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Hello everyone,

I'm currently working on an old Lyon and Healy mandolin and the owner would like to keep the pickgaurd.

it's cracked at the mounting bolt hole and warped up into the line of pick travel. I need to flatten it and repair the crack.

I've heard it referred to as ,"

vulcanized fiber"

I plan on putting an Ebony cleat on the underside but am wondering about the right type of adhesive to use to minimize visibility on the top and be strong as well. Anyone have experience with these?

someone on Manado Cafe said it could be flattened w/ hot water.

any thoughts/ Ideas?

hear are some pics.

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 I believe those pickguards are indeed made of hard rubber, and that stuff is notoriously difficult to repair under the best of circumstances, and as an added feature, it's rather brittle.  My bet guess is that cyanoacrylate may adhere well enough to stick on a reinforcement, but  you will want to maximize the gluing surface.

I've not heard of techniques to bend or reshape hard rubber.

Nor have I. But the heated waterbath is at least worth a try. I do this operation from time to time on celluloid, and it goes like this:

I'd recommend against using any kind of dry heat on that pickguard, because it's a rather flammable stuff. And take out the metal pins before putting it through the microwave.

 

My usual method is to sandwich the piece face down in a flat pyrex baking pan under another strategically chosen glass weight (1/4" plate cut to size, with a nice big rock on top works well) and fill the pyrex pan with enough water to cover the guard and then some, and nuke the whole sandwich in a microwave. The water makes ignition or even scorching impossible, and the heat of the boiling water is sufficient to make celluloid—and, I hope, the hard rubber—go limp. The glass over the top, with some additional weight, combines with gravity to allow it to go flat during the heating process. After it has gotten up to temp for a few minutes, and the microwave has shut off, leave everything in place until it's dead cold. The thing should be flat. Or as flat as the place you made for it. 

But I also warn you that this kind of cure may be temporary. It may potatochip again. If it does, I'd just make a replica guard out of ebony. 

Thanks so much for the replies.

 I have explained that there is not much to loose  as it's non functional now and as long as he wants to give it a shot I'll try the microwave method.

I'm guessing it get's too floppy to just place it in hot water and then clamp it ?

David, I think the idea is to allow the weight to flatten the plate over a period of time rather than applying heat then forcing the plate flat immediately. I doubt that the rubber will get soft enough to turn floppy with this technique.

Ned's got it. You don't heat it and then clamp it, you put it in the shape you want it to be in while it's at full temp for a bit, then leave it there until it's cold and the new shape is set. It's not unlike a perm at the beauty shop.

But once again, the caveat: this is vulcanized rubber and my experience is with celluloid. Let us know what results you get.

I've felt guilty for not adding to the knowledge base ever since asking for others suggestions, so I thought I'd update.

Success.

I used Paul's method w/ 1/2" glass chunk on top. Boiled, let cool fully, flat as a pancake.

Left it on the bench and 24hrs later it was a potato chip again!

seemed like a drying issue as it was stone cold and flat before I took it out of the water. So I repeated the whole procedure but after it cooled I held it flat in between newspaper and weight while it dried. worked like a charm and has been flat on the instrument for over a year now.

I'm guessing the fiber in the rubber takes up and gives off water much the same as a thin piece of spruce would if you wet or dry it on one side only.

Hope this is useful for someone in the future.

Again, thanks for the suggestions.

Glad to hear it finally worked. I think what’s going on is that the heat softens the actual rubber, which binds the filler material. This is made difficult by the simple fact that the stuff was developed in the first place to be extremely heat-resistant. But if you got all the way through it with enough prolonged heat, all the components in it finally accepted the realignment. No wonder you had to really cook it!

But because it’s basically oil, sulfur and fiber filler, water doesn’t penetrate it. It just kept it from bursting into flames while you heated it long enough. 

With all do respect, I hear what your saying but I think my experience shows something different. It was cold and flat as it sat in the water. Only re-warping when air got to one side and not the other. I wish I had weighed it at the time to see if it absorbed any moisture. Next time.

 

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