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PostPosted: Tue Apr 25, 2017 6:39 am 
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Location: Clifton Park, NY
Loren wrote:
Bore the inner diameter first, while the material is thick enough to resist flexing, don't over tighten the chuck or collet, and don't take big cuts.

Then, mount the piece on a mandrel to turn down the exterior to spec.

"Hairy when abraded", what exactly are you doing and how, when this occurs?


Exactly.
OP-- how are you turning your polymer? A machine lathe as opposed to a wood lathe I'd imagine.
I've found that Delrin or Acetal turns best with a very sharp lathe tool and taking very small cuts, especially as you approach the final outside diameter. It's definitely tricky stuff, but it makes a terrific whistle.
These polymers don't respond well to sanding, which is what I think you mean by "hairy". The sandpaper pulls up very tiny threads of the stuff but they don't fly off, remaining attached to the piece. You can sand it WET using automotive wet/dry sandpaper in the 400 grit and up. Keep it very wet. If anyone knows a good way to buff it, post it here.

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PostPosted: Tue Apr 25, 2017 7:55 am 
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Wet sanding - thanks Paul. I'll try that on some of our old models. A friend tipped me off to a couple other websites:

https://www.cuestik.com/store/?DEPARTMENT_ID=106 - has Phenolic in nice colors

and

https://www.webbwood.com/qshop.php?PH/dowel

The blue and red colors at Webb wood might be nice for a generation-inspired mouthpiece.


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PostPosted: Wed Jul 12, 2017 10:19 am 
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For a good finish on acetal, these methods may prove useful:
Drill and ream with an oil mist. A machinist using an enclosed CNC machine will use a flood of soluble oil; that's good, too. One of my guys used a water mist with good results.
Use High Speed Steel or 5% Cobalt for drilling the side-holes, and for turning. These come with a sharper edge than carbide. Ask your machinist what he's using. The service life of replacing HSS tools may cost a little, but the results are worth it.
Make sure your tools have a positive rake and a 0.015 radius. If the work chatters, you may need an internal steel arbor for support. "Reduce surface speed, increase feed" is the watchword for a better finish.
Walt Sweet


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