Belly splints

[DC]

Don't know what the real name is but I'm referring to a layer you glue on the belly to make up for a stupid tillering/ planning mistake. Almost every time I've used one I have trouble with the transition between the old and the new. It seems like if you have a hinge and glue a splint on it when you start scraping, the hinge just moves over to the end of the splint. I wrote it off to making the splint too short so this time I made sure and added 3" to my estimate. I used a plane to taper out the splint and still got a weak spot at the end of the splint on one limb. The other worked fine. I'll recover from this one but I'm wondering if there is something about this I'm not understanding. Any work arounds to make it easier?

[Pat B]

DC, I've had to do this with a couple of bows due to frets, etc. What I did was ground the belly below the fret and added a complete belly lam, retillered and moved on. All worked very well for me. I've never tried to patch a smaller spot with an overlay.

[Deerhunter21]

would it be a good idea to completely reduce the bow to maybe be a quarter of an inch, put a belly on the limb(s) and treat it as (if the bow was hickory lets say) a hickory backed Osage bow or something?? kinda a wooden lam with the backing being the original bow???

[mmattockx]

I used a plane to taper out the splint and still got a weak spot at the end of the splint on one limb. The other worked fine. I'll recover from this one but I'm wondering if there is something about this I'm not understanding. Any work arounds to make it easier?

Are you adding the splint over the belly, or removing wood from the belly and putting the patch into that hollow? Adding wood will very rapidly increase the stiffness at that point, as you well know. How long was your taper on the ends of the splint? How thick was the splint?How thick is the limb where you put the splint?


Mark

[DC]

Because it wasn't going to be a "real" bow I just took a few passes on the belt sander to square up the round corners on the belly. I stopped well short of where the splint would end. The splint was 15" long and is 13" once it was blended in. The weak place was just outside the fades. It's pretty well tapered from one end to the other. You can kind of see it on the picture. Here is a case for a bad glue line, it would show up . The splint was just over an eighth thick. The limb was about 1/2" thick. In the FD pic you can see how it's bending a little too much mid limb on the right limb. That's just past the end of the splint. You can see in the second pic how it's blended in. I tried to make it a gradual as I could. You can see a little smear of epoxy where I feathered it. The epoxy colour matched the splint very well. I wish they would all blend(color wise) as well as this one.

[mmattockx]

The splint was just over an eighth thick. The limb was about 1/2" thick.

That's a huge increase in thickness. Going from 1/2" to 5/8" makes it 95% stiffer. It is not surprising that a hinge developed at the end of that much reinforcement. Even with the really gentle taper off the end of the splint the big change in stiffness (basically doubling the stiffness off the fade) forced the the limb bend to change a bunch.

I would have said you needed maybe 0.030" extra thickness to stiffen an incipient hinge. That equates to 19% stiffer and 12% stronger (that is, 12% lower max stress), which I think should be enough to nip the hinge in the bud. I am constantly amazed at how little wood it takes to really alter the bend of the limb once you are getting close to your final tiller. I suspect you simply added too much in the one spot and overloaded the rest of the limb that was already close to final shape and thickness. If you like to floor tiller that might be a good way to get the splint down close to final thickness before putting it back on the tree, but I can't say. I suck at floor tillering, can't tell much at all about the bend aside from if it is reasonable for weight or not.

You do such a good job with the patches I would suggest trying to stiffen it by sanding more off the belly and putting the same thickness of splint on, then working it down to only that extra 0.030"-0.040" thickness and tillering from there. If you take more off the belly and use a thicker splint that would leave a reasonable thickness on the patch once you have it worked down to the final thickness.


Mark

[willie]

presuming you have gotten the splint worked down close to finished thickness, I would follow the same method for tillering it in as with a new stave to the point where the bow can be braced. perhaps back to the longstring? and not drawing past where you can see a hinge developing, etc.

At brace height, and because the split is new materiel being married to a belly already having been drawn further, I would consider a method advocated by Paul Comstock for new staves. Once he braced a bow, he left it strung for a number of hours to "sweat in the compaction".

In your case of a splint, you would be trying to find a way to "exercise" the new materiel, without overstraining the adjacent limb area, so the bow might need to be re-exercised as it is retillered all the way out.