Fixing the ST:TNG Shield Lenses

Start Trek: The Next Generation had three large banana-shaped lenses on the front of the starship, located in the middle of the playfield. These lenses each sit over two GI lamps and one flasher. These lenses run warm, either because of the GI or maybe stuck-on flashers. Heat causes the clearocat to delaminate.

So I set out to fix them. To compensate for my inability to draw any kind of line better than a 3-year-old with a crayon, I made some mylar sanding and painting templates. I also wanted to do the fix in the machine.

Here's the before. Nasty cracked and delaminating lenses

And the mostly after. The black rings are nice. The lenses look great when the machine is on. The uglies are mostly surface imperfections. The next step is block sanding down (with mask), light clearcoat over the whole area, and machine polish.

Materials:
Krylon Fusion black paint
Varathane Diamond water-based polyurethane
Mylar sanding mask
Mylar painting mask
Coarse emery cloth
400 grit sandpaper
Green Scotchbrite pad
Masking tape
Masking paper

Process
Step 1: Install sanding template.
Step 2: Crack off loose clearcoat
Step 3: Sand lenses clean with coarse emery cloth
Step 4: Sand lenses with 400 grit sandpaper.
Step 5: Varathane coat to level lenses and fill dips.
Step 6: Sand cured Varathane to level gouges.
Step 7: Remove sanding mask, install paint mask
Step 8: Install lens masks, leaving a thin gap
Step 8: Krylon black spray
Setp 9: Remove lens masks, 5 coats of Varathane
Step 10: remove masks
Step 11: Fill any surface imperfections, run a bead around the outside edge to eliminate the step

Here's the playfield as it started. The lenses have cracked and delaminating clearcoat, cause by heat from the GI and flashers under the playfield.	Closeup of the center lens. This is the worst of the three. Big chunks of the clearcoat have come off.
This is the left lens. It has some separation going on, and a couple of gouges in the center.	Here's how we started to clean off the clearcoat. the blade is flexible, so the sharp edge cuts nearly parallel to the surface of the lens.
Next, sanding with a sanding sponge. Not good for surrounding artwork! This mess was easily cleaned up with a light rub of clearcoat, but this is obviously not the right approach.	Here's a sanding mask. This one is vinyl. Turns out that vinyl is a bot soft for a sanding mask.
After sanding. Nice rough surfaces for the clearcoat. I lost some of the black.	OK, on goes the clearcoat mask. This is precisely cut to outline the lenses.
Masked. All this work was done in the machine without removing any parts.	Level in the long axis. Conveniently, this is with the plalyfiled resting on the edge of the cabinet.
Level horizontally.	On goes the clearcoat. There were some pits in the plastic. I dripped some spray into a coke bottle cap, and dropped it into the pits with a fine brush. The spray is very thin, so building it up is important.
More coats.
Removed the masking after the final coat. Note the milky appearance.	And the final result. Not bad, but I wasn't able to touch up the black, and did not like the surface. So I made some mylar masks, sanded it, and started again...
Here's the new masking, after a spray of Krylon Fusion black. The mask goes to the outside edge of the black, and has a cover for the clear part of the insert.	Clear covers removed. I have a nice sharp line around the outside of the lenses.
After a couple of coats.	After the final coat. Removing the mask was tricky. Where wet, the mask lifted up the entire top layer. Where dry, I got a rough edge.
I filled in some of the lost area, and beaded around the raised edge, from my coke bottle top. The result looks pretty good when lit from behind. Somehow, the varathane ended up slightly milky - which is what we want!

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