb. Damn things like to go sideways on me too easily…..
Here are a couple basic rules of engagement for taper rates and lam thickness and number.
Most long R/D bows use a FT of .002 -.004 and the number of lams and total limb thickness depends on limb length, limb shape, and draw weight. A good rule of thumb is to never exceed .080 in lam thickness.
Let’s say you have a stack height of 320 for a mild reflex long bow and are using .040 glass…. That leaves .240 in the core. Most guys measure their stack heights at the thickest portion of the tapered stack. I’m an old ball in that dept and measure my stack 10” up from the butt so I do not have any false readings from snipe in the sander….. but anyway….
With a .240 core you could use 3 lams at .080 , or 4 lams at .060 to get the same stack height…. The 4 @ .060 would be the better choice. Why? Having More thinner lams hold the shape of your limbs coming out of the form better with less spring back, and the thinner lams are going to be stronger in compression than the thicker lams. You will often notice a slight increase in draw weight using more laminations.
The faster the taper rate, the more the limb tips bend. But you can build a long bow with an .004 taper rate, and use an 8” tip wedge coming back the other direction to keep it from being too whippy tipped, and it forces the energy storage into a smaller section of the limb. This is very desirable for performance.
With an RC bow your FT will typically run from .002 , to a parallel depending on how radical your hook is, limb shape, and limb pad angle. You’ll also find that as you start building lighter draw weight recurve bows, that the thinner limbs go sideways easier.
So using the same form, you can have a perfectly stable limb at 50-55# and at 35-40# you can’t keep a string on it as you draw the bow. But…. If you build that lighter draw weight bow using a parallel stack it adds more beef to the base of the curl and you pick your torsional stability back up…. The magic number on my glass backed RC bows when things start getting squirrelly is .190 at the base of the hook…. I’ve even used reverse tapers to thicken that outer limb on ultra light bows.
Just recently I have gone back to using a twill carbon back on my ultra light static tip recurves. This makes a huge difference on torsional stability. I was at the point where I just wouldn’t build a static tip recurve under 35@28. I’ve got one going right now drawing 34 @ 30 that feels like a 65# bow in torsional strength.
But….. you start talking about carbon backed bows and that is a whole different rabbit hole. An expensive one to go down too.
Kirk
Topic: Looking for a book: Crafting Laminated Longbows by Mike Basher (Read 4222 times)
