Polishing 7-segment displays

[groinksan]

Aloha!

I have a bunch of 7-segment single-digit displays. When testing them, I notice that some of them have a dull surface, and/or they have scratches. I'd like to sand the surface down with high grit sandpaper, and then use some kind of a compound to make the display shine like it was new. Any suggestions on the kind of compound and/or grade of sandpaper I should use?

[jpanhalt]

I would not start with anything coarser than 600 grit, and since plastic is soft, might start even higher to see how well the scratches are removed.   You can always go coarser more easily than finer if needed.  In other words start with the highest grit that removes the scratches.  Remember to use water as a lubricant.

As for my next step, it depends on what you have access to and how much money you want to spend.  The cheapest and most convenient source is probably an autobody paint supply store.  Ask for "color sanding paper."   I prefer 3M but there are other brands.  They go up to grits over 6000.

If you have access to3M, you may also consider its  "Microfinishing Film."  You can get extremely fine finishes with that.  Years ago, I used it to flatten (lap) flat and polish glassy carbon to a mirror finish for electrodes.  A final polish was not necessary.

Finally, 3M abrasive pads come in various grits.  Most people have seen the green and purple maroon pads.   The finest pad I have is white.  It will polish harder materials but probably leave a little haze on plastic.  Since they are pads, you may get a little rounding at the edges and the surface will not be super flat.

Then you need a final polish.  There are lots of them available.  For very small amounts, consider toothpaste.

[Fraser]

I recommend Nova plastic and acrylic polish. I have used it for many years. Collectors of pin ball machines swear by it for polishing pinball machine decks.

It lasts for years and is well worth having on the shelf for all manner of polishing tasks. Read up on the product, it is brilliant.

https://www.amazon.co.uk/Novus-Acrylic-Scratch-Remover-Plastic/dp/B00LL99T9W/ref=pd_lpo_1?pd_rd_i=B00LL99T9W&psc=1

The grade 2 polish is the one I use most often and leaves a lovely shiny surface. Grade 1 is really just a cleaning solution. Grade 3 is the hardest fir removing “spider web” scratches before moving on to grade 2 for a fine polish to high gloss. You only need a polishing cloth, no power tools.

Fraser

[perdrix]

I've polished perspex before now using "Duraglit" (Brasso brand) - basically a wadding impregnated with rouge and a lubricant (probably white spirit).

David

[Halcyon]

I've polished perspex before now using "Duraglit" (Brasso brand) - basically a wadding impregnated with rouge and a lubricant (probably white spirit).

+1 for this. Often used in retro-computing restoration. If I recall, I think The 8-bit Guy uses it on his Youtube channel? Or I could be thinking of someone else.