This was borne out of a cockup, but might be of interest to someone else. I'd originally intended to have some bellows covering the rails and ballscrew on the gantry (my X axis), but when I came to fit them I found I'd made an error in the drawing and there wasn't quite enough clearance at the bottom so they fouled the carriage plates. It won't be a problem in the long run as I was intending to remake the carriage plates anyway now that I have proper milling capacity, but that's been put back a bit due to work pressure and supply problems with aluminium stock due to the virus. Observing that the X axis ballscrew was frequently getting sprinkled with chips, I thought some other form of protection was in order. I rang a few of the machine guarding people but everything they had on offer was too big and/or too expensive. After a bit of thought and fiddling, it looked like some kind of blind arrangement would be the best option given the limited space. I fiddled around with springs out of an old window blind, but the force was far from constant and it was a pain to put together without getting custom springs made. Then the thought struck me that a DC motor supplied with a constant current gave constant torque..... So I came up with these:
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Not a 100% perfect solution, but they seem to be keeping the ballscrew clean, and apart from a couple of £10 motors off the Bay of fleas, were made from scrap bits lying around. I've set them up so they're switched on by the X axis enable signal, though the motors don't even get warm if on continuously.