need help with rawhide patch

[lesken2011]

I have to patch a back violation on a bamboo backing. I have decided to use a small rawhide patch. I have knox gelatin and tb2 and 3. Which would be better? If they are similar with respect to the holding power, which will be ready to work sooner? I read a post recently where I guy using hide glue on siyahs had to wait 10 days for them to be ready. I would like to get to sanding and finish tillering as soon as possible.


I have some thin rawhide. Would you recommend wrapping it with artificial sinew as well? I don't have any real sinew. The patch area is about 6 inches from the tip so I want to avoid any unecessary mass.

[tom sawyer]

I just used some TBIII thinned with water on a rawhide backing and it worked great, was basically dry overnight.

What happened did the bamboo lift a splinter on a node?  I don't know if a rawhide patch would work on that.

[lesken2011]

This is a pretty serious violation in the backing and this is really an experiment. I have been doing some repairs to various bows to educate myself on what works and what doesn't. I may just use the Titebond for expediency. Thanks!!

[Lee Slikkers]

Instead of a patch and since you don't have sinew...how about a heavy Silk wrap?  A pic of the violation might help us give you the best case scenario for success.

[lesken2011]

You guys don't laugh, but I had to try to salvage it. Here is the story behind it and pics...


After I got my trade bow sent, my next project was a bamboo backed ipe for Half Eye who sent me a really nice ash backed elm bendy handle bow. (I'll post some pics, later) This was my first attempt at gluing in some reflex. Since I have little experience with tillering bows with reflex, I kept it to a minimum by putting the tips on 1" blocks, clamping down the limb about 14" from the tips and then wrapping them. Here are a couple of pics of the bow. This one is at rest on the tiller tree.





another pic...





I really liked how the glue-up turned out. The shape of the bow was great and tillering was a breeze....until. I had the bow braced and pulled to about 20". All of a sudden a hinge appeared about 6" from the tips....or what I thought was a hinge. It turned out to be that the glue had "failed" and a gap appeared between the laminations. I tried re-gluing and the same thing happened. I won't bore you with the details, but I have used tb 2 and 3 several times and never had the glue fail. The was the first time, however, I had glued in reflex and that is the only place it failed. After reading up on the titebond glue, their site says to give a "stressed joint" 24 hours to cure. In the past I have only waited overnight for straight glue ups. I think when I took the straps off after about 12 hours the glue was not ready for the stress put on the relex and eventually gave way. The only way I could see to repair it was to sand down the gummy surface of the bamboo where the glue line failed. The only way I could think of to do that was to remove it and put it on the belt sander. After I got it cleaned up I put it back on, but had a gap where the kerf of the saw was.



I filled it with a sliver of bamboo and sanded it all back down. I did the glue up with a gap filling 3500 psi epoxy. Here it is all sanded down ready for the rawhide and wrap.





Well...is it an impossible fix??

[DarkSoul]

That's gonna be a difficult repair. A cut like that straight across the back, through the entire backing, is seriously compromising strength. The seam wants to be pulled open really hard.  It might have been better if you'd made a cut at a 45 degree angle as seen from above. Then a patch and/or wrapping would have had something to keep together.

By the way, in that last pic, you also seem to have violated the node one inch to the left of that seam. I hope you haven't violated the other nodes as wel...

How about a belly lamination of about ten inches long? That might keep the tip from bending?

[lesken2011]

 By the way, in that last pic, you also seem to have violated the node one inch to the left of that seam. I hope you haven't violated the other nodes as wel...

I just sanded it down. I read that you could sand them reasonably smooth without compromising them. Did I go too far? If so, how do you know how far you can go?

[tom sawyer]

You went pretty far on those nodes.  I generally just scrape the rind off and leave the node otherwise.  Some smooth the overlapping top part a little more.  It scares me.

I'm not hopeful on the fix but short of cutting the entire backing off and starting over I don't see what could be done.  You might've cut off the backing from the tip back past the loose part and tried to clean it.  Cutting the fibers in half was drastic, there's no continuity there now.

Titebond isn't gap-filling and its really hard to get perfect surface matches on a backed bow.  Thats why so many people use a gap-filling glue like resorcinol or URAC.  Gluing in reflex really puts a lot of ongoing stress on the glue lines.

Good luck on the patch.  I know how you feel, I have a few failed glueups in the shop waiting on some kind of fix.  My fix is usually to pass them by and start with new materials.  But it ain't broke until you say its broke.

[lesken2011]

Thanks for the feedback guys. I figured it was an uphill battle. Here it is after I pulled the hemp rope off the rawhide patch. I also covered the node in case I sanded it too much. I will do a little sanding on the rawhide and then wrap with artficial sinew set in super glue. We'll see!!

[Pat B]

What glue did you use to glue up the back and belly? If TB glue I would heat it up and peel off the boo backing and add another backing. If that backing fails it will most likely ruin the bow.

[lesken2011]

I used TB3 for the initial glue up, but epoxy for the re-glued tip. I think I am going to chance it. I need to see how far these patches will go. I will probably keep this one, though, rather than send it out. I'll let you know how it turns out.

[Eastman]

Something similar happened to a BBO r/d bow of mine. Long story short, the whole bottom tip (about 4'' long) completely broke off. but.....that bow is still shooting today

A part of the boo backing was still left overhanging where the tip broke off, so the piece that broke off was glued back on to that, as well as a small strip of wood covering that on the belly side, and the whole patch wrapped with fishing line. and its still holding up.
I know im not really making sense, but i'll post a pic just now.

[lesken2011]

Thanks for the feedback. It's nice to hear a success story. It give me hope!