Electronics

I originally bought the Leadshine MX3660 which is an integrated 3 axis digital stepper driver and breakout board. It worked well for the first part of the build but has no provisions for an encoder. I didn't understand at the time but you don't need a breakout board. All you need is a Mesa 5i25 (or 6i25 if you have pci-e slots) and a 7i76. Mesa sells this combo for $200 and I recommend you just start with that. I swapped out the MX3660 for the Mesa 5i25/7i76 combo and bought Leadshine DM556 (x/y) and AM882 stepper drivers off ebay. I'm not sure if it was the Mesa hardware or the stepper drivers but the mill ran incredibly smooth after the upgrade. With the MX3660 the motors would whine a little while idle and my rapids were half the speed I expected them to be.

For stepper motors I bought a Keling KL34H295-43-8A Nema 34 906oz motor for the z axis and two Keling KL23H2100-50-4B Nema 23 570oz motors for the x/y axes. These are very powerful and have worked great. I run them all at 48V with a 12amp power supply I bought off ebay.

You need a functioning e-stop button. I bought one off ebay. I also bought proximity limit switches, a number of toggle switches, momentary switches, relays, Solid State Relays, and lots of 3,4,5 pin 16mm panel mount XLR connectors. I bought most of these electronics off ebay. The shipping from China is actually quite fast.

I used the XLR connectors to make a panel on the electronics enclosure. That way the cables go from the panel to the electronics and it's easy to unplug and replace/move components. Soldering all the XLR connectors was a lot of work but I still feel some sort of panel based system is needed. I also used a lot of 18/4, 18/2, 22/4 shielded security wire from Home Depot to wire everything up.

For rigid tapping you need a quadrature encoder and an index pulse. The encoder can be scaled, the index pulse must match the spindle rotation. In my case with a 1:2 pulley ratio (one motor turn, two spindle turns) I found it easiest to mount the encoder on the back of the motor and a separate index sensor on the spindle. The index sensor is a simple slotted photo interrupter. I used the original g0704 speed sensor and filled in all the holes except one. That provides a nice index pulse.

Rigid tapping was hard to wrap my head around but it's actually very simple in Linuxcnc. They slave the z axis travel to the spindle rotation. Instead of trying to force the spindle to go a very precise speed while the z axis is descending the linuxcnc control will adjust the z axis speed to match the spindle rotation. It uses the quadrature encoder for this matching and the index pulse is used so you enter the hole at the exact same spot every time. I rigid tap all the time at 1500rpm with no issues.

I chose to run all my electronics at 12v because I have the mini-itx computer in the same enclosure as the mill hardware so a 12v tap off the power supply was easiest. You should run 12v or 24v. 12v led switches are much easier to find and was a large factor in my choice. I like the lit switches so you know at a glance whether something is on or not.