Part diametrically shrunk at lbottom 3/16" of parts

My prints using TAZ 6, ABS with Cura are great with one exception: Consistently, the parts seem to by diametrically shrunk in approximately bottom 3/16". As the elevation rises, an subtle outward tape can be seen as (at the top of taper and the approx 3/16") the part is correctly sized. Eyeballing it, the base of the part is diametrically shrunk by roughly 3-4% as it tapers outward up the 3/16" of the part. This applies to all parts.

Any ideas? The shrink and taper is NOT in the cad model, and never happened on my old makerbot. Don’t misconstrue mu complaint, however, I love the TAZ 6, but need to resolve this one issue.

There are a couple things that can cause that in theory. The most likely one is slight overextrusion that builds as the layers go up. To compensate for that, adjust your esteps accordingly.

It could also be a racked frame or a loose belt if the part is shifted offset to one side.

It could be the extruder temperature as well, if you are printing too warm for the material but starting the print early it may be flowing more than it should as it goes up. This can also be present with excess fan, or if you are using fan cooling for lower layers and not upper (ABS doesn’t need any fan at all unless bridging operations or very small layer operations are occuring)

Running TAZ 6 with Cura slicer. Matterhackers 3mm ABS.
Extruder = 240C
Bed Temp = 110C
Layer height 0.18mm
Shell thk 1.0mm
print speed 50mm/s
Flow filament 100%
nozzle size 0.5mm
bottom layer speed 15mm/s
infill speed 40 mm/s
top/bottom speed 30mm/s
outer shell speed 30 mm/s
inner shell speed 35mm/s
Cool: min layer time 20sec
Need help!!!
Errin in Kentucky