Reducing the Speed of PROXXON MF70

I had problems when I milled plastics. They melt because of high speed of my PROXXON MF70. The minimal RPMs are around 5k. So I had to slow down them.
The regulation of the speed is phase control with triac. I used simple circuit of additional RC circuit and a trimer. This way, the phase capacitor C1 is charged and discharged with additional current trough variable resistor R3 and phase voltage on C2. You can achieve 5 to 95% regulation that way.

The additional elements are soldered on the original board. There is enough space for this.

Be careful of voltage and power ratings! The values I used are

R4 150k/2W Carbon type C2 330nF/250VAC Polyester (WIMA) R3 100k/1W linear trimmer (PIHER)

Be careful when tuning! The whole board is not isolated and can cause electrical shock. Keep this in mind all the time, please.

Step 1: Result

You can use audio to measure the speed. I did it.

Step 2: Work

How i did so much panels manually ? Well i will explain that next time. Thanks for reading.

Boyan Petrov LZ1FOB

Step 3:

Not quite good simulation, but it works a little bit better.