Polishing Polycarbonate Plastic
We feel that we have come up with a great polishing system for Polycarbonate Plastic used on Vintage Snowmobiles. Hoods, trunks, side panels are some of the applications.
Polycarbonate is generally a colored plastic when used on hoods etc. It is colored all the way through and is smooth on the inside. This is different than Fiberglass hoods that have a rough finish on the inside.
Also the snowmobile industry seemed to start using some ABS hoods in the late 70's. Scorpion is one of them? If you sand this plastic aggressively, you may cause issues.
ABS and Polycarbonate are very similar in appearance and are sometime blended together.
Sand at your own risk.
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| 1973 Polaris trunk piece at start | Close up of color
difference. |
Polycarbonate quite frequently changes color as it ages. This piece was originally blue, now closer to a brown. This piece is probably as extreme as most people would tackle.
If we can clean this up, more than likely we can clean your item up also!
Sanding Tips
If using a machine sander, watch for heat build up. Polycarbonate will melt while sanding and then stick to itself. This causes a lot of extra work. Keep your heat down by slowing your disc speed down.
You can dry or wet sand by hand
Always start as fine as you can comfortably sand your item with to achieve the necessary results
You need to remove any scratches by sanding if you want to minimize the scratches before polishing. If the plastic is gouged severely you may weaken the plastic if you sand aggressively and remove large amounts of material.
Sand flat, if you sand at a angle on one spot to remove a defect, you will have a divot or dent there.
Always refine a coarser grit scratch to a finer grit scratch completely before proceeding to the next finer grit sandpaper.
If you jump too far between steps, the sandpaper cannot remove the previous coarser grit scratch properly.
The oxidation will tend to plug your sandpaper up. Change frequently to minimize it melting back onto the surface of the plastic. Sanding at slower speeds will help to keep the heat down also.
Lets get started!
I first started with 400 grit. I found that I was not getting all of the oxidation off the surface. So I then moved to 240 grit. I would only go this coarse IF NECESSARY! I sanded with a small 3 inch buffer using 3 inch paper.
Next step was to sand with 400 grit to remove the 240 grit scratches. I also used the 3 inch buffer for this step.
Next was to sand with a 3 inch DA (orbital) sander with 400. This leaves a finer grit 400 scratch than the buffer with the same 400 grit.
Next was to sand with the 3 inch DA using 600 grit.
This was followed with 1500 grit and then 2000 grit "sponge back paper"
The sponge back paper that I refer to in this case was Mirka Abralon. While there are other paper out there, this is a nice paper. The sponge back gives some cushion and the paper really refines the scratch allowing easy polishing. If you leave it coarser, you will have to polish harder.
Pictures of the progress
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| Sanded with Buffer to 400 grit | Refining the rotary scratch to a 400 DA scratch. You can see the need to further sand this before moving to the next step. | Refined the scratch to a 600 grit scratch | Refined the 600 grit scratch to a 1500 grit scratch. |
Final sanding step. 2000 grit sponge back paper.
You can see that we already have a semi gloss appearance.
A picture of Abralon sandpaper. If you look closely you can see that it is fairly thick with a sponge back, but also that is has a mesh front which allows air to go through and cool it. A important feature to keep our polycarbonate cool.
Polishing
Step one, coarse plastic polish used with a Loose sewn buff wheel
This step will remove the scratches from sanding. You will leave a few scratches in the plastic from the polishing step/buff wheel. It will look pretty good at this point. Step 2 optional, but it is a simple step that will give it a nicer finish.
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| Loose sewn buff wheel. Only use the type with
one row of stitching for plastic. Keep the wheel clean with a rake
and keep the speed down. I use about 1500-1750 rpm's with this wheel. if you have a 3750 rpm buff motor, use a smaller 4 inch diameter wheel to drop your surface speed of the wheel down to avoid melting the plastic. Still be careful. |
Sept two, fine plastic polish used with a Loose sewn buff wheel. A quick run over with this polish with a FRESH loose sewn wheel will yield nice results. Do not use a wheel contaminated with a coarser compound.
Polishing Tips
Do not use too much wheel speed.
Buff in different directions. This helps to polish out the scratches easier.
Clean between each step, previous step compound could reintroduce a coarse scratch
Keep buffing wheel clean,
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| Course plastic polish. | Fine plastic polish |
Now a before and after shot. Final light polish by hand with a microfiber cloth.
The imperfections that you see are actually reflections from my shop.
You will see some imperfections in the plastic itself yet. This has to do with manufacturing processes. You now see these due to the extreme gloss that we are achieving.