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Double Bass Most Common adjuster thread sizes
- Thread starter Chris Fitzgerald
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That's pretty much what most of @james condino 's threads are, right?
There are two significant bending loads on the adjuster shaft, one (which varies) due to the tendency of the strings to pull the bridge top toward the scroll; and the other one (which you can't do anything about) caused by the arch in the top, which makes the bridge feet want to separate.
Frankly, as a mechanical engineer, the weakest material I would contemplate in that place is 6061-T6 aluminum (or, in the UK, one could use 6061-T6 aluminium). Certainly not wood or plastic. From the mechanical strength standpoint the best would be steel with a brass insert set into the wood for the threads, but I understand that keeping the mass down is important. Not important enough, though, to use wood or plastic there. Sure, "it will work" MOST of the time, right up till it doesn't.
Sure. But how great would those be in twenty-five-minute episodes available for streaming with beautiful cinematography and an original soundtrack?
With all those gorgeous luthiers like James, Arnold, and Nnick shot in a flattering blue light except in the action scenes? It would be spectacular!
Greg Clinkingbeard
Commercial User
The ones I have worked on are 1/4”-20. I believe these are original to the bass because several Shens I have seen have them.
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- Jan 12, 2004
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- Owner, Stand Up Guy Basses (Repair/Sell/Buy upright basses)
Slightly off/on topic. I made aluminum shims that fill the space between bridge and bridge foot. I made these to stabilize the bridge and reduce the bending that seemed to be occurring w/tuning. The bridge no longer needs adjusting not sure if it is an improvement in tone. I made a couple of pairs 1/16" & 1/8".
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I make my own 1/4-20 threaded shafts out of titanium; I just don't sell them commercially...'same thing with my titanium adjustable truss rods for the smaller instruments and slabs....
The videos sound great; another 500 hour project with a 50 cent return!
The videos sound great; another 500 hour project with a 50 cent return!
My adjusters are almost all the way down. To my surprise I read someone wrote that the sound is better with the adjusters just clear, than all the way down. And I found it to be true. So "all the way down" is 1/8 turn up to me now. A long rant to say I do not think the shims help with sound. Allthough I totally get the idea.
Do you mean you cut 1/4-20 shafts from Ti all-thread, or you thread it yourself? You add the wheels later, or turn the whole thing down from a big bar of Ti? Or the wheels are separate from the shaft and have a female thread? On the truss rods, what material do you use for the nuts to prevent the well known titanium galling of threaded joints?
If you're threading Ti on the lathe, my hat's off to you, that stuff ain't easy.
On the other hand, the reduced mass would surely be a good thing in that location. (and help at least a little bit with neck dive on the electrics)
Based on my (surely limited) understanding of the theories of the somewhat controversial Chuck Traeger, when you cut the bridge in half to install adjusters, you're adding a wee bit of flexibility in the system side to side, while still maintaining stiffness vertically. Theoretically the bridge should be taking only vertical loads and transmitting them to the top, so any micro-movements within the bridge, or at adjusters all the way down, create a tiny bit of friction which means a tiny bit of loss of transmission from the strings to the top. Note that Traeger also suggests things like putting a thin sheet of PTFE under each bridge foot, and rounding off the ends of the soundpost so lateral deflection of it doesn't hinder the vibration of the top and transmission to the back.
I am DEEPLY UNQUALIFIED to say whether these theories are accurate, or whether the theoretical losses for which Traeger makes the case are actually meaningful in practice, but it sounds like your experience (bass sounds better with adjusters just a wee bit off the bottom) would tend to support the theories.
Mine just broke too... Bass side only... I had removed most of the tension from the strings and fortunately nothing evil happened... It was installed on my Rogeri by String Emporium!
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Turf: I buy straight 3/2 Ti rod and then thread it myself for the needed area. It is not as difficult as you might think; pretty easy with the right grade of die.
One thing that always bugs me about all of the commercially made one piece adjusters it that they make them so that the solid round section is a different drill bit hole than the threaded section. I've worked on a machinist lathe and know that there is no reason why they don't make them this way; it seems lazy to me. If the desired production outcome is a threaded wheel that makes life better for luthiers and players, why do they take the lazy step and make an adjuster that saves one step for the machinist (at best); I'm not even sure it is a savings.
For folks wondering what the #&!! I'm talking about: for discussion purposes, most adjusters come with a straight 1/4" round shaft on one side of the wheel and then on the other side is threaded at 1/4-20. To tap a 1/4-20 receiving hole, it requires a smaller drill bit that just a straight 1/4" shaft. Therefore, for the installer, you drill a smaller hole through the entire bridge leg. Next you guillotine the feet off the legs, then you tap one side for the threaded part, and then you have to drill out the straight part again with a slightly larger 1/4" drill bit. Why not make an adjuster where either the threads or the solid shaft is compensated so that you just need to drill one single hole size???????? Making the adjustment on the aluminum section is much safer and more reliable than drilling and tapping multiple times on a whimpy weak section of maple bridge!!!!!!!!!!!!!!!!!
Enough ranting.....
For a while there was a company in Europe who made custom bridge adjusters out of titanium that were a ball and socket type that created a very smooth fulcrum for the contact point of the adjusters and the wheel. Their claim was that it allowed the entire bridge assembly to oscillate better under tension and eliminated and breaking issues. If I remember correctly, they charged something like $150 for just the adjusters. I have not heard form them in several years....
I saw some sweet looking all maple wooden adjusters on Arnold Schnitzer's most recent bass that were made by Robbie McIntosh.
One thing that always bugs me about all of the commercially made one piece adjusters it that they make them so that the solid round section is a different drill bit hole than the threaded section. I've worked on a machinist lathe and know that there is no reason why they don't make them this way; it seems lazy to me. If the desired production outcome is a threaded wheel that makes life better for luthiers and players, why do they take the lazy step and make an adjuster that saves one step for the machinist (at best); I'm not even sure it is a savings.
For folks wondering what the #&!! I'm talking about: for discussion purposes, most adjusters come with a straight 1/4" round shaft on one side of the wheel and then on the other side is threaded at 1/4-20. To tap a 1/4-20 receiving hole, it requires a smaller drill bit that just a straight 1/4" shaft. Therefore, for the installer, you drill a smaller hole through the entire bridge leg. Next you guillotine the feet off the legs, then you tap one side for the threaded part, and then you have to drill out the straight part again with a slightly larger 1/4" drill bit. Why not make an adjuster where either the threads or the solid shaft is compensated so that you just need to drill one single hole size???????? Making the adjustment on the aluminum section is much safer and more reliable than drilling and tapping multiple times on a whimpy weak section of maple bridge!!!!!!!!!!!!!!!!!
Enough ranting.....
For a while there was a company in Europe who made custom bridge adjusters out of titanium that were a ball and socket type that created a very smooth fulcrum for the contact point of the adjusters and the wheel. Their claim was that it allowed the entire bridge assembly to oscillate better under tension and eliminated and breaking issues. If I remember correctly, they charged something like $150 for just the adjusters. I have not heard form them in several years....
I saw some sweet looking all maple wooden adjusters on Arnold Schnitzer's most recent bass that were made by Robbie McIntosh.
I saw those too and assumed it was only the wheels that were made of maple... Would threaded maple adjuster legs be hard enough to hold up under all that string tension?
These are the Moser adjusters. Two or three years ago I still saw them at Musikmesse Frankfurt, so I think they are still available.
The price is a bit high, but they need more work to manufacture them and selling volume is rather low. At least here in Europe where the climate swing is much lower than in the USA and adjusters are not commonly used at all.
So, you’re saying make (turn down) the solid shaft to #7 (.201)? I may have to get a set of aluminum adjusters to try this. Have you ever tried it on existing adjusters?
Well, if you're making these parts on a bar feeding lathe, the ones with a separate wheel there would be a tiny savings of time because you would start with .250" bar (for 1/4 threads and do no turning on the unthreaded part, just part it off. But if the wheel is integral to the shaft, you've got to turn that whole unthreaded section down from the raw bar diameter which is the diameter of the wheel, so in that case it costs the same to turn it down to 1/4"-20 pilot hole diameter as to turn it down to .250".
I suspect the real cause is lazy designer not cost savings. The other aspect of this is that when you go to enlarge the pilot hole on the upper half of the bridge, having cut the feet off it, there's a risk of misaligning the new enlarged hole with the original. A hole in wood won't pilot the drill the way it would in metal.
