Dual Extruder on Polar Printer

LüDi

Hello,
I'm currently building a custom Polar 3D printer with two fixed extruders mounted along a straight X-axis. Only the bed moves – the printheads are stationary.

Setup:
Duet 3 Mini 5+ with RepRapFirmware 3.5.4

Polar kinematics:
M669 K7 R0:90 H37.5 F200 A200

Nozzle 1 is positioned above the center of the bed.
Nozzle 2 is positioned next to Nozzle 1.

The offset for nozzle 2 is defined using:
G10 P1 X80 Y0 Z0

When printing a simple dual extrusion object (like two overlaid rings), the part printed with extruder 2 is misaligned or distorted. I use CUra as Slicer with the dual extrusion setup. Looks like the G10 Offset does not work with polar kinematics?

I want both tools to print at exactly the same spot on the bed, so that switching from T0 to T1 places the same coordinate under the other nozzle, taking into account their physical 80 mm spacing.

Thanks for help.

o_lampe

@LüDi
Did you try Cura taking charge of the tool offset?
Using offsets in RRF is a bit counterintuitive regarding the +/- sign of the offset.
Check out the G10 L2 or G10 L20 description. It might give you another option to make it work.

dc42

@LüDi tool offsets won't work in a polar printer either in RRF or in Cura, unless you use an extra motor to rotate the tool head to remain parallel to the bed.

Depending on the alignment of the two nozzles, when you switch nozzles you are either changing the relative angle of the nozzle and the bed (if the two nozzles are the same distance from bed centre), or changing the distance between the nozzle and bed centre (if the two nozzles are aligned with the radial motion), or both.

To handle changing the relative angle of the bed is easy enough. In the tool change file you can save the current XY coordinates, use a G1 H2 command to rotate the bed by the required angle, then use G92 to set the XY coordinates back to the saved values.

Likewise you can change the radius in the tool change by saving the XY coordinates, using a G1 H2 move to adjust the radius, then use G92 to restore the XY position to the saved values.

This is all theoretical, I haven't tried it! Your homing files should check that the secondary nozzle is not selected.