G30 H parameter - effect on calibration?

I have started using the H parameter when using the G30 commands in my bed.g file. I did this because my calibration result converged at about 0.100 with obvious problems when printing with some edges of the printed object fouling.
Now I get awesome calibration convergence at about 0.005 (no not a typo). But when I print the same persistent bed skew remains. So I am wondering whether the H parameter really makes any difference.... the bed level matrix seems unaffected...

- Could you describe the "bed skew" you are experiencing in more detail?
- How many calibration points are you using, and how many factors are you calibrating?
- Which firmware version are you running?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for replying dc42.

Let's say Z is @ 0.2 @ x0,y0, move along the x axis to x-40, y0, Z is now = 0 and the nozzle doesn't extrude but at x40, y0 Z = 0.3+ and filament has adherence problems.

For calibration I have tried 4, 7 and 16 points. Each time I will include points underneath the towers plus center. Also halfway between each tower and on 16 points I pick points following the where the print has been fouled. I have tried running my calcbed script with S-1 and copying and pasting these figures into my bed.g file this gives great convergence figures but does seem to be reflected in the print.

I'm running RepRapFirmware-1.09j-dc42.

Have you checked that the Z height is consistent at all the probe points? How did you establish what H correction you needed at each one?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I ran the probe point with S-1 to see the height displayed and then pasted that figure into my bed.g file for that same probe point and ran the bed.g script to calibrate using S6....

sometimes people appear to forget the goal of calibration is not to get a great convergence but to get an acceptable bed level and acceptable prints, the convergence factor is just an indicator, as you are proving here.

A couple of guesses

1. have you 'fudged' the H parameters to give you a good convergence, H parameters need to be set to compensate for the mechanical differences in switch sensitivity at different positions on the bed....see DCs Question
2. Are you using 7 factor calibration instead of 6 factor calibration

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RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

Thanks bgkdavis for replying...

Lol, yes indeed I have given a master class in fudging the figures. No seriously it's my lack of understanding that is leading me astray.

So I can't for instance run a command like:

G30 P3 X60 Y23 Z-99999 S-1

Which outputs a figure like -0.5 difference and use that figure for my H parameter eg.

G30 P3 X60 Y23 Z-99999 H-0.5

This is what I have been doing. I assumed that the H parameter was an Z offset for that section of the build platform and the firmware triangulates all the probe points to determine what Z offsets to apply at any given point on the build platform.

So I need to use a different technique to 'compensate for the mechanical differences in switch sensitivity'.

If I was to move to my probe point and lower the Z axis by increments of -0.1 until the probe registered a value other than zero would this be better? Does the probe figure displayed on the web interface correspond to distance in any way?

To get the H parameters at each point you need to move the head to the point you want to probe and do a manual probe,

Next you manually move the head 1mm above the bed and place a piece of paper between the nozzle and bed and jog down until the paper is just trapped.

Now note the Z position, this is your offset factor

repeat for all positions, you should notice that the offset factor is greater towards the centre than it is immediately above each spring, this is because the force required at the centre is 3x the force required at each spring.

---

RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

Do I need to add the H parameter to the bed probing in my starting script? It probes the centre of the bed but no H parameter. The calibration scripts have different H parameters for each probing point. Since I flipped my bed over and it doesn't have a huge dip in the middle it seems to start too close to the bed. However, I also updated to 109k and the nozzle bangs into the part throughout the build so it could be something else.

I added H-0.4 to the G30 in my starting script and it seems to have made a world of difference!

Quote
Theolodian
I added H-0.4 to the G30 in my starting script and it seems to have made a world of difference!

Did you calibrate your G31 Z parameter to the trigger height at bed centre?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I set the first one to -0.4 and left the 2nd one at -0.1

I am now running the G30 in my starting script at H-0.25 and it gives a really nice finish on the bottom of the part, hard to remove from the bed. HUGE improvement on before.