Top caving in under tailpiece

[Steve Frost]

I posted the following over at the Mandolin Cafe a few days ago. I figured I'd try it here as well to collect as many ideas as possible before I start on a repair. My apologies to any who have already seen my dilemma.

While taking off all the strings to replace the first 7 frets- (the others must be a lot harder..) I noticed a crack in the center seam just below the tailpiece. You know that sinking feeling as your day suddenly heads south? So, I remove the tailpiece and and discove that it's showing alot more recurve than I recall carving. It's pushed in, and I can see some cross-grain cracks in the lacquer and probably the top.
I've read the threads I could find that relate to this issue, and it seems like a clear case of carving to thin in this area. So, nobody has to be shy about breaking that news to me. What's curious is that I built this mando 26 years ago, and it's been strung ever since. Hence my surprise to find an issue at this point.
I assume I'm looking making at a new top. Not really thrilled about the prospect, but it is do-able. My question is: has anybody found a way to repair this problem? It's an awful place to get at without removing the top or back. I did read about how Frank Ford patched a A-4 with the same problem. Disclosure: I ain't Frank Ford!! He removed the back to get at it. Worth it in the case of a vintage instrument, but I'm thinking that if I get that far into it, I'll take the top off and just replace it.
I may try to fix it, mainly because I don't have a lot to lose at this point.Here's a few pix, assuming all works as hoped:
[img]http://usera.ImageCave.com/dfrosto/WorkbenchFeb09/Crumple%201.JPG[/img]
Here's why its worth troubling with;


I daydream of a guitar tuner pulling on a steel string through a tiny drilled hole to locate and clamp a patch inside the top. Friendly plastic to act as an outside caul.....Does anybody have a method that has worked well?
Thanks for listening, and though I apologize for running on, this has been a painful chapter!

[Joshua Levin-Epstein]

Hi Steve,

Let's say the worst thing you need to do is to carve a new top.

I've seen this type of repair is older violins and I've seen it done on what looked to be basket case double basses.

In broad strokes:

Remove the top (you were going to replace it anyway). You will need to get the affected area very wet and heat it until you can reshape it to it's former curve. You then lay in wood underneath it that will be carved to the thickness that will support it.

I was working on an old archtop that was in much worse condition. I farmed that out to someone for a new top. This looks like the top can be saved. On the other hand, you made this mandolin and might feel the right thing is to replace the top. That's between you and your customer.

Good luck.

Joshua

[Steve Frost]

Thanks Joshua- just to clarify, I made this mandolin for myself in 1982,so I don't have to please anyone else.

[Joshua Levin-Epstein]

Steve,

You might be the hardest customer to please.

Joshua

[Ned Knepp]

That's a real shame, Steve. It looks like a nice mando.

I've put a lot of thought in to a puzzle like this because I have a Martin 2-15 that has a cross grain break like the Gibson in Mr. Ford's demo. I can't decide if I should carve a new top, remove the face and repair it off of the instrument or pull the back and repair the top while it is attached to the ribs. I'm actually leaning towards that since I will have to thin the existing top and may want the support of the ribs while doing this and I won't have to mess with the fingerboard extension. I hesitate because someone already removed the binding around the top while the back is unbound and in very good shape.

In your case, I agree with Joshua. I think a new top is overkill. Reshaping and patching the existing top has to be easier than carving and tuning a new top. One thing to consider is how your neck/fingerboard is constructed where it meets the body. It might be easier to pull the back and work on the face from there.

These are just some of my thoughts on the matter. I'm not certain what would work, obviously or I would have fixed my own mandolin long ago.

Ned

[FRANK]

wow I would try to save it first

[Steve Frost]

PAUL- I'm certainly inclined to save it. Right now I'm looking for the least invasive way to repair it effectively. Whatcha got?

"One thing to consider is how your neck/fingerboard is constructed where it meets the body."
Replacing the top is a last resort, or at least something I'm not dying to do. At the least ,I'd have to free the fretboard from thr extension, and remove the extension.Then.. the question is, did I use the Siminoff method of using a screw to clamp the extension down on this mandolin ? If so, the FB has to come off, to remove the screw, to remove the extension.... It's been literally half a lifetime since I completed this mandolin, so I have no idea on this detail.
Any thoughts on how to use magnets to unpucker the top, and eventually clamp a patch to the area? I'd be content if I didn't have to remove either plate to repair it. Maybe wishful thinking....

[Ned Knepp]

Steve,
I thought the neck joint might be a problem. My wife has a blood pressure cuff that I once tried to used as a jack to hold a brace. It would have worked fairly well but was a bit big to really focus on a brace. If you have access to one, it might be a good way to add pressure gradually to the deformation. With moisture and heat, you may be able to get it back into shape without removing anything. I think I would make a cauld for the outside just to make sure I didn't over do it. It's easy to apply a lot of pressure without realizing it so don't deform the back while you try to fix the top. Come to think of it, it might be a good idea to make one of Mr. Fords plaster forms to support the back too.

I think the real trick will be reinforcing the area without opening the box. I'm assuming that you do not need to add much material to this to keep it from happening again. If you prepare a patch that is thin enough that it will easily conform to the inside of the top, you may be able to use an inflatable cuff to press it into place. The catch is that you will have to come up with some way of positioning the patch before you inflate the cuff. You may be able to use magnets to do this but I have no experience with this.

One more thought I just had. The seam is already split, perhaps you can use the trick with a machine head and guitar string through a hole (or two) in the patch trick to pull and hold the patch in position until you can use a cuff or something to clamp it up.

Just some thoughts.

Ned

[Steve Frost]

Ned- the blood pressure cuff is a new one to me. I'm not famliar with the item, but I'm thinking that fitting one in place through the f hole might be a snag. Would it fit? I have a Stew Mac scissor jack, but there's no way of getting that in there. I mentioned the guitar tuner and string rig in my first post, and possibly there's some merit in it. If I drill a tiny hole next to the seam, perhaps I could gradually pull it back to shape, then use the same setup to snug up a patch with a backing caul.
I don't have any experience with magnets either, but they seem like one of the only "magic" clamping methods
I appreciate the brainstorming!

Steve

[john r toothman]

steve,i think youre on the right track with the guitar string through a tiny hole that will be covered with the tailpiece anyway. a thin maple patch or spruce. with a 1\4 " plywood caul behind, holes through the middle of both pre glued with the string ball to pull it all up tite (you might want to put another string through the ball to pull it back out with after it dries. probably the weight of the mandolin is enough to put the top back to rights????? seems like the easiest way out to me best of luck , john

[Ned Knepp]

Steve,
A blood pressure cuff is one of those air bladders that fit around your arm when a nurse takes your blood pressure. Now days, they are usually automatic and attached to the wall but there are still portable "manual" models available that are pumped up and released by hand. They come in different sizes to fit children up to big arms. They are all held by velcro when they fit around the arm. Once the cuff is in place it is pumped up by a small rubber palm pump that forces air through a one way valve and a rubber/plastic tube attached to the air bladders. There is another hose that is attached to a pressure gauge.

I might take a bit of fanigleing but, unrolled they should be thin enough to fit through your "F" hole with the pump and release valve remaining outside along with the pressure gauge. The reason I mentioned it is that it could be a good way to make a patch conform to the shape of the inside of the top. I'm assuming that you will need to conform to the compound curvature of the top because it looks like you have a bit of a crease forming across the grain in the middle of the sinking area and I think a patch should extend above and below this area as well as across the center seam. Of course I could be wrong about all of this.

Ned

[Bob Gaddis]

I believe I'd have to replace the top. I suppose you could lay a patching plate under the damage and regraduate after clamping to restore the original profile. I don''t have much faith in that approach. Since you'd have the top off anyway, I think you'd be happier in the long term with a new top.

[Rory]

I tackled a different yet similar issue & this is what I'd do:
Drill a hole on the center line of the affected area. Feed some thin braided stainless steel wire in and fish it out one of the f-holes. Make a patch that you think will fit area as best as you can. Drill a hole in it. Feed stainless wire into the hole in the patch & knot it. Cover patch in some glue & feed back into the f-hole- pull it back into position under the offending spot. Have a jig setup to hold the mando vertically & very stoutly with padding. Then take the stainless wire, affix it to a basic hardware store turnbuckle, vise grip other end to the bench & very slowly tighten the turnbuckle. I pulled a ghastly imploded guitar crack out this way to perfectly level with no magnets & no internal work. Maybe some steaming & slow pulling with a dummy patch 1st might be in order too? I dunno- worked for me.
Rory