[TCML] Polishing Lexan (small, recessed areas)

[Jim Lux]

McCauley, Daniel H wrote:
> Need some expert opinions on polishing lexan.
> Basically, i'm looking to polish small recessed pockets that have been
> machined into blocks of lexan.  For example, a 2"x2" pocket, 0.5" deep.

How smooth?  glass like surface?

Scrape with a razor blade held perpendicular to the surface.
Flame polish with a propane torch or a low speed heat gun.

Practice on a scrap.  It sounds hard and risky, but 20 minutes of 
playing around will teach you all you need to know to do it right 
without screwing up the workpiece.

Polycarbonate is nice for flame polishing too, because it has a real 
characteristic smell well before it catches fire so you can pull the 
flame off and blow cool air or plunge it into a bucket of water.

But really.. it's not as hard as it seems.  Go slow and keep the torch a 
fair distance away. What you're looking for is a fairly gentle, but hot, 
stream of air.

Those little butane torches are very hard to control in this kind of 
application (too much heat in too small an area).  The regular old 
Bernz-o-matic like you'd use for sweating copper pipe fittings is what 
you want.



> 
> Not too keen about flame polishing, especially on a part that will take
> a long time to machine.  Although i have read that MEK solvent is
> something frequently used or a plastic polishing compound such as NOVUS.

The problem with grit polishing is that you need to have something to 
move the grit with, and it's awfully easy to push too hard in one place 
and make a depression.  Polycarbonate is tough but very soft.  It's also 
hard to get a good polish in inside corners.

if you know a place that does abrasive polishing with the mud like 
compound under pressure, that might work.  It's used a lot on things 
like intake and exhaust manifolds.  The problem will be whether they can 
work with plastics and whether they'll have the process controls figured 
out.


> 
> Any thoughts?
> Thanks
> 
> Dan
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