An invisible third hand
Vacuum Leveling for Crack Repair
© Frank Ford, 11/4/01; Photos by FF

This one caught me by surprise. It's a small crunch in the spruce top, right near the end block:

Except, it turns out to be one of those new guitars with a "double" top --two incredibly thin layers of spruce separated by a lattice of internal struts, much like a hollow core door:

So, now I have a little trap door with no way to poke or clamp it up to level:

In fact, if you look closely, you'll see that the spruce is only about a half millimeter thick. On top of that, it's jammed downward and tucked under at the end of the "flap."

First, I undercut the end section a bit so the little flap of spruce could fit flush with the surface:

I tried stabbing the flap gently with my pointy knife, but I wasn't able to lift it that way.

A section of vinyl tubing attached to my vacuum pump was sufficient to grip the surface and lift the piece into position, but it would only slip right back the minute I let go. I needed a method of clamping it in place for gluing.

I saturated the cracks with clear hide glue to avoid discoloring the wood, and, to allow a bit of working time, I diluted the glue to about 2/3 strength:

Then, using plain water as my only "gasket" I was able to suck the piece right up against a flat plate of acrylic, using that same vinyl tube:

The tube was a slip fit in the acrylic plate, so I could stick the tube down to the little flap of spruce and then bring it up to the surface by pulling on the tube. The acrylic plate acted as a stop to make sure the flap matched the surrounding surface.

Then I was able to leave it under vacuum for a few hours as the glue dried:

The result? Not bad, considering:

The end of the flap had just a bit of space left after I chipped the crunched flakes away, so the glue shows in that area, but it's level and strong as it was before.

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