Double Bass Slipping/stripping bridge adjuster threads

[KeyserSoze]

With the weather changing (humidity up) I've found my string height has recently risen perceptibly, enough that I thought I'd lower my adjusters for the first time ever -- on a one year old Christopher carved, lots of work done on the bridge by luthier a year ago, including removing material from the bridge above the adjusters to facillitate lowering, as there was no room to lower the bridge with the factory adjuster setup.

After loosening the string tension(s) a turn or two, I turned the bass-side bridge adjuster, say two or three quarter-to-half turns. All of a sudden... Whoomp! The threads in the upper section of the bridge "gave" -- stripped a little, it seems -- and the (remaining) string tension "pulled" the upper portion of the bridge down flush on the adjuster, as if it were at its lowest "setting."

After marking the position of my bridge feet, I further lowered the string tension, allowing for pulling the strings off the bridge (to the sides) and removed the bridge and feet for inspection. The (Christopher factory) black (aluminum?) adjusters will both "catch" -- engage the threads -- all the way on the bridge's treble side threads. Neither adjuster will *fully* engage the threads in the (seemingly newly partially stripped) bass side of the bridge. They turn, as if the threads are working, until a little pressure is applied, then they "slip" or give, going to the all the way down flush position.

So my question is; how has this thread-stripping problem been dealt with by others, particularly our esteemed luthiers? Is there a reasonable "quick fix?" I wondered about plumbers' silicon tape, in that it wouldn't seem to do any permanent harm. Am I gonna have to spring for a new bridge, or is there a reasonable repair for this condition?

Yes, I'm gonna call my luthier, but I wanted to tap the experience and expertise on this list too.

Thanks in advance.

 

[Bob Branstetter]

I've found that the maple or what ever Asian wood they use in the Christopher bridges is somewhat softer than the maple used for the typical European bridges. If the threads in the bridge are stripped, the only permanent cure is a new bridge. The Christopher adjusters are 1/4" x 20 tpi threads, so your luthier should be able to re-fit the adjusters in a new bridge if you desire. As a temporary fix, you can put a 1/4 x 20 hex nut onto the threaded part of the adjuster and use a wrench to raise and lower it. Kind of hokey, but it works - temporarily.

 

[Chasarms]

My bass is fitted with a larger shafted wheel that also has a much more coarse thread. They are made out of some sort of synthetic material.

Would it be possible to re-tap the existing bridge to fit it with this type of wheel?

If not, you may want to at least consider using this type of wheel on the new bridge as it seems to make more sense with a threaded wood application.

 

[Bob Branstetter]

My bass is fitted with a larger shafted wheel that also has a much more coarse thread. They are made out of some sort of synthetic material.

Would it be possible to re-tap the existing bridge to fit it with this type of wheel?

If not, you may want to at least consider using this type of wheel on the new bridge as it seems to make more sense with a threaded wood application.

It sounds like you are describing the Robertson adjusters. They are indeed an superior product. However, it would be a waste of both time and money to retrofit something that good into a bridge of inferior wood (even if you were able to do it successfully). While aluminum adjusters may not be my first choice, there are many thousands of them in use by bass players around the world. Improper (i.e. poor workmanship quality) installation is the usual cause of problems with aluminum (1/4" x 20tpi) adjuster - not the adjusters themselves.

 

[John Sprague]

installation is the usual cause of problems with aluminum (1/4" x 20tpi) adjuster

Ain't it the truth! And Bob's probably right without even looking at it that the bridge may not be worth the investment in a larger shaft size, though the operation should work.

We sell aluminum/walnut 1/4-20 adjusters, and publish on our site a method for installation that has worked very well for us over the years on Chinese maple bridges. We put that out there because some folks were doing a so-so job and blaming the adjuster.

 

[Bob Branstetter]

We sell aluminum/walnut 1/4-20 adjusters, and publish on our site a method for installation that has worked very well for us over the years on Chinese maple bridges. We put that out there because some folks were doing a so-so job and blaming the adjuster.

I was going to suggest that the Shen article on adjuster installation should be required reading for anyone who does or wants to do adjuster installations, but then I noticed that the link is not working now. John, Can you post the correct link if the old one has changed?

 

[Chasarms]

I was going to suggest that the Shen article on adjuster installation should be required reading for anyone who does or wants to do adjuster installations, but then I noticed that the link is not working now. John, Can you post the correct link if the old one has changed?

I don't think the link is bad. I think the whole site is down. You can't even hit the CSC home page through the link in John's profile. It'll come back. You never know.

We once had a server that started crashing almost nightly. Even after hours of speculation by all the techowiz guys (AKA: Nerds) and several costly diagnostics, we all remained amiss. Once someone actually bothered to hang around and watch the thing on a 24-hour basis, it was quickly linked to the visits by the cleaning staff.

Hey, she had to plug in that vacuum cleaner somewhere!!

 

[KeyserSoze]

Thanks Bob, Chasarms and John. I put a 1/4" hex nut on the adjuster and its working for now. Unfortunately, while in the diagnostic process, my soundpost fell. I reset it with my bent coat hanger and bent BBQ skewer and knowing that I'd have to make a trip to my luthier pretty soon for his soundpost voodoo kept me from implementing any of my hair-brained repair schemes.

Chasarms, your profile says you have a Shen, you say you have larger "bore" adjusters, John says Shen sells the stock 1/4" adjusters. Are your adjusters aftermarket? If so, what kind are they, where'd you get 'em, how much?

Being a newbie when I bought the bass a year ago, I got a drop-shipped bass for a great price, figuring to put the "savings' into a setup, which I did. Unfortunately, my luthier was unfamiliar with "Chinese factory basses" as he dismissively called mine and was unaware, unlike Bob, about the less-than-quality wood used for this bridge. So he did quite a bit of work on the bridge, including contouring the crown(?) for pizzicato, running the setup bill "over budget." Now, a year later, the bridge craps out on me. I'd consider having the larger bore adjusters put in this bridge, just to see if I can eke out another year out of it. If the threads crap out again, then I'll have no bridge but two sets of adjusters and can have the pair I prefer put into a new bridge, pass the others along.

Thanks again for your advice, fellas.

 

[Bob Branstetter]

I'd consider having the larger bore adjusters put in this bridge, just to see if I can eke out another year out of it. If the threads crap out again, then I'll have no bridge but two sets of adjusters and can have the pair I prefer put into a new bridge, pass the others along.

If you go with the larger bore adjusters, you should be aware that it is not just a matter of getting a larger tap (5/16" would be the logical next size up). You also have to enlarge the hole on the other side. It's hard enough to keep everything in alignment when you are starting with a new bridge blank, but when you are reboring old holes - well there can be problems. The wood in those Christopher bridges does not take well to reboring and will fracture if not done with great care. If you are wondering how I happen to know so much about these bridges, it's because I once made the mistake of buying a dozen of them because the price was so good. Like everything else, you get what you pay for.

 

[Chasarms]

Chasarms, your profile says you have a Shen, you say you have larger "bore" adjusters, John says Shen sells the stock 1/4" adjusters. Are your adjusters aftermarket? If so, what kind are they, where'd you get 'em, how much?

I purchased my Shen from a well-respected luthier. I gather that he is of the opinion that the larger, coarse-thread wheels are the way to go, because he set it up like that from the start.

I have no clue who made the wheels, I'll attach a photo. Perhaps Herr Branstetter can confirm or deny that they ar Robertson.

BTW, I won't tell you who set it up, but you are welcome to guess.

Link Removed

 

[Bob Branstetter]

I have no clue who made the wheels, I'll attach a photo. Perhaps Herr Branstetter can confirm or deny that they ar Robertson.

No, they don't look like Robertson's adjusters. Since the bridge has Nick Lloyd's stamp on it, I would assume that Nick could tell us exactly what they are.

 

[basswraith]

To fix the stripped threads in the bridge one can take a q tip dip it in high quality supper glue and soak the hole and the stripped threads. Let it dry and repeat this 5 or 6 times. Then after there has been enough build up inside that hole...retap it with the 1/4 20 and the adjuster should work just fine. !!!! you must wait and be 100% positive the glue is DRY before u tap out the new threads or put an adjuster in there!!!! If you fail to do this you may have glued your tap or your adjuster into the bridge. Cursing loudly will not loosen what u have just super glued into the bridge. Make sure the customer is not present when u do this. Such mistakes may require a ritual suicide to regain your shame.
Christopher bass bridges are less then spectacular. The quality of wood is not what I would choose for a bridge ... too soft.

 

[Bob Branstetter]

That's an interesting idea. The only problem I can see is if the wood threads had been loaded with parafin or similar waxy lubricant so that the super glue couldn't sink into and bond with the remaining wood threads.

 

[basswraith]

The other way to do it is to drill out the hole just a little bigger and fill it with a maple dowel..or hard wood dowel, glue that in there, then drill that, tap it and put the adjuster back in. The dowel is now a filler/bushing for a new solid hole to be tapped. I would recommend a 90 degree jig to hold the bridge under the drill press. Do not just drill the hole with a hand drill.
Remember when drilling out the dowel that the drill bit and wood get very very hot from the friction...some heat will melt the glue that you used to glue in the dowel. In that case start over and use different glue.
AND VERY IMPORTANT....Clamp the leg that u are tapping with a cam clamp or something solid. Sometimes tapping that hole in the leg will crack the leg on the way out. The clamping the keeps that from happening.
.............I have no idea what I am doing.

 

[basswraith]

That's an interesting idea. The only problem I can see is if the wood threads had been loaded with parafin or similar waxy lubricant so that the super glue couldn't sink into and bond with the remaining wood threads.

I know what u mean. One could retap that hole to try and scrap all that crap out. Also super glue is thinner than water, it will find its way into any thing. When applying the glue with a Q tip, the fibers of the Q tip also become part of the built up inside the hole. BUt dont try to do this..it will just happen.

 

[Bob Branstetter]

The other way to do it is to drill out the hole just a little bigger and fill it with a maple dowel..or hard wood dowel, glue that in there, then drill that, tap it and put the adjuster back in. The dowel is now a filler/bushing for a new solid hole to be tapped. I would recommend a 90 degree jig to hold the bridge under the drill press. Do not just drill the hole with a hand drill.

The odds that you can drill out the hole (even with a jig) and have the hole be in alignment with the hole in the detached feet is questionable. And then tapping into a dowel where the grain of the wood is anything but straight sounds like an invitation to more trouble than it's worth. If you are going to go to that much trouble, why not just fit a new bridge?