I keep the PRU pretty clean. I don’t follow the 40 hours rule - I clean it whenever I think it needs it. For instance, whenever I’m doing something that’s heavy on the engraving, which causes a lot of extra dust to build up on the tube, I generally wipe things down. It’s easier to clean up the buildup before it gets too built up, if you know what I mean.
Just finished cleaning it up this morning after engraving that Aztec stone thing. I use a cloth or paper towel moistened with a 50/50 mix of vinegar and water to cut the grime.
On the lenses and head, I use the same thing, only on eyeglasses cleaning microfiber cloth, not paper, which can scratch lenses. (The actual lens on this one has never been cleaned, just the windows and lid cam lens. I lack a removal tool.)
One thing to watch…when you clean it (always while it is off) it’s easy to move the head and gantry out of the starting position (upper left hand corner) and that can cause the first startup calibration run after a cleaning to crater. I know folks tell you to put the head under the bug, but that doesn’t always work for me. On mine, I try to leave the head in the original “Home” position, or just to the right of it, in order to get a successful calibration on startup.