Pulling bushings is often carried out using all manner of hair-brained ideas, many of which can easily damage the sensitive finish of an instrument. The simple fact of the matter is that the physics of pulling something buried deeply inside an instrument are not in your favour!
One popular method is to insert a spare bolt and use some sort of crowbar action to lever the bushing out....whilst working most of the time, the fulcrum point can easily dent the finish or even the wood. Even commercially-available tools for this job bear all of their working force upon the face of the instrument. This is simply not an option for soft lacquer finishes, softer woods or archtops!
The solution is deceptively simple; for a start we have an internal thread on the bushing which instantly gives us a mechanical advantage. This can be used exactly the same way as the worm gears on a tuner, to convert the torque of an advancing thread into one that pushes the bushing out instead of pulling it.
The patient: One heavily distressed, dusty workhorse bass.
Firstly, we need to ensure that two things; that the bushing is open-ended and the depth of the hole itself.
I already knew this was an open-ended bushing. The (dirty) calipers show the hole depth is 29mm. The entire body is 39mm thick in dense Birch, leaving 10mm of wood from the bottom of the hole to the outside world. Anything significantly thinner could run the risk of blowing out the back of your instrument. If the body wood is soft (Mahogany, Alder, Basswood, etc.) and/or with a thinner amount of wood behind the bushing then consider supporting the back using painter's tape and a hardwood caul....better yet, comment below and we can confirm whether or not you might have problems....
The bridge bolt itself has a thread length of 25mm....
What we're going to do is to drop a small metal rod, some nuts or whatever will fit through the bottom of the bushing. These sit on the bottom of the hole, so when we advance a bolt back into the bushing, the bottom hits this and starts to advance the bushing back out. I used a shelf support post from a cabinet since I have lots on hand.
Fire in the hole!
Threading the bolt back in until it hits the post I dropped in.
- If possible, use a spare bolt with the same thread size/pitch rather than the original. This instrument has been antiqued pretty well, so a little scratch here and there won't be noticed!
I know....I'm going to hell for using a Torx bit in a hex head; I blame familial access to my tools for this one. We all know this is a transparent lie but hey.
note from member kmensik: the post can crack/chip the lacquer on its way out....check the comments below for his solution
As we turn the bolt, it can no longer advance into the body since the small post is in the way. It's immediately clear how important it is that the body has sufficient remaining thickness so that this force does not push the post out of the back or deform it. We can't emphasise this point enough!
We're starting to get to the end of the bolt's travel. Time to back her out and drop in a second post.
Repeat the process until you have completely advanced the bushing back out.
The end result; a safe bushing removal at zero cost and with a little thought, zero risk to the instrument. Unlike the "crowbar" method, this advances the bushing out parallel to the bushing hole; too often wedging a bushing out crushes the walls making reinsertion of a bushing less likely to be secure and snug.
How To Pull TOM/Stoptail Bushes by Carl Maltby is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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