Matt just going to make some things a bit clearer for sake of others not picking on you here mate but it's not clear and your Soooooo wrong on some it. .

Quote Originally Posted by kingcreaky View Post
The way i think of it is, the Acceleration and Velocity settings in Mach act like your speed limiter, they over-ride whatever settings the CAM software specifies in the job.

As mentioned above, Mach is your speed limit. So if you have set your velocity to 6000mm/min in mach, and your tool to 8000mm/min in vectric (or your cam software) mach wont let the machine exceed 6000.

The machine jogs (ie with the arrow keys, at the maximum speed stated in mach)
The machine moves (between cuts, at whatever speed the Gcode outputted by your cam software) -- but limited by mach.
This is true but I'll make it clearer because it does apply here.

In the G-code this will only apply to the G1 moves which have F### feed rate parameter but all G0 moves will be at the Velocity setting in motor tuning. So if your over tuned on velocity then you will still lose position if G0 moves are in the g-code even if you lower the feedrate in Cam software.!


Quote Originally Posted by kingcreaky View Post
Its also critical (although I cannot explain why) to ensure the Acceleration and Velocity settings are the same for both your Y axis and X axis. (Z can be different) Otherwise (I found) it effects 90deg corners. Where (I think) the machine is still decelerating (moving) when the next move starts

Personally (others will disagree, I set the accelleration very low (often 100), and the velocity to a comfortable speed for the machine as Im far more interested in quality, than speed) I also find having acceleration set so low helps when jogging your machine manually into a start position and also makes a nice smooth start and stop to each move.
This is the bit your Sooooo wrong about matt... .Lol

It's not critical and perfectly fine to have differant setting for each axis, Mach will only go fast has the slowest axis anyway when moving 2 axis at same time. Try it.!! . . Double the Speed of Y axis velocity (if machine can do it) and home the machine and jog away good distance and Type G1 X0 Y0 F ( Feed value abobe X axis velocity or same has Y axis velocity) in the MDI box.

Like Jonathan pointed out most if not all of trouble is coming from having the Accel far far to low.
Molasses moves faster than that so MAch's gets tired of waitng and Knobs off to the pub for a quicky but has few too many so when it gets back it's forgot where it was upto and thinks bollocks to it i'll just carry on from here and that's why your getting square circles.!!. . . . Mach pissed.!! . .Lol . . . . Ok well maybe being bit silly but the point is your messed up on tuning.!

You really want to be within 500-800 just for normal use and 1000 and above this if doing mostly 3D type work.
Just remember the golden rule that you can't have High Accel and High Velocity you need a balance and you won't go wrong.