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[Guide] My method of polishing ABS keycaps


Keycap shine is perhaps an inevitability on certain plastics, so for my current build I've decided to just get it over with and polish my keycaps. (I'm also just a big fan of the glossy keycaps seen on certain vintage keyboards.)

I'll spare you my life's story but just say that I've been in the jewelry/silversmithing trade for almost 15 years now, and I've learned a lot about polishing. When you get into this field, you typically spend several years working full time as a polisher. Day in, day out, you are polishing things to a mirror finish and coming home coated in red rouge. (I remember taking a shower every night to get that crap off me, and watching the red water go down the drain like some overdone parody of that scene in Psycho.) You don't start out with this job because it's easy; it’s actually one of the most difficult techniques to truly do well. No, it's mostly because the senior jewelers don’t want to spend their time on something so tedious and time consuming--just get the apprentice/intern/fresh blood to do it. That's not to say that you ever stop polishing; I'm no longer a full time polisher but it's still something I need to do pretty frequently.

Anyway. I work primarily in silver, however I've done a lot of work with Bakelite and I wanted to see how well these methods would transfer over to ABS. Honestly, I'm pretty happy with the results, so I have decided to share what I've learned on the off chance any of you are as crazy as I am. The keycaps I'm polishing are the Matt3o MT3 3277 from Drop. They are double-shot ABS. I have not tried PBT, so I cannot guarantee these techniques would work for that plastic, but I think there's a good chance it could.

Step 1:
Wet sand the keycap by hand with aluminum oxide sandpaper. (Under running water if you can, in a bowl/basin of water if you can’t.) My favorite sandpaper is the “Black Ice” line from Norton Abrasives. I started with 800 grit and sanded them until the texture was gone. Then I moved on to 1,200 grit until all the 800 grit scratches were gone. (Drying it off occasionally to inspect it.) Afterwards I repeated those steps with 2,000 grit and 2,500 grit. Make sure to really jam your finger in there and move the sandpaper around in random directions. The keycaps I have are the MT3 profile, so they are slightly concave on the top face; I chose to sand them by hand this way to make sure I maintained all the crisp edges and didn’t ruin that nice dish shape.

Step 2:
Using a handheld rotary tool (I have a Foredom TX flex shaft.) buff the keycap with a 1 inch Stoddard Miniature Cotton Buff loaded up with Lustre Bar polishing compound. (Don't worry, there is a list at the end that tells you where to buy all this stuff.)

I mainly use this compound for high polishing Bakelite, but it looks like it worked great here too. I made sure to run the flex shaft at a pretty low speed--I couldn’t tell you exactly what the RPM was since I use a foot pedal, but I can say is that it was like pushing down on the gas pedal of a car to go 20 to 30 miles an hour. (Well, at least it's like that in my Civic.)

NOTE: Heat is your worst enemy. When you polish metal, the heat from the friction of polishing will disperse, but plastic will absorb all that heat and it will cause serious problems. The most common one is creating these deep gouges from spots where little “hairs” of plastic were melted/ripped out from heat and friction. These lines will need to be aggressively sanded out; buffing with the compound alone will just accentuate them and make matters worse.

For this reason I do not recommend using a buffing lathe. The “slow” setting on most jewelry/dental/metal buffing machines is still too fast, and they often have way too much torque for plastic. If you are dead set on using one, then I recommend that you use a buffing wheel with a diameter no larger than 4 inches. Here’s what my buffing lathe did to the keycap on the slowest setting, and with the softest balloon cloth buffing wheel available:

Step 3:
If you did everything else correctly you will end up with a nice shine, but there will still be some very small micro-scratches if you look closely under bright light.

This is OK I guess, but I wanted a perfect polish. So after a bit of trial and error I ended up using a product called “Polywatch” to finish the job. This is a small tube of white gunk that you use to polish plastic watch crystals, but it works great on ABS too it seems. (When I worked for a luxury watch brokerage we would use this stuff to fix the plastic crystals on vintage Rolexes and certain Panerai watches.)

Just squeeze out a small amount of the Polywatch on to the top of the keycap, and then buff the crap out of it by hand with the included cloth for around three minutes. (If you ever lose that cloth, you can use a glasses cleaning cloth instead—do not use a tee-shirt cloth though.) Afterwards, you’re left with a polish that’s pretty damn good. Unfortunately, this also means that it will scratch cartoonishly easy from now on, as the grit on your fingertips alone are enough to put tiny scratches into the plastic. But if you’re polishing keycaps, it’s probably not out of a sense of pragmatism.

I have done a lot of experiments to try and expedite this process, but the tedious sanding method has always produced the best results. If you want to read about these various failed attempts and the postmortems detailing what went wrong, you can read about it here on my website:

The keyboard I’m building is an 1800 layout with 100+ keys, so I’ve got a lot of work ahead of me.

Supply list:
* Sandpaper – 800 grit:
* Sandpaper – 1,200 grit:
* Sandpaper – 2,000 grit:
* Sandpaper – 2,500 grit:
* Lustre Bar:
* Stoddard Buffs:
* Alternative to the Stoddard Buffs:
* Polywatch:

This was a really informative read, thanks. Wouldn't have considered the heat artifacts from rubbing the plastic.

Saving it for future reference :thumb:

Thank dude, that was quite helpful.


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