Spindle RPM control and Z-axis homing

Hi!

I'm now almost done with my Shapeoko2 build, based on the Leadshine MX3660 stepper driver, but two small kinks remain.

The first is homing of the Z-axis. Manual homing, when working with wood for example, works well. Also, switching to auto-homing with a touch plate works fine. However, I'm not able to easily switch between the two. I know of course I could always use a touch plate (I need auto-homing for PCB milling), but I was hoping to have one "auto-home Z" and one "manually set home Z" button in Axis. Is it possible to have it both ways, or can I only chose one type of homing?

The second issue is spindle RPM. I have a "Quiet Cut" spindle, and a matching PWM-based speed controller from Inventables. The setup is a bit cumbersome, as LinuxCNC provides the MX3660 stepper driver a PWM signal (MX3660 requirement), which it in turn outputs as an analog voltage. Since the spindle speed controller needs a PWM signal, I make an Arduino UNO read the analog voltage from the MX3660, and convert it back to a PWM signal for the spindle speed controller. Cumbersome, I know, but I don't have easy physical access to the PWM pin from the parallel port. Still, it works, so I'm ok with it. The problem is however, to control the spindle RPM.

When I click the "clockwise rotation" button in Axis, it starts from 0 RPM, completely ignoring the "DEFAULT_SPINDLE_SPEED = 12000" line in my INI-file, meaning I have to click like mad on the "increase RPM" button to get it to full speed. I haven't found a way of adjusting the steps (like one would for jogging) for the spindle speed. I presume this doesn't matter much in practice, as spindle speed would normally be given by the g-code anyways, but there are cases when I would like to have manual control. Does this mean that the DEFAULT_SPINDLE_SPEED is only used when the G-code does not explicitly specify a spindle speed? And can I solve this though MDI commands and buttons in axis? (A "Set spindle 100%" button for example)? And finally, to deal with imprecisions from my digital-analog-digital conversion, can I specify more PWM/RPM relationships using spindlepwm1, spindlepwm2, spindlepwm3 etc., or is only spindlepwm1 and spindlepwm2 understood by LinuxCNC?

Just to quickly address the homing issue first, I believe I am aware of the difference between homing and touching off, but if I'm not mistaken one needs to home an axis before touching it off. This means two possibilities: either home to a homing plate (or switch), i.e. do an automatic homing. Or, if of doesn't have a plate, or simply wants to set home manually, one can disable autohoming in the INI-file and just home the axis manually in the Axis GUI (either on the work piece or somewhere random and then touch off on the work piece). I used to auto-home X and Y, and manually set home for Z. What I'm looking for is a trick where I can perform auto-home whenever I use a touch plate, and set manual home via Axis whenever I don't. The reason is that I only want auto-home for the Z axis when I mill PCBs, and then I connect the Z-axis homing switch pins to the spindle on one end, and the PCB's copper surface on the other. When working with wood, I just manually home the axis somewhere and touch off on the surface of the wood. I don't know if that makes sense?

For the spindle speed, yes, I am using 2.6.x and Axis GUI. As for the exact version, I would have to check. I didn't know that the options was so brand new. Since I'm using official Ubuntu repositories, I am probably a few versions behind. Thank you for that - saved me a bit of frustration, as this is more me being a details fanatic than any critical issue, I will simply wait I think.

If you don't mind, I just wanted to revisit the options from the stepconfig file, spindlepwm1/spindlepwm2 and spindlespeed1/spindlespeed2. I'm trying to understand how they affect the PWM LinuxCNC creates. My guess is that LinuxCNC assumes a linear relationship from 0 PWM / 0 RPM to spindlepwm1/spindlespeed1, then a separate linear relationship from spindlepwm1/spindlespeed1 to spindlepwm2/spindlespeed2, and finally a similarly linear relationship from spindlepwm2/spindlespeed2 to maximum PWM / maximum spindle speed. Meaning that if you drew a graph it would look like I've sketched here. Is that correct?

Funny, now I start thinking that you're right about me being confused about homing and touching off

After some reading I realize that it's not really confusion about homing and touching off, as much as confusion between homing and probing. What I'm trying to do is illustrated here:

Which means that I need another pin set up in LinuxCNC, a pull-up resistor and 5V source
Sorry about the confusion. I now think I need to read up on probing, since it seems I had the wrong idea all along. I wanted probing, and used homing instead, which seems to be the wrong approach (though it does "work" I suppose). Sorry, this is new to me, so the concepts confuse me somewhat.

Thanks for the update on DEFAULT_SPINDLE_SPEED - much appreciated!

Not an answer to your original question, but my preferred method to turn on the spindle at the desired speed is to go the the MDI tab (press F5), and enter S<desired rpm>M3. Thus, if you want 12000rpm, you enter S12000M3. Then press F3 to go back to the jogging/homing tab.

DaBit wrote:

Not an answer to your original question, but my preferred method to turn on the spindle at the desired speed is to go the the MDI tab (press F5), and enter S<desired rpm>M3. Thus, if you want 12000rpm, you enter S12000M3. Then press F3 to go back to the jogging/homing tab.

Yes, that sounds like a good manual override. I can't for the life of me get the RPMs to fit at all with the PWM ("non-linear" is a massive understatement), but since I'm using an Arduino between the PWM from LinuxCNC and the final PWM the speed controller is getting, I'll probably cheat and simply do the conversion on the Arudino, so that S12000M3 in your example, _actually_ gives me 12000RPM

Maybe you can use a lincurve component between the spindle speed output of motion and the PWM?