Mesh compensation results backwards

fcwilt

Just remember that when checking the Z=0 position of your tools it needs to be done at the same XY point you used for setting the Z=0 datum, otherwise bed unevenness may affect the reading.

And mesh compensation should be disabled.

Frederick

Gamefanatic3D

@fcwilt
I ran a similar test to what you were asking, I think.

I turned off mesh compensation and measured at my typical 0 (X200, Y200) location with a feeler gauge (0.8mm) and then moved to a spot that was lower and found that I needed to move the head down. The results were very different from what was recorded either by my manual mesh macro attempts or the systems.

I believe the deviation the probe is finding is accurate, but for some reason is not being applied properly when the tool is engaged and thus having a larger than a normal gap. Not sure about this quite yet.

fcwilt

@gamefanatic3d said in Mesh compensation results backwards:

I believe the deviation the probe is finding is accurate, but for some reason is not being applied properly when the tool is engaged and thus having a larger than a normal gap. Not sure about this quite yet.

That is why you need to verify, using the procedure I suggested, that when a tool is positioned at Z=0 the nozzle will be just touching the bed.

It may be simply a question of the Z offset setting for the tool is not quite right.

Frederick

Gamefanatic3D

@fcwilt
I'm not sure if you saw my comment, but I have performed the procedure. I didn't drag the head across the bed, but rather my feeler gauge. The result was there was a gap at the end as I expected. Rather that was coming from the gantry or the bed height I could not tell you, but there was a variation in the height from when it started to when it finished.

I'm not sure if your goal in this was to prove there was variation in the bed or that mesh leveling had been turned off successfully. I know that my bed leveling measures at X180 Y200 and my typical measuring point is X200 Y200, and have tested the gap at both locations with and without the mesh compensation engaged. Each time I get the same result.

If it seems that I'm not providing you the feedback you are looking for, I may just be miss understanding the intended goal or I may not be describing it correctly?

fcwilt

@gamefanatic3d said in Mesh compensation results backwards:

@fcwilt
I'm not sure if you saw my comment, but I have performed the procedure. I didn't drag the head across the bed, but rather my feeler gauge. The result was there was a gap at the end as I expected. Rather that was coming from the gantry or the bed height I could not tell you, but there was a variation in the height from when it started to when it finished.

I'm not sure if your goal in this was to prove there was variation in the bed or that mesh leveling had been turned off successfully. I know that my bed leveling measures at X180 Y200 and my typical measuring point is X200 Y200, and have tested the gap at both locations with and without the mesh compensation engaged. Each time I get the same result.

If it seems that I'm not providing you the feedback you are looking for, I may just be miss understanding the intended goal or I may not be describing it correctly?

It is likely that I am not making myself clear.

My goal is to verify that the Z probe Z Trigger Height setting is correct and that the Z Offset settings of the tools are correct.

The point of setting the Z=0 datum is to get the logical Z position (what the firmware "thinks" the Z position is) to match the actual Z position.

If the Z probe Z Trigger Height setting is off then the logical Z position will be off.

When you have a single tool printer like mine to verify that the Z probe Z Trigger Height setting is correct you position the nozzle at the exact same XY point you used to set the Z=0 datum and jog the nozzle down until it just touches the bed (or some object of a known thickness) and verify the Z position reported in the DWC is correct.

When you have a multiple tool printer you have the added complication of getting the Tool Z offset setting correct.

It would seem that both the Z probe Z Trigger Height setting and the Tool Z offset setting could lead to the Z logical position being wrong.

Having not worked with a multiple tool printer I don't know how you work that out. Perhaps it is in the Duet documentation.

How do you determine the Tool Z offset setting is correct?

Frederick

Gamefanatic3D

@fcwilt said in Mesh compensation results backwards:

What happens if you do this:

disable mesh compensation

set the Z=0 datum at a XY point on the bed where the height map suggests it is quite flat

move tool 0 to that XY point

move tool 0 to Z=0

does the nozzle is just touch the bed?

move tool 1 to that XY point

move tool 1 to Z=0

does the nozzle is just touch the bed?

So to respond to this request:

I used an area near the edge of the bed to ensure the feeler gauge isn't being supported by another higher area. My probe is offset from my Nozzles: X= 31.75, Y= -34.4

So when I move to a location I want to test both the probe and the nozzle at the same location I use the above to offset the Duets coordinates for the probe. There is no offset for the Nozzle as those are set by the associated G10 commands and will move to the spot shown by the Duet.

I perform a homing of Z. The process disables mesh compensation, performs the homing, and when done enables mesh compensation.

Step-1 - Prepare Environment

Heat Bed: 70°C
T0: 230°C
T1: 230°C

Step 2 - Probe Height:

Disable mesh compensation using Duet WebGUI
G1 X338.25 Y54.4 Z6
G30 S-1
Result:

8/22/2021, 12:15:34 PM	M98 P"0:/macros/Homing/Bed/Bed_Height_Test"
Stopped at height 0.949 mm
0.049

Step 3 - T0 Height

T0 (Selected from GUI)
G1 X370 Y20 Z6
Using PanelDue Z-5 to achieve Z1.0 height.
Using Z-0.05 movements after 4 adjustments I'm at Z0.8 and the feeler gauge is now just barely getting a tap when I wiggle it under the tip.
Using PanelDue Z+5

Step 4 - T1 Height

T1 (Selected from GUI, system knows to put the T0 back and grab T1)
G1 X370 Y20 Z6 (Entered it again, but is redundant at this point as my Tools will automatically move to the last point on the bed.)
Using PanelDue Z-5 to achieve Z1.0 height.
Using Z-0.05 movements after 5 adjustments I'm at Z0.75 and the feeler gauge is now just barely getting a tap when I wiggle it under the tip.
Using PanelDue Z+5

It's probably worth noting that my Probe Trigger height is 0.9. So the result noted in Step 2 was the difference from the point measured and my trigger height thus 0.049.

Gamefanatic3D

@fcwilt said in Mesh compensation results backwards:

@gamefanatic3d said in Mesh compensation results backwards:
My goal is to verify that the Z probe Z Trigger Height setting is correct and that the Z Offset settings of the tools are correct.

So I repeated the steps above which are essentially how I get my G10 settings so that I can ensure I've performed as you noted.

Step 1 - Pre environment:

Bed Temp: 70
T0 Temp: 230°C
T1 Temp: 230°C
Click Home All in WebGUI
Click Disable Mesh Compensation in WebGUI

Step 2 - Probe Height:

G1 X168.25 Y234.4 Z6
G30 S-1
Result:

8/22/2021, 12:47:32 PM	M98 P"0:/macros/Homing/Bed/Bed_Height_Test"
Stopped at height 0.871 mm
-0.029

Step 3 - T0 Height:

Click Tool-0 in WebGUI
G1 X200 Y200 Z6
Using PanelDue move Z-5 (Z=1.0)
Using Z-0.05 movements, after 3 adjustments I'm at Z0.85, and the feeler gauge is now just barely getting a tap when I wiggle it under the tip.
Using PanelDue Z+5

Step 4 - T1 Height:

Click Tool-1 in WebGUI
G1 X200 Y200 Z6
Using PanelDue move Z-5 (Z=1.0)
Using Z-0.05 movements, after 3 adjustments I'm at Z0.85, and the feeler gauge is now just barely getting a tap when I wiggle it under the tip.
Using PanelDue Z+5
Click Tool-1 in WebGUI to dock.

Blow on fingers and look for ice and a band-aide...

Gamefanatic3D

I use this macro when just probing a single point on the bed during the previous tests:

Bed_Height_Test

G1 Z5 F6000
G30 S-1
G1 Z5 F6000
echo (sensors.probes[0].lastStopHeight - sensors.probes[0].triggerHeight)

fcwilt

@gamefanatic3d said in Mesh compensation results backwards:

G1 X168.25 Y234.4 Z6

Where does those X and Y values come from?

They are different from the X and Y values you use in homez.g when setting the Z=0 Datum.

Given that with a single tool printer the nozzle becomes the reference for checking the Z probe Z Trigger Height setting I'm thinking that to deal with multiple tools the tool 0 Z Offset setting would be 0 so you take the value out of the equation and you can now use the nozzle of that tool as your reference for checking the Z probe Z Trigger Height setting.

Then you set the other tool(s) Z offset based on tool 0.

Frederick

Gamefanatic3D

@fcwilt
I think this issue is related to a failing Z-Axis motor. I heard a noise once when letting things sit idle earlier today which resulted in an obvious deviation in the Z-Level. I thought this might be due to the motors going idle and possibly the bed falling. Normally with power off, I don't get more than 0.08 of drift between the two lead screws.

However, I was printing just a moment ago and hit the pause button, but when I resumed I heard that noise again when the bed was lifting. So instead of continuing, I paused again and moved the X-Gantry to dead center between the lead screws and measured with my calipers from the top of the rails on either side with an approximately 2.3 mm deviation.

I'm really hoping this is the root cause. They are the original motors operating for over 4 years on my inexpensive starter kit!
I have to take a bit of it apart to get after them so that will have to wait until next weekend, time permitting!

Gamefanatic3D

@fcwilt said in Mesh compensation results backwards:

@gamefanatic3d said in Mesh compensation results backwards:

G1 X168.25 Y234.4 Z6

Where does those X and Y values come from?

That is technically where the Probe - probes when I do my startup. The X/Y noted in the G1 command are where 0 would be at the time, in my case, it's the front of my tool plate (not including the shaft).
The offset of my probe from that location is X31.75 Y-34.4.
When I perform a G1 X200 Y200 the probe is actually probing at X168.25 Y234.4.

Gamefanatic3D

@gamefanatic3d

Okay I'm back and after much testing over the past week, I'm convinced there is nothing wrong with my Z-Motors, even though the issue I experienced was real. I believe the Duet may have just been having a moment as I was getting a homing error with negative values when performed the first homez.g after startup. Any future homing would be successful. This appears to have cleared itself up as easily as it came with me doing nothing to the system other than turning it off and back on a few times...

Moving back to the issue at hand here I have mounted a Dial Indicator tool to my system and validated my original statement that the Z-Probing being done and recorded is in fact opposite of what I would expect.

Note: I made the mount for the Dial Indicator such that I could probe with the BLTouch while having the Dial Indicator tool attached. I realize there is a tension that is created as the Dial Indicator gets closer to the end of its measuring.

Probing at a point with the BLTouch will return a positive value to the homing file when it should in fact be a negative value.

My BLTouch trigger value is 0.9.

I validated this by performing the following procedure:

Step 1: Setup

G28
Disable Mesh Compensation
Attach Dial Indicator tool. (Manual process for now)
G1 X180 Y227 Z6 (Move the BLTouch to a center point on bed)
G30
G1 X206.8 Y143.4 Z15 (Move Dial Indicator to same point on the bed with specific height/trigger point)
Set the Dial Indicator to 0.000

Now I go to a spot on the bed shown on the heightmap that I know to be a low spot (further away from tools)

Step 2: Probing Low

G1 X328.23 Y224.37 Z6
M98 P"/macros/Homing/Bed/MyMeshCompStep1"
G1 X355.03 Y140.77 Z15

The result of BLTouch

8/28/2021, 2:37:40 PM	G1 X355.03 Y140.77 Z15
8/28/2021, 2:37:29 PM	Stopped at height 0.987 mm
-0.085
8/28/2021, 2:37:28 PM	M98 P"/macros/Homing/Bed/MyMeshCompStep1"
Stopped at height 0.983 mm
8/28/2021, 2:36:46 PM	G1 X328.23 Y224.37 Z6
8/28/2021, 2:36:14 PM	G1 X206.8 Y143.4 Z15
8/28/2021, 2:36:03 PM	G30

Dial Indicator: -0.08

I repeat this procedure 3 times in the same spot to validate any potential mechanical issues. Keeping in mind the dial indicator is not as accurate as of the BLTouch and validate the numbers are still roughly the same.

The heightmap.g in this area is showing a positive value in this area. I believe this is due to the BLTouch returning a positive number when subtracting the two probing values which are greater than my trigger (Z-0) value.
IE)
Probe1 returns: 0.918
Probe2 returns: 0.923
The resulting value would be acceptable as it's within 0.005
The value returned should be:

-0.0205 = 0.9 - ((0.918+0.923)/2)

But what is recorded in the heightmap is 0.0205

This is my assumption of what is happening based on the heightmaps I am obtaining. I could be missing something here still...

MyMeshCompStep1

var probezHeight = 6
var TravelSpeed = 6000

var probezOne = 0
var probezTwo = 0

	while true
		if iterations = 5
			abort "Too many auto calibration attempts"

		G1 Z{var.probezHeight} F{var.TravelSpeed}
		G30 S-1
		set var.probezOne = sensors.probes[0].lastStopHeight
		G1 Z{var.probezHeight} F{var.TravelSpeed}
		G1 Z{var.probezHeight} F{var.TravelSpeed}
		G30 S-1
		set var.probezTwo = sensors.probes[0].lastStopHeight
		G1 Z{var.probezHeight} F{var.TravelSpeed}
		if var.probezOne - var.probezTwo <= 0.005
			echo sensors.probes[0].triggerHeight-((var.probezOne + var.probezTwo)/2)
			break

fcwilt

@gamefanatic3d

In your MyMeshCompStep1 file you have

if var.probezOne - var.probezTwo <= 0.005

Ignoring any floating point errors:

if var.probezOne = 1.006 and var.probeTwo = 1.000 then var.probezOne - var.probezTwo = 0.006 and the test fails.

if var.probezOne = 1.000 and var.probeTwo = 1.006 then var.probezOne - var.probezTwo = -0.006 and the test succeeds.

In both cases the difference is 0.006.

I don't understand what you are testing for.

Also the number returned by G30 S-1 does not have a fixed relationship to the probe Z Trigger Height setting.

Thanks.

Frederick

Phaedrux

@gamefanatic3d said in Mesh compensation results backwards:

I believe the Duet may have just been having a moment as I was getting a homing error with negative values when performed the first homez.g after startup. Any future homing would be successful. This appears to have cleared itself up as easily as it came with me doing nothing to the system other than turning it off and back on a few times...

Have you tried a homez.g without the conditional gcode?

Gamefanatic3D

@phaedrux said in Mesh compensation results backwards:

@gamefanatic3d said in Mesh compensation results backwards:
Have you tried a homez.g without the conditional gcode?

I started off without the conditional code and only added it due to a recommendation by @fcwilt.

Gamefanatic3D

@fcwilt said in Mesh compensation results backwards:

@gamefanatic3d

In your MyMeshCompStep1 file you have
if var.probezOne - var.probezTwo <= 0.005
Ignoring any floating point errors:

if var.probezOne = 1.006 and var.probeTwo = 1.000 then var.probezOne - var.probezTwo = 0.006 and the test fails.

if var.probezOne = 1.000 and var.probeTwo = 1.006 then var.probezOne - var.probezTwo = -0.006 and the test succeeds.

In both cases the difference is 0.006.

I don't understand what you are testing for.

Also the number returned by G30 S-1 does not have a fixed relationship to the probe Z Trigger Height setting.

Thanks.

Frederick

I'm attempting to get a height value from the BLTouch that represents the difference from Z-0 which I am interpreting to be in direct relation to when I run my G30.
In this case, I'm interested in the return values so I can better understand what is happening and see the variations. I'm not so sure how much it matters on the macro as it's not what's actually coming up with the heightmap values, I'm just using it to test my theory and why I can manually set my values in the heightmap vs using the BLTouch and the G29.

fcwilt

@gamefanatic3d

Thanks.

I just got back from testing on my printer. I setup the M557 to probe a 3x3 grid. I placed a 1mm thickness gauge at the point at the center of the grid. I created the height map. Below are the values. As you can see the 1mm thickness gauge is showing as a positive value which is as it should be.

 -0.243, -0.082,  0.013
 -0.217,  1.115,  0.050
 -0.195, -0.053,  0.027

Here I used a larger and thicker object leaving it in place at the center of the bed so it's thickness was affecting the Z=0 Datum. As you can see the center point is now reading near 0 and all that other points are reading low by appx the thickness of the object.

 -3.311, -3.171, -3.068
 -3.306,  0.001, -3.036
 -3.278, -3.145, -3.065

So all I can think of is your Z=0 Datum is off.

Frederick

Gamefanatic3D

@fcwilt

Going with where you are headed I did 3 heightmaps. All will use the same points and were done with the bed at 70°C.

Map1
Normal height map

 -0.050, -0.086,  0.053
  0.067,  0.007,  0.090
  0.251,  0.020, -0.019

Map2
Normal level with 0.8 feeler gauge put in after in the middle:

 -0.031, -0.124, -0.038
  0.061,  0.836, -0.013
  0.242, -0.035, -0.120

Map3
0.8 feeler gauge in place when G30 performed:

 -0.927, -0.969, -0.847
 -0.833, -0.004, -0.807
 -0.653, -0.874, -0.904

Now taking a look at just the difference between Map1 and Map2 we can see the obvious and expected difference at the middle point. I am a little plagued by the right values being nearly 0.1mm difference. I now wonder if this is my probe or my hardware.

When I run my Dial Guage out from the middle I get a negative value of ~ -0.14 after setting its Z-0 at my middle probing point. This is about what I expect based on my manual leveling.

https://youtu.be/GCf9Ta9aJSo

fcwilt

@gamefanatic3d

Hmm... Curious.

Some Z axis movement error perhaps?

What is your Z axis setup? What is the Z axis movement for one full stepper step - not a micro-step?

Frederick

Gamefanatic3D

@fcwilt
So I'm not exactly sure how to move a single step, but mechanically this is how I am setup:
Dual 1.8° steppers w/ TR8*2 lead screws

M350 X16 Y16 Z16 E16:16 I1                ; Configure microstepping with interpolation
M92 X201.2499 Y201.2499 Z1601.584008 C100 E421.1332199:690    ; T8x2 1-Start Lead Screw

When I perform a single rotation of the Z motor my Dial Gauge reads 2mm at bed center, which is expected. It reads the same when moved to the lead screws and moved one full rotation.

Maybe I need to perform some tests for repeatability?