Just looked over an old Harmony Patrician archtop (per the customer, no name on it) to be restored to playing condition. Overall, the body is in pretty good condition, only one small crack in the back. But there is some flat bracing/reinforcement across the back that has come unglued most of the way across. I tried to get some pictures, I hope they help.
Both braces are loose, and there is probably 1/8" clearance between it and the back. I can get glue to these, but I am coming up short on ways to keep them tight to the back while the glue sets. I thought about trying something inflatable, like a balloon - but I also don't want it to put too much strain on the rest of the body while it is in place.
You folks have saved me multiple times, both by answering my questions, and just reading how you have done things. Has anyone in here done this repair? Or is there something I haven't considered that might make this doable without removing the back?
Many thanks in advance!
Rare Earth magnets can do a great job in this situation. I use some of these:
I have sets of 3 epoxied to plexiglas with alternating polarity. The inside and outside strips align automatically and offer plenty of pull to close up that brace. You need to be sure there isn't old chunks of glue under there first, of course.
I agree with Greg and I'm only adding a comment to give my experience with using inflatables for a repair like this.
I've tried to use various inflatable things in the past for this sort of thing and found that I needed to use some support on the outside of the "box" to keep things from moving too much. In the end, I've pretty much abandon the idea of using anything that could be thought of as a "large area" inflatable because I found it to be a lot of work to support the instrument body and because I've had mixed results. To me, the biggest problem is that I lose that ability to see the repair area once I inflate a "ball" ( or whatever) and didn't always get the pressure focused where I wanted. It's not a matter of just applying a lot of pressure and getting a good fit. Depending on what you are trying to hold, too much pressure can be as bad as not enough. This coupled with the loss of any good way to check that the part is still in place or even making good contact, makes it a crapshoot.
Magnets are a much better option. I took apart a pile of old Hard disk drives and have a shoe box full of various sized magnets now.
Thanks guys - I was leery of the whole inflatable thing, but hadn't gotten enough outside the box to think of magnets. I think that is the way I will have to go, I have some of the old hard drive magnets laying around here somewhere.
Working through the F holes is a problem keeping glue from getting everywhere. I rebuilt a 1935 Harmony Cremona I was able to separate the top and back using a knife tool without much damage.
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