G30 X50 Y50 does not move before Zprobe

mikeabuilder

This is a follow-up on a post from last week, but I wanted to be more specific in my question, so I started a new thread.

I have a Duet2 running fw 3.3...

After successfully homing X and Y, I'm getting unexpected behavior when using my touch probe to home Z.

An outline of my steps to get to the point of my question:

In config.g, I set the zprobe offset using G31 X,value> Y <value>
I home X
I home Y
Rather than calling homez.g, I run G30 X175 Y175 Z0 This is the functional command in my homez.g macro. The X175 Y175 is the center of my bed.

I expect the print head to move so that the probe is positioned over the middle of the bed, then the probe to occur and set the Z home value.

What I observe is that there is no movement of the print head, but the bed is probed and Z is homed at the current print head position.

Reading the G30 wiki page, I don;r see an explicit example of G30 with no P parameter, no S parameter, but an X, Y and Z. Is my command a valid command?

I tried moving the print head with a G0 command to a new location and then running the G30. Same behavior.

I tried running adding P0 (G30 P0 X175 Y175 Z0). I got no movement and no Zprobing.

I also ran a G31 to verify that my probe offsets were correct.

In a previous version of my homez.g, I used a G1 command to move the print head to the center of the bed, then a G30 (no parameters) to home Z, and it worked perfectly, but I needed to add the probe offsets to my G1 command. I thought the change would eliminate one line of gcode and also automatically add the probe offsets.

Any thoughts?

Here's my complete config.g config.g

fcwilt

@mikeabuilder

Your previous approach was correct.

Use a G1 taking into account the probe offsets then the single G30.

Frederick

droftarts

@mikeabuilder See G30 in the GCode dictionary. To use X and Y in a G30 command, you need a P parameter as well. And if you have a P parameter, you need an S parameter. And that S parameter has to be positive, so it's not homing. Indeed any G30 P... command is "used for operations that are performed after the printer has been homed and that require the height error at more than one probe point to be measured."

Ian

mikeabuilder

Thanks for setting me straight.

A follow up question regarding our observations when we ran G30 P0 X175 Y175 Z0 from the web interface. We saw no movement, but I expected that the print head would move and probe to "collect" P0.

Seeing this line in the G30 wiki in the "with a P parameter section" makes me see our error.

If a "normal" Z parameter is given instead of -9999 or lower, then the bed is not probed, but instead that value is used as if the Z probe had triggered at that height.

What we actually did with this command was to tell the Duet to set Z=0 to the current Z position of the bed.

What we should have done is G30 P0 X175 Y175 Z-9999*. This would have moved to the probe to the (175,175) and captured the height.

It's tricksy, this gcode business.