Hi,

I'm using Mach3 42.20 and it seems that in this version, the CV mode makes smooth transition from G1 to G0 move (eg. tool retract move). This may be less obvious on setups with high acceleration.
Example:
N1 G1 Z0 F100 (plunge)
N2 G1 X100 F4000 (cut)
N3 G0 Z100 (retract)
This may present a problem (especially when engraving) on line 2, because G1 move is not completed on Z axis/level. CV smoothes the transition between lines 2 and 3 and starts retracting the tool before the end of G1 move.
Workaround for this is to check "CV stop at angles" option in General settings (89 degrees worked for me in this particular example, but since this option is used for transitions on all axes, exact value depends on desired behavior on all axes and acceleration/feed settings).
Attached picture shows the example engraving with "CV stop on angles" option unchecked (left, notice 2 unfinished lines) and checked->89(right) done with 0.1g@4m/min. It also shows for 90 deg angles CV radius to be:
radius = (feed^2)/(2*acceleration)
distance between engraved lines is 2.5mm, calculated CV radius for 0.1g@4m/min is 2.2mm (with 0.3g, radius is 0.7mm - which is much less noticeable)

Regards,
Mihael

Hi Mihael - I took this up with Brian about 3 years ago but AFAIK nothing came of it. If you're interested, the history is here and here.

The CV stop angle is IMHO not the best way to deal with this - you're better off breaking the blend with a G4 P0 between your feed and rapid moves and leave CV to do it's job un-hindered.

Ian

Nice workaround, thanks Ian.