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I added flip down caster wheels to my table saw. Cheaper than a mobile base.
(edmomot.github.io)
Pretty happy with how this turned out, even months later
This is awesome.
You mentioned it was hard to get the wheels down because the crossbars match (saw + wheels). Instead of using spacers, you might also consider putting a small tab of wood in the middle on top of each wood crossbar so it sits above the saw crossbar, but not big enough to touch the floor when down.
That's a good point, I thought about that too. Not sure how sturdy that would be. I'd probably step on it and break it eventually.