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Double Bass How to fix bridge adjuster threads? Luthier to blame?

A

AuxOne

Sep 10, 2010
27
0
Brooklyn
#1
I just wanted to share an experience with you guys and maybe get some feedback...

When I got my (used) bass the first thing I did was have adjusters installed. Just recently I put new strings on it and while tuning up I heard the loud sound of the bass side bridge adjuster slipping a few threads.

Immediately I lowered the treble side to compensate and I noticed and there was so little pressure on it the foot actually rotated around a quarter turn without much effort. I tried a few things but the bass adjuster keeps slipping so I think it removed the bridge threading.

I told my luthier about it and he says that's rare, and that a new fitted bridge is upwards of $400. Should I make him do it cheaper because maybe the adjuster was installed poorly? He has 17 years experience and is fairly well known in the area.

Just bad luck? Think it could be fixed with a wooden dowel?

Thanks
 
#3
If the threads had been ruined during installation you would have noticed immediately. My guess is the wood on your bridge was relatively soft and couldn't handle the new string tension.

A $400 bridge is going to be a much stronger bridge. Not only should the threading work without any problem, it will probably make your bass sound better.
 
#7
Although I said that's the first time I used the adjuster I was mistaken; I did raise the treble side of the bridge very slightly about 3 weeks ago after the heat turned on in my house. It was uneven by less than 1/8 of an inch.

Right before this incident happened I raised both adjusters into slap friendly height (evenly) while my strings were detuned, and the thread slipped while tuning back up.
 
#8
Are your adjusters 1/4 - 20 thread? You might be able to avoid a new bridge by having adjusters installed that have a larger thread. For example: Install adjusters with a 3/8 - 16 thread. You simply drill through and remove the damaged threaded area with a 5/16 drill which works as the tap drill for the 3/8 - 16. The larger thread size has a better chance of not disintegrating in your soft bridge.
 
#9
vejesse said:
Are your adjusters 1/4 - 20 thread? You might be able to avoid a new bridge by having adjusters installed that have a larger thread. For example: Install adjusters with a 3/8 - 16 thread. You simply drill through and remove the damaged threaded area with a 5/16 drill which works as the tap drill for the 3/8 - 16. The larger thread size has a better chance of not disintegrating in your soft bridge.
Click to expand...

I suggested that to my luthier, but the problem is I also want a Full Circle PickUp installed eventually and he says the pickups he has are the same thread size as the adjusters he installed.

Maybe I should go check out Full Circle PickUp thread sizes... and just order it in.
 
#10
Full Circle pickups come as large as 5/16 -18 but I don't think that's going to help you. If you still want to save the bridge and use a Full circle, I'd say you could tap the 3/8 - 16 threads and then use an adapter to bridge the 3/8 -16 to 1/4 - 20 (or 6mm) Full Circle.

Or, install oversized boxwood dowels and re tap for the Full Circle. Dense boxwood can handle the threads.
 
#12
vejesse said:
Full Circle pickups come as large as 5/16 -18 but I don't think that's going to help you. If you still want to save the bridge and use a Full circle, I'd say you could tap the 3/8 - 16 threads and then use an adapter to bridge the 3/8 -16 to 1/4 - 20 (or 6mm) Full Circle.

Or, install oversized boxwood dowels and re tap for the Full Circle. Dense boxwood can handle the threads.
Click to expand...

This is what I'd recommend as well. When you get it fixed, don't raise an adjuster without raising the other one at the same time. This leans the top of the bridge while the adjuster remains straight up. That'll compromise your threads.
 
#13
Still, going back to the blame question. It seems highly probable to me that the luthier did a sloppy job drilling and tapping. My first guess would be that the vice wasn't bolted down when he was drilling the tap hole, and the work chattered when the tap drill was coming up, but he thought the hole was still good enough to hold a thread. What was you're luthier's explanation as to why this happened? Ime, stripped adjuster threads are very rare, especially in a recent installation.
 
#14
The original poster didn't tell us about the bridge. If it's made from soft Chinese wood then 1/4 - 20 threads will occasionally crumble, especially if the adjusters are raised up very high. Then again maybe he used a dull tap, or the hole was drilled badly and he tried to "correct" things by repeatedly running the tap in and out, creating an oversized, misshapen thread. Or the bridge got "tweaked" somehow. Who knows. I will say that when things go badly ( and I've been there) you know when it's time to either stop to patch the damage or just start over.

A couple basic considerations regarding assemblies with fasteners: If the parts are not the same hardness ( i.e. aluminum engine blocks, upright bass bridges) or there's a possibility of the threads crumbling, it's better to use coarse threads. I don't see any advantage to using 1/4 - 20 threads in bridges other than the fact that it's a really widely available thread. But that seems to be the standard.
 
#16
I got my bridge fixed yesterday. We fixed it by ordering the largest diameter Fishman Full Circle which had much thicker threads, however ultimately it was found that the original adjuster tapping was completely off center in such a way that my luthier deemed it unusable and he was kind enough to just give me one of his old bridges to finish the job with. It was then that I also realized my original post was in error.

My luthier did NOT install the adjusters originally as I mistakenly had reported (I just wasn't thinking), he actually only shortened the legs of the bridge so my adjusters had a greater range of movement. He explained to me that he cuts the legs from the side opposite of the threads so whatever he did is unrelated to the threads.

Thanks so much for all your advice. I just wanted to update you on my situation and correct my original post. I guess the problem was a combination of old bridge and poorly tapped/angled threads.
 
#17
AuxOne said:
I got my bridge fixed yesterday. We fixed it by ordering the largest diameter Fishman Full Circle which had much thicker threads, however ultimately it was found that the original adjuster tapping was completely off center in such a way that my luthier deemed it unusable and he was kind enough to just give me one of his old bridges to finish the job with. It was then that I also realized my original post was in error.

My luthier did NOT install the adjusters originally as I mistakenly had reported (I just wasn't thinking), he actually only shortened the legs of the bridge so my adjusters had a greater range of movement. He explained to me that he cuts the legs from the side opposite of the threads so whatever he did is unrelated to the threads.

Thanks so much for all your advice. I just wanted to update you on my situation and correct my original post. I guess the problem was a combination of old bridge and poorly tapped/angled threads.
Click to expand...

I don't buy it. Sounds like a conspiricy here.
Sorry, just kidding:D
 

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