What do you think of this idea to fix a sunken top?

redir · #1 03-11-2021, 09:07 AM

Working on a very old and very damaged parlor guitar. It's fan braced with 3 fans. The center fan was cracked and actually missing a small section that was right over the bridge patch which is probably why the top sunk. There is a crack that was repaired across the grain right at the front edge of the bridge in front of the bridge patch. Removing the patch is not possible and would cause a lot of damage.

I made a new center fan brace and I arched it which helped bring the top up a bit. As it is now if I hold a straight edge across the lower bout right over the bridge foot print and parallel to it, it's sunk dead center about 1/8th inch.

So my idea? Arch the bottom of the bridge and force clamp it in place with an arched caul on the inside. I'm thinking if I clamp the wings down first then clamp the middle it will putt the top up into the arch of the bridge. The bridge after all is a brace so it's not unlike clamping a top to an arched x-brace.

Your thoughts?

Alan Carruth · #2 03-11-2021, 09:17 AM

That should help.

Many years ago I had to fix a nice violin with a collapsed top. Somebody had glued in a bass bar using Elmer's glue, a long time ago. That stuff is the equivalent of bubble gum: it won't hold under stress but you can't get it loose either. Both ends of the bar were still down tight (!) but you could almost lay a straight edge on the top: the glue line had slid. The post held the other side up. Once I got the bar off I had to use a hot sand bag to get some arch back into the top, and then 'spring' the bar a lot to boot. It more or less worked, in the end. With any luck the top will 'remember' what it was supposed to do, at least for a while.

redir · #3 03-11-2021, 10:06 AM

I thought about making a Belly Reducer for this one But I don't think it would work with fan braces. But a hot sand bag? Hmmm. I imagine being a violin you had to do that from the outside? Or did you remove the top to work on it?

Bill Kraus · #4 03-11-2021, 05:35 PM

I did a similar job on a late 40's Gibson LG-2. This guitar was so dry that a lot of braces were loose, and one popped completely off the back when I re-humidified the guitar. It also had a shrinking pick guard that caused a dip in the top of over 1/8 inch. I made two matching clamping cauls, one concave, for the outside of the guitar, and one convex for the inside. The convex one using one of my building radius forms, and the concave one was made by attaching sandpaper to the mate and sanding against each other . I notched the inside caul to go over the braces. I warmed the inside caul with a heat lamp, and boiled some water. I dipped a piece of heavy cloth in the boiling water, pulled it out with tongs, and draped it across my inside caul. I then quickly put the hot cloth covered caul in the guitar and clamped it up with it's opposing outside caul and left it all clamped for a few days. The results were amazing, A near perfect looking top. It looked like there was never a problem once I glued the pick guard back on. An expensive and time consuming job, but it worked well.

redir · #5 03-11-2021, 06:38 PM

Great idea Bill! I think I will give this a lot of thought and come up with something. I have made the same kind of caul with the notched braces. Might need to arch it a bit more.

redir · #6 03-22-2021, 01:33 PM

Quote:

Originally Posted by Bill Kraus

I did a similar job on a late 40's Gibson LG-2. This guitar was so dry that a lot of braces were loose, and one popped completely off the back when I re-humidified the guitar. It also had a shrinking pick guard that caused a dip in the top of over 1/8 inch. I made two matching clamping cauls, one concave, for the outside of the guitar, and one convex for the inside. The convex one using one of my building radius forms, and the concave one was made by attaching sandpaper to the mate and sanding against each other . I notched the inside caul to go over the braces. I warmed the inside caul with a heat lamp, and boiled some water. I dipped a piece of heavy cloth in the boiling water, pulled it out with tongs, and draped it across my inside caul. I then quickly put the hot cloth covered caul in the guitar and clamped it up with it's opposing outside caul and left it all clamped for a few days. The results were amazing, A near perfect looking top. It looked like there was never a problem once I glued the pick guard back on. An expensive and time consuming job, but it worked well.

Bill it worked like a charm. Left it in traction for a week and it came out nice and flat.

https://www.tiktok.com/@piusone/vide...81200673441285