I see others have had this problem in the past, but I don’t see what the answer was(?).
So, twice in a row while cutting the router starts going deeper. Once at the start of the job and today in the last minutes of the job. I heard a sound change ( I was working at my bench), rushed over at the cut had plunges a full 1/8 of an inch deep into the spoil board. The first time it started to plunge while it was moving to the starting point of the cut from the centered zero position (0:0:0).
The blank was secure. It was attached to a spoil board which was sitting on the deck. The blank was attached to the spoil board using painters tape on the spoil board and the bottom of the blank and the tape was glued using CS Glue. The spoil board was clamped to the deck with hold down clamps.
I use the precision collets and the bit did not slip or move during the operation.
I’m running a Shapeoko Pro (the 4 version - uses belts) and Carbide Motion Build 564 (not the latest build).
The cutter - a 1/8" FEM - looked fine. I use the precision collets and they hang on to the mills quite well - I have to use soft grip pliers to remove the collet and mill. The mill then slips out of the collet. In other words, I have to remove the collet from the machine to remove the mill from the collet. This happened twice and I used a different 1/8" FEM each time.
Here in the Seattle area, we are experiencing a cold snap. Teens and low humidity, the shop had 10 percent this week. It could be static. I have grounded my machine and still experience issues during this cold snap. “Z” zero, origin zero. Fun and games. Put a big pot of water on the wood stove to help.