Problem With Cupping/Distortion at Base of ABS Print

[minuteman64 4]

I posted this in the "Cura" section, but maybe more appropriate here since I'm asking for help with a print.  So, I'll give it a shot here (apologies if I'm violating board protocols).

 

Trying to print a hollow cylinder in ABS.  OD is 23mm and wall thickness is 1.5mm.  Height 30mm.  Having trouble getting bottom without the "(" shrinkage (see photo).   Tried raft and brim - no difference.  Both raft and brim seemed fused to cylinder (hard to remove).  Currently printing at 240 extruder and 105 bed.  Printing bottom 10mm at 1/2 normal print speed.

 

Using Anet A8 in enclosure.  Cura 3.2.1 is slicer program.

 

I'd keep experimenting, but there are so many variables it would be a big assist if someone could clue me in as to where to focus.

 

BTW, yes, ABS is the much preferred medium for this application - I don't want to go with PLA. 

 

Anyways, appreciate any advice.