71B: repair/polish LCD screen scratches

[Hans Brueggemann]

(05-29-2019 05:32 PM)cdmackay Wrote:  thanks for the warning Hans; I will stay well clear of the bezel

I tried some Polywatch on the scratched perspex, but I struggled to see that I was making any difference. Now pondering whether to try again, pressing harder, and/or polishing longer, or just leave well enough alone.

ah, i see.. you're just just using polywatch and nothing else. that will take forever.
pressing harder won't help at all in the process.

before you are going to ruin the perspex of your calculator, try your polishing method on some scrap piece of perspex:
1) purchase "wet" (never use "dry") sanding paper with 600, 800, 1000, 1500, 2000 grit , 1 sheet each.
2) fill a cup of cold water and add a squirt of liquid dish washing detergent.
3) starting at the lowest number, thoroughly sand the perspex in circular motions with snippets of the sand paper, using a generous amount of the dish washing solution as lubricant. if the sand paper seems to get "blunt", rinse it under fresh water. do only apply very slight pressure. objective is to get an obsolutely evenly sanded surface. check the perspex against the light. it should have become evenly "foggy" or semitransparent, with no more individual scratch marks visible.
4) thoroughly rinse the perspex under fresh water. also, discard the rest of the dish cleaning solution, clean the cup, and make some fresh solution. we want to get rid of all sanding particles from the sand paper, before we go on with the next higher grit number.
5) repeat from step 3) with the next higher grit number until 2000 grit. dry the perspex with a lint-free paper towel.
6) now, use the Polywatch and a package of q-tips to give the perspex the final touch. done!

now that you got the hook of it, apply this procedure to the perspex of the calculator.

as i said before, in case the scratch is very deep, you may to try to fill it with a drop of UV-curable resin. you can determine whether the scratch requires filling if it is still visible after using the 600 grit.
this stuff is available at brick&mortar stores, including the UV light source for curing it. just leave the repaired area untouched for 24 hours, befor you start again at step 2) with the coarsest grit.