Height Map and Leveling Issues + Head Movement

[Veti]

can you turn off the bed compensation and see if the movement still surges?

what can happen is that while moving, it needs to adjust the z position. so it needs to slow down and wait for it to happen.

[dc42]

The clue to the height map is that RRF probes alternate rows in alternate X directions. So ridges parallel to the X axis indicate that the nozzle height and/or the probe height depend on whether you approach the point from the +X or -X direction.

The surges you mention are a direct result of the height map. RRF is slowing down motion at the peaks ans troughs of the ridges in order to meet the Z jerk limit when crossing them.

[tdm418]

Thanks for all the input.
@infiniteloop - I have two screws that are not physically connected or synced.
@Veti - Yes, turning off compensation allows for smooth movement
@dc42 - So why would this problem suddenly pop up, and what is there to be done about it?

[Veti]

@tdm418 said in Height Map and Leveling Issues + Head Movement:

So why would this problem suddenly pop up, and what is there to be done about it?

worn down bearings for example.

your print head assembly is not rigid enough and allows for roational movement

[tdm418]

The printer is only a couple of months old. Everything is still tight and responsive, and I regularly check all my bearings, belt tension, and print head assembly. Also, the problem is surfacing during mesh compensation, which doesn't stress any of the mechanisms or head very much at all.

[Phaedrux]

Can you post your config.g, bed.g and homing files?

How is the BLTouch mounted?

[tdm418]

Here it is:
The BLTouch is mounted on a modular printhead design specific to it.
It is shimmed with a couple of nuts, but it is rock solid.

config.g
bed.g
homeall.g
homey.g
homez.g
homex.g

[fcwilt]

Hi,

Try writing a macro that does a series of G30 S-1 commands

That command probes the bed are the current X,Y position and reports the triggered height of the Z probe.

It will let you know if the probe is consistent.

You can try different X,Y locations and compare the results.

Frederick

[Phaedrux]

In homeall.g and bed.g

M401 ; deploy probe
G30 ; home z0
M402 ; retract probe

You should remove the M401 and M402. Unnecessary since the firmware will deploy and retract as needed.

From config.g

M558 P9 H5 F500 T6000

Your dive speed is 500mm/min but your maximum Z axis speed is set to 360mm/min. Either way this is higher than the recommended speed of 120mm/min. I don't think this explains your heightmap, but it should help the BLTouch be more consistent.

G31 X35 Y0 Z1.202 P5

The P value is for trigger sensitivity. For the BLTouch it's recommended to be P25.

[tdm418]

@fcwilt, there was little consistency moving the probe and testing different areas. There appeared to be good uniformity, as one corner of the bed gave low values, and the other corner gave high values, and all points in between seemed to be pretty linear in their reported values. But overall, from the minimum value to the maximum was over 1mm. This is probably symptomatic of the problem, but I still don't have any idea what the problem is.

@Phaedrux, I edited the files as you recommended. Reran mesh compensation and the height map has the same patterns in it. It appears lower relative to the mesh, but not much else has changed.

[fcwilt]

Hi,

Sorry I wasn't clear.

I wasn't expecting different areas of the bed to give the same reading, I was just interested if the probe gave consistent readings when repeated at a given position, regardless of position.

Different positions are going to likely yield different readings but any given position should yield consistent readings.

Frederick

[Phaedrux]

You can try adding some rest time between probe points to let the bltouch settle.

M558 R0.5

But that pattern would appear to be mechanical in nature. Backlash.

[infiniteloop]

@tdm418 If you height map still shows this „sawtooth“ pattern over X, it might be worth to rethink the clue @dc42 gave you: maybe your X-axis, the print carriage, the head or some part of it has come loose and can tilt a bit? At least, I can’t imagine anything but a mechanical reason…

[tdm418]

@fcwilt, I do get pretty consistent results in the same location. I was under the impression that the value returned was the z offset to the from the nozzle, or more from Z=0, to the height that the probe triggers at. If that is the case, why shouldn't the value be the same regardless of the probe's location, as that is pretty much a fixed distance?

[tdm418]

@infiniteloop, I have poked, probed, and prodded every component on this printer and can find nothing loose, slipping, or moving. It seems like the logical and probable cause of my pattern, but I can't find anything at all...

[jens55]

@tdm418 said in Height Map and Leveling Issues + Head Movement:
why shouldn't the value be the same regardless of the probe's location, as that is pretty much a fixed distance?

Because the glass isn't flat, the mechanics aren't perfect and there really isn't anything in this world that is a 'fixed distance'. Heck, even continents move!

[jens55]

An interesting thought since I also have this kind of a sawtooth pattern ....
If I manually move to a given point on the bed while approaching it from the left, take 10 measurements while staying at that point, then move further right and return, this time approaching the same point from the right and take 10 measurements .... should I see a discrepancy of the second set of numbers compared to the first set?
I think I will run that test and see what happens, should be interesting to see the outcome!
Is there a way to probe the bed that doesn't involve the linear travel and uses a more random pattern ?

[Veti]

@fcwilt said in Height Map and Leveling Issues + Head Movement:

Try writing a macro that does a series of G30 S-1 commands

here is a link to the complete m48 macro
https://forum.duet3d.com/topic/6962/m48-measure-z-probe-repeatability-and-print-to-serial-output

please run at different positions

[tdm418]

I am traveling for the next couple of days. I'll try it and let you know when I return.
Thank you

[tdm418]

So I have once again gone through the entire machine, tightening and testing. I did notice that there was some wobble motion in the Z axis during Mesh Compensation. So I reconfigured the leadscrews to get them a bit off the center of gravity for the bed and tore apart the guides. There was a backplate that had cracked, and whether that was the issue or not, the bed now moves smoothly and with no unwanted motion.
Unfortunately, the height map is no better than it was initially.
A great suggestion and link from @fcwilt and @Veti - The results are below. I have only had time to run about five tests,one in the center and at each corner:

11/22/2019, 11:25:01 PM M98 P"0:/macros/BLTouch/BLTouch Uniformity Test"
G32 bed probe heights: 0.138 0.140 0.140 0.140 0.138 0.135 0.138 0.135 0.135 0.138, mean 0.138, deviation from mean 0.002

11/22/2019, 11:19:56 PM M98 P"0:/macros/BLTouch/BLTouch Uniformity Test"
G32 bed probe heights: -0.130 -0.130 -0.130 -0.130 -0.132 -0.130 -0.132 -0.132 -0.132 -0.130, mean -0.131, deviation from mean 0.001

11/22/2019, 11:26:56 PM M98 P"0:/macros/BLTouch/BLTouch Uniformity Test"
G32 bed probe heights: -0.350 -0.345 -0.345 -0.345 -0.350 -0.352 -0.354 -0.350 -0.354 -0.354, mean -0.350, deviation from mean 0.004

11/22/2019, 11:28:40 PM M98 P"0:/macros/BLTouch/BLTouch Uniformity Test"
G32 bed probe heights: 0.465 0.463 0.463 0.465 0.463 0.463 0.465 0.461 0.461 0.463, mean 0.463, deviation from mean 0.002

11/22/2019, 11:30:19 PM M98 P"0:/macros/BLTouch/BLTouch Uniformity Test"
G32 bed probe heights: 0.758 0.760 0.758 0.758 0.758 0.760 0.758 0.760 0.758 0.758, mean 0.759, deviation from mean 0.001

It seems like this is indicative of pretty good uniformity, so unless I'm missing something, I still have not found my gremlin.