Quoted from nate1981s:why was this playfield not rejected?
Because there is nothing wrong with it.
Wood is hydroscopic, so it absorbs water, swells and shrinks.
Even out of the exact same tree, different pieces of wood will shrink and swell differently.
That wood was completely flat when the playfield was manufactured, or else there is no way the ink would have covered the surface when it was pressed through the silkscreen. That is why playfields are dimpled AFTER they are printed, otherwise every dimple would result in an 1/8" circle of unprinted wood.
Playfields are sanded on a giant belt sander to make them totally flat with the installed inserts. The wood is sealed and sanded once more to make sure they are 100% flat.
Then they are silkscreened.
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Now, a year or so after being manufactured, the humidity has changed and the wood has shrank.
Totally normal.
Once the playfield gets compressed with 1,000,000,000 dimples in it, it will appear to be totally flat again - just like your 30 year old B/W games.
https://pinside.com/pinball/forum/topic/playfield-dimple-reality-check