Awkward crack

[Keith Somerville]

Hi, guys. Hope you're all busy!

On the bench, I have this J45 with a long crack. On the inside, you can see a section of the kerfing has also cracked and the rest of the crack runs right along the top of the kerfing. Looking for a few opinions on how best to approach it. As you can imagine, it's quite stiff, and difficult to get the two sides to mate properly. Thinking maybe a band clamp with some appropriately-shaped cauls to push the kerfed side of the crack into alignment? Cleating? Linen reinforcement?

[Mike Kolb]

Wow, that took quite the hit, huh?  I've always liked using little homemade tuning machine devices for crack-leveling, especially on something so stiff and curvy, where magnets may not have the "oommmph" to hold ...and flat pieces of clear acrylic won't work with the curves.

Rather than trying to reinvent the wheel, I found this video by Robert O'Brien that gives a good overview on the process. 

https://www.youtube.com/watch?v=BxaFdXC-jc8

The only question remaining might be...do you also remove the cracked section of cleat, then replace it with a new section afterward repairing the long crack?  Or maybe just leave the cleating in as-is and start the fix?  Hmmm.

It'll be an interesting repair to watch... Smooth sailing!

[Keith Somerville]

Hmmm... I do have some of those machinehead thingies made up. They don't see that much use since everything went over to magnets! That's a definite option I'll give some thought to.

[George Roberts]

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Substitute For Teeter Tuner Clamps

• Posted by George Roberts on January 30, 2014 at 3:27pm in Luthier Talk
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I hope I'm not re-inventing the wheel with this.  I have been trying to glue cleats to the inside of a long side crack.  I wanted to use HHG, but there was no way that that I could get the Teeter clamps in place and wound up in the time available.  Mulling over different approaches, I finally came up with this one.

These clamps are available for $1.99 at Harbor Freight.  The top image shows how they come in the store, but they have a wing nut that allows you to reverse the action, so that they push apart rather than clamp.  Bottom image shows that configuration.  Harbor Freight sells two similar clamps, but the one that works the best has a grey release button.  A 1/16 hole is drilled through each of the pads.

I made up some string clamps out of 1/4 inch hexagonal brass rod.  The rod is drilled and tapped for a screw (I used 8-32), and then a 1/16 inch hole drilled through the side.  Guitar 2nd strings with 0.016 diameter have worked well.

Where the crack comes together, I have been using a hand drill with a #74 drill (0.0225), thread the guitar string through that hole from the outside, and then add the cleat, the caul, and the brass string clamp.

The outside part of the guitar string is threaded through the Harbor Freight clamp, and another brass string clamp.  I don't tighten that clamp yet, but use clothespin type of clamp to keep it from sliding off.

I have been able to put the HHG on, pull it into place, slide everything up, tighten the brass string clamp, and expand the HF clamp in under a minute.  There is much better control of the amount of pressure applied.  Plucking the string between the two pads also lets you know how tight it is.

Hope this makes somebody's life easier. 

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[Thomas James]

George, thank you for the detailed info on your clamping jig solution.  I will give this a go. 

[Walter W Wright]

OK that's awesome! 

in these situations i've just gone with the little tuning machine drawup thingy and regular titebond-type glue (the LMI stuff actually) because of the time factor.

if we want the hide glue style joint where the glue serves to pull itself in further, maybe go with fish glue as a best of both worlds solution? tightens up like hot hide but you have a long open time like aliphatic

[Dave Richard]

George Roberts, that clamp modification is brilliant! I'll be using it.

[Mark McLean]

George, I think that clamping method is very clever.  Thanks for sharing it.  

[Keith Somerville]

Well, I tried the band clamp and it was no good. Then, I tried drilling a small hole for a guitar string clamp through the crack, like usual, but the kerfing made it so that pressure was applied unevenly and it didn't help at all. In the end, I tried a different way of using the tuning machine clamps (see photo). Much better.

[Chris Vallillo]

I'm not real clear as to how this is working.  Precisely what is the guitar string clamp doing now?  

[Keith Somerville]

I've no idea if this terrible picture will help. Imagine this as though you're sighting down the neck.

[jbbancroft]

Just speculating here, but I think I would use a bar clamp across the top or back of guitar to align crack, then camp clamps to pull the crack together.

Jim

[jbbancroft]

Looked at your photos again. From the inside view it looks like the crack is in perfect alignment already. It looks like you could simply rub some glue into the crack from the outside, looking inside to make sure it penetrates completely, then apply clamp pressure from top to bottom to pull crack as tight as possible. You could use a CA finish touchup to the exterior once the glued crack is dried.

Jim