I'd whip the back off clean as possible, do what needs to be done, and use a load of spool clamps and nudge the sides in or out as is required when replacing it.
I have made a couple of clamps that can go accross the main bout to equalize the overall shape, they're just 2 lengths of threaded bar each, with a curved 6 inch or so wooden piece joining them. Effectively they stretch pretty much accross the X brace, but on the outside. Its a lot of clamping but it makes the whole thing very controllable - which i like :)
If I am going to have the back off for any length of time I will either trace around the guitar outline (prior to back removal) and cut it out of 3/4 inch plywood, which I then place around the guitar, or I will use an "adjustable" mold that allows a number of points to be held in alignment.
I have never used a form to reinstall a back, or made a tracing of the body before removal.
The sides will easily move in or out as needed, while applying spool clamps. I just try to get it as close as possible to the original position, and that is the best you can expect.
Sometimes with instruments without binding, I may have to trim off some overhang here or there, after the glue dries.
Instruments with a binding ledge will need to be rerouted to remove glue or excess material, before reinstalling binding.
That has been my experience.
Man, is this a timely post ! I am about to glue the back back onto my D35, after an adventure in rebracing the top. I came up with a bar clamp, stabilized with 2 C clamps to squeeze the sides in at the waist. (photo1) That seems to get me in the ballpark. Then I'm using a piece of the old binding (photo2 ) to push in the sides as I install the spool clamps. I'll need 3 hands for this so an assistant will be needed to hold the binding while I install the spool clamps.
Did you change the 1/4 bracing and if so what did you re-brace it with? Those 35 tops are pretty touchy and the HD with the scalloped bracing even more so, but boy I love the way they sound.
yes I removed the 1/4" X- brace and tone bars and replaced them with 5/16" scalloped braces I got from StewMac. The top was just bellying too much and the bridge tilted toward the soundhole, making it impossible to keep a bridge glued to the top. The problem was worse in hot, humid weather. I'm hoping that 5/16" scalloped braces are a little stronger than 1/4" straight braces ??
This is my boldest adventure to date but the guitar was near useless as-is and probably could only sell as a "project guitar" so I figured I had nothing to lose and it was a good candidate to try to work on my first "real" guitar. I've practiced on beaters up to now.
I also replaced the large rosewood bridgeplate with a maple one, the same size as my D18GE has, and fixed a loose brace in the back that I couldnt reach thru the soundhole. I'm hoping to get the back glued on over the weekend. Then I'll string 'er up for a test drive before putting the binding on.
Sounds like a good move all the way around. I'd guess you've done nothing but learned a bunch while making the guitar worth way way more. Good for you, let us know how it turns out and thanks for posting the photos.
Peter et al,
Well I got my D35's back glued on and my idea of using that little piece of old binding as a guide while I installed the spool clamps went generally well. Some areas I didnt watch as well as I should have and are now a little misaligned. I will have to do some sanding to restore that ledge in the top where the little piece of black/white binding goes. Other than that hitch, I strung her up and the top is nice and flat, even thru some humid days we've had here this week. It sounds good too, although it now needs a neck reset. I put a real low saddle on it just to get playable action and hear how it sounds with the new braces...sounds good but lacks volume. The neck reset should restore the volume to full voice. It's the project that keeps on going !
Thanks for the encouragement. It's been a fun learning experience.
Not too long ago we removed the back from a 1934 000-18. When removing it we had a few chips of the linings stay on the back. we left these alone and they were very useful as "keys" to help put the back on in exactly the same place. We were able to replace the original binding in one piece and did not have to do any touch up. It was all done with hide glue. there is a good two part article with photos in the ASIA magazine, GUITARMAKER. (second instalment is not out yet) the key is, as always, work very slow and carefully.