3D Printer Geometry Problem

[Gina]

Well, I've calibrated the X and Y and they are the same within 0.1mm though a couple of tenths high now.  BUT the orthogonality is way out - 139mm and 143mm across diagonals.  It's worse than before I adjusted the X and Y calibration.  I've checked XY mechanical orthogonality with a set square and it's fine so the problem is the firmware that does the Core-XY system.  Seems the X and Y calibration is exactly that and not motor calibration.  Core-XY needs motor calibration.  I'll have to check the Duet firmware update history and see if this has been corrected.

[Chriske]

3 hours ago, tekkydave said:

Could it be the belt tensions? If one is tighter than the other this can happen.

To produce an error of this magnitude belts should be very loose. It's not a millimetre error or so we're talking about here Dave.

[Gina]

The belts are at normal tensions and pretty much the same.

[Gina]

Been having a look through the firmware history to see if there was an update for CoreXY that allowed calibration of the motors rather than actual X and Y, because setting the calibration for X and Y put orthogonality way out, but haven't found anything so assume this is still the same.

Edited June 20, 2019 by Gina

[Gina]

I'm sure I saw somewhere when I was originally setting up a printer with Duet control board about adjusting orthogonality to make the X and Y axes orthogonal ie. at right-angles but I can't find it now.

[Gina]

Worked my way through the G codes and found this :-

Quote

M667: Select CoreXY or related mode

This command is deprecated in RRF 2.03 and later. Use M669 instead.

Parameters

• Snnn CoreXY mode
• Xnnn X axis scale factor (RRF 2.02 and earlier)
• Ynnn Y axis scale factor (RRF 2.02 and earlier)
• Znnn Z axis scale factor (RRF 2.02 and earlier)

Order dependency

• M667 must come earlier in config.g than any M671 command.

Example

• M667 S1

M667 S0 selects Cartesian mode (unless the printer is configured as a delta using the M665 command). Forward motion of the X motor moves the head in the +X direction. Similarly for the Y motor and Y axis, and the Z motor and Z axis. This is the default state of the firmware on power up.

M667 S1 selects CoreXY mode. Forward movement of the X motor moves the head in the +X and +Y directions. In firmware 1.19 and later, forward movement of the Y motor moves the head in the +X and -Y directions.

M667 S2 selects CoreXZ mode. Forward movement of the X motor moves the head in the +X and +Z directions. In firmware 1.19 and later, forward movement of the Z motor moves the head in the -X and +Z directions.

In versions of RRF prior to 2.03, additional parameters X, Y and Z may be given to specify factors to scale the motor movements by for the corresponding axes. For example, to specify a CoreXZ machine in which the Z axis moves 1/3 of the distance of the X axis for the same motor movement, use M667 S2 Z3. The default scaling factor after power up is 1.0 for all axes.

 

 

[Gina]

Decided to try resetting the XY calibration back to 80steps/mm and adjusting the physical XY orthogonality slightly off in the direction required to correct the print.  Now printing a new test.

Result :- X = 100.25mm, Y = 100.00mm, D1 = 140mm, D2 = 142mm so it's better.  Previously D1=139 and D2=143 so error halved.  Have adjusted it about the same again and reprinting.  X and Y axes are now 2mm off square in 500mm.  D1 and D2 are the diagonals.

Edited June 20, 2019 by Gina

[Gina]

X=100.12mm, Y=99.97mm, D1=142mm, D2=141mm.  Corners seem square compared with a square envelope. 

50mm test cube :- X=50.12mm, Y=49.67mm, Z=50.08mm, D1=69.75mm, D2 70.02mm.   All corners square as far as I can tell.

[Gina]

Anyway, geometry problem is solved and now it's just a matter of tweaking.  Couple of parts to make for the printer then I expect to get back to 3D printing astro parts.

Edited June 20, 2019 by Gina