I have 1961 Gtb insert that is over 1” in diameter. It is pretty concave. Someone mentioned a method of flattening it using a heat gun. Anyone know the link to the method?

All I could find is the PinballHelp video that suggests sanding. Don’t think it would work on a large, concave piece.

Thanks. If this doesn’t work, I’ll try buying a new one. Ordered the wrong insert by mistake and wanted to get to the project while I’m on a short break.

1 3/16 insert. This was so concave a ball could sit in it without rolling out or touching the edges.

Flattened using the method in the above link and then sanding with 400 grit. Finished with 1000, 1500, 2000 , 3000, Novus 2, Novus 1.

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Oops… the insert fits very loosely now, even the surface, which you wouldn’t expect to shrink with time.

A new one fits tightly. Too bad I bought the wrong one- got a faceted one by mistake. Correct one is on its way from Marcos.

New one will be a shade lighter, but I guess it’s better than using wood epoxy to fit the old one.

Heated the old one, stretched out the sides with a socket wrench. Polished with Novus. If the glue holds, we're good.

Here's what worked for me:

I used a ceramic tile on my table. I also used a screwdriver with a plastic handle that pretty much fit inside the insert with a little room to move around. Didn’t use a socket because I didn’t want cold metal that would cool down the plastic insert immediately.

With the insert face up on the tile, heat with heat gun on low about 4" - 8” away , moving the heat around. I did it face up so the surface would soften but not so much the sides. After about 10-15 seconds, flip it over and press down with the screwdriver handle. Keep pressing until you think the plastic has cooled. Flip it right side up and place a pinball on it. That shows you if you are good or need to keep working on it. You might have to repeat & press flat with the screwdriver in another place.

If the sides of the insert are warped, you can use the heat and something round like a wooden dowel to work it back into shape.

I was working on inserts from a 1961 Gottlieb. Your mileage may vary.