This article is a followup to my article on the conversion of a g0704 mini mill to a CNC machine using LinuxCNC. To reduce the backlash on the machine I have upgraded to ballscrews on all axes. To get faster spindle speeds and lower noise, I've upgraded the spindle to a pulley drive, while keeping the quill working.

My open-source designs for both upgrades are included below.

Ballscrew Upgrade

The CNC conversion of the G0704 using leadscrews worked well, but there was still quite a bit of backlash. The machine worked well for larger parts, but machining small holes was inaccurate. With ballscrews, I've got the backlash down to 0.003". I've also converted the machine from Metric units in LinuxCNC to English units and it makes small, beautiful cuts now.

The gameplan for my ballscrew upgrade was to swap out the leadscrews on all axes with C7 ballscrews, which I ordered straight from a manufacturer in China. You'll need a 350mm, a 600mm, and a 800mm ballscrew. I used DFU1605 (DFU is the double-nut version). I received the ballscrews with the ends machined in the normal way and then machined them myself as shown here:

The conversion uses 2x NEMA 23 motors and 1x NEMA 34 motor. The drivers are the same DM556E Leadshine stepper motor drivers used in the leadscrew CNC conversion.

You'll also need 4x M12 retaining nuts, 3x 7001 12x28x8mm P5 DB paired angular contact bearings, and a single 6000 ZZ 10x26x8 bearing.

I machined all the mounting parts for the upgrade kit on the mill, but they can be easily ordered from a company that cuts waterjet parts. I highly suggest you waterjet these parts, and then machine the necessary countersunk holes and various features to spec.

CNC Conversion Design Files

The dxf files for waterjet cutting are available on Thingiverse:

The drawings for final machining are here: g0704-ballscrew-drawings.pdf.

The G0704 Saddle will also need to be machined as described in this PDF by

Spindle Pulley Conversion Upgrade

The main limitation of the G0704 is the spindle. It runs far too slow for CNC operations and is quite loud.

There are several options to convert the gear-drive to a pulley-drive system, but these options often remove the ability to use the quill or require expensive retrofit parts. In particular a new part that interfaces with the splines on the quill would require a difficult broaching operation.

I've come up with a solution that allows conversion to a much quieter pulley drive while keeping the quill. It does not require machining of a new part that interfaces with the spline, but re-uses the existing hardware.

Using this design and the default motor, my machine can hit 3000 RPM on the higher pully ratio and 2000 RPM on the lower ratio. Even running faster, it is much quieter than using the original plastic gears.

You'll need a 3L190 V-Belt, 2 long M3 bolts, 7 set screws, and some aluminum.

Pulley Conversion Design Files

The dxf files for waterjet cutting and the 3D printed pulley covers are available on Thingiverse:

The drawings for final machining are here: g0704-pully-conversion.pdf.

The two pulleys were machined on a lathe from 1.5" and 2" stock, cut round-ish on the bandsaw and then machined to spec. The standoffs were cut from aluminum barstock and the other parts were waterjet from 0.35" aluminum plate.

Pulley Conversion Guide

Start by stripping the head as described in this guide by

Install standoffs into the rear lower plate. Then install the lower plate onto the mill. Install the front lower plate as well. Here is a photo of the rear lower plate installed along with the standoffs:

Re-install the spindle and bearings. Attach the motor to the top plate and install it. Install the machined motor pulley. Note, you must use threadlock on the set screws in this pulley. If you do not use threadlock or it is poor quality, the pulley will fall off!

Connect the machined sensor disk to the machined spindle pulley.

Re-install the RPM sensor.

Install the 3L190 V-Belt and insert the spring.

Finally, re-install the drawbar and spindle cap. Note the small aluminum washer in the left of the photo. This should be cut to hold down the spring. I did not model this part, but cut it so the cap fits inside the lip of the washer and the drawbar can pass through.