3 lam Hill Style stack help?

[longrifle]

Looking to build a 66" 55# @27" hill style
With 1" at fades to 3/8" at nocks, but want to make it out of 3 lams of boo plus glass any suggestions you guys?

[canopyboy]

What's your riser length? Planning on 0.040 glass? Straight, backset, or string follow?

[longrifle]

14" riser, .040 glass, straight

[longrifle]

I've made a few hill styles with 4  tapered lams.
 That were .002 tapered and I guess that's too much of a limb taper. So I wanted to have 1 parallel and 2 tapered but don't know where to start.

[bamboo]

figure your stack---figure your taper--say .005per inch = one.003 plus one.002-then one parallel on the belly ramps
   I like three lam bows and try to keep the thicknesses similar-[divide by 3] true or not I feel that I have one lam in tension -one neutral-and one in compression
  by the way if I'm reading your post right it sounds like you used ,008per inch IMO twice what I would try--good luck!!

[longrifle]

Your right Mike they were .008 per inch, that's why I want to get to a .004 per inch bow so hopefully there's a little less bend in the tip area. Do you have any stack info that you have used on your own bows?
I'm thinking I would like to have my stack as follows:
.040 glass
.002 taper
Parallel
.002 taper
.040 glass no belly ramp lam all on back.

[JamesV]

The number of lams shouldn't matter as long as the total stack is correct.

For a 66" straight longbow 55# @ 27" I would use:

14" riser, .005 total taper, 1 1/8" at the fades, .040 glass with a total stack of .400 measured at the fades.

Good luck and post some pics when you get her built

James

[bamboo]

I run .002 taper on mine [no help]

James's sounds like a good starting place to me

  is that stack measurement @the butt or fade?

james do you trap that bow?

[canopyboy]

Didn't make it to my formula book last night. James' numbers sound about right for stack at the fades, but I usually meaure mine at the butt. You will get variation with wood. I know yew for instance comes in 10% lighter for the same stack (perhaps unless it's old-growth, tight-grain yew which I hear has the opposite effect.) So be a little flexible on your final weight or just narrow up at the fades until you get to weight.

But I definitely recommend 5-6 thou taper. Otherwise you're carrying a lot of extra weight in a design like this at the tips which just makes the bow shocky. I also like trapping the limbs, especially towards the tips for the same reason.

[fujimo]

you are correct skyboy,        the yew will produce a lighter bow, but yew is pretty much all old growth- well the stuff we are using for bows , that is. it is an understory tree- and grows in the old growth- and i have used stuff from 35rpi to 70 rpi- ( remembering good aircraft , or music wood grade spruce is about20 to 30rpi) seems to  consistently need a 10% add to the stack- it just seems that some particular yew trees just seem to yield different results, to other yew trees- as i use more  and more of it, i will get more defined answers to this, and let people know- i do believe chackworth uses a lot of yew- would be interesting to hear what his results are on using yew

[fujimo]

i know nothing about hill bows, besides what i have read on here- but from what i understand that hills that work more in their outer 1/3 's as apposed to closer to the fades, are better and smoother shooters- is this true Dave?, and if so, why?
but guessing that will concur with your methods of taper rate and trapping , esp towards the tips--am i barking up the wrong tree here???

[bamboo]

yew drives me crazy!!makes a really nice bow
...but I've been inconsistently coming in low!!!

[Stagmitis]

Canopy Boy and JamesV have good advice with a 5- 6 thou taper rate especially since its 66" and 3 lams. This is a personal choice as the bow will feel different  between the two. Having built many I would opt for the faster rate. Dropping to .30 on the back would also enhance speed and add smoothness to the draw and reduce thump.  
A slower taper like 4 thou will not only make a sluggish bow due to excess core material but also risk breakage due to undue stress at the belly ramps.

Also going slightly over an inch to  1" 90-125 thou will give you a more stable bow especially if you trap.

Good luck with build and lets see some pics!

[fujimo]

yup bamboo- i have the same problems- some will be 10% light the next might be 15%- it does seem a tad inconsistent!- trying to find a pattern???

[longrifle]

So from what your saying I should use 3 tapers at .002 per inch to get the proper taper rate.
I looked at a Miller ASL over the summer and it had 2 tapers and 1 parallel ?

[BenM]

Here's the stats of one I made this fall
66"
14" Riser
64#@28"
.545 Total Stack
3 - .155 actionboo tapers .002 taper
and .040 black glass back and belly
1-1/8" at fades
1/2" at tips
3" .030 tip wedges
trapped back
I would think you could reduce the total stack by .015-.020 and be pretty close to 55@27

But then you want to have it 1" at fades and 3/8" at tips so maybe lean towards the .015 reduction so .530 total stack with .040 glass
Good luck, post your results

[JamesV]

Michels.................

Everything on your build sounds spot on except the .545 total stack. Maybe a typo or you might be doing this from memory. From my charts a 66" straight long bow with a .445 stack would be in excess of 75# and at .548 on a 68" bow you would be pulling 140#

James

[BenM]

James...

My numbers are correct.

[longrifle]

Thank you all you guys for the info, this gives me a good place to start. Now it's time to grind some lams. I know I'll have a curly maple riser and black glass but not sure of the core woods. Thinking about bamboo but would like a contrast between the riser and lams so I might go with walnut or eastern red cedar or a combination of the 3. Any thoughts on my combo choices? Opinions?

[BenM]

I have searched and referenced this post so many times to figure out a stack recipe or answer a question.  

 http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=011162