A 1/4" drill will not clean up the remnants of 1/4-20 threads, that's why you need to go up to 3/8 -16. Or plug the hole if you prefer.
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Double Bass Fill and resize bridge adjusters?
- Thread starter Jeremy Darrow
- Start date
- Aug 1, 2005
- 3,546
- 1,421
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- Private Inventor - Bass Capos
I think I disagree. Unless the hole has really been abused, I don't see why this would be so. I'll try it next time I am fooling around.
Rob: A class 2B 1/4-20 tap is about 0.254" in diameter. That combined with cutting pressure compresses the soft wood as well, creating an even larger opening. So if you run a 0.250 drill through a 1/4 tapped hole in maple, the marks from the crest of the tap cutting flutes aren't fully removed. With fine threads in wood that might crumble its something I think about, but maybe it doesn't matter. I've tried it a bunch so that's how I know.
We'll I'll be....
This is the measurement I get, as well. (0.254") I never knew that. Now I do.
Thanks, vejesse.
Thanks Don, finally an acknowledgement I'm not some loon. Sometimes I feel like Rodney Dangerfield around here.
There might be a case for matching taps to adjusters. My run-of-the-mill VA tap is .2475. The adjuster I have measures .2425. Considering this thread is in wood and will compress, tighter might be better?
If your adjusters are right at 0.250" and the tap is undersized like that, the adjusters won't go up and down at tension without a lot of effort. But I've found that a lot of adjusters are undersized on the OD (i.e. Fishman Full Circle adjusters are around 0.005" under) so that helps. You can also run a 0.005" oversize tap through the hole if the adjusters are oversize.
vejesse,
Do you think that vigorously running the .250 adjusters up and down the threads, (prior to installation, along with some powdered graphite), might "open up" and loosen or improve the fit? - it is "wood" vs. "metal", after all.
Just spitballin' here.
IANAMOAL (I Am Not A Machinist Or A Luthier.)
Respectfully,
I had never seen these before - Yes, you're adding a metal insert, but these look smaller/shorter and lighter(?) than the "externally threaded" insert type.
Could these be installed using epoxy? (Yes, this is not a reversible solution.)
I believe a standard 1/4-20 counterbore is 7/16". I don't know the exact O.D. of the insert.
Hmmm....
"The CN-Q20-6 Counterbore Nut Thread Adaptor provides an 1/4-20 thread to a standard 1/4-20 counterbore. Threaded counterbore nuts are used to convert a counterbore into a threaded hole."
Could these be installed using epoxy? (Yes, this is not a reversible solution.)
I believe a standard 1/4-20 counterbore is 7/16". I don't know the exact O.D. of the insert.
Hmmm....
"The CN-Q20-6 Counterbore Nut Thread Adaptor provides an 1/4-20 thread to a standard 1/4-20 counterbore. Threaded counterbore nuts are used to convert a counterbore into a threaded hole."
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Well , obviously just running any old tap in and out a bunch of times helps. I've tried thread forming taps too but they didn't seem to make the fit any better. Keep in mind the hole turns into a slight oval with some seasonal wood movement, so you have to run the tap through again sometimes much later to true up the hole.
Maybe were getting too precise for what were dealing with here, but it's a drag when the adjusters don't move up and down easily. I will say that if the fit is really loose that can jam things up too. I don't happen to think the 1/4-20 thread is ideal for this, I think a coarser thread like 3/8-16 or M10 1.5 works better. I know some folks get uneasy taking that much material away from the bridge, but the Boehm and New Harmony adjusters use 3/8-16 thread to good effect. In fact those New Harmony Delrin adjusters are pretty slick with the natural lubricity of black delrin.
Delrin is a very interesting engineering material and has some great uses, but not for basses. These are some delrin adjusters that come on a well known Chinese bass supplier's instruments. The adjuster broke in half while the bass was sitting in the shop on the rack next many other basses, under normal tension with nobody playing it:
Delrin does offer incredible slickness; you can turn the wheels effortlessly in either direction while under tension. I'd like to see regular aluminum adjusters with some type of thin coating of this or a teflon like substance.
As for plugging a bridge, it comes down to who it is for. If it is on my personal bridge, I do all kinds of random things to get me through times when money is tight or I feel like experimenting. Quite often it works out fine. Once I broke a bridge in three pieces on a gig, found an old tube of superglue and flooded everything with it. 15 minutes later I had it back up to tension and I left it that way for six months before I made a new one. If it is work being done for someone else that is paid for, then keep it clean and orderly. A new Despiau bridge blank is only $46 from International Violin or MET music. 'Better to not have some duck dynasty creation out on the world that people are judging your work by.
j.
www.kaybassrepair.com
www.condino.com
Delrin does offer incredible slickness; you can turn the wheels effortlessly in either direction while under tension. I'd like to see regular aluminum adjusters with some type of thin coating of this or a teflon like substance.
As for plugging a bridge, it comes down to who it is for. If it is on my personal bridge, I do all kinds of random things to get me through times when money is tight or I feel like experimenting. Quite often it works out fine. Once I broke a bridge in three pieces on a gig, found an old tube of superglue and flooded everything with it. 15 minutes later I had it back up to tension and I left it that way for six months before I made a new one. If it is work being done for someone else that is paid for, then keep it clean and orderly. A new Despiau bridge blank is only $46 from International Violin or MET music. 'Better to not have some duck dynasty creation out on the world that people are judging your work by.
j.
www.kaybassrepair.com
www.condino.com
james,
That break location, direction, (and resulting "wound"), looks like it was caused by stress introduced as the result of misalignment between, (or tilting of), the top of the bridge and the feet, causing the non-threaded axle to snap off at the top of the adjusting wheel. If the adjuster was made of more substantial/unbreakable material, do you think the stress force might have then cracked the bridge, or that the misalignment would have led to binding of that axle in the bridge blind hole?
Just wondering.
Thanks for your time and expertise.
Good questions. All I know was that from the outside, everything looked fine. I did not install it. The delrin adjuster was significantly larger than a 1/4-20 aluminum one. This was someone else's bass that looked fine; the bridge had nothing to do with why it was here for a visit. I just remember working across the room and then hearing the dreaded explosion and the parts were on the floor and there was a nice fresh dent in the bass. That was enough for me. I've never seen anything like that happen with metal adjusters. Personally, a few years ago I took the adjustable bridges off my main gig bass. I'd have some issue and kept getting distracted on the gig trying to fuss with the wheels. I switched to a fixed bridge and now I accept that the bass is fine and the issue is with me and I just play through the difficult parts.
That bridge with the delrin adjusters reminded me of when I worked at the old Tumalo guitar factory for Kim Breedlove. They had a very expensive guitar hanging on the rack at one of their dealers with an overly complicated visual claw looking bridge. During business hours the bridge pulled off the guitar at full tension, shot into the guitar next to it, and caused a domino effect whereby about six instruments all got knocked down to the ground. 'Not a good day in the guitar shop.....
That bridge with the delrin adjusters reminded me of when I worked at the old Tumalo guitar factory for Kim Breedlove. They had a very expensive guitar hanging on the rack at one of their dealers with an overly complicated visual claw looking bridge. During business hours the bridge pulled off the guitar at full tension, shot into the guitar next to it, and caused a domino effect whereby about six instruments all got knocked down to the ground. 'Not a good day in the guitar shop.....
I agree that folks seem to become obsessed with minute string heights when they have adjusters. I have them on my bass, but here in SoCal, I only need to do a slight adjustment about every 6 months, (Up, then back Down), if at all.
I also obsess a bit about the alignment of the whole system, especially during, and the few weeks after, changing strings - I've had zero problems. (Knock on Spruce!)
They Call Me Mr. Lucky, I guess.
Also - both stories (above) are downright CREEPY, and would have scared the S*** out of me.
Thanks, James!
A couple of points from a mechanical engineer with over 30 years experience and a lot of it spent designing threaded joints.
1) Using a helicoil will consume a lot less wood than the solid inserts shown a couple of posts above.
2) The OP did not (I believe) describe what are the holes currently there. If they are just stripped-out 1/4-20 holes, then I think helicoil is the mechanically superior solution. If they are some other thread, and are in good condition, I would make up adjusters with the correct thread; some of the other threads can be found in adjusters; but I think a pair of adjusters which are just a disk with a post on one side and a threaded post on the other - will end up being cheaper than a new bridge.
3) I do not trust threads in wood. I know that's the standard for bridge adjusters, but wood is a lousy material for threads.
4) If you have metal threads you can use a fine pitch thread which will be easier to adjust and more durable, but probably is not available on pre-made adjusters. With wood threads you will need to keep them coarse.
5) I wouldn't get into trying to glue Delrin or UHMW polyethylene into wood. They are low surface energy materials and the chance of finding an adhesive that will reliably work for wood and low surface energy plastics is pretty low. Of course if you design the joint so the adhesive is not necessary to the success of the joint, then the adhesive might just be there to kind of keep things in place. But I suspect that you would end up with great big pieces of Delrin that would sacrifice a lot more wood than Helicoils.
All the above notwithstanding, I have not ever fitted a bass bridge with adjusters.
1) Using a helicoil will consume a lot less wood than the solid inserts shown a couple of posts above.
2) The OP did not (I believe) describe what are the holes currently there. If they are just stripped-out 1/4-20 holes, then I think helicoil is the mechanically superior solution. If they are some other thread, and are in good condition, I would make up adjusters with the correct thread; some of the other threads can be found in adjusters; but I think a pair of adjusters which are just a disk with a post on one side and a threaded post on the other - will end up being cheaper than a new bridge.
3) I do not trust threads in wood. I know that's the standard for bridge adjusters, but wood is a lousy material for threads.
4) If you have metal threads you can use a fine pitch thread which will be easier to adjust and more durable, but probably is not available on pre-made adjusters. With wood threads you will need to keep them coarse.
5) I wouldn't get into trying to glue Delrin or UHMW polyethylene into wood. They are low surface energy materials and the chance of finding an adhesive that will reliably work for wood and low surface energy plastics is pretty low. Of course if you design the joint so the adhesive is not necessary to the success of the joint, then the adhesive might just be there to kind of keep things in place. But I suspect that you would end up with great big pieces of Delrin that would sacrifice a lot more wood than Helicoils.
All the above notwithstanding, I have not ever fitted a bass bridge with adjusters.
- Aug 1, 2005
- 3,546
- 1,421
- Disclosures
- Private Inventor - Bass Capos
- Aug 1, 2005
- 3,546
- 1,421
- Disclosures
- Private Inventor - Bass Capos
Vejesse,
No one thinks you are a loon. I just don't understand the maths here. I don't know exactly what "class 2b" means, but my information is that a 1/4" NC H3 tap is about .0015" over dimension, making the hole .2515". A letter F drill (recommended for tapping 5/16 NC) is .2570". That should cover things, even if the hole is .254. I haven't experienced compression issues when tapping wood. Perhaps the problem comes from using too small a tap drill (1/4" for 5/16NC or 3/16" for 1/4NC), and maybe a dull tap?
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Well I guess it depends on the tap you have and the tap drill you use. I use U.S. made spiral flute taps from Cleveland, Greenfield, etc. because they cut better in wood compared to straight flute taps. I don't pay attention to the thread tolerance (who does unless you're buying special taps?) but the class of fit is 2 which is the standard more or less around here and B means internal. The diameters of these taps tend to run bigger but shaves wood better and doesn't crumble the threads.
As far as using a .257" vs. 1/4 tap drill for a 5/16 -18 thread you may have me on that one. I would definitely use the proper tap drill for steel otherwise the fit is too tight, but for wood I use 3/16", 1/4", and 5/16" tap drills to get full threads for 1/4, 5/16 and 3/8. Because the wood is compressing a bit and the adjusters are undersize you still get a nice running fit. And with a fine thread like 1/4 - 20 in wood you'll want all the thread % you can get.
Considering the fact that it's virtually impossible to get 5/16 - 18 adjusters maybe it doesn't matter (I have a bunch of them by the way if someone is looking for some) Plus a 5/16 OD, 1/4 ID adapter is too thin to work. But yes, you're right in that the bigger the drill the more it cleans up - at the cost of thread %.
Happy New Year
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- Aug 1, 2005
- 3,546
- 1,421
- Disclosures
- Private Inventor - Bass Capos
