How does this tri lam formula sound?

[Zradix]

Hey guys..

Just wanted to run this by some of ya that have made one of these tri lams before.
How's this plan sound?
I really don't know how wide to make this thing.
I was thinking wider because of the heavy curves...but I have hopes it doesn't need to be.

I'm hoping for around 45-50# at 28"


62" long
1/8" hickory back

3/16"x17" PL Tapered to center or maybe an inch or two flat in the center..

3/16" core flat for 17" then taper .007( leaves tips 1/32") or do .006" taper (leaves ends 1/16")

1/4" osage belly

1.75" wide for 17" then taper to 1/2" tips
..maybe 1.75" for 13" then taper to 1.25" over 2" then taper to .5" tips…?

8" handle

Form…
Center  3" high
pads .5" high
tips 5"
pads to center 14"
Pads to end 15"

I'm trying to make this bow with similar curves to a Kanati.

Here's some pics of my form set at the above specs.
One of them has a Kanati overlay.
Only the right side is worth looking at.
The scrap piece of wood I had laying around wasn't quite long enough..so It's not up on the tip post on the left.

 

 

[Roy from Pa]

1 1/4 wide at flares, hold the 1 1/4 width out 6 more inches then straight taper to 1/2 at tips. Skip the power lam. 12" riser. Your form numbers have me confused. My center post is 4" high, mid limb posts are 2 3/4 high and end posts are 6" high. My midlimb posts are 12" out from flares. If you want more reflex, slide the end posts in more towards the riser. Do a dry clamp up and see how it looks.

I drew you a picture:) LOL

 

[Zradix]

What has you confused Roy?
12" riser on a 62"?
Will that leave me enough working limb?

Are you saying I should keep the 1 1/4" out 6" past each flare?

Thanks

[Roy from Pa]

What has you confused Roy?
12" riser on a 62"?
Will that leave me enough working limb?
Yes.


Are you saying I should keep the 1 1/4" out 6" past each flare?
Yes.

[Zradix]

ok man...
You haven't steered me wrong yet...
that's a 3" longer riser than I did on the 66"..lol

Having that much wood to work with sounds fantastic..just didn't think I could go that long...COOL!

The 1.25" is much better sounding too...I guess I don't have much of a "feel" for this stuff yet..lol

[Roy from Pa]

Just remember, there will be 2 inches out past your flares to the end of the riser. The area from the flares to the end of the riser will have an angle cut in them so they fade into the limbs.
See?

 

[LittleBen]

FWIW, a 17" powerlam is just like having a 17" riser unless your powerlam is paper thin. So actually Roy's plan leaves you with 2.5" more working limb than you were heading for.

I think it sounds reasonable. I'd probably taper the core like .003, and also taper the belly .003 or something like that.

Osage is the heaviest part of that bow, and probably any core material will be the lightest, no need to have more than necessary at the limb tips. The vast majority of the work done by the limb is done by the outermost 10% - 25% on the back and belly ... so really your belly lam only needs to be like 25% of the total thickness ... I usually make each lam the same thickness and taper if I can on a tri lam, that way each one is roughly 1/3 of the total thickness at any/all points along the limb.

Since your limb tips will be thinner, you can taper the belly at .003" and still have like 30%+ of the limb thickness at the tip being osage instead of 50% or more, which is where you'll end up with only tapering the core. Plus, it's going to be more difficult to bend an untapered osage belly than a tapered one, and it may be tough to cut that core with so much taper because you're gonna have less than 1/16" thickness at the tips ... closer to 3/64 if my calc is correct.

[LittleBen]

With all that said, Roy won;'t steer you wrong and what your proposing will definately work ...

[Zradix]

OK Gents.

Your points are well taken.
What you say makes a heck of a lot of sense Ben.

So lets say I go with the 12" riser.
and keep 1.25" wide for 24" total on center.
..and taper the core and belly about .003" (.006" total)
( all sounds smart to me)

Should I leave the core's and belly's center parallel for that 24" as well?

also...should the core have the tapered side toward the back?
and the belly have the tapered side toward the belly?
( keep the flat sides touching each other)

Thanks guys...I woulda screwed this all up...lol

[jsweka]

Man, with all that higher math, you tri-lam guys will be using glass before you know it    

[Zradix]

nope..don't wanna build that kind of form..lol

[Roy from Pa]

Should I leave the core's and belly's center parallel for that 24" as well?
Yes.

also...should the core have the tapered side toward the back?
No, towards the belly.

and the belly have the tapered side toward the belly?
Yes.

[Bowjunkie]

It depends on how you want it tillered related to your design and needs for the bow, but since I usually design mine as petite and short as possible, I wouldn't keep the center of the lams parallel any farther than needed to reach just past the dips. If I glued on a 12" handle/riser piece, I would leave the lams parallel  for about 14", centered with that handle piece. Leaving that much(24") of the inner limb parallel in width AND thickness is too much, IMO, because I want every inch of the limb to share the burden as evenly as possible.

[Roy from Pa]

Ya not the 24, my bad.. Parallel 2 inches past the end of the riser at most.

[Zradix]

Alright, Thanks guys.
Sure am glad I have you boys to hold my hand...lol

I don't have any experience fitting tapers together...
I'm surprised that you can can two basically identical tapered pieces stacked tapered side to flat side.

Surprised there won't be a gap right where the taper starts after the parallel between the belly and core...

[Roy from Pa]

Surprised there won't be a gap right where the taper starts after the parallel between the belly and core...
You prolly will have to blend that in a little by hand. But not much. Heck it's only a wooden bow...  

[Zradix]

Originally posted by Roy from Pa:
.... Heck it's only a wooden bow...      

I know right...I thought this was going to be simple..lol
I guess learning to walk was pretty complicated for me once too..lol

[Roy from Pa]

Anymore questions before you start building?        

[LittleBen]

There was less planning involved in the first 3 apollo missions combined than this bow.

From this I have deduced that this bow will shoot an arrow all the way to the moon and back, eventually striking the bullseye 20yds from where it was shot.

In all seriousness, just do some dry runs and you'll see any problems with gaps. sand a little here .. .little there, dry fit again ... when it's good then glue it.

[Zradix]

 

ok ok ok..lol