Different XY speed for probing moves

[tekkydave]

@fcwilt when homing it uses the Fxxx value in the G1 command which is usually much lower than the max. I think there needs to be another speed parameter in M558 or G30 to cover the G30 lift speed. Or it should use the dive speed for the lift. Maybe this is a bug?

[droftarts]

G30 dive speed is controlled by the M558 F parameter. The speed the probe then lifts in Z, and moves to the next probe point, is controlled by the M558 T parameter. If this is higher than the max Z speed set in config.g, then max Z speed is used. Make sure your Z is capable of actually running at the max Z speed you have set! So, not a bug.

If you want slower lift speeds, you could reduce max Z speed (and/or jerk and acceleration) before probing, and revert afterwards. If repeated probing shows the gap getting smaller, or is inconsistent, your Z axis is probably skipping steps, and you need to tune jerk, acceleration and max speed until it doesn’t.

Ian

[tekkydave]

@droftarts Surely the T parameter is for the X & Y axis speeds. Why would it be applied to the Z axis at all? It assumes the Z axis has the same speed capabilities as X & Y. Only the Z max speed is stopping it from moving too fast. If that is set correctly then all is good but it may not be for someone setting up RRF for the first time.
Whilst I agree this isn't a bug as it is probably designed to work that way I think its something that needs looking at.
I would rather see the lift speed being set by the F parameter (the first one if there are two as in the most recent releases). Either that or a new parameter for lift speed in M558.

[dc42]

@tekkydave if the Z max speed isn't set up correctly, users will have other issue besides this one. I'm sure that your suggestion of using the F speed would annoy many users, because it would slow down probing.

[tekkydave]

@dc42 Fair point and I suppose it depends on the system. On my D-Bot I probe at 6mm/s (F param). It moves between probes at 150mm/s (T param). On each probe it only lifts 3mm. It tries to do it at 150mm/s which is way beyond the capabilities of the Z axis which has a max speed of 10mm/s set.
Therefore it probes at 6mm/s & lifts at 10mm/s. To a raw beginner it may not be obvious what is going on. In my case it would only have a minor impact on probing speed but if a system was lifting say, 20mm between probes then it would.
Maybe just a note in the M558 gcode documentation to clarify that it will attempt to move all 3 axes at the Tnnn speed to avoid any future confusion.

[dc42]

@tekkydave I have added note to the description of the M558 T parameter.

[tekkydave]

@dc42 Cheers. I still think the Z lift speed should have it's own M558 param but I'll shut up and go away now

[fcwilt]

@tekkydave said in Different XY speed for probing moves:

@dc42 Cheers. I still think the Z lift speed should have it's own M558 param but I'll shut up and go away now

Did we verify that the T parameter is actually being used for the Z lift speed?

Or does it simply use the Z max speed from M203?

If the Z max speed is putting on limit on the Z lift speed you, in effect, have the "missing" speed parameter from M558. Just temporarily set Z max with a M203 before you begin probing and restore it when done.

I would test it myself if I didn't already have a two page "to-do" list that I need to attend to to get ready for summer.

[tekkydave]

@fcwilt Just tested it by changing my M558 from:

M558 P1 C"zprobe.in" R0.25 H3 F360 T9000 A5 S0.03

to

M558 P1 C"zprobe.in" R0.25 H3 F360 T540 A5 S0.03

and the lift speed went down from 10mm/s (z max speed) to 9mm/s (540mm/min)

so yes - it is using the T param to control the Z speed.

[fcwilt]

@tekkydave said in Different XY speed for probing moves:

@fcwilt Just tested it by changing my M558 from:
so yes - it is using the T param to control the Z speed.

Thanks much.

I've never encountered this issue before because I have always set my max speeds based on testing well before I get around to dealing with a probe.

Good to know how it actually works.

Frederick

[Nahsiro]

@fcwilt I actually set all the probing move speed a lot lower when I wasn't printing a lot but it was apparent to some extent. I kinda just lived with it because it doesn't skip steps when the rods are clean and lubed. Also, things like the dive height also affected how quickly it would start to loose steps. A short dive height < 5mm worked better. And probing a single point was not as dramatic as multiple points. My max z-axis speed is probably somewhere between 600 and 700 mm/min, so depending on how much friction the threaded rods experienced, it would z probe fine or not.
I also only truly started to investigate when I started getting "motor phase may be disconnected errors".
I checked all the motor wires and found no issue there
Then I started visibly seeing step lost in Z. Plus I also wanted to probe faster and be hands-off as much as possible in the pre-print process.
Lessons learned:

• keep threaded rod lubricated (obviously)

• Read the fine print of my gcode commands and understand how they inter-relate

• give myself some room around the max limits of the machine in the config.

Thanks to you all for helping me learn a bit and solve this issue.
Thanks @dc42 for adding the note in the documentation.
@tekkydave I second having the z lift speed independent for probing.

[Phaedrux]

Does it really need to be a separate parameter in M558? It's got nearly a dozen as it is and it's quite easy to modify the Z max speed before and after probing. bed.g and mesh.g seem like the right place to control this and it's possible right now.

[tekkydave]

@phaedrux I can't disagree with the number of parameters on M558 but equally I can't understand why we have the Z lift speed being controlled by a parameter intended for XY movement.
In theory I could have my Z max speed set to a crazy value but it not affect any other movements as they all have their own speeds specified. Only M558 will cause issues when it tries to lift the probe at say 150mm/s.
Sure every printer should have it's limits set up correctly but for me it's an inconsistency in the probing process that needs looking at.

[Phaedrux]

@tekkydave said in Different XY speed for probing moves:

Only M558 will cause issues when it tries to lift the probe at say 150mm/s.
Sure every printer should have it's limits set up correctly but for me it's an inconsistency in the probing process that needs looking at.

Well I'd say if you don't have a sane limit set for Z max speed the issue will arise at some point eventually. I'll admit though I was surprised that M558 T had an effect on Z at all. I had assumed it would have just used the Z max speed as default.

[gloomyandy]

@phaedrux I may be wrong, but doesn't the F parameter to G0/G1 apply to all axis (including Z)? Isn't the T parameter to M588 simply specifying a feedrate to be used during probe operations? If both of the previous statements are true, then I'd be surprised if T did not apply to Z.

[Phaedrux]

@gloomyandy Yes. And usually the Z axis max speed would be set low enough to limit it to a safe speed in all cases so it's never really noticed.