LOL - Hey Kolias it's your gig, your free to do this however you like.
You posted a link to your manufacturer's manual and refered to page 9 fig 8. For some reason you've decided to ignore it and come up with your own scheme - that's cool - nothing wrong with that per se, but here's a couple of questions for you.
Q: In THEIR scheme what happens if you accidentally earth your clip or if your tool is grounded (which they often are and worse intermittently)
A: The probe input is activated, Mach lights a LED and it gets better - if you're probing - Mach stops.
Q: In YOUR scheme what happens if you accidentally earth your clip or if your tool is grounded (which they often are and worse intermittently)
A: Absolutely nothing (to alert you) and it gets worse - if you're probing OR go on to probe (because remember you've had no sort of indication) - Mach just carries on and probes it's way through your table. Sh1t you say to yourself as you race for the E-Stop - maybe I should have listened to that tosser Stirling.
Personally I do it slightly differently - I reverse the scheme in your manual and ground my spindle with the clip and I put my plate onto the input. Why? because then I don't care if the spindle is grounded by itself or worse intermittently grounded because I now KNOW it's grounded. Of course this only works if your table and work are not metal and grounded but that's the case here. Anyway - even if you have a metal table, you can't have the plate AND the tool at ground if you want any "ohmic" contact scheme to work so you're going to have to insulate at least one of them and the plate is usually easier.
The point is, EITHER way you do not need a resistor - you're better off without it. In yours the only reason you need a resistor is (IMVHO) to bandaid a poor solution.
But like I say - do it any way you like - it's your gig.
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