Splicing Thin Billets, Your Preference?

[tom sawyer]

Here's a question that came to mind after I finished splicing some billets recently.  One of the billets didn't have quite enough wood for the full width of the handle, so I cut them both down to about 3/4" and made the splice, then glued a handle piece over the splice to get enough thickness.  Seemed like a good way to go, having a flat piece bolstering the joint.

Then I remembered how my blank from Gary Davis was made.  He had glued his extra wood on the individual billets prior to splicing, so the full thickness was there.  That made me wonder if that might not be the better way to go.  I could have simply flattened the one billet that lacked enough thickness and glued a piece on it, then did my splice like normal.

I suppose either way is acceptable, just wondering what your thoughts were about this subject.  I want to start using more billets, I think its the way to go.

[Pat B]

Lennie, On a few lam bows I have built I spliced thin wood(for belly and core and in some cases the backing[hickory]), staggered the splices and covered the belly area with a handle riser and a back overlay. I think this gives better support to the splice. Pat

[Dano]

Lennie, I would think the way you did it would be the best and easiest, it can't help but make a stronger joint. As long as grain orientation matched.

[tom sawyer]

That was my thinking, that the handle piece would support the splice.  I suppose either way would be strong enough though.

Dano, how do you think grain orientation would come into play?  I think I put the handle piece on as quarter-sawn for added strength and for looks, although I expect the whole thing will wind up under a leather grip.

[Dano]

Quarter-sawn will hold just fine, I have used it and it does look great. The joint would just be a little stronger with the same grain patern IMHO.

[brian melton]

Lennie,

                    Thats the way I have always done it. I remember asking Marc why he glued slats with the z splice the added the handle, he said because of strength. I would wonder about that.....but there is looking at the finished splice in your handle to deal with...you must wrap to keep from seeing the splice..


Brian

[tom sawyer]

Another good point, the handle piece not showing the splice would be visually nicer.  You still have to cover the back though, so really it is a moot point.

Dano, I would think the quartersawn handle would be stronger than plain-sawn (what it'd be if you didn't have to add wood.)  That handle is on the cpmression side, its resisting movement and I think quartersawn is supposed to be a little stronger in this respect.

There's maybe another reason to do it the other way.  In my case, I had one billet that needed more wood and one that didn't, I could simply have glued additional wood to the deficient billet and left the other intact.  I think that might be what Gary Davis did on the bow I have.

[DCM]

Just to offer an opposing view I'll offer this.

Premise 1:  When properly joined, a glue line is stronger than the surrounding wood.

Premise 2:  When properly joined, the principle determinant of stength in the joint is the surface area in the mating pieces.

Using this perpective, the billets which are first built up in thickness, then joined together are stronger as they enjoy a larger surface area.

From a purely vector physics pov, a lap joint, or overlay in this case, is not particularly desireable and the forces tend to put the joint in tension perpendicular to the joint versus in shear along the lines of or parallel to the joint.  I'm sure we've all seen a handle build up "pop" off.  It's not because of improper or weak glue, it's because of the force vectors.  The limbs act as levers, if the overlay is thick enough, in effect pulling the joint apart in tension.

Practically, I don't think it matters.  I do prefer a W joint however over a Z, more surface area and for me easier to cut.

[Dano]

Good point David, but the reason we use a Z or W splice is; we are mateing end grain together which in it self is a weak joint, thus the need for a splice that isn't all end grain. If an overlayed handle doesn't  extend into the working fade then you have a strong joint IMO. I would love to get Gary Davis' oppinion since he makes these splices more than any one I know.

[tom sawyer]

I would agree that a lap joint is going to be under more stress than the z/w splice joint, but you have a lap joint either way you go.  The only way you'd avoid it is to do the buildup on the deficient billet(s) in such a way that the joint surface isn't parallel and to the limb back.  I'm surprised you think a W is easier to cut.  Its more cuts and thinner wood remaining.  Not to mention, the z-splice can be laid out pretty simply.  How is the easier in your opinion?  I thought you were just showing off.

I wonder why a power lam that extends out through the fades, doesn't pop off?  It is certainly a glue joint that is under maximal stress to come off, in the working region of the limb.  I've never seen one of those fail.  The handle pieces, on the other hand, have a much greater tendency to fail if the handle is flexing too much.  Guess its all about the thickness of the piee, and whether the stress to make it bend is less than the stress required to cause the joint to fail.

[tom sawyer]

By the way, you can do a z-splice in a bendy handle bow.  I've done them.

[Marc St Louis]

You are mistaken Brian but I think I remember your question and it was in relation to a rare time that I did use a Z splice and it failed.

The fact is that I almost never use a Z splice, always a W splice. I find that it's a stronger splice with the type of handle that I usually make.

What I do with thin billets is I cut and glue up the splice then I glue a power lam of about 1/8" thick that extends to just past where the handle will finish, this is between the backing and the core. Then I glue on the backing while supporting the handle area and finally the handle piece is glued on. This works for me and is a strong joint.

I have on occasion glued on a thin power lam between the handle and core but don't care for that method as much

[brian melton]

Marc,

                 To be more accurate this is what I questioned.... 

"What I do with thin billets is I cut and glue up the splice then I glue a power lam of about 1/8" thick that extends to just past where the handle will finish, this is between the backing and the core. Then I glue on the backing while supporting the handle area and finally the handle piece is glued on. This works for me and is a strong joint."

   I was asking why you spliced, then backed. It is more eye appealing, granted.


Brian

[Marc St Louis]

Well  Brian sometimes you have no choice but to splice, 2 short pieces of wood  = splice  . That thin lam over the splice increases its strength quite a bit. As you know every time you laminate something you increase its strength, that's why I was kerfing my recurves for flight shooting for awhile but the flight committee didn't like it so it was banned.

[brian melton]