[Milling_man]

The dual stage pump is what I am saying NOT to use if you are going to use coolant. It will draw down the vacuum enough to easily boil water, which you do not want in your oil. Plus you are supposed to change the oil out daily with those pumps. You should also filter the air going into them. I do have one so I know all about them from first hand experience.

Our situation is exactly the opposite - a two-stage vacuum pump works great when cutting plastic (POM), using a coolant. We used to change the oil about once a week of continuous operation, but the reason was not coolant, but rust from the vacuum receiver After replacing the receiver with a stainless one (I bought a stainless tank from a storage water heater), the problem disappeared, and the oil lasts at least a month of work. Our scheme is as follows: a vacuum table - a transparent flask from a water filter for the primary coolant separation - a water filter for separating small chips - a receiver - a 5 micron water filter from rust in the receiver (I think we will remove it now) - vacuum pump.