Making a Spruce Cleat for the Back Crack

I think we've seen this movie before.

With all the handling and clamping to put the neck back on the body, one of the cracks I previously repaired opened back up.  The good news is the crack right beside it is still closed, and this one is still closed at the ends. 

There's a lot of flex in this area of the back, which contributed to the original cracks and the repair opening back up.  So this time I'm going to put a cleat behind the crack on the inside.

I have some spruce to use as a cleat.  Just for the heck of it, I measured its thickness.  It's .135 inches, or just a shade less than 3.5mm.  I'm going to take some thickness out, and I was curious to see the original thickness.

(I really just wanted to play with my dial calipers).

So it's over to the ROSS.  I used a piece of masking tape to hold the spruce against the belt.  I'm still getting the hang of using the sander - mainly learning how to keep the workpiece square against the belt.

Now, I have played (and own) many guitars with spruce tops, so I know of its great reputation as a tonewood.  I also know it's soft.  But I hadn't worked with it until now.  I learned a few things:

- It's light.  If you don't hang onto it when using a belt sander, it may fly off into never never land behind the furnace.
- It's strong across the grain, but will crack relatively easily along the length of its grain.

I learned these things on piece #1 of spruce.  I had better success with piece #2 after my education.

After thickness sanding, the cleat is .0935 inches, or a shade under 2.8mm.  I didn't want it too thick - it seemed overly thick at first.

Ideally, I'd use mahogany for this cleat, but spruce is what I have, so there it is.

I cut the cleat to follow the curve of the side.  You can also see where it will run across the cracks.  The grain of the spruce is also perpendicular to the grain of the back.  This is the bottom side of the cleat which will go against the inside back of the uku.

I figured cutting the curve would help align it inside the body of the ukulele.  It will be mostly hidden, but I want to do a tidy job regardless.

Here's the top side, almost finished. 

I did an edge bevel like a perfesshunal luthier would do.  Golly.

Now the real fun starts.

I've been pondering how to get the cleat clamped down.  I don't have any clamps that will reach that far into the body.  Then I saw these rare earth magnets in the Stew Mac catalog.  Just the thing for holding a crack or cleat or brace in place while gluing.

They're super strong.  And they have a little handle you can put on one of the mating magnets to help move it.  You will need it.  It's hard to get these things apart when they're together.  Super strong.

 So again we open the crack and spread glue on it, then work it in, and close the crack.

Spread glue on the bottom of the cleat and put it into place.  I used a bit of masking tape on the cleat and tweezers to lower it in.  I had a few dry runs with the cleat and this seemed to work best.

That soundhole is small and it's hard to work in there.  Another reason to play a tenor ukulele instead of a soprano, I suppose.

Cleat in place, and one of the magnets on top of it. 

I tried to get as much excess glue off as I could, but it's such a small space, I'm sure there will be some to get at later.  I don't want to disturb the repair too much at this point.

The other magnet with the handle goes on the outside.  The cleat is held down into place by the magnets' attraction.   Crazy, huh?

I also used masking tape to close up the rest of the crack.

We shall see how strong this repair is after it dries.