Centroid Community CNC Support Forum

Helical arcs in G17, using W instead of Z, should work just fine.

Arcs in G18 or G19 will not work with the W axis. You would have to get your CAM software to post them as a series of short G1 moves instead.

cncsnw wrote: ↑Wed Apr 17, 2024 11:42 am Helical arcs in G17, using W instead of Z, should work just fine.

Arcs in G18 or G19 will not work with the W axis. You would have to get your CAM software to post them as a series of short G1 moves instead.

Hmm… thank you for the info, that is unfortunate.

This takes me back to square one for a bit as I don’t think modifying post processors is in my future.

I really look forward to either the finalization of the M333 command or subsequent improvements that allow for multiple spindle/z axis control.

its best to have the cad/cam system use short vectors and stick to g1's and g0's which is common these days.
then you can get any type of "move" to work in any plane with any other axis.

cnckeith wrote: ↑Wed Apr 17, 2024 2:31 pm its best to have the cad/cam system use short vectors and stick to g1's and g0's which is common these days.
then you can get any type of "move" to work in any plane with any other axis.

Ah, thank you. I wasn’t sure what is considered best practice. Does the standard centroid fusion 360 post use lines vs arcs?

you'll have to try it or ask the guy who wrote the post! i don't use Fusion.

May i ask you, which CAD CAM System you use? Thank you

cnckeith wrote: ↑Wed Apr 17, 2024 3:39 pm you'll have to try it or ask the guy who wrote the post! i don't use Fusion.

For anyone following along, I thought I'd provide a possible course of action I may take. Ideally this would superseded by future features of the centroid software. I have broken the approach up into 2 phases, with phase 1 being simpler to implement, but a bit more labor intensive for each cut file, and phase 2 being a more significant edit to the post processor to add in the features by default

I'll also try to explain my initial plan based on my LIMITED understanding of the Autodesk Fusion post processor.

• Edit the default centroid post to permit only arc movements on the XY plane by setting allowedCircularPlanes to PLANE_XY (alternatively, disallow them all by setting it to 0)
• Set allowHelicalMoves=0
• Post process the CAM From fusion, with the setup having an a WCS of G55
• Do a file wide find and replace to change all Z to W
• Manually append to a standard XYZ gcode file (g54)

.

Phase 2 would include

• Editing the Fusion post to look for active tool number, if T1, then use Z and G54, if T2, then use W and G55.

This would need to be paired with proper setup of the WCS in the machine, and I'm not sure how to address tool lengths with this approach yet either. It also seems that if this approach works, it would allow for up to 4 independent "Z" axis. (I MIGHT go up to 3 if possible). Finally, I would plan to duplicate the voltage signal to each VFD, and use a relay to enable/disable the drives. I think this will work because only 1 spindle needs to be on at once.

For anyone else interested, I have a new updated plan.

Based upon some more research into the Fusion 360 Post Processor, it appears a complete solution is much simpler than I originally thought.

1. Configure the machine with 4 linear axis, X, Y, Z, W
2. Set custom machine parameters that provide an X and Y offset for the W axis (from the Z axis). Parameters 700, 701
3. Modify the M6 macro to call G52 using the parameters 700 and 701 for T2, and zero G52 for T1
4. Use a modified fusion post that changes the prefix for Z component outputs to Z or W based upon tool number
5. Run the same voltage signal to 2 VFDs, spindle on/off is controlled by custom M3 and M4 macros driving outputs. If spindle voltage can't supply enough current, set VFD analog output to control the other VFD or use signal duplicator.

This approach seems to check all the boxes and shouldn't be that complicated. Thanks at CNCKeith, sometimes I forget that a CNC machine is just a programmable interpolation machine and that I can just tell it exactly what I want it to do.

Wiring the analog signal to two or three VFDs in parallel is generally not a problem.

The maximum load on the analog output for most Centroid boards is 10mA.

Typical VFD analog input impedance is 10K or higher, so the draw at 10V would usually be ca. 1mA per VFD.