Step 1: See mill, get mill

Proxxon product page

This was something of an impulse purchase on eBay, and I have to thank TSD for offering experience in what's good and bad in mills and CNC conversions.

The owner was using this as a key-cutting machine but was upgrading. The only slight drawback was a small pocket milled into the bed at one end which held the key-cutting fixture, but that's no biggie. More importantly, it was a tidy conversion using decent motors and the machine could be shown working.

The important specs are:

• Table 200 x 70mm
• X travel of 134mm
• Y travel of 46mm
• Z travel 80mm
• 1mm/turn on each leadscrew
• Variable spindle speed 5,000 - 20,000rpm
• Collets for 1.0 - 1.5 - 2.0 - 2.4 - 3.0 and 3.2mm diameter cutters
• Actually designed to mill metal, unlike many cheap / small hobby ones from China:
  • “grey-cast iron, hardened cast iron, steel, cast steel, brass, aluminium, glass, plastic and carbon fibre”
• um, stuff.

So, yes it's tiiiny but for learning that doesn't matter - with a big mill you can make really big fuck-ups, this little thing fits on the desk next to my computer so I can fart about learning G-Code and stuff sat in a comfy chair with a cup of tea and the entire internet to answer any questions.

And yes it really can mill hard metals with the right cutters, from Proxxon's website:

NO 27 116     3 pieces
NO 28 758 	Ø 1mm
NO 28 759 	Ø 2mm
NO 28 761 	Ø 3mm

This is where a properly designed & built mill (even a tiny one) stands above a lot of the cheaper stuff flowing out of China - precision, rigidity, and reliability cost money. You may not need them if you're doing occasional hobby stuff or using soft materials, but I'm likely to do a fair bit in metal, as well as a bit of PCB work, so it's nice to know I can.

The mill had a previously done CNC conversion (stepper motors mounted where the hand wheels used to be and a driver board to control them), you can buy mills which are CNC out of the box but it's usually cheaper to DIY it as there are more manual mills kicking around. As with any modifications, some people make a nice job of it and others commit a total lash-up, so you've got to be wary of what's been done - especially if they've butchered the machine beyond the point where you could restore it to a nicer condition.

The motors are decent Mclennan 23HSX206 steppers, nicely mounted using carbon-fibre and Oldham couplings.

The motor specs are:

• 200 steps/rev (1.8deg/step)
• 3A max current
• 60n/cm torque from 0 to 6000 steps/sec

The controller is a cheap no-name TB6560 3-axis parallel port controller + 24v PSU.

The specs claim from a similar eBay advert:

• Toshiba TB6560AHQ chip - High power, maximum 3.5A drive current .
• Professional design, two-stage signal processing, super anti-jamming.
• 1-1/16 microstep setting - Higher accuracy.
• Adjustable drive current settings for each axis - 25%,50%,75%,100% of full current can be set for different stepper motors .
• Overload, over-current and over-temperature safety - Full protection for your computer and peripheral equipment .
• On board current switching - Power output can be set according to specific user requirement .
• Relay spindle interface - Outputs Max. 36V 7.5A for spindle motors or coolant pump (only one device can be powered by this output!)
• 4 channel inputs interface- Can be used for XYZ limit and emergency stop .
• Bipolar constant current chopper drive with non-resonant region .
• Full closed-type optical isolation to protect the user's computer and equipment
• Four control inputs (divided into pairs of knives) - Allows setting of limit and emergency stop.
• Universal architecture - Supports most parallel software MACH3, KCAM4, EMC2 etc.

Voltage Selection:

• 12-16V DC power supply for Nema 17 stepper motors
• 16-24V DC power supply for Nema 23 stepper motors
• 24-36V DC power supply for Nema 34 stepper motors