Some lam thickness questions

[twitchstick]

I started making a couple of Tri-lams this week. I have bamboo for the backings with ether maple or cherry as the core and osage as the belly. I didn't do the best job keeping the osage square when cutting it. The thinnest board is 3/16" thick on the thin side and the other board is 1/4 on the thin side. Are they too thin to work as the belly lam? I'm shooting for a bow weight around 50-55 @ 28". How thick will the core lam have to be? Thanks

[mikkekeswick]

What design of bow are you making? Length?
!/4 inch isn't necessarily too thin but you would have to glue-up the bow very close to final tiller.

[twitchstick]

Not sure on design? following something similar to Roy's build along at 66" NTN.

[LittleBen]

Since those slats are pretty thin. I would do two things.

Build one bow at a time. If first one comes in too light or heavy you can make adjustments for the second.

1/4" belly slat, 1/4" core, 1/8" backing. That should get you pretty close assuming you keep a relatively flat belly.

Taper the core lam from 1/4" thick at the center to 1/16" at the tips. I find it easier to taper two 36" lams and splice them back together than to try to make one long 72" lam which is skinny at both ends and thick in the middle.

If you don't taper the core before you glue it up, you will likely end up scraping right through the belly lam towards the tips when you tiller.

Last thing, I know many will tell you that narrower is always better, and they might be right, but if you leave it a bit wider to start, you can always narrow later to bring the weight down and to tiller.

BTW Jimmy, I haven't forgotten about our conversation, hang in there, shop is currently packed up because we're moving.

[Roy from Pa]

X's 2 on what Ben said

[Bowjunkie]

Twitch, you mentioned a 'thin side'...you'll have to have those lams very accurate in thickness across their width prior to glue up, or you can end up with built in limb twist that's hard or impossible to remove.

If they don't get thinner than that while 'fixing them', you should have plenty of wood. I often grind the osage belly lam down to .200" or a little less for a bow in the mid to high 50's in draw weight... but that depends on the core thickness and taper rate, overall length, length of stiff handle section, etc.

[twitchstick]

Thanks everyone for the advise.

[macbow]

Ben or Roy when you put the two short tapers together how do you splice. Skive joint? Just butt them?

[Roy from Pa]

I butt them at the center of the handle, then I string the bow to mark it straight before glue up and drill 2 holes in the handle area, one in each core lam for a tooth pick, they never move.

[Wolftrail]

Originally posted by Roy from Pa:
I butt them at the center of the handle, then I string the bow to mark it straight before glue up and drill 2 holes in the handle area, one in each core lam for a tooth pick, they never move.

Done the toothpick thing before, had me fussing like crazy to line up the lams with slippery glue on them. How about using a 1/4" or 5/16" dowel .

[Roy from Pa]

If you drill a hole a tad smaller than the tooth pick diameter,  then you need to tap the tooth pick in and it gets nice and snug. I clamp the materials down, string it straight,  ya have to play with the clamps and clamp again once it's straight. Then drill the holes. Never had a problem with things moving at glue up. But this is for a wooden lam bow, not glass.
After the glue is applied,  I slip the tooth pick through the core lam so it sticks out the other side a 1/4". Then it's easy to start it through the belly lam hole. By the time I apply glue to the back of the core lam and the belly side of the boo, the first glue surface is stuck enough,  I can pull the tooth pick out of the core lam, slide it into the boo backing hole letting it stick out the other side, and stick the protruding tooth pick into the core lam hole and tap it down into the belly lam.

[Bowjunkie]

I Z-splice them while the slats/boards are thicker. Then resaw them into full length lams 1/4" thick... or whatever is needed, then grind. I don't like butt splices in my bows, let alone doing them on the fly during glue up.

[Roy from Pa]

You're worse than a mother hen, lol. The butt splice is covered with glue 360 degrees, and into the butt end also. Then it's in cased between the boo, belly lam, and a 1" thick riser. It's not going anywhere Uncle Jeffy.    

[Roy from Pa]

MORNING BRO..

[Bowjunkie]

Morning gimpy.

Yeah, but the handle piece is added later. What if the belly lam is two pieces as well and the bow has a lot of deflex? I'd also be concerned because some of my bows bend into the handle and are over 70 lbs. I just don't trust butt joints.

Hey it's all good, if it works for ya, have at it.

[Roy from Pa]

Ya need to buy some real glue son..  

[macbow]

Thanks.
I like the idea of glueing in a one piece core. Just have to figure out how to do a better Z splice.

Will probably try Roy' s method also.

[Wolftrail]

Originally posted by Roy from Pa:
If you drill a hole a tad smaller than the tooth pick diameter,  then you need to tap the tooth pick in and it gets nice and snug. I clamp the materials down, string it straight,  ya have to play with the clamps and clamp again once it's straight. Then drill the holes. Never had a problem with things moving at glue up. But this is for a wooden lam bow, not glass.
After the glue is applied,  I slip the tooth pick through the core lam so it sticks out the other side a 1/4". Then it's easy to start it through the belly lam hole. By the time I apply glue to the back of the core lam and the belly side of the boo, the first glue surface is stuck enough,  I can pull the tooth pick out of the core lam, slide it into the boo backing hole letting it stick out the other side, and stick the protruding tooth pick into the core lam hole and tap it down into the belly lam.

Thanks for the explanation Roy but thats why I'm here.  Ask and get the right answers.
Why didn't I think about that....  
 

[Roy from Pa]

I DUNNO....

LOL