Neale: Cheers - you're right, you're optimistically trying to keep to within a few microns (hah!) under a varying surface. But, by far the worst effect is the warp on what is a flexible board. Flattening is the first tool in the armoury. (Re. first.... this is definitely not the first time I've tried, but the first time I've had what I consider good success. Driven on by eyeing up a £1750 PCB router on flea-bay the night before, I figured (a) don't have the space, (b) wtf am I doing with the Starmill.... turns out the star mill can be pretty precise, once I've had it in many bits, and replaced the crashed limit sensor).

m_c: Agreed - in principle, I gave my vacuum table (bought for this purpose when I had the MD router) away. I would say that I could easily adapt my PCB fixture plate to be a vacuum table. I'm curious about using the compressor - I do have a 50l silent compressor (recent casuality of the failing pub trade... collateral damage of Covid), but curious how to change a blow to a suck??? Besides, I do have a vacuum pump somewhere... and if all else fails then I have Henry (or the Wicks equivalent).

I was thinking more about this last night. I have the luxury that the StarMill is.. a mill. I don't have to chase the spindle around, I just need a device that is referenced to the column. so this might be easier (and cheaper) than I previously thought. Certainly a spindle-mounted device (where I started thinking) is entirely the wrong approach.