Anyone do metalwork / bass bridge fabrication?

[bob p]

Just wondering if anyone here does much in the way of basic metalwork. I need to fabricate a replacement bridge for a P-Bass and I'm looking for some help sourcing materials.

Essentially, I need to clone a vintage-type P-bass bridge baseplate, which is nothing more complicated than an L-shaped piece of chrome plated brass with 13 holes drilled into it. I need to keep the 5 mounting holes on the baseplate in the stock location, but I need to move the 4 holes for the string mounts to the right a bit, and perhaps move the 4 holes for the intonation screws to the right as well. I can recycle the stock hardware (threaded barrels, height adjustment screws, etc.).

Basically, I'm trying to compensate for a bridge that was mounted too far to the left on a bass that I just picked up, and I'm trying to avoid re-drilling the guitar, moving the bridge to the right, and exposing holes in the finish.

TIA.

[big_teee]

That's a pretty tall order.
I've moved a lot of bridges, mostly on strat type guitars.
If the bass doesn't have string ferules and the strings go through the body?
I would just move the bridge and use dowels in the holes.
Maybe it will be on a black area, and you can use some black paint to cover the dowels.
Didn't know the bridge plate was brass, I figured they were all steel?
GL,
T
** You may want to contact Bruce Johnson.
He can make anything in his machine shop.
He will do work for members.
He also has his on line of bass guitars.
http://music-electronics-forum.com/users/10547/

[bob p]

Thanks for the ideas.

I don't think the problem is really all that complicated, now that I've decided what to do. What was complicated was thinking through all of the alternate ways to approach the problem (changing the neck mount, moving the bridge, etc.) and determining that they weren't the best solution to the problem.

The project bass has no through body ferrules, this is just a simple L-shaped bridge with holes in it. Moving the bridge across the face of the guitar and plugging the holes is the first thing that anyone would think of, but after thinking the problem through, it's not a valid option.

The bridge can't be moved because it has to fit under an "ashtray" bridge cover. The ashtray can't be moved because it was installed with oversize screws, and moving the ashtray by the amount required for the string geometry will leave a huge gaping hole in the face of the guitar, which would require a refinish. I want to avoid that.

The only solution that doesn't involve refinishing a 4-layer candy apple finish is to move the bridge under the ashtray (but there's not enough room to do that), or to fabricate a replacement bridge baseplate that doesn't have the normal string pass-through holes in it, and to drill the holes for the strings into new locations farther to the right that will give better string alignment.

I honestly don't think that fabbing the baseplate would be that hard -- it's just a piece of brass that would need to be bent on a brake. Then it's just a matter of drilling holes in the right locations. The bend is pretty simple -- it's just one bend. I'm thinking that I could do it in a vise with heat, and do all the trimming / grinding / filing / drilling / finishing work myself. The hardest part of the problem seems to be where to find the proper thickness brass stock for the project.

[Mick Bailey]

I use stainless for such jobs and polish it to avoid plating.

One of the problems with heating brass is the alloy composition; some of it is 'hot short' which means it goes granular and cracks when bent under heat. I always anneal brass along the bend line, quench it and then bend. A decent vice (vise) and some heavy, smooth clamping plates will do it. Use a piece of aluminium or hardwood between the material and hammer, and make sure it doesn't move. You need to slightly angle this to concentrate force at the root of the bend, otherwise it will come out with an overly-large radius.

When you mark out, make the material a little longer, bend it, then cut to size. That way you won't be reliant on your bend being exactly positioned. The bend-radius, material thickness and hardness affect where the bend will form. I'd add 1/4" to each leg of the bend and trim it afterwards.

I've recently bent up a tailpiece from 4mm stainless sheet in the vice with no problems at all. Most non-ferrous stockholders carry suitable material - either brass or stainless. Most will cut to size or even bend it for you as well. Ask if they have any offcuts that can do the job.

[bob p]

Thanks. I had thought about brass and not stainless because I thought stainless plate would be too hard to find and/or too difficult to work with. I was thinking that I could just use brass and not worry about plating it because it would be hidden under an ashtray. But if stainless is available then I might as well use stainless because it will look better, and I might even be able to use stainless with the bridge cover removed.

Thanks for the tips working with the metal. It always helps to hear from someone who has experience doing this sort of thing.

[Mick Bailey]

Some grades of stainless are pretty easy to work. I also buy free cutting bar and this machines as easily as brass.

Here's the tailpiece. It needs polishing as it was just an idea to try out. It started out as 4mm but looked too clumsy so I thinned it out and radiussed it where the strings pass through. 2mm would have been plenty. I may replace it with brass for cosmetic reasons to match my bridge.

[Paleo Pete]

Mick is right about handling the brass, as a machinist I worked with a lot of it. About the only idea I Can add to what he suggested is drill the holes in the flat plate before bending. Makes it a lot easier to get them placed right. otherwise you have to try and find a way to drill through that 1/2 inch or so bend...the other holes can be drilled afterward. But then you need to be pretty picky about where the bend is.

You can mark everything out wit a sharpie then scratch accurate marks into that with an awl. If you drill by hand definitely center punch everything before drilling, drills will walk in metal. Machine shops use Dykem, a blue marking dye, but for a home project a simple red blue or black sharpie will work. Scotchbrite should take it off after it's done.

Check around your area, find some machine shops. They should be able to tell you where to get any kind of material you need, some of the smaller shops may even have something big enough lying around in a scrap bin. I made the bridge for my old Epiphone Strat from a scrap piece of aircraft aluminum out of the scrap bin in a shop I worked for. Lots more work there, it was the block behind the bridge plate, tremolo arm hole wallowed out so bad it was way noisy so I made another one...but I had a milling machine handy...

[Mick Bailey]

There's another way out of this - I used to make clocks and sometimes despite the most accurate marking a hole will drift in one of the plates and this has to be corrected and re-drilled. The way this is done is to use a stub of brass rod and make sure it's a tight fit in the hole. It needs to project a little on both sides. Now, one side is supported on something smooth and heavy (like a block of steel or smooth anvil face) and the other side given a few heavy blows with a hammer. This expands the plug into the hole and it just needs filing smooth and re-drilling in the correct place. The plug will bulge in the middle and hold in the hole because it will be barrel-shaped. You need heavy blows so that the plug will expand. Lots of light blows will rivet it over and work-harden the plug

I've used similar techniques on all kinds of work. Other techniques are; thread the hole with a taper tap so that it just about forms the thread, then screw in a very tight screw and expand that. Or countersink both sides of the hole and rivet an annealed plug in place.

Sometimes the old hole is better drawn over in the opposite direction of where the new hole needs to be, and opened up by filing. A larger hole can then be drilled for the plug, which is then expanded in and filed flat. This is necessary when the displacement of the new hole position is so small that a plug expanded into the old hole would be nearly drilled out. In effect you want the new hole to be on the edge of the plug.

A last resort that I sometimes use to fill a hole up is to tap it out, very lightly countersink the top side and use oxy-propane to silver-solder a fluxed and threaded plug in place. This will destroy the chrome but the rest of the plate could be clamped up to protect it.

If you drill the holes before bending make sure you don't try to apply bending force above the centreline of the holes. The metal will bend along that line and not where you intend it to. Also, if your bend is not 100% accurate the holes will end up being too high or too low. That's why I like to bend first and mark & drill afterwards for this kind of work. When I machine bend it doesn't matter as the force is applied directly to the bend line (or it would be if the seals han't gone in my hydraulics) and it's precise.

If you want to drill first the best way is to make the drilled part longer, clamp that, bend the undrilled side of the plate and finally trim the long edge to size.

[bob p]

Thanks. I was wondering what the best methods would be for addressing the problem of overlapping holes. You guys have made some great recommendations, just what I needed to hear.

In this bridge the holes for the string pass-throughs are pretty big, and the new holes that need to be displaced to the right won't be far enough to the right to make "new" holes that do not overlap. They're going to end up overlapping the existing holes. The amount of overlap will not be enough to make the resulting hole look like an ellipse or an oval, they're likely to be far enough to the right that the resulting shape might resemble more of a figure-8 lying on it's side, or an infinity symbol. (I'm not exactly sure about the amount of overlap that I'll have in the end. It's hard for me to tell with the naked eye, but I think that I'm more likely to have a sideways 8 than a sideways zero.)

Does the difference between an oval hole (without protrusions from above and below into the middle) and a figure-8 holes (with protrusions from above and below into the middle) help to determine which sort of plugging method would work best?

TIA.

[big_teee]

Before I went to all the trouble to fill metal holes, I would just make a new plate.
A clean plate with no holes would probably look better, and should be easy peasy!
The metal I have with a nice clean 90 bend has no radius on the inside, it's a nice tight 90.
It has a minimum radius on the outside, and is .090" thick.
If you cut it a little long, you could even put a couple support screws in the corners toward the neck, for added sustain.
T

[bob p]

This is going to be a learning experience, you know.

That metal stock that you're talking about sounds like it might just be the ticket. Now it's just a question of drilling 13 holes accurately vs. drilling 4 holes accurately and pounding with a hammer.

I hate to admit it, but I don't have a good handle on how thick 90-thousandths really is. It sounds right, but I'm going to have to ask someone to put caliper on the stock bridge baseplate to figure that out.

[big_teee]

1/16 inch is .0625, and 1/8 inch would be .1250".
So .090 would be between 1/16. and 1/8 inch.
in the 3/32" range.
About the same thickness of a strat bridge, or the bottom fiber base of a strat pickup.
I had it laid out, going to heave it back on the scrap pile.
Surprised you don't have a cheap dial caliper, or Micrometer laying around.
I use them all the time.
The cheapies from harbor freight work great for knock about work.
T

[bob p]

No, I don't have a micrometer. Never really needed one.

Since you took all the trouble to haul in the piece of angle iron that we had talked about, go ahead and cut a few small of pieces off of the end for me. i can guarantee that i'll try using them, but given my metalworking skills i can't make any guarantees about not screwing them up, or what i'll actually end up using in the end.

Width of the OEM bridge is a bit over 3" so a 4" cut would be great.

[big_teee]

I'll cut some out.
Does your bridge look something like this.
http://www.stewmac.com/catalog/specs/0093_1spec.gif
Notice this one has the 5 holes in the rear, and 2 in the front for extra Umph, and sustain.
I'll leave some extra metal all the way around.
T

[bob p]

That technical drawing looks like a Gotoh copy of the generic Fender bass bridge.



The big differences seem to be that the string pass through holes are larger on the Fender bridge than on the Gotoh bridge, and the Fender doesn't have the two added holes on the front corners. The Fenders also have threaded barrels, like shown here:

FENDER: (larger string-through holes)


GOTOH: (smaller string-through holes)



I think the dimensions in that drawing of the Gotoh from StewMac look right.