Machine cutting off 3D model corners on last passes

[Guido666]

I am machining a 3D model of geographical terrain, and it completes nearly the entire model with a top-to-bottom equidistant offset toolpath, then on the very last couple passes around the base of the model the bit goes crazy and cuts off a couple inches of the bottom two corners.

I ran the toolpath through CutViewer, and it looks fine. I've attached a picture of CutViewer's output, and added red lines where it cuts off the corners on the last 3-4 passes around the model.

I'm a novice, and I'm hoping I just have something set wrong. Can anyone help?

[Guido666]

A little more info...

It definitely has something to do with the feedrate clashing with Mach3. I ran the same program a couple more times, and full speed, and every time it would cut those corners off, around line N92000. Then I ran it again, and when it got close to line N92000, I overrode the speed to 30% in Mach3, and it finished perfectly.

I have similar other pieces of this geographical topography, and they do the exact same thing too. At the very end of the cut it chops the corners off.

Can anybody help me understand what's happening?

[wjfiles]

Go into General config page and change Mach constant velocity to exact stop.

WJF

[Guido666]

Go into General config page and change Mach constant velocity to exact stop.

WJF

You think it's a constant velocity problem? Are you wanting me to try turning CV off to test if it's the cause, or are you suggesting to run the models completely with CV off?

I'd like to better understand the issue, and why it only happens on the last passes of these models. It will machine them for hours without missing a beat, then destroy it all in the last 30 seconds.