I wonder if caustic soda is an element of the bleaching/whitening agents in your paper?

Paul

Interesting, we mill a lot of aluminium for our label application machines and never have this problem. So we can assume that it is the paper?

Our engineers never use paper to raise, or clamp surface protect and I never have a problem with their finishes, as I am the BOSS who has to be pleased before a machine leaves our factory. All our aluminium is anodised in either natural or red finish and again this always looks great.

If your milling the edges as you say and raising the piece to clear the bed the paper your using must be very thick to achieve this, so why not use another piece of plate to raise it?

Just a thought

Bri

Just a thought that the aluminium, paper, cast iron (presumably) bed and acidic coolant would make a reasonable battery so the effect could be electrolytic.

Hi Chris

I wonder if the clear semi rigid plastic A4 sheet as supplied by office supplies for ring binding would work as well as paper. Being plastic it would creep a little under compression but I doubt it would creep very much. It is not particularly slippery.

With luck you will have an old manual or similar to use for a trial.

Being an insulator electrolysis would be stopped. And no problem with the PH.

Regards
John

A further thought…waxed paper might help

There is a couple of reasons, 1st to look at is the Ph of the coolant. If new coolant still does the same result, it could well be an electrical issue with you mill . A bad earth or insulation breaking down and creating electrolyses.

Seen 1st hand what happens when a motor windings have the insulation breaking down. Even though you do not get an electrical shock, there is current running through it causing electrolyses.

Neil