Matte finish on ABS and Delrin?

Hi folks,
I'm a mediocre self-taught machinist, but I can usually make parts
that *function* as I would like for prototypes, etc. For production
work, I use local machine shops. My favorite shop went out of
business a couple of years ago, and now I'm stuck. They used to make
some cylindrical parts for me turned from black delrin. They had a
very nice matte finish -- almost as if it had been etched or tumbled,
but I don't *think* that was the case. I hadn't needed any more of
these parts for awhile, but now that I do, the other shops tell me
they don't know how to duplicate the finish. The owner of the first
shop is no longer available.
So, does anyone know how to do this? I'd also like to get the same
matte finish on turned black ABS parts. My experiments with different
grits of SiC sandpaper, with and without oil or water, have gotten me
a little close, but still not the lovely, even, original finish. I
still get this little bit of whitishness (sp?)to the surface, as well
as little "hairs" of plastic. Also, the sandpaper loads up pretty
fast.
For the ABS, I've been thinking about using a very dilute solution of
acetone and water or acetone and alcohol after the sanding. Pure
acetone dissolves ABS quickly, leaving a very shiny surface after it
evaporates. My thought is that the dilute solution might wipe out the
hairs without dissolving the bulk material much.
Thanks very much for any advice you can provide.
Spencer
Reply to
Spencer
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Maybe bead blast? You might try:
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supply spray coatings for various thermoplastics. They have specific grades of matte and eggshell finishes. It does work pretty well, and you can request a sample.
Reply to
Billy Hiebert
Bead blasted? (glass beads)
Reply to
Dave Berryhill
put an ad in the local paper for any former employees of the shop to contact you.. they might have a home shop and work on the side also.. they would know what he did or they did....
Reply to
jim
Just a long shot, Spencer, but it's possible the components were run in a tumbler with plastic media. You might be able to tell by looking closely with a loupe. You'll see a perfectly random matt finish, but any tight corners may not be touched at all, and that would tell the tale. Plastic media often has very fine abrasive particles in its makeup, which would account for the cleaning, deburring and blending it does.
Harold
Reply to
Harold & Susan Vordos
Greetings Spencer, You can get a matte finish on delrin by tumbling. I know because I did this inadvertently. After tumbling to deburr all the parts had a matte finish. The biggest problem was polishing the parts in the tumbler after I ruined the finish by tumbling them in the first place. I seem to recall that I used a plastic media, little triangles, to achieve the matte in the first place. You can experiment fairly cheaply by buying a small tumbler from a gun supply and small bags of different media to match. Then, buy a big tumbler and large bags of media. Cheers, Eric
Reply to
Eric R Snow
Hi Harold,
Thanks very much for the advice. I hadn't thought to do this. Upon close inspection with a high power loupe, I see fine structure all in a tangential direction. It certainly seems to be a surface finish produced on a lathe, with *possibly* some post-turning ...something ... done to it. The inside surface of the cylinders have a different finish, more like what I'm used to seeing from fresh cut delrin. Maybe the outside surface is just a cut surface, but with great care taken with tooling, angles, lubricant, etc. I don't cut delrin with any kind of fluid, I just go slow.
Thanks as well to everyone else who responded. The Chem-Pak site was a revelation. Not useful for this particular application, but I'll certainly be getting a sample and maybe incorporating it into other stuff. Thanks, Billy!
Spencer
Reply to
Spencer
I turned a piece of ABS and then blasted it with glass beads. Looks matte to me, see what you think:
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Reply to
Don Foreman
Try "polishing" with Scotch Brite Pads.
Reply to
Randy Replogle
snip----
snip---.
Hey Spencer,
Just a little tip on cutting Delrin. The faster you run it, the better it performs. If you keep your tool nice and sharp, the finish is superb. Delrin does not get gummy from heat like many other plastics. I've had chips coming off in a continuous ribbon that shot over my shoulder and piled up on the floor in a nice heap. It is one of the nicest of all the plastics to machine, the only problem with it is it has considerable stress and moves about a great deal as you rough it. Be certain to rough parts before finishing, leaving a reasonable amount so you can remove the error generated by the movement. I've often done it in three phases to get parts straight. I used to make telescopic blowpipes for bagpipes, which is where I learned of the tremendous movement it displays.
Regards,
Harold
Reply to
Harold & Susan Vordos
for auto work. Fantastic on brass, copper, steel and the like.
I haven't looked, I suspect it is a chunk of Dover Cliff :-) IIRC, diatamacious (sp) earth. Martin
Reply to
Martin H. Eastburn
Once again, thanks to everyone who responded! Great stuff.
BTW: Harold, it's funny you should mention delrin bagpipe blowpipes. A couple years ago someone gave me a chanter as a gift. (I'm a big Corries fan and they figured it kind of, sort of fit. Alas, I've developed no talent for it. They were wise to leave it at just the chanter.) At any rate, I've also suspected this was made from delrin. I know that "African blackwood" (ebony) is the traditional high quality material, but could this cheap chanter be delrin?
Spencer
Reply to
Spencer
Actually, Blackwood is not the same as ebony. It is another very dark wood, but quite a different species.
It's incredibly rare in larger sizes these days, too.
CJ
Spencer wrote:
Reply to
Chris Johnson
Hey Spencer,
Yep! The plastic models I've seen have all been made from Delrin.
Interesting you should mention your lack of talent. Unlike you, I jumped in with both feet, purchased a beautiful set of pipes, ordered directly from Sinclair in Scotland. Silver and ivory, in fact (all legal, done under proper license for the ivory at that time, mid 80's). They sit unused. I still screw around with the chanter, though, and have two of them, one a Delrin model, the other blackwood. A musician I am not.
I think if you'll check a little closer you'll find that the blackwood used in pipes is not ebony. The color of the wood in pipes is a rich dark brown color whereas ebony is truly black. Unfortunately I do not recall what the wood is, but it is commonly called (African) blackwood. I've machined a small amount of it and I'd liken it almost to machining a plastic. It's quite nice to work with, unlike so many of the woods we see with coarser grain. It is also rather difficult to obtain according to the pipe major of the Salt Lake Scots (he's engaged in pipe building), where I struggled to gain some semblance of skill at the pipes. Didn't happen! :-(
Harold
Reply to
Harold & Susan Vordos
Should have read your post first, CJ, would have saved me repeating that which you had already stated. :-)
Harold
Reply to
Harold & Susan Vordos

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