Warped Part  

RE:

ABS warps because it shrinks as it cools.  The bottom layers are near the heated bed so they stay hotter than the upper layers.  The upper layers therefore shrink more than the lower layers, which sets up differential shrinkage, leading to the warping.

There are a few of ways to tackle this.  By far the best is to make sure that the print doesn't cool too much while it's printing, so an enclosure helps a great deal.  This traps the heat from the heat bed and creates a warm atmosphere around the print, and it also prevents drafts from rapidly cooling the print.  If you don't have a dedicated enclosure, maybe you can improvise by placing a cardboard box over the printer.  Aim to get an internal temperature above 35C, preferably a bit higher. Printing in the middle of a hot summer day will give you a few extra degrees. You can also use the Draft Shield feature in Prusaslicer to print a tall skirt around the part to shield it from drafts.  Nudging the build plate temperature up by 5 to 10 degrees can also help, both by increasing the ambient temperature around the print, and helping it to directly influence a few layers more.

Another thing that helps is some form of adhesive on the build plate.  Glue stick is popular (use a thin smear and then smoosh it around with a wet paper towel to leave a thin, even layer), and you can also buy dedicated 3D printing adhesives.  However, using glue stick I've personally had cases where the adhesion is so good that the differential shrinkage has actually lifted the magnetic build plate away from the magnets.  This is why preventing the shrinkage in the first place is the best approach.

Another way is to print a 'brim' around the object.  This provides some resistance to lifting, but in my experience it only helps a little, and if your part can shrink enough to lift the build plate it can certainly overcome a bit of extra adhesion from a brim.  It's worth trying though - a brim is fairly easy to remove afterwards.

RE: Warped Part

Thanks for the reply. I have the printer in a closet with my server, router and modem. It stays warm in there. Pretty constant. Checked it with a thermometer and it says 90° F (32°C).  I did start using a Brim but for different reasons. My sharp corners were getting rounded. The Brim stopped that. Looks like PSlicer sets the build plate to 110°C for ABS.  I can try bumping that up. I was using a thick layer of glue stick.
Thanks for the suggestions.
Mike

RE: Warped Part

Hmm - I've had plenty of success with ABS on a MK4/MK4S, inside an enclosure.  In the depths of winter, when the ambient temperature in the room where I have my printers is only 19C, my Prusa enclosure just about sees 35C during an ABS print.  I always used glue stick in that setup, and rarely had any warped prints.  I now also have a CORE One, which has a smaller enclosed chamber for the heat bed to heat up - on days like to today, when the ambient temperature is around 30C, the chamber is easily reaching 55C and higher - I saw 58C today.  I've printed a few things today in ASA (arguably worse than ABS for shrinkage/warping in my experience) without any sort of bed adhesive and on the satin sheet (I normally use a textured sheet to help with adhesion), with no sign or warping.

I think the key really is to get some heat into the air around the print.  Perhaps you can take a leaf from Prusa's book and do what the CORE One does at the start of a print - firstly it sits and waits for a specified minimum chamber temperature (40C I think for ABS), and then it sits for another 10-12 minutes 'absorbing heat'.  The former is merely to get a good chamber temperature to avoid warping, and I think the latter is so that the structure has finished expanding before the print starts, for dimensional stability.  But during the 'absorbing heat' stage the chamber temperature continues to rise of course, and typically gets to around 50C before the print actually starts.  So perhaps you can leave your printer 'pre-heating' in the closet for a while before you print, just to make it nice an toasty in there.  Can you start the print remotely without having to open the closet door?  Do you perhaps have a fan heater that can be used to raise the closet temperature independently?