Mini lathe conversion to CNC

Interesting. That homing process sounds pretty straight forward and should give repeatable results as well. The only issue I can see with that is some stepper motor/servo have a tendency to jitter or move slightly when it's first powered on. If that happens then it would throw off your last home position that you saved. Have you ever experienced that?

My plan is to use one proximity sensor for limit and homing function for each axis. I still have to wait for some more parts before I can get that going.

Interesting. That homing process sounds pretty straight forward and should give repeatable results as well. The only issue I can see with that is some stepper motor/servo have a tendency to jitter or move slightly when it's first powered on. If that happens then it would throw off your last home position that you saved. Have you ever experienced that?

If I'm chasing accurate diameters, I always chuck some scrap and confirm that the diameter Linux CNC thinks it's making is the diameter it's actually making. Then I touch off X on the measured just machined diameter to compensate for the x=0 in machine coordinates being a little off.

Every now an then I'll do the above, command the machine to X=0 in part coordinates, turn off the drives, then command the machine to X=0 in machine coordinates and re-home.

I always command the lathe back to the home location when I'm done, so it starts up pretty close to x=0, as you noted sometimes the axis jiggles a little on startup. Having a real home switch on the X would be a real timesaver though!

Wow it's been such a long time since I last did some thing on this conversion that I almost forgot about the thread. Most of that time I only used the lathe occasionally making some odd parts here and there by hands. Anyway right now it has NEMA 23 stepper motors, driven by two Gecko G251X controllers. A PNP N.C. type inductive proximity sensor is installed for limit/homing for each axis. My next step is wiring up an e-stop button because I want to add some protection in case any thing goes wrong and a tool crash. On the Gecko G251X there is a disable pin that is supposed to stop the stepper motor when shorted to ground (common pin). So I'm getting a N.O. contact block to wire up to those terminals. I have plan to stop the lathe motor in case of emergency by wiring up a N.C. contact block to the motor controller's on/off switch wire. I don't know if the Mesa 7i76 board has some terminals I should hook up the e-stop wiring to, to notify it when the button is pushed ... I would think it's a good idea to let LinuxCNC know. I'll have to look into this later as I've been away from all this for a while.

- Tim

Hi Andy,
I have another N.C. contact block that I can use to connect to the 7i76. Am I right in thinking that my +24V goes to the E-stop switch, then run the other wire from the switch to one of the 7i76's field input connectors?

Okay, I got the switch hooked up and it does disable the stepper motors when I press it (it's a latching type push switch). But on my Axis screen, the X button (emergency toggle) does not show it's pressed down. I've checked the "Show HAL Configuration" screen and can verify that it does change status from brown to yellow when I press the switch. Why the X button doesn't change when I press the switch I don't understand.

Hi Andy,
The button is connected to a signal called estop-ext. Attached is a screen shot of my HAL Configuration screen.