2-piece backing

[upstatenybowyer]

I recently glued up a D/R with 2 pieces of maple for backing. The first went from the tip to about an inch over the center of the handle splice and the second continued flush from there to the opposite tip.

The second lifted away from the handle about half way through tillering. The glue lines looked really good, so I was surprised. Should I have glued a thin lam over where the two strips met?

[DC]

I glue one on and then grind the end flat with the other limb(if that makes sense). Then the second one overlaps the first. Then grind the second one flat fo the back of the bow. Marc puts a short "power lam" over the splice before gluing on the backs. I do too except for this last one. I forgot. I use epoxy. The power lam tapers out each way, I think you can see it.

[Bayou Ben]

Sometimes I'll do an overlay lam, but that's more or less to hide the joint and make it look nicer.  But it's not necessary.  Saying that, I always do a power lam over the core splice and under the backing anytime I'm splicing core materials (regardless if it's a 2 pc backing or not). 1/8" thick tapered to a feather edge on both sides and a couple inches longer than the handle is sufficient.  I sometimes go thicker to make the handle more rounded looking from the side.  The splice should be reinforced from the top (power lam) and bottom (from your handle build up)  imo.  I guess you could get by if your handle build up is stout enough, but I feel better with a lam directly over the splice.  You don't want the splice flexing at all.

[Springbuck]

  I can't tell you why your backing lifted, upenstatebowyer, specifically.  I'd suspect flex in the handle, I suppose.  I have great luck with two piece backings as long as the glue joints are good, and the handle is MUCH stiffer than the limbs and into the fades.  I have even left a 3-4" gap between backing pieces on lam R/D bows that had relatively long and massive risers (12-plus inches fade to fade).   On these I ground the corners to flush tapers (like in DC's pic) and covered them with a lam mostly for looks. 

You mentioned running one backing up to about an inch over a handle splice.  Does that mean you spliced your core pieces as well?  Or belly lams?   I know any flex in that area is a LOT harder to get away with, enough that about any splice I do I leave in a stiff area.  I think imperceptible handle flex is your enemy here.  Powerlams are one cure.

I usually DO lay a thin lam over the backing splices, and I think it helps.  But I've left it bare and been fine, too.   Also, depending on handle configurations and if you have long enough lams, it doesn't hurt to shave or cut them at a diagonal so they match up and taper out next to each other.  Kind of like an 'N".

[upstatenybowyer]

This is all excellent input guys thanks.

DC, thanks a bunch for posting that pic. My backing strips just met at a butt joint, which doesn't make nearly as much sense as what you do.

Sounds like a power lam is the way to go. They're tricky to get perfect. I've tried one once before and the joint above and below it wasn't perfect.

Ben, I'm pretty confident about my handle build up and the joint there. I think it's what I do above the splice that needs improvement. Sounds like perfecting the power lam is what I need to do.

Springbuck, the bow is two billets of BL spliced into deflex with a 2" tapered finger joint and a maple backing. I made one backing strip longer than the other and bent it over the peak of the deflex curve. I think you could be right about flex in the handle, or at least too much in the fades. It probably doesn't take much to lift the backing the way I had it without a power lam.

I'm really digging the challenge of making this type of bow. There's so much preparation involved though! So much to think about before gluing it all together. It's putting my ADD to the test for sure.   

[Springbuck]

"It's putting my ADD to the test for sure.   "

That makes two of us, at least.

[DC]

When I remember to put in the lam I do it by itself, let it dry and then regrind the back nice and smooth. Next day I glue on one backing strip, let it dry and so on. it takes three days but I've got time(I hope). If you're recurving the bow the one limb at a time approach is good because after you've got everything wrapped with bike tubes and you go to reflex it the recurve locks the backing at the tip so that the extra caused by bending pushes the backing toward the handle. If you tried to do both at once I'm afraid they would mess up the overlap joint. This last one I glued didn't have recurves so I chanced it and did them both at once. It worked fine. Would have been better if i'd remembered the power lam. I think I'll put an external one on tonight. Your experience has got me shook

[upstatenybowyer]

"When I remember to put in the lam I do it by itself, let it dry and then regrind the back nice and smooth. Next day I glue on one backing strip, let it dry and so on."

This makes so much sense. I owe ya big time Don. Hope you don't mind if I put your experience to further use.  If I ever succeed in this endeavor I'll be sure to give credit where credit is due. 

[DC]

Just passin' on what I got from Marc

[Aaron H]

A 2" finger joint seems awfully short to me.  Next time, I would go with at least 3" on your splice.  I prefer a 4" Z splice myself.

[Marc St Louis]

A 2" finger joint seems awfully short to me.  Next time, I would go with at least 3" on your splice.  I prefer a 4" Z splice myself.

I have made a lot of bows with a 2" tapered finger joints and even made a number of bows with an even shorter joint without any problems.  The only splice that I have ever had fail was a Z splice

[upstatenybowyer]

I didn't think a 2" tapered finger joint would work either until I tried it. It's the one thing I've become absolutely confident about when making these types of bows. I've had lots of other things fail, but never the splice.

[DC]

Do you do a 2" splice on selfbows or just backed bows where you can powerlam to hold it together? When you're saying finger joint do you mean a "W" or a "Z" or maybe a "V"?  I'm just about to splice a selfbow and I would like to try a 2" splice.