ASL stack thickness questions

[Dmorris]

I have a few questions about total stack thickness on a Hill style longbow. I built my first laminated bow last year with some old tapered laminations a buddy of mine had laying around. I used all 3 tapered lams, total stack thickness at thickest part was .435. The bow ended up around 49#@28”. Bow shoots really good and extremely quiet. For my next one I was wanting the same dimensions of the bow, but would like around 55#@28”. Looking at the charts I am kind of confused on the stack thickness. When using tapers how do you know how to figure the wieght close to what the chart says? Would just adding .020 on each end of my laminations be somewhat accurate? I hope I am making sense here. Thanks

[Mad Max]

.435 is with the glass?
This stack calculator works good for Recurves and R/D's for me.



Your buddy's lams may or may not have snipe, I mark a line at 10" from the butt (thick end of the lam) and
measure the thickness there.
.001 taper @ 10" add .010
.002                          .020
.003                          .030
This way you get a true stack thickness.

so .435 stack is 49#----.452 should give you 55#, for all things being equal.

[Dmorris]

That makes sense, I was wondering if somewhere in middle of limb would be close to accurate. Would it be better to go with a parallel core first, then 2 tapers behind it? If so would the total stack still figure close at 10” out?

[Mad Max]

That makes sense, I was wondering if somewhere in middle of limb would be close to accurate. Would it be better to go with a parallel core first, then 2 tapers behind it? If so would the total stack still figure close at 10” out?

It does not matter were the different tapers or parallel's go in the stack to hit your target weight.
The thinnest lams may need to go on the belly ramps of the riser because they will bend up the ramp easy.

I not sure I'm understanding you.
Do you know what snipe is??
On a wood planer or thickness sander there are 2 pressure roller that hold down the wood, when the wood go's in and is being milled, then it hits the 2nd pressure roller and it holds it down better,  you end up with a small hump about 6" or so form the butt.

[Dmorris]

No, have never heard of snipe before. I thank you for answering the question though. I was not sure if thickness charts were for thick or thin end of taper. Your explanation makes a lot more sense.

[jsweka]

I’ve used that same stack calculator Max references many times for ASLs.  It works and I would trust those results. The key is that all other design considerations remain the same (limb width profile, taper rate, limb length, riser length, and glass thickness).

[Kirkll]

Like Max, I've been measuring my stack heights at 10" from the butt for years. Too easy to get things off measuring the butt.  I also use the same lam stack calculator and its pretty darn accurate as long as wedge material and length, taper rates, and and laminations used are similar.  Once you start changing taper rates its a SWAG again.  (Scientific Wild Ass Guess)  Kirk

[Mad Max]

Mike at Rosewood Archery told me about the 10" measure.
He makes a lot of lams for big archery companies and need to hit the stack correctly

[Dmorris]

Thanks for all the help guys! On my last bow I used Osage tapers for my lams, this one I plan on using an old piece of bamboo flooring, I have read in some places that materials don’t make that much of a difference as long as total stack thickness is the same. What are your guys opinions on this and will I need to adjust thickness for bamboo?

[Miguel Gasso]

Mike at Rosewood Archery told me about the 10" measure.
He makes a lot of lams for big archery companies and need to hit the stack correctly

Hello Mad Max, when you and Kirk II say that you take the measure at 10" you mean 10" from the center of the bow near by the fade outs?

[Mad Max]

Mike at Rosewood Archery told me about the 10" measure.
He makes a lot of lams for big archery companies and need to hit the stack correctly

Hello Mad Max, when you and Kirk II say that you take the measure at 10" you mean 10" from the center of the bow near by the fade outs?

No
10" from the big/thick end   
Go back to reply #1 and read again

[Kirkll]

Thanks for all the help guys! On my last bow I used Osage tapers for my lams, this one I plan on using an old piece of bamboo flooring, I have read in some places that materials don’t make that much of a difference as long as total stack thickness is the same. What are your guys opinions on this and will I need to adjust thickness for bamboo?

Basically the thickness between two pieces of glass determines the draw weight. lighter mass weight core woods are typically higher in performance.... BUT.... the tension and compression properties of the core wood can make a big difference in longevity. Bamboo is excellent in tension, but very poor in compression ratings. Osage would have excellent compression and tension ratings, but its very heavy in mas weight. 

The perfect combo in my experience for a recurve limb has been  bamboo on the back side, and hard maple on the belly.

To answer your question. I dont think your stack will change very much from bamboo to osage unless you are talking a 100% bamboo core. Then you may have to add .010-.015 due to the compression issue.