Polishing polycarbonate

My pencil rocket will have polycarbonate (Lexan) fins, first time I've worked with it. Didn't realize how easy it is to scratch, so I scratched the heck out of the first two while cleaning them before I realized my mistake. Not a big deal but I'm trying to see if I can clean them up.

So I tried a sanding/polishing regimen as follows:
1) Sand with 1500, then 2000, then 3000 grit
2) Polish with Turtle Wax polishing compound
3) Polish with Mother's Plastic Polish

The end result is extremely smooth and scratch free but slightly cloudy. I can't seem to get it over the finish line to perfect clarity. Am I missing some step that would finish the job for me?

I've heard of using toothpaste to remove fine scratches but somehow I expect it would slot in somewhere between #2 and #3. Haven't tried it yet though.

Just a thought. Haven't tried this (disclaimer) but what about those automotive products that polish dull headlight covers and make them clear again?

kuririn said:

Just a thought. Haven't tried this (disclaimer) but what about those automotive products that polish dull headlight covers and make them clear again?

Click to expand...

In theory that's what the Mother's plastic polish is. I dunno, maybe I just need to apply more elbow grease? It did improve the clarity compared to the results of the polishing compound, but still not totally clear. I'm less interested in one of those full blown headlight repair kits, because (a) they are expensive, and (b) they are mainly (as far as I can tell) a collection of abrasives and sandpaper finish with a plastic polish like what I bought. My impression on that could be wrong, though.

I think I'm gonna get some of this stuff and try it out. These fins are turning out to be expensive, but hopefully I'll find other uses for this in the future.

OK, I tried the Novus polishing system and have made very little progress; it is still *far* from perfectly clear (although it feels smooth). I mean, it might be good enough for a rocket but I still feel like it ought to be better. I sent them a question and we'll see if they respond.

Try a flame. With a small torch, just make a pass rapidly on the scratch.

Works also with the ends. If you cut them smooth, the torch will make them transparent.

My edges have already been flamed, but it seems to be a dicey process. What I have right now is a light fog on the flat surfaces. It was not my impression that that was the ideal application of flaming.

Interestingly, I saw something only that said you should not flame polycarbonate, although it seems to have produced good results (mostly) on my fins.

Give it a quick wipe with acetone. Might flow the surface and clear it up.
If that doesn't work, resand with 600 and 800, then give it a light coat of your favorite rattle can clearcoat. Bunch of solvents in that, in addition to the clear, which can fill.
If that doesn't work, you might need to get into some more potent solvents and vapor polishing. At that point, might be better to just restart.

Had a polycarb nose cone I spent hours trying to get perfect. Looked great after the clear, until I dropped it, still wet.

Clearcoating is definitely an option. I was actually thinking about trying Future (which should fill the surface and leave it clear), but I don't know if there is downside to that.

My understanding is that the cloudiness is only surface level, likely caused by moisture. That's why I suggested a bunch of solvent based methods, to melt that layer.

I don't know if Future would have the same effect, I haven't used it. But it's probably worth a test or two, if you've got the scrap poly. Should check if it works on normal poly and poly you've treated with everything you've done to your fins.

Good thoughts.

In the headlight polishing kits, the compound only gets you to an even light haze. Then you wipe on the UV protective clearcoat and it INSTANTLY goes crystal clear. Not sure what all is in that, but it makes the final difference.
-Ken

new2hpr said:

In the headlight polishing kits, the compound only gets you to an even light haze. Then you wipe on the UV protective clearcoat and it INSTANTLY goes crystal clear. Not sure what all is in that, but it makes the final difference.
-Ken

Click to expand...

Probably a filler. In theory, the Future should serve a similar role for me. I'm not sure why I'm not getting equivalent results from the Novus stuff.

neil_w said:

I think I'm gonna get some of this stuff and try it out. These fins are turning out to be expensive, but hopefully I'll find other uses for this in the future.

Click to expand...

That Novus stuff is what we use for fine scratch repair on instruments at the music store. Anything from wood violins with varnish to lacquered electric guitars.

BBowmaster said:

That Novus stuff is what we use for fine scratch repair on instruments at the music store. Anything from wood violins with varnish to lacquered electric guitars.

Click to expand...

Out of curiosity, what cloth do you use for application and buffing?

I also tried flaming the edges, but it didn't seem to help much (and it's easy to haze the flat sides). I think that may be meant more for Acrylic. It's interesting to hear the ideas about solvents and fillers. I may try that with the fins on my Ariane 6.

Auto headlight covers are generally polycarbonate, so products meant to clear and protect headlights are probably appropriate.

I suspect the reason why the Turtle Wax polish didn’t finish the job is probably because a “polish” is actually too fine, and you need to use a more abrasive paste (“buffing compound”)

Generally you do wet sanding -> compound -> polish -> wax. It kind of sounds like you missed a step.

new2hpr said:

In the headlight polishing kits, the compound only gets you to an even light haze. Then you wipe on the UV protective clearcoat and it INSTANTLY goes crystal clear. Not sure what all is in that, but it makes the final difference.
-Ken

Click to expand...

Walmart probably sells Meguiars headlight spray, among other brands.

Any of these will work well, along with many others that are made. I use an air buffer to apply. They come out like glass when done. When using a buffer though, do not run to fast nor hold in one place too long as it may melt plastic.