Hi All,
I am brand new to this forum, I have a problem with  Mach 3, can anyone help. I am using Mach 3 for cnc mill control, the part that I am milling has a G-Code line number of 20075 when the controller is 3/4 way down through the G-Code the X axis starts to deviate from the Mach 3 DRO, the start of the deviation is 0.1-0.2mm with each cycle of the milling cutter it gets worse and worse. The maximum deviation is as much as 1.3mm. The part was modelled in Fusion 360, this machining strategy is adaptive clearing with a tolerance of 0.1mm. I am having ruined parts after ruined parts, I have run out of steel stock.

check to make sure your X axis isnt hitting something causing your X motor to lose steps.

Thanks for your reply, I have checked this and its okay. It is as if the stepper motor is gaining steps, can this happen?

Half your velocity and double you acceleration and see if it looses position.

Is fusion using fast feeds or rapids, we have seen fast feeds cause problems before.

The Fusion feeds are quite low, the machine has recently been finished, I have had this problem from the start. It maintains correct table movements up to the fourth line of Gcode after this it starts to deviate.

The testing was carried out using a stand alone DRO with the glass linear scales held onto the machine table. With the X, Y and Z axis disabled I could then examine movement in the X plane, which is what is giving me trouble. It is advancing as the Z axis steps down, its like 0.1mm for every step down, the step downs are 0.3mm each cycle, the part is 6.35 thick.

Some code may be needed to check the movement and also some pictures of the setup including the breakout board etc.

For now here are some pictures of the part with the machining problem and a photo of the set up for examining the X axis travel.

and the part

Why is it only tapered at one side?