Hi Folks,

I've been using Mach4 on my CNC for ages but yesterday the following happened.

I was just trying to cut a simple rectangle 300mm by 110mm by 18mm deep using a 6mm bit.

this forum is really crap at loading images but:
IMG_1 is the regened toolpath. It's clearly a rectangle

IMG_2 is the g-code. It's clearly a rectangle.

and IMG_3 is what it cut. Now its a rectangle with one corner rounded off (top right)

What the hell? It did it on purpose as it did the same thing on all 4 passes.
I'm at a loss as to why it did it - anyone have any ideas?

do you know use the CV?
what is yours accl deccl value? what speed do you run?

Thanks for replying.

My machine has been running perfectly for years and it has cut 3 out of the 4 corners perfectly so my accel and decel values are all good.
As was my feed speed. My CNC was coping just fine.
If anything was off I'd be VERY surprised that is was off consistently just in one spot on the machine.

Something else is wrong. Mach 4 decided to tell my CNC to do this for some reason as can be seen in the trace.

Although yours insist not to check,the  answer for your problem it's CV + acceleration deceleration

Simple test...

Turn off CV then run the Gcode.

If it does not round the particular corner then turn CV back on and increase your X, Y Acceleration values in Motor Tuning (and / or reduce your Velocity in Motor Tuning) and then save your changes. Run the Gcode again.
This 'tuning' may need to be repeated a few times until you get the corner rounding produced by CV to within acceptable limits.

Although yours insist not to check,the  answer for your problem it's CV + acceleration deceleration

Sorry, I'm not insisting anything - I'm asking for help and was just clarifying.
I haven't needed to look at CV before (as I said, my CNC has been working fine for ages) but I'll do as instructed and report back.

I'll explain you from my experience ( more then 20 cnc mach4) there is big problem in mach that not have jerk control, because that you must put accl decll very low ,and because of that cv can't calculate correct ,and t hi is corner round appear
It's not new problem it's not only yours problem
The solution I found it's use the jerk on servo drive then can increase accl decll for normal values