VFD spindle control safety

[Kitwn]

At present I'm following Doddy's principle of taking what I see as an acceptable risk when tool changing but I'm aware my machine has a built in risk which is that the relay that starts the spindle will pulse briefly during power up/down of the controller. I use a cheap Chinese breakout board and LinuxCNC. The relay on the board operates a relay on the wall that activates the spindle and the dust extractor.

Not a problem when it's all switched on but if I wait long enough there'll be a power cut just as I have a firm grip on a tool to pull it out of the (still quite tight) collet and there'll be enough stored charge in the VFD capacitors to modify my finger prints.

It's all a balance of probabilities but reading this thread does remind me I should add some kind of interlock. Perhaps a nice big switch in series with the VFD control relay which includes a back contact for a warning light. I have all the necessary bits in the shed so it's not exactly beyond what is 'reasonably practicable' as the legislation says.

I would never criticise routercnc's KISS approach but know myself well enough to predict the odd oversight, especially towards the end of a tiring day and am therefore in favour of the more automatic control for my own machine.