Bridge pad caul with a magnetic personality - a question of sorts.

[John Cartwright]

Hello,

I need to repair a bridge pad on an otherwise near mint '63 Epiphone Caballero (as well as replace the plastic bridge, which goes without saying.) I've read in Dan Erlewine's guitar repair book, that a great way of doing this is to use a caul with Bondo smeared on it, waxed paper to separate, and clamp this down in the guitar. The idea being that the Bondo will form to the exact topography of the bridge pad top curvature making for a better fix.

OK, sounds great, but I can see the possibility of the Bondo squeezing out and sticking to something, giving me a one way ticket to Problemville.

Question: What about rare earth magnets? Could I use the magnets against, say a piece of framer's mat board (which is stiff but flexible) then the waxed paper, then do the super glue and sawdust trick? I'm thinking four or five magnets placed along the mat board caul would allow the caul to conform to the shape of things.

Good idea? Bad idea?

Ooooo, just thought of this, what about one of those stress balls (the cheap ones that are basically balloons with sand in them) and just clamping one of these in there with the mat board and waxed paper with turnbuckle clamps?

Thoughts?

Thanks! John

[Rob Mercure]

Was just recycling a batch of old computers a friend had given me - mostly I only get hardware and such as the technology changes so fast and removing SMT components is far more trouble than they're worth - but when I opened up an older CD-ROM I found a round flat rare earth magnet/rubber compound used for the stepper motor. As I was disassembling it so as not to chip it I got the flesh of my thumb caught between the steel magnet case and the magnet - and thought I'd wind up screaming before I could carefully prize the parts apart sufficiently to remove my flesh (a quick piece of ice prevented more damage). But the point I'm making is that using these buggers is tricky and I could see not only inappropriate glue squeeze-out everywhere but a pinched blood blister in the middle. Now if you've got a good set up to practice these can be a great tool but if you've got a set up to practice with the magnet then you could also probably also practice with the bondo as well - and the bondo ain't gonna squeeze a blister on you. If you've ever worked with bondo it's just a filled epoxy and you can regulate the thickness and setting rate by using differing amounts of hardner and varying the temperature. Not that I like it - actually hate the odor - but I've used the Earlwine trick once without problem (with old fibered "gorila hair" bondo yet) without problem. While you don't want a greasy guitar anywhere you don't want the bondo to attach to could be lightly coated with petroleum jelly (although I wouldn't mess with it) and there are probably some other materials that might work - how about putting a layer of cellophane tape inside, for example?

Rob

[Frank Ford]

For what its' worth, I always use a flat aluminum caul on the inside when gluing bridge plates or bridges. Some folks think that you shouldn't introduce stress into that joint when clamping a bridge by flattening the top in that area. Others, including myself, think its a good idea to introduce that stress to stiffen the area a bit to help reduce the deformation caused by string tension.

[Ry Charters]

If you have a radius dish, just take a piece of dieboard and sand it to the radius. Wax it up nice and good, and you've got a curved caul. Or, if you find something thats the right stiffness (that had a little flex in it, like 1/4" or 3/8" maple) a couple of cam clamps in the middle should also pull the ends of the bridge plate tight against the underside of the top. If the top is bowing up, I'd definitely use a flat caul to pull it back into shape a bit. Its a judgement call.

[Chris Sisson]

I've been reading this thread but I didn't get a clear idea of what you mean by "repairing" the bridge plate (or pad). Is it cracked?, loose? It seems that the responses assume that you want to reglue it.

[John Cartwright]

Chris: Sorry, the bridge pad itself is solid and actually pristine except there is some tear out where the string balls sit and tear out where one of the mounting bolts was located (the one located located about 1/16" from the center two string holes on these plastic Epi bridges). I'm no expert, but this seems like a really stupid design to me, what was Gibson/Epi thinking? I understand the LGO's of similar vintage had these bridges too.

In short, I wasn't planning on replacing the pad, just repairing the tear out with sawdust and super glue as Erlewine suggests in some cases.

Also, there is a little splitting of the top itself, though slight. This slight top splintering is right around the the two center string holes, where the weakest point seems to be due to that central mounting bolt. At least this is what I've deduced. I'm really seeing now the point Frank just made about applying a little tension with a flat or flatter caul.

Frank: would you advise going with the flat caul in this situation? If so would I need to heat the top before beginning the repair?

Rob: You mentioned that you've used the sawdust and super glue method once before with success. Is there another method that you prefer and why? Or were you referring strictly to the Bondo issue?

I'm trying to be sponge and soak up everything I can :-)
Hope this helps clarify. Many thanks for your thoughts!

best,
John

[Rob Mercure]

John, the super glue and sawdust is just a variation of "something that binds" and sawdust that goes back as far as there were woodworkerd using adhesives. I've just vouious varnishes and shelac depeding there it's to be used and the hassle factor. And you can even vary the sawdst. While it's expenisve Lignum Virae sawdust retains it's slipper lbricity when mixed with glue and even the same sawdust abraded more or less fine can give you some material control. Super Glue sers quickly and I suspect that this is why we use it. Since to cheap to buy expensive glues that may not store until a second use I tend to use regular super glue and a really, really dry punky bit of apply that seems to be workable quikcly with sufficient attachments etup but your experienzez will be unigue. Purchasings some of the slow setup SG types combined with a variey of sawdusts might provide you wiith what your want. Just make our sown sawdust "clean" for each used as there is no "universal match" sawdust and you wind with dirt, grit, and metal contaminated funk.

Rob

[John Cartwright]

Thanks! Will do.

[Tom Krebs]

Can you stick a camera or cell phone in there and snap some pics??

[John Cartwright]

[Ry Charters]

Ah....I thought you were replacing the plate. I have a very similar guitar in for repair right now. Its not a very expensive guitar, and the ball ends are creeping up into the bridge from years of wear. Here's my fix...
Put some tape on over the holes from the inside. Mix some (tough) epoxy with some silica for thickness and pour it in the holes. (the bridge pin holes are also oblonged) Dry overnight, redrill the holes (with a block of wood under the plate to prevent chipout) and then I'll install a "platemate" available from stumac.
I thought about getting some waxed up 3/16" derlin rods to put in the holes while the epoxy dries to keep the hole spacing and angle more accurate than drilling out by hand later.
That's my technique....

[Chris Sisson]

Bingo!

[John Cartwright]

Ry, thanks for the info! I see that the Plate Mate from Stewmac is brass. Wouldn't this alter the tone? ...perhaps a touch metallic? Maybe not? I recently picked up a 1/16" thick piece of hard maple from Woodcraft (blessed to have one within 20 minutes drive) After doing the glue-fill technique, would a subsequent pad of maple like this work instead?

Also, I know it's got to be a case by case situation, but when is the plate "generally" considered too far gone for repair and must be replaced?

PS, checked out your site. Beautiful work your doing! Loved the details in the bridge of the lap steel and the flamed maple necks on the guit-fiddle.