Low tack is possibly not the best way to go David, it would be quite easy to lift the edge of a low tack tape while machining which would then allow the paint to bleed under the tape when applied.
What you want is a removable vinyl, one that comes off clean & doesn't leave lots of glue residue behind. I would try & get some samples of Paint mask films & short term removable vinyl films. If your not using a liquid coolant then even a medium tack application tape might do, that would be the cheapest option if it worked.