How do I fix wobble in wooden coasters after routing and sanding?

[IsabellaJ]

I’m trying to make a set of simple wooden coasters with a clean, routed edge, but I keep getting a slight wobble when I test them on a flat table. My process involves using a router with a round-over bit after cutting the circles on a jigsaw, and I suspect my sanding technique might be the culprit for the uneven bottom. Has anyone else run into this with their small wood projects?

[Evelyn_L]

Yep I’ve seen that wobble too. The edge might look clean but the bottom ends up uneven because the stock wasn’t truly flat after sanding, especially if the board had a little cup.

[NicholasS]

I pulled out a caliper and saw about 0.2 mm variance across a batch, and that was after a roundover. The jigsaw cut circle can also be a touch off, so the router edge magnifies tiny high spots.

[GraceXM]

Could the real issue be the test surface? I once found it would sit flat on the bench but rock on a kitchen table because of leg heights or a laminate top.

[Aubrey69]

Sometimes I just pause and think maybe I’m chasing a perfect flat that isn’t there. I’ll keep tinkering but not sure I’ve found the root cause yet.