Martin D-1: Help with a Crack

[Robbie Collins]

I just received this guitar and it has a nasty crack on the right side of the back. Owner says his girlfriend stuck it in the attic, but it looks to me like it may have experienced trauma as well. At the center of the crack, and as seen in the photo, the upper part is 1/16" proud of the lower. 

Looking inside, the 1st brace is still attached at the end but detached an inch on each side of the crack. The end of the 2nd brace is broken and missing but is solidly attached over the crack.

My plan is first put a humidifier inside the case and see if I can get the crack to close, then make 4 molded magnetic clamps (http://frets.com/FretsPages/Luthier/HighTechDept/Magnets/MoldMagCau...) and use them to level the edges before clamping the crack shut. When the crack is solid then I'd reglue the braces. Q: is it important to replace the end of the 2nd brace?

I'm thinking that if I coat the clamp form with a thin layer of vaseline that I might be able to reuse the form. Has anyone tried this?

I'm also thinking that because the crack is so displaced, and because it is so near the side where more torque will be required, that neither HHG nor CA will withstand the stress and epoxy might be better.

Lastly, in the first photo you can see that the tortoise binding has come loose over the waist. Ditto for the other side. The upper binding is fine.  I plan on using a hair dryer to soften and expand it and tape it into place so it retains its shape after cooling.

Any and all comments and suggestions appreciated. Thanks, Robbie.

[David Farmer]

 my 2 cents.

It does not look like a drying crack to me.  Any other signs of  extreme drying? Fret ends, sunken top, etc.?

The crack appears to cross many grain lines and I have never heard of or seen a drying crack blow a brace end off.
Of course it makes no difference in the repair.

I don't think you need a fitted caul.

3/16 flat Plexiglas or polycarb W/clear packing tape on the glue side let's you see what's going on while you squeeze the crack

I wouldn't get near the raw wood w/Vaseline. there are better ways of protecting cauls from sticking.

If the crack is difficult to close in terms of thickness, It's going to be hard to get enough  force w/ magnets. I would opt for the old fashion way of putting flat cauls on all four surfaces, putting  jacks between the cauls on the inside top and bottom and  putting clamps on the outside of the Instrument over the jacks.

just be carful w/ how much and where  the pressure is going. don't distort the contours w/ the jacks and clamps.

coming up w/ a method (dry runs, pre heating etc.) that allows you to use hide glue is worth the effort. Unless your totally sure of the outcome,  try not to use epoxy. The comeback is difficult.

Just some quick thoughts. Others may have more or better ones.

 

[Robbie Collins]

Thanks, David. The fret ends aren't sharp and the top seems normal. Of course, the guitar probably has been somewhat re-humidified. I agree with you about the crack crossing grain lines.

No...I'm not talking about putting vaseline on the guitar. I was referring to how Frank broke apart the forms he made for pouring epoxy around 5/8" x 5/8" magnets. I was thinking that thin vaseline on the inside of the forms would prevent the epoxy from sticking and make them reusable.  I don't want to waste that much epoxy without research.

I plan to try to level the crack using N42 magnets in the force multiplier configuration described by Frank & move to older methods if that doesn't work out. One magnet by itself has 23 lbs of pressure when exerted against a steel bar, more if placed against a magnet, and far more if two are connected via a steel bar. I ordered 10 magnets so I can make multiple configurations. If anyone is interested, I found the best price on Amazon:

http://www.amazon.com/gp/product/B0089Y6U12/ref=ox_sc_sfl_title_1?i...

I don't think leveling will be the issue. What I meant was that it's easier to close a crack in the center of the back than at the edge so it stands to reason that, once the clamps are released the crack might have more force trying to pull it apart.

[David Farmer]

Sorry Robbie, I miss understood your issues.

seems like you will have to rely on good cleats and the braces to spread the load out.

I use small magnets all the time but have yet to delve into high power configurations.

high power magnets kind of make me nervous.

let us now how it goes. 

[Andrew]

Perhaps a healthy dose of paste wax would save the form/mould. I doubt the dried wax would migrate into the epoxy enough to affect it. You could always try it on a piece of scrap first to see if it releases.

[Jelle van Tilburg]

Hello Robbie, 

Looks like someone stepped/leaned on the guitar, causing the damage.

Personally I would use HHG or Titebond (especially with clean-up in mind) and the old fashion set-up. Gluing en closing the crack properly, regluing the braces, and cleats should keep the crack from reopening. 

Just some thoughts. With the magnetic clamping caul idea, did you keep the arch of the back in mind? Also I can't really tell from the picture, but half of the cracked area still seems to be partially glued to the brace this might fight alignment when you're going to use the magnetic clamping cauls on the back to level the crack. 

Good luck!

[Ned Knepp]

Robbie, that looks like an impact break to me too. I wouldn't use epoxy either. Once things are lined up, glued up and the split is cleated everything should holdup fine.  I use HHG for a lot of things and I like the way HHG tightens up when it drys but this may take a bit more work time than HHG will allow. I think you could work Titebond into this one when you have some of the clamps in place and have enough work time to get it done properly. Another consideration is that it's not such an old guitar that HHG would be expected on all repairs.

I think I would try to repair that broken brace's end too because it will help stabilize the crack. The missing end looks like something that happened when the back was cracked and seems to be another indication of an impact. I don't suppose the broken end in in the guitar or the case?  

[Robbie Collins]

Thanks, guys. I was thinking Titebond last night...don't know why I overlooked it.

David, I have the smaller magnets like StewMac sells. They almost hold it closed. I too am wary of magnets but the ones I ordered aren't the 2" monsters for which Frank created the acrylic lift. I have a steel plate on a wall from my bench where magnets reside when not in use.

Jelle, the magnets will be embedded in epoxy and have about a 3/4" (19mm) x 2" (50mm) footprint. I was planning to place them lengthwise along the crack to more closely fit the curve.  It will only overlap about 9.5mm on each side.   I'm thinking that this will align them in the correct plane especially since the first and second derivatives of the curve are small in that area.

Ned...the brace tip is missing and the end is rough. It seems to me that to have any structural strength the tip would need to be jointed to the brace. I can imagine slotting the top of the brace and tip with a Dremel and gluing in a wooden key but it would be delicate. Otherwise, I'd just slice off the end with an xacto saw and glue them end to end. Maybe slide some wax paper under the joint and use a very small, thin line of epoxy (no squeezeout) to butt the two then use HHG to reglue the brace to the back? Clamping is always important when securing joints and I suppose I could tack rubber bands on each side. Stretchy tape would be great if I could find it.

I was also thinking that once I aligned the crack that I would about loosen both braces from the kerfing to the other side of the crack. Then I wouldn't be fighting both the back and the braces at the same time.

[Ned Knepp]

Robbie, I was thinking about the possibility of tapering the end of the brace so you have a fairly consistent slope to nothing then laying a piece of brace next to that one to trace your new slope. Taper the new piece to the line and fine tune. It looks like you could fit a scab on top of the broken brace and under the lining in this way. Once it's glued up the lap joint could probably do with a bit of linen glued over it like the X joint center.

 ( It's always SO much easier to "do" this sort of thing from this far away. )

Any way, that's what I was thinking when I looked at it.  

[Robbie Collins]

Thanks, Ned...that's a good idea...that would create more surface area and strengthen the joint.  Would you use a thumb plane to taper the brace?

[Jelle van Tilburg]

Robbie,

I think you would have a better chance with a (wide) chisel (and something underneath the brace end, to keep from accidentally cutting/hitting the back). But that is if you have a chisel that would fit in there (bend one or maybe, take the handle off of one). In my opinion you would have a better visual with a chisel/compared to the thumb plane (+ don't think you could make a decent stroke/ get the end of the brace with the thumb plane without bumping into the lining, and this would affect the gluing area you are trying to create)

[Ned Knepp]

 IF I was doing it, I'd probably use my small carving chisels. I have a curved shank straight blade chisel that's about 4 inches long and a skewed chisel from the same set that might do the trick. I also have a small (paring sized) knife that's pretty thin bladed and nice for this sort of thing. If you do it this way, it might be a good idea to cut the slope then trace both sides of the brace so you can mark your scab for each side. That would help with the almost unavoidable fact that you probably won't be able to get it level given what you're trying to do.

 Of course, now that I think about it again, it's completely possible that it would be easier to simply remove the brace and make a new one. It's already loose and you're thinking about freeing it up some more anyway. Maybe you should just get it out of the way until everything is aligned with the crack then glue in a new one.  

( You see how I lead you down one track then jumped over the wall to a new path? Now you know why I keep pointing out that I'm an amateur with experience, not a pro. ) 

[Robbie Collins]

Thanks, Jelle & Ned.

I received my magnets today and experimented with them using some thin acrylic to protect the finish. They are very difficult to control and, strangely, appear to be magnetized at a 90 degree angle to my other magnets. I switched to my turnbuckle jacks. They will level most of the crack but not within 1-1/2" of the end.

I do have a very small 4" carving chisel of dubious quality. It doesn't stay sharp long but maybe long enough.

This guitar is has a catalyzed lacquer finish and satin at that. Any tips on repairing it? Maybe touching up with stain, letting it dry overnight, then drop filling with superglue?