I've run into a situation with the CAM file generated by MECSOFT AlibreCAM
appears to have a problem. I've asked this on the support group for AlibreCAM
but I think it's a more general question involving simultaneous 4 axis milling
where I write the G-Code myself.
N1 G17 G20 G40 G90
(4th Axis Create Cylinder/Round)
N2 T2 M06
N3 S20000 M3
N4 G0 X-2.2788 Y0. Z1.664 A46.8 F0.
N5 G1 Z1.45 A46.8 F11.
N6 X-2.4983 Z1.4113 A46.8
N7 X-2.5389 Z1.404 A46.3
N8 Z1.4 A45.
N9 X-2.5388 A43.7 F14.7
N10 X-2.4959 A43.2
N11 X-0.0018 A43.2
Effectively the feed rate on the X,Y and Z is 11 IPM or 14.7 IPM. But the
rotary axis is angular under LinuxCNC and measured in degrees per minute.
I believe that makes sense because the diameter of the part being rotated
determines the actual feed rate. So if the circumference was 14.7" and the
cutting speed is set at 14.7 IPM then the rotary axis should turn 360 degrees
per minute.
But as shown in line N9 we have simultaneous motion on X and A but at F14.7.
Clearly if the diameter was such that the circumference was 29.4" then the feed
rate of the A axis would have to be half or 180 degrees/minute.
Running the G-Code above sees the Z or X axis moving at the expected speed.
Watching paint dry is more interesting than watching the A axis turn. But if I
just do a G1 A360 F360 the motion of the A axis at 4.68 diameter appears to be
about the same speed as the X or Z horizontally. It also takes exactly 1
minute to move 360 degrees at 360 degrees/minute.
So how is this solved? How would the A axis know the diameter and be able to
translate that a request of F14.7 should really be F360 when Z is being moved
at the same time? Odds are I've configured the CAM software wrong but if I was
going to just manually write some G-Code that involved simultaneous motion what
would I do?
The AXIS display shows 14.7 for speed. The Z is known. Is there something
missing so that the A axis actually gets a much faster rate?
Thanks
John
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