Quoted from Topcard:
I've been tempted to try filling the inserts, but I'm always afraid of screwing it up. I can't imagine dry clear coat in an insert being easy to remove if necessary. You're a braver man than me!
I haven’t dug too deep but I’m sure there are probably whole threads on it. I’m ultra conservative and wasn’t confident myself either so I started as low risk as possible.
Jacked up legs with shims and stuff until the surface was perfectly level in all directions. Put a ball on it and it doesn’t roll away in any direction.
I wanted as thin a coat as I could make so I used a water based clear coat and thinned it with distilled water. I started with the smallest inserts as far away from the player as possible... so 2 or 3 of the golden cliff inserts, a thin layer of clear coat and waited to see what that looked like... couldn’t see any difference at all when it dried (good) so did a few more, added more layers etc... I didn’t touch the large Paragon inserts til the very last after I had been doing it on the smaller inserts for several weeks. Eventually used less distilled water to thin it for fill layers, and only used thinned clear coat for the top layers when it’s almost flat.
Experimented with different size brushes and medicine droppers. The object is to try to fill the circle completely each time with no bubbles or brush lines.
The biggest gotcha is having any pinhole sized bubbles left when it’s wet as they show up as white dots when the light shines through them. If that happened i’d sand them out before putting on another layer. Only have a couple of those that aren’t really noticeable unless you are specifically looking for them. I’d also lightly sand out any brush lines from the previous layer til it looked smooth again before putting on another layer. I’m sure there were times that I ended up sanding off a full layer that I just put on, but I wanted to be sure the surface was smooth between every layer.
I looked around to find the finest sandpaper available... 800-1000+... maybe 600 if I needed to sand out a bubble I left. For final layers I’d polish with just a fibery cotton cloth. I used fine steel wool a bit but was a concerned about the metal dust getting into electrical stuff so ended up mostly using emery type paper.
I’d slowly roll a pinball over the filled insert to see if it was flat enough or if I made it too high. Kept playing with it until the ball had little it no deflection on a perfectly level surface.
Anyway... If you go slow and learn as you go it’s a good skill to pick up and really not that hard. I tried looking for a used scrap playfield to practice on but nothing really available at a decent price so just went for it extremely cautiously.