Currently (2005-) my latest CNC machine project is about retrofitting a Optimum BF20 Vario mill/drill under CNC controls. Optimum's websites gives impression of German made machines but these probably aren't built anywhere near Germany. I'm bit disappointed with quality of Optimum machines and quality of their service.

Specifications are looking quite good for the price. Trapezoidal XY screws have 2 mm pitch and are rigidly beared without any axial play. Nuts are adjustable but friction seems to grow when adjususting backlash under 0.02-0.03 mm. This is a real problem in CNC. Probably molded Moglice nuts would do the trick if I could get it somewere.

I've already finished fitting stepper for X and Y axis. I'm using MAE neodymiun steppers and AT5 timing pulleys with 2:3 gear ratio. That makes 1.5 mm movement per motor revolution.

I'm planning to make new handwheels that can be attached on pulleys so manual use would still be possible.

Some progress in the Z axis. Here you can see the Z axis plate that moves the Z cylinder of the mill. There will be a nut in the smaller hole. Stepper goes to the top of the spindle box.

The second largest hole is meant to be attachment for high speed spindle. Rotational rigidity of Z cylinder will be a problem here.

You may wonder where my workpiece holders are in the machining picures. The aluminium piece is attached to MDF piece with hot glue! Seems to be very handy way attaching this kind of workpieces. It doesn't cause any stress in part and holders will not be blocking the way when machining. Workpiece can be detached by heating.

I abandoned the previous plan of Z axis and put a huge DC servo motor for Z leadscrew. The motor has enough torque to drive directly the Z axis leadscrew with 1:1 coupling without any counterweight.

The motor I used was a Pacific Scientific 130 Vdc motor without encoder. I attached a small 'real' servo (not seen in photo) above the PacSci to get encoder signals.