Re-threading a bridge to include Full Circle PU.

Chasarms · #1 03-01-2010, 09:47 AM

I have a Shen SB 180 that Nick Lloyd did for me a while back. I have decided that I want to try a Full Circle, which seems innocent enough, except that Nick has fitted the bass with a very unusual set of adjustment wheels. These things are giant. Last night, I dropped the tension on the bass and took off the bridge. The posts on these things are probably something lke 3/8" or so. They're massive.

I know that I could simply have a new bridge cut for the bass, but I would like to preserve this one if at all possible. I like the look of it, and it has Nick's brand on it.

I was thinking that I could fill in the threads and holes with a slow-setting, super hard epoxy and then re-drill and re-tap it to the smaller size. I understand that drilling a bridge that has already been done isn't easy, but I have a few ideas for a little jig that ought to keep it aligned and steady and won't be too difficult to craft.

My main concern is the stability of the threads. I have used JB Weld for other applications, and it was very solid. I am seeking thoughts on the idea of it holding up as the threads in a bridge.

Thanks

Charles

jdombrow · #2 03-01-2010, 11:17 AM

I'd suggest gluing a hardwood dowel in the hole and then drilling and tapping. It would preserve the integrity of the wooden tone, especially since you're installing your pickup in the hole.

arnoldschnitzer · #3 03-01-2010, 11:56 AM

You could use the existing adjusters to fill in the space, then drill and tap for the Full Circle threads. The best way to do this is to first drill and tap, using a small lathe; then glue in the old adjuster part, and then cut off the excess. Fitting the top shaft will be more difficult, as you will probably need to make a spacer. But anyone with a small lathe and some experience should have no trouble.

robobass · #4 03-02-2010, 07:06 AM

Quote:

Originally Posted by arnoldschnitzer

You could use the existing adjusters to fill in the space, then drill and tap for the Full Circle threads. The best way to do this is to first drill and tap, using a small lathe; then glue in the old adjuster part, and then cut off the excess. Fitting the top shaft will be more difficult, as you will probably need to make a spacer. But anyone with a small lathe and some experience should have no trouble.

As a former machinist, I would say it's possible, but pretty tricky, to make a 1/4-20 threaded hole in a 3/8-16 (if that's what it is) screw. Also, if you can find a machinist willing to do this, then just do it with some 3/8-16 aluminum stud, rather than destroying the original adjusters (the machinist will appreciate some extra material to make mistakes with!). It might work, but if this were my job, I'd plug the holes with hardwood dowel and hide glue, but first bore 3/16" holes in them, so that I could later push pins into the holes, allowing proper positioning on the drill press, and then drill and tap afterwards. Whether you fill the holes with epoxy or hardwood, the biggest challenge will be drilling straight holes.

Greg Clinkingbeard · #5 03-02-2010, 08:17 AM

I used hardware store threaded inserts and bushings for the non-threaded side. It was necessary to enlarge the holes a bit, so I reversed the drill and went at it. Hide glue has held it all together for the last year and a half. This cost me about $5 and a couple of hours which was a no-brainer compared to paying for a new bridge.
Toad used this method on his Cleveland, I think.

vejesse · #6 03-02-2010, 09:22 AM

We make aluminum or brass 3/8 -16 to 1/4 -20 adapters for Full Circle pickups. Plenty of meat there. If you're going to drill and tap the existing adjusters then getting the tapped hole concentric is the trick. A collet setup on a lathe is nice but if you lay out the holes correctly, center drill and get the parts square in a drill press that should work. A nice thing about having a lathe is that you can make anything work with anything and all the parts stay concentric, but if you get some misalignment you can always open things up a bit or use a .005" oversize tap.

If you use dowels it's sure nice to use boxwood. The wood is hard as a rock and holds a threads well.

arnoldschnitzer · #7 03-02-2010, 11:09 AM

Quote:

Originally Posted by robobass

As a former machinist, I would say it's possible, but pretty tricky, to make a 1/4-20 threaded hole in a 3/8-16 (if that's what it is) screw.

I have done this many times with no issues. In actuality, the OP is talking about 7/16" threads, not 3/8".

Mark Carlsen · #8 03-02-2010, 11:49 AM

I had some inserts made a few years back... 7/16's on the outside 1/4" on the inside. A few clients keep the original adjuster[wooden] on the G side. Works nice...

Chasarms · #9 03-03-2010, 10:23 AM

Well, it may not have been the ideal solution, but it worked.

I ended up filling both the threaded and non-threaded parts of the bridge with J.B. Weld using a syringe with no needle attached. I then constructed a little jig that kept the feet and the main bridge piece in alignment and perpendicular to the crill press table.

I don't have a drill press, so I took the whole little rig to work yesterday, and the head carpenter in the carpenter shop drilled it out on his drill press and tapped the threads for me. I put it back together last night with no issues.

It works really well.

He said that the J.B. Weld is at least as strong as threads in wood. I bought a 5/16 18 FC PU, so the threads are a little more coarse than the 1/4 20 design. I don't know if this matters or not, but I expect it will serve just fine.

BTW, at first blush, I love the sound of the FC. My best PU experience to date.

james condino · #10 03-03-2010, 01:53 PM

I'm a little late on the discussion, but couldn't you have just used a simple helicoil insert to change the thread sizes and test out things before you did the JB weld mod?

My other question is did Nick put those original adjusters on, or are they just some of the standard issue funky Chinese models that I see all of the time?

j.

Uncletoad · #11 03-03-2010, 02:23 PM

Quote:

Originally Posted by james condino

couldn't you have just used a simple helicoil insert to change the thread sizes

I did just that in 2005 and it's still working fine.

Chasarms · #12 03-04-2010, 08:04 AM

Quote:

Originally Posted by james condino

I'm a little late on the discussion, but couldn't you have just used a simple helicoil insert to change the thread sizes and test out things before you did the JB weld mod?

My other question is did Nick put those original adjusters on, or are they just some of the standard issue funky Chinese models that I see all of the time?

j.

I had never heard of helicoil inserts until your thread. That would have been a preferable solution I suppose. Although, it would not have addressed the over-sized unthreaded hole in the main bridge piece. i suppose I could have found some sort of bushing or the like if I looked long enough.

As your other question, Yes. the adjusters were installed by Nick when he set up the bass for me. I have no idea of their origin. I always liked them though. They are very easy to use and seem of good quality.

james condino · #13 03-04-2010, 10:58 AM

A helicoil insert is basically a 50 cent gadget available at any auto parts store. The idea is that you strip out part of your engine block while wrenching and cussing away at it; no big deal. Go down to the local parts place, they'll laugh your conundrum, and pull out a box of 'em in all sorts of sizes. It looks sort of like a hardened spring that screws into what is left of the threads and then gives you another smalller diameter.

With either your engine or bass bridge, it isn't the perfect solution, but it saves you a bit of time and you won't have to pull the whole engine block and re-tap or redo the threaded hole. 'Very nice to have in your bag of tricks for a variety of situations; sounds like it gets the Toad stamp of approval too...

j