MIMF

For a tenor guitar I am restoring.

As expected, the sides have relaxed.

I made a 1/4" plywood form using the back outline as reference, but it is to light and distorted when trying to force sides in position, besides, how to clamp with it in position. Tried clamping back to sides dry and hand forcing sides into alignment. Thought I could then glue in small sections. Unsuccessful. I suppose I could try and try again.

Checked library. About the only solution I can think of is to make a custom adjustable mold with incorporated clamps. Or attaching back without edges lining up and installing binding --- don't like that.

Any suggestions?

Maybe Cumpiano's clamping method using a cut inner tube would work - it's pretty much self-aligning:

http://instrumentmakers.net/LLcom/tutor ... CN2888.jpg

Thanks Peter.

Lmii has some rubber strips, but kind of expensive. Maybe go to my local tire dealer and get some inner tubes to try. Looks like that just might work.

My local Big O let me go through their dumpster for tubes - I'm sure Les Schwab or Discount Tires would be glad to let you have some too. Apparently some tires still have tubes in them. Bicycle tubes would work too, you'd just need more of them.

Good luck with the repair.

Surgical tubing?

Pat

Tried using the elastic bands designed for this application that Stew-mac sells. Not enough side pressure to bring sides in.

Built an adjustable form that could adjustably push sides in. No matter what I do with this fixture, cannot get perfect alignment. It is as if the circumference of the sides is longer than the outline of the back. Push in here, moves out there. Don't know what to do with it. Maybe add binding to the back. Still don't like that idea. Would like to be as original as possible.

John: You may be creating your own problem. The elaborate jig may be too low where it pushes in and is causing the sides to buckle outward. At least that would be my guess.
Tom

You may never get it any better than that. When you remove a back from an old instrument, the stresses from years set in and the wood will shrink and change very quickly, and let's face it, it only takes a little bit of change to make a big difference in that fit. Maybe a binding will be the best way to deal with it.

Tom: I set the height of the supports so that the 5/8" diameter pads were even with the edge at the narrowest part of the sides, at the neck. That made them about .4" lower at the bridge end. That does make sense, though.

Mark: Binding is looking more and more the solution. The fixture was worth the try. At least it was fun to make. Hang it on the wall as decoration for my shop.

Oh John that is a really nice and well-made fixture! I have seen folks use molds like that to build instruments of many different shapes. You can make different guitars and never need to make a mold for a one-off design.

Thanks, Mark.

What I ended up doing was using the fixture to align and glue as best as possible, but still slightly misaligned. I then chamferd the edge as in the sketch, stained it and done. I kept the amount taken off the side even, so even though it shows, doesn't look bad. I posted pictures in the Other Instrument section. I like the look even better than binding. The instrument looks more like it originally did.

You did a very good job making the best out of the situation!

Thanks, Mark --- as usual, this forum helped me to do this.

Well, a basic truth we all can hold to be self evident is.....a tree will always get even with you for cutting it down. I have yet to be proved wrong on this.

Nice jig! I've seen similar ones, but none that were this nicely made. Perhaps everyone except me understands this, but what is the purpose of the two Philips screws that go perpendicular to the "push bolt"? And did you screw the wooden blocks to the bottom of the jig from below? Does the "push bolt" go trough (an) inlaid nut(s), or did you just tap the wood? I have an early teens Gibson A-style mando with no back binding in the shop right now, where the back has been off for decades so nothing fits, so its pretty much the same situation. I was leaning towards gluing it up as precisely as possible, and adding binding, but your solution looks promising too. Didn't see the pictures you mentioned...?

Frank Ford has something like this in his restoration project of a Gibson Mando-Cello. I also love that jig set up! Well done.

Thanks guys.

The picture posted was shown without the clamps in place. The two Philips screws act as a push pull clamp. The blocks are attached to the bottom with screws (attached drawing doesn't show these screws). The wood is not tapped, metal inserts are used. The pictures are in the "Other string instrument" section, "What kind of Instrument is this".

Thanks again to all for the replies. I really enjoyed this project.

When the back has shrunk and pulled-away from the sides, the best fix is to separate the sides at the end block, and trim them shorter, -then- make one of the clamping jigs to force the sides to conform again; just trying to force them usually won't work.

Would it help to put the back in a higher humidity environment for a few days to try to get it to expand in the side-to-side direction?

Mario --- Trying to understand this procedure. Can this be done without removing the top? The only way I can see would be to taper the amount trimmed from the sides, tilting them out towards the back, decreasing the circumference on the back edge only. If not, then the top would have to removed, trimmed, re-bound. How would one determine the amount to trim off the sides? Trial and error? Can the sides even be removed from the end block without disturbing the front?

Doug --- I also had that same question/thought. Had I thought of it earlier, would have tried it. I keep the humidity in my shop at 45-50%. When increased humidity of back returns to that of sides, added stress?