Slight taper/angle to Aluminum cut

Have been running some test pieces. Basic 2D cutout of 4mm Aluminum. Have a 2.2kw water cooled spindle etc, nice clean cuts, eats through it with ease.

However, noticed there is a very slight stepping/taper/angle to the sides of the cut. Always going further out from cut piece further down the cut we go. So the base of the cutout piece is about 0.2-0.3mm further out than the outline at the top of the cutout.

Have it set to 1mm steps.

Wondering if this is something machine calibration related, or simply have selected a wrong option in the CAM process when selecting the steps down through the material.

Simulating it in Fusion, it doesn’t seem like there should be a taper though. So maybe a calibration aspect of the machine.

Deflection. The material is pushing your end mill out of the way. You could come back with a full depth finish pass. Also, make sure the tool isn’t sticking out too far.

Another keyword is “tramming” as in tramming the spindle.

Are the steps more pronounced on one side (think “east/west/north/south”) => spindle out of tram.
If the steps are equal in all directions then it is dominantly deflection.

2D cutout, are you doing a 4mm slot? Chips clearing or being recut? If the latter do a wider slot so only one side of the tool is engaged and nut “bumping” into the other wall.