Oh! I didn't think the intake was powered. It looked like a plain air

exchange tube and I couldn' see a filter element in there.

Yeah. There's a fan on the door at the end of each tube. The top one blows out (filter in the box) and the bottom one blows in. I stop the bottom tube at the other end with a bucket. I suppose some dust will accumulate in the bottom tube, but so far the blades on both fans are totally clean, so my filter seems to be effective.

As to dust on the ways, I'm with PCS. I've always done a lot of sanding and shaping with a scraper over the ways, and never seen any consequence. Just clean up after yourself, and not only the ways, but the lead screw too. That thing really likes to crud up when dust is around!