Centroid Community CNC Support Forum

Posted: **Fri Jun 27, 2025 8:42 pm**

I have an Avid 4x4 router with the Acorn based EX controller and Clearpath SDSK servo motors. A while ago I built a C-Axis add-on to use the machine as a tangential knife fabric cutter (documented here: viewtopic.php?t=11460). In short there is an additional clearpath servo that indexes the de-energized spindle via a timing belt to orient a spring loaded rotary knife. The homing macro was modified to spin the C-axis servo until a ferrous sensor flag trips a non-contact prox switch. This sets the C-axis machine coordinate to 0.00 degrees on completion.

The problem I am having is at the start of a program on initial machine start up. The way I have the fusion 360 post configured is to initially command a G0C0 move which, mysteriously, starts an enormous "unwind" of the C-axis to the tune of 65000 degrees. This isn't necessarily a "problem" per-se but the 30 seconds of spinning the rotary axis before the program starts is pretty silly and annoying. When the program actually starts after this ridiculous display everything seems to run perfectly fine. The same thing happens if I command any other angle via MDI right after machine start up. Calling M151/C also has no effect on this behavior.

My guess is there is some kind of parameter I have configured incorrectly here but I can't figure out what that is. I have attached a fresh report file for perusal.

Posted: **Fri Jun 27, 2025 11:23 pm**

Code: Select all

Axis    Origin    Origin    Origin    Origin    Origin    Origin
        #1(G54)   #2(G55)   #3(G56)   #4(G57)   #5(G58)   #6(G59)
 X      1.59976    0.00000    0.00000    0.00000    0.00000    0.00000 
 Y      1.48980    0.00000    0.00000    0.00000    0.00000    0.00000 
 Z     -2.36516    0.00000    0.00000    0.00000    0.00000    0.00000 
 C   65519.99500    0.00000    0.00000    0.00000    0.00000    0.00000 
 N      0.00000    0.00000    0.00000    0.00000    0.00000    0.00000 
 N      0.00000    0.00000    0.00000    0.00000    0.00000    0.00000 
 N      0.00000    0.00000    0.00000    0.00000    0.00000    0.00000 
 N      0.00000    0.00000    0.00000    0.00000    0.00000    0.00000 
CSR  0.000000 0.000000 0.000000 0.000000 0.000000 0.000000

Set C to 0 in WCS G54

Uwe

Posted: **Sat Jun 28, 2025 12:22 am**

Uwe, welp that would certainly explain the issue. Thank you!

Can I edit the cncm.job.xml file directly or is this better set in a CNC12 menu somewhere that I have yet to find?

Posted: **Sat Jun 28, 2025 12:59 am**

Setup / Part / WCS / Origin in CNC12

pls. read Part Setup in the manual

Uwe

Posted: **Mon Jun 30, 2025 7:53 am**

You can also go to MDI and type "M26 /C" and this will zero it in the machine home coordinates

Posted: **Tue Jul 01, 2025 2:20 pm**

What he needs here is not "M26/C", but instead "G92 C0". Optionally both, in that order.

With the WCS offset already set to 65520 degrees, then immediately after power-up, the axis is at machine zero / machine home, but it is 65520 degrees away from part zero.

M151 resets machine position, not part position. That is why M151/C did not help.

Centroid Community CNC Support Forum

Enormous C-Axis "unwind" on program start <Resolved>

Enormous C-Axis "unwind" on program start <Resolved>

Re: Enormous C-Axis "unwind" on program start

Re: Enormous C-Axis "unwind" on program start

Re: Enormous C-Axis "unwind" on program start

Re: Enormous C-Axis "unwind" on program start

Re: Enormous C-Axis "unwind" on program start