 The Clarinet BBoard
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Author: puffball
Date: 2013-08-19 15:40
The screws on my thumbrest on my Bb clarinet keep loosening themselves. I'm a little concerned that something is partially stripped. I need to use a neckstrap while playing, so there's quite a bit of force on the thumbrest while I'm playing.
I've been just tightening the screws when they come loose, but I'm afraid the thumbrest will come loose during a performance. I'm also afraid that the constant re-tightening could lead to a crack. Any ideas for a quick fix?
Thanks!
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Author: kdk
Date: 2013-08-19 16:34
Is this a wood clarinet or a plastic/composite one?
Karl
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Author: puffball
Date: 2013-08-19 17:27
It's wood -- a late-90s R13. It needs an overhaul, but that's going to have a wait a few more months.
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Author: Paul Aviles
Date: 2013-08-19 17:45
It'd be REAL easy for a tech to tap some new holes just slightly higher (or lower) for the screws to be refastened. It does sound as though there is stripping involved.
..................Paul Aviles
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Author: SteveG_CT
Date: 2013-08-19 20:54
There are a number of things you could do to address this issue. The most permanent solutions would be to either plug the existing holes with dowels and then re-drill them or relocate the thumbrest slightly and drill new holes as Paul suggested.
Another thing you might try is placing a single drop of low-viscosity superglue in each hole (just enough to coat the sides of the hole, not enough to fill it) and letting it dry before re-installing the screws. This should reduce the diameter of the holes by enough to give the screws a bit more purchase and hopefully keep them from backing out so easily.
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Author: kdk
Date: 2013-08-20 01:07
But is it a good idea to force them into the existing holes, or should the holes be tapped bigger with the correct tools? My impression (based on no personal experience at all) is that you risk cracking along a grain line that runs through the hole if you try to make a bigger screw cut its own new thread.
Karl
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Author: Tony F
Date: 2013-08-20 01:12
if you use a jewellers knife-blade file to cut a v-notch into the first few threads on the screw, similar to a sheet-metal screw, it will act like a tap and cut its own thread, avoiding the risk of cracking.
Tony F.
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Author: clarnibass
Date: 2013-08-20 05:09
>> if you use a jewellers knife-blade file to cut a v-notch into the first few threads on the screw, similar to a sheet-metal screw, it will act like a tap and cut its own thread, avoiding the risk of cracking. <<
Yes, the same technique is used for many sitations where you want to turn a screw into a tap. It works with steel and strong screws (which most thumbrest screws aren't).
Here is an example of this shown on a crack pin. I usually prefer to do more than one notch.
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Author: Chris P
Date: 2013-08-20 05:45
Another thing you can do is have larger diameter brass or nickel silver bushes screwed deeply and glued into the joints which have been internally tapped to take an M2 screw, then screw the thumbrest into this which will be more secure than small wood screws screwed directly into the joint.
Former oboe finisher
Howarth of London
1998 - 2010
The opinions I express are my own.
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Author: Steven Ocone
Date: 2013-08-22 11:38
Thumb rest screws aren't tapped though they could be for a fresh hole. For an old thumb rest hole, a tap would probably just tear out the wood and make a larger hole.
I'll have to check the thread sizes of various thumb rest screws and see if there are any taps available.
For the one we did yesterday, we filled in the old holes and moved the (adjustable) thumb rest to a slightly higher location.
Steve Ocone
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Author: cyclopathic
Date: 2013-08-22 12:05
> oversized screws are available.
or you could partially fill holes with epoxy. Put just enough with toothpick to make them tight again
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Author: kdk
Date: 2013-08-22 12:07
That's the way I've always heard of doing this, but then I'm not sure why you'd need larger screws to use with new holes. Your idea about larger screws sounded like you were suggesting to just force them into the old holes by force. Would that even be realistic in grenadilla?
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Author: Gordon (NZ)
Date: 2013-08-22 12:25
The timber thread is almost certainly stripped to some degree.
As is often the case for any repair process, the devil is in the detail.
If it is done right, the holes can be filled, drilled and re-tapped.
Oversize screws really need to have the same pitch.
Oversize-diameter screws are usually only about 0.1 to 0.2 mm diameter so retapping for them is not necessary. The wood will not split. But if you try to use a self tapping screw or wood screw from a hardware store, you are very likely to
Some screws are ridiculously short.
Oversize-length screws can help a lot. But holes need to be drilled deeper first, without going through to the bore. IMO tapped as well.
A variety of taps of suitable pitch have been available from our tool suppliers, but I'm not sure if that has been so recent. (I have about 6 threads.)
If you come across a steel screw, of suitable pitch, it can be turned into a tap by silver-soldering a rod to it and cutting appropriate "flutes". I don't think a copper alloy tap would last long.
Firm pressure should be put along the blade on a screw driver while tightening a screw. That reduces the friction that can damage the timber threads.
There are different degrees of oversize, all the way up to a screw for holding on the valve guide of a Yamaha flugel horn!
Another approach is to put superglue gel in the hole, and assemble before it sets. One advantage of gel is that it doesn't make such an appalling mess if you spill some on a clarinet with black paint/filler/die on its surface. I also dries slower, allowing time to put the screws in.
IMO turning a screw into a tap by cutting part way down its length has to be done so that there is no bur. Otherwise in a soft material like timber, you may well cut an oversize hole.
A variety of resources, and a fair bit of experience help to do the job successfully.
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Author: Garth Libre
Date: 2013-08-23 02:49
I like the idea of a little saw dust tossed into the hole and one drop of superglue. It should hold.
Garth, 305-981-4705. garthlibre@yahoo.com
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