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Thread: Shining up delrin
05-26-2010, 06:11 AM #1
Shining up delrin
I made some parts that I deburred and blended radius's with scotch brite.I think the parts look great but customer wants a glossy finish not matte.I have made thousands of delrin parts and this is the first to not like it.They are comparing it to a sample and the print has no call out.The sample had sharp edges and fuzzies which I did not like.Any ideas on bringing the gloss back?
05-26-2010, 07:06 AM #2
To bring back the shine on Delrin, you will need to re-cut the surface. Once Delrin is scuffed you'll never bring back the shine.
05-26-2010, 07:32 AM #3
don't try to flame polish it! I had some small parts with the fuzzies and tried flame polishing, but the parts started burning with an invisible flame and then burned like a marshmallo!
05-26-2010, 07:37 AM #4
Go to a good woodworking tool store and get a small (1/2" to 1" wide) wood plane. You can set these to take the fin off and leave a perfect chamfer. Just the thing for customers who don't like the fuzzies on their plastic parts.
05-26-2010, 07:55 AM #5
on second thought, maybe a heat gun would work vs a torch.
05-26-2010, 08:15 AM #6
How odd; how timely...
I tried doing this just yesterday. Like they said, flame polishing is not the way. I did have some luck with a light buffing on a soft cotton buffing wheel, with very fine compound.
Didn't do enough to make a science out of it though. Might take another stab at it later.
05-26-2010, 08:24 AM #7
From what I have seen, the best finish youll ever get on Delrin/Acetal is from the tool (assuming youre using a good sharp pos cutter)
From there it all goes down hill.... sand it and its much worse, flaming... like said above - no go, steel wool, scotchbrite, and so on... same thing.
The closest thing to the original cut surface finish I have been able to get on Acetal after its been boogered up (sand paper etc) is some Dico polishing compound (blueish color - I got it from enco I think) and a buffing wheel on a grinder. And even still... ugh... but better than it was.
If there isnt a reason to not use some sort of chemical on the surface, you could try buffing with a little floor wax or wipe down with an oily rag...
For future reference, if there is any way to do everything on the machine, and always have your cutter push the edge its going to push up ahead of the cutter and then finally leave it in one place thats easy to debur - that will save you the most effort... but it may not be possible with your part.
I feel your pain, the acetal parts I make need the "pretty factor" because its 80% aesthetic.... and 20% function.
05-26-2010, 09:27 AM #8
Are you familiar with woodworking style scrapers, and how they're made? You basically take a piece of steel, polish the end flat, then burnish the end to create a tiny micro cutting edge. A good sharp scraper like that will do a pretty good job "polishing" plastics like Delrin. You just drag it lightly one time across the surface, and it peels off a thousandth or so of the surface. The scraper is particularly good for taking file marks off edges and reaching into corners.
For precision woodworking, I make up all kinds of custom scrapers out of plain O-1 tool steel flat stock, usually 1/8" x 1". You don't even have to harden it. Just polish and burnish it and it'll make nice sharp micro cutting edges.
As the other guys have said, you can't really polish Delrin. The best shiny finish comes from a straight cut with a very sharp blade.
05-26-2010, 09:47 AM #9
This ia a new customer to me and I am finding out that looks are what matters.These parts were not rejected but they would like them"prettier".I think I will work on getting them to allow this finish.I am quoting anodized parts for them that they all want to match,I think I can only tell them that I will supply mat.certs and use approved platers but can not guaratee a match.makes me miss aircraft,etc that spelled it all out, not much left for interpatation.
05-26-2010, 10:06 AM #10
Oh yea the reason that I want to be able to scotch brite is it has slot of operations and radius that need to blend thati would be working in tenths on features that fit to air.excuse the typing done on a phone.
05-26-2010, 10:52 AM #11
I had pretty good luck flame polishing Delrin.
The parts were about 3/8ths in diameter and I had a fixture to hold a bunch.
I used a propane torch hanging over the mill table. I programmed it to feed past the parts.
I did it fast at first to see how it worked and then kept slowing it down until I got the finish I wanted. Glossy!
You really can't do it by hand.
05-26-2010, 12:50 PM #12
with plastic i start with coarse sandpaper and when you use finer and finer at 600 grit it starts to shine then use micron paper.
lapping film is hard and if on a flat surface abrasive up you can rub flat parts on it.
some jewelry supply places like
Jewelry Making Supplies | Abrasives / Sand Paper - Beading Supplies, Metal Working Tools
have different sandpapers and the backing matters
soft tissue type sandpaper / polishing paper will go into small irregularities and of course nylon abrasives come in different grits that will go in deeper grooves.
also places that sell mold polishing supplies might have something of use too
05-26-2010, 01:30 PM #13
Cheats way to get a polish on not quite shiny plastics is a quick squirt'n wipe with a silicone carrying aerosol. Can last a couple of years or more. Depends on what you use and the plastic. If I ever needed that particular get out of jail card again it would be tempting to try one of those "never polish your car again" nostrums.
Agreed that generally delrin is never better than fresh from the tool. Super tip about scrapers from Bruce. Have seen what was clearly the same style of technique and tool done with excellent results and never thought to ask what exactly was going on. Dismal results a couple or three years alter when trying what, according to my memory, was an equivalent way of working proved that there was a devil in the detail. Namely that micro cutting edge.
05-26-2010, 02:15 PM #14
acrylic welding solvent
Wipe your part with a rag dampened with this solvent leaves a gloss finish on acrylic and polycarbonate. Wipe once then let dry before wiping again. If you try to wipe twice in the same spot without drying it'll be a mess. I haven't dipped a part but I'll bet that works even better.
Maybe it works on acetal, I don't know. Might be worth a try.
05-26-2010, 02:22 PM #15
+1 for Bruce's reply, and here's a link that spells it out in case someone's interested.
Sharpening and Burnishing a Card Scraper
I also have polished with auto rubbing compounds, and a formula I made up by mixing glazing compound w/.08 micron aluminum oxide powder (from Diamond Pacific Tool) into a paste.
05-26-2010, 07:15 PM #16
Just tried the solvent on a piece of Delrin and it does NOT work.
05-26-2010, 09:33 PM #17
Do your homework. Certain plastics react to certain solvents. Check the DuPont website, they have information, and contacts to get more information.
As for flame polishing... done thousands of parts over the years. Chuck it in a lathe, crank up the speed and just KISS it with the torch. You don't need much in the way of dwell time. It's one of those art-feel things.
I spent a summer "sealing" bottles fresh off an EBM machine. Mold would clamp around an extruded tube of plastic, machine would then inject air into the tube blow-molding the part. There was an enormous amount of flash. You cut that off with a big knife then went around the parting line with a torch to seal imprefections and even out the excess. This was HDPE which has a far lower melting point than Delrin.
Last word, WORK SAFELY. Delrin gives off Bad Fumes when it burns/overheats so have plenty of ventilation around your work area and a means to extinguish any fires that start.