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How would you turn these rubber bushings smaller


Matt Harwood
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I bought some new rubber bushings to replace the motor mounts in the '35 Lincoln and they're VERY close to what was in there. I need to turn them down about 3/16" to press them into the mounts. Any suggestions on how I might do that? I thought I'd chuck them into my drill press and use sandpaper or a belt sander or something like that to gently grind them down.

 

Any other ideas?

 

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I don’t know how precise you need to be; I did something similar by putting the item on a bolt and mounting in a portable drill, and then running it against my table-mounted disk sander.   Clogs up the paper and maybe even makes a little smoke, but you only have do do it once (or twice).  Not elegant, but effective.  I like the idea of chilling the part.  Clever.

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I actually put a bolt through the bushing and mounted it on my drill press. Then I used a cutoff wheel on a die grinder to gently grind away at it. Between the two fast-spinning objects, it created a lot of fine black dust and a little smoke, but definitely shaved it down quickly and easily. Was able to press the bushing into the engine mount with a little effort and a 12-ton press.

 

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@Matt Harwood, You did very well. The best thing to do to assist with machining, grinding or shaping any rubber part is to chill it first!  At the very least put it in the freezer overnight and then work quickly. You may need to refreeze if it needs a lot of material removed. If you really need to do precision work or many parts liquid nitrogen is your best friend. It is very quick to cool and easy to use. JUST BE VERY CAREFUL!!! Liquid nitrogen is very unforgiving if it spills or splashes. Gloves and face shield is a must for safety.

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  • 2 weeks later...

I just sized two bushings with a wood rasp.It took a while,but the bushings fit well.I wish I had seen these posts earlier.I didn't think of chilling the bushings.That would have certainly made it easier.

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play with sanding speed.  To sand instead of stretch you want the rubber to be more brittle.  Two things make it more brittle - lowering temperature and increasing deformation speed.  But, the sanding heats the material up.  So short bouts followed by recooling will probably work best.  Liquid nitrogen or even dry ice will be much better than a freezer because you have a chance to get below the glass transition temperature, where behavior will change in your favor.

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Sometimes abrading rubber is challenging, and can really mar the surface up (in addition to stinking the place up).  As mentioned, chilling it helps quite a bit, but only lasts so long.  Razors cut great and leave a nice surface behind, but I'm sure I don't have to point out what a bad idea that would be with a drill press. Catching an edge would be inevitable.  I do wonder if turning on a wood lathe would be feasible if it were chilled adequately, or if it would just want to catch an edge. 

 

One thing I'd be tempted to try is a really sharp hand plane against the rubber while it spins.  Lubrication of some sort may be in order, but at least you could control depth of cut and prevent catching an edge.  

A 36 grit flap disc on the angle grinder will get it done for sure, but it's messy, and will leave a rough surface.  I'm sure it'd be serviceable if you're careful.  I always know something like that will work, but like to experiment with other methods just to see if I can find a better way.  Sometimes you'll be surprised how well an experiment works out.  

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I turned mine by inserting a bolt through with a tight nut and turned it in my lathe. 

 The drill press with a disk grinder with 36 grit would work just as well.

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