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Discussion: Buffing compass housing

in: Orienteering; General

Sep 19, 2017 12:25 AM # 
KFish:
I have a very scratched up Moscow compass and I'd like to clear it up a little. Does anyone have any suggestions? I'm thinking of using a dremmel with a pad and some kind of buffing paste.
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Sep 19, 2017 12:33 AM # 
edwarddes:
I think the housings are polycarbonate, which is very sensitive to solvents. If you use the wrong chemicals on PC, it looks good while you are cleaning it, but then crazes very quickly, becomes very brittle, and is worse than when you started.
Some form of abrasive buffing compound is probably safe. Maybe start with toothpaste?
Sep 19, 2017 12:42 AM # 
jvincent:
Would some sort of headlight cleaning compound work, or do you think even that might be too abrasive?
Sep 19, 2017 12:56 AM # 
edwarddes:
Headlights are often also PC, so something that works on headlights and is safe will probably be ok on the compass.
Sep 19, 2017 12:09 PM # 
chitownclark:
Forget the abrasives! Boats have a lot of plastic that is exposed to the weather and wear such as hatch covers and windshields. So there are many marine products like this one that are formulated for polycarbonate plastics. According to one of the reviews, it can be used most successfully with an orbital buffer.

I have used such a product for shining up the plastic windows on microwave ovens with some success. But heavy scratches are usually permanent.
Sep 19, 2017 5:53 PM # 
haywoodkb:
I would be afraid that buffing and polishing would induce static electricity that would make the needle dance about randomly.
Sep 19, 2017 6:17 PM # 
cedarcreek:
I use this stuff for DVD scratches. You can moderate pressure and amount of compound to adjust the polishing action.

https://smile.amazon.com/gp/product/B00B42MOJI/ref...

I've seen numerous recommendations from the 70s and 80s to use toothpaste to take scratches out of plastic. However, new toothpastes seem to be formulated without the same abrasives.

I've used headlight polishing kits as well as very high numbered grit wet-dry sandpaper (I'm thinking 2000-4000-8000 but I'd have to look. For headlights, you need a shiny coating after the sandpaper or abrasive, or it just looks hazed anyway. But it might work on a compass.

Finally, you can possibly take it to a jeweler or a watch-battery kiosk in a mall. They were able to polish a plastic crystal on a Swatch watch I had in college several times. Make sure they know it's plastic so they don't take off a lot.

If you have a broken one to practice on---and this is really dodgy so be careful---try spraying DEET bug spray on it and wiping it with a soft, smooth rag. When you're done, degrease it with soap and water or something like windex. There are videos of people doing this on hazed plastic headlight housings, but my chemist friends are very skeptical. They think it's just a bad idea. DEET is a plasticizer, which means it dissolves certain plastics. For all I know, DEET might not work on the compass material.
Sep 19, 2017 7:14 PM # 
JayXC:
From experience, DEET will remove the red scale markings from the Suunto thumb compass baseplate.
Sep 19, 2017 9:18 PM # 
jjcote:
I would be afraid that buffing and polishing would induce static electricity that would make the needle dance about randomly.

Hmm. Static electricity. Magnets. Random dancing?

I'm not going to lose sleep over that theory.
Sep 19, 2017 9:20 PM # 
GuyO:
DEET also makes the ink on bibs sticky (at least it did at the Canada 150 O-Fest)
Sep 20, 2017 1:01 AM # 
JimBaker:
Given that DEET dissolved my compass lanyard and left my fingerprints in mylar (back when mylar was a mapping thing), I'm not so sure about letting it contact a compass of unknown polymer, so I'd agree with the suggestion to only try it on a ruined compass.
Sep 20, 2017 2:32 AM # 
walk:
Traveling to WY one year, I packed a DEET container in its own plastic bag and then in another plastic that included various items including a Swiss Army knife. The DEET leaked enough to get to the handle pieces of the knife and dissolve chunks of it. The handle remained quite sticky and took quite a bit of washing to neutralize.
Sep 20, 2017 2:42 AM # 
jjcote:
I think if DEET were destructive to compasses, we'd know it, because there are plenty of opportunities for those two things to encounter each other. But using it to de-haze a compass really doesn't sound like a great idea.
Sep 20, 2017 3:00 AM # 
cedarcreek:
hold my beer. I've got a ruined compass somewhere...
Sep 20, 2017 3:40 AM # 
cedarcreek:
Okay.

Sprayed Ben's 30% DEET "Wilderness Formula" onto a folded paper towel.

Rubbed the face of a Moscow compass capsule, then dried with the same towel (unfolded a bit). Degreased with a squirt of Dawn, covered entire capsule with fingers, and then rinsed under the faucet. Dried with a soft cotton towel.

No apparent change. Possibly cleaner and brighter, but no visible change to scratches that show depth.

Repeated on bottom of capsule (paint side). No apparent change. No removal of paint.

Repeated on top but sprayed directly onto the capsule. Created some new surface scratches with my fingernail, but the plastic doesn't seem gummy or soft.

Tried the Memorex DVD kit compound with the supplied microfiber cloth (like that used for eyeglasses). No apparent change to deeper scratches. The flat surface seems a little brighter, but I honestly can't see any real difference to any scratches. And this stuff really works on DVDs. It's very gentle, definitely a consumer product grade. Difficult to get into trouble with this stuff.

I always guessed compasses were acrylic. But I have no proof. Polycarbonate always seems to have a give that acrylic doesn't have, and I don't detect that with any compass I've held. (And yes, there are different grades, so this means nothing.)

Now, for real, I'm pouring a beer.
Sep 20, 2017 3:57 AM # 
jjcote:
Don't bother trying kerosene. That's what's on the inside.
Sep 20, 2017 4:22 AM # 
cedarcreek:
serious warnings for this one.

probably a bad idea.

https://www.youtube.com/watch?v=h2lm6FuaAWI
Sep 20, 2017 11:12 AM # 
tRicky:
Do any of these suggestions work to bring back a lost compass?
Sep 20, 2017 1:38 PM # 
chitownclark:
Wow! Cold acetone vapor finishing! Very interesting and simple process. But for a base plate compass, probably not practical since I assume the vapor would weld the rotating compass to the baseplate while it produced that shiny surface.

But thanks cedarcreek! I might try it on my plastic microwave oven doors in a larger vaporization chamber. For a lot of cleaning services, when all you've got is a big can of Ajax, the whole world looks like it needs scouring!
Sep 20, 2017 9:11 PM # 
cedarcreek:
I was working with a capsule with no thumb- or baseplate. That process would almost certainly make the capsule not fit into the plates. Honestly, I probably won't do it. My first step would be to check if acetone softens the compass material.
Sep 21, 2017 4:14 AM # 
mintore:
Excerpt from the a Lexan polycarbonate solvent compatibility sheet (the_plastic_shop_UK).

"In the first case the chemical is absorbed into the plastic, and plasticisation and/or crystallisation occurs. The visible signs of this type of attack are swelling or surface whitening. Lexan polycarbonate is affected in this way by partial solvents such as low molecular weight aldehydes and ethers, ketones, esters, aromatic hydrocarbons (read DEET) and perchlorinated hydrocarbons.
....
The third type of attack is often the most difficult to predict since environmental conditions dictate whether or not the plastic will be affected. Combinations of certain environments, coupled with stress and/or strain upon the material, cause stress cracking or crazing of the polycarbonate sheet. Crazing can be induced at moderate to high stress levels by low molecular weight hydrocarbons. Products such as acetone and xylene may cause stress cracking even at very low stress levels and should therefore be avoided."

Acrylic has similar chemical resistance: no to acetone or other ketones, chlorinated or aromatic solvents (toluene, xylene, DEET). If any of these are on the plastic long enough to soften and dissolve out scratches, bad things will happen.

I would buff -- cedarcreek's 2000-4000-8000 (I think headlight kits often only go to 6000) suggestion.
Sep 21, 2017 4:55 AM # 
jjcote:
KFish: can you post a picture of what it looks like now?
Sep 21, 2017 3:20 PM # 
KFish:
https://m.imgur.com/gallery/3bs48
Sep 21, 2017 3:31 PM # 
Mr Wonderful:
Were you wearing it during a motorcycle crash?!
Sep 21, 2017 4:58 PM # 
KFish:
Multiple, High speed orienteering crashes
Sep 21, 2017 5:14 PM # 
fossil:
So why try to clear it up? It tells a better story as is!
Sep 21, 2017 5:25 PM # 
JimBaker:
Yeah, I'm with fossil, mount it proudly above your awards. :-)
Sep 22, 2017 1:53 AM # 
jjcote:
Looks like it's used up. You deserve a new one.
Sep 30, 2017 11:19 AM # 
KFish:
I ended up using polishing paste that came with my dremel. It was a small clay like brick, not sure of what. It actually worked quite well, it's clear again! Thanks for the help!
Sep 30, 2017 12:30 PM # 
jjcote:
Need the "after" picture!
Sep 30, 2017 12:32 PM # 
Cristina:
yeah, pics or it didn't happen
Sep 30, 2017 3:18 PM # 
KFish:
Turns out its harder to take a picture showing its clear than it was to take one showing its scratched! heres the best I could do;

Sep 30, 2017 3:35 PM # 
JimBaker:
Pretty nice. Some hope for my old clouded compasses in drawers, perhaps.
Sep 30, 2017 4:47 PM # 
jjcote:
Nice work!

(Hutch was known for keeping his compass in his drawers, but I didn't know you did that, Jim.)
Sep 30, 2017 5:16 PM # 
chitownclark:
Nice job...I'm sure the Russians approve.

Sounds like you used a form of Jeweler's Rouge for plastic. For anyone else who might want to buff up their Moscow, PJ Tool sells a kit with six compounds, some specifically for plastic.
Sep 30, 2017 6:27 PM # 
JimBaker:
My old compasses have ended up in drawers, in part a result of various long distance moves. My newish ones are in my O kit mesh bag, or in the original box for protection from, well, scratches.
Sep 30, 2017 6:48 PM # 
jjcote:
Yeah, not what I meant. Ask me for the story next time you see me, Jim. :-)
Sep 30, 2017 7:24 PM # 
JimBaker:
Oh dear. Sounds potentially uncomfortable. I think that we should give this thread back to the OPs, and miraculous before and after photos.
Sep 30, 2017 11:34 PM # 
Juffy:
So...is North that way, or are you just pleased to see me?
Oct 1, 2017 12:06 AM # 
GuyO:
My compasses have always gotten bubbles before they've needed buffing...

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