The spindle on this system has been used on two previous CNC machines. It is a Bosch 1617 that has been converted to be a shunt motor. The shunt motor has a far flatter torque curve than the universal motor. But, especially with heavier cuts, it does bog down a little. I decided to convert this to a closed loop system. The method I chose is a Super-PID 2. This changes this:
To this:
My previous cutting experiments were running in the 3000-4000 RPM region, but the lowest setting on this unit is 5000 RPM. So I set it to that and increased the feed rate a bit. It looked like I had some room anyway. The SuperPID does seem to be able to hold the speed ok, but it is hunting a bit when the cut load changes. What I am missing is an indication of power usage. I do have a Kill-A-Watt power meter connected, but this is a pretty blunt tool.
My test cut was on a 316 Stainless block, with a cutting depth of 0.02", a feed rate of 16 IPM and a step over distance of 0.125". The result was interesting. I noticed several things: