You have an IR? Can you please tell the temperature difference from center to the edges of the bed? I would like to know how big the difference is. maybe the edges are too cold to allow sticking and thats why i get warping when printing saome large objects. Thanks.

They are with in 10 degrees from the center to aprox. 1/2" from outside edge. Some spots are with in 5 degrees.

Just recently bought a SD4 and started off  having lifting issues.  Several things attributed to the problem. The print table was warped really bad so I straighted it out on a press.  The Temperature is off by 25 degrees.  Program shows it being 110 degrees and IR shows 85 to 90 degrees. Hairspray helped the adheasion.

temps can vary like +/- 25c  on printers easy, is why some do fine at temps others dont. and hair spray is ok long as you have removable glass bed and dont mind the smell. just dont use it inside printer as it gums up everything that moves bad

n2ri wrote:

over heating bed causes warp and burn on long prints over an hour. its why I went with 80c

I'm not sure I agree with this statement as the numbers just don't add up.
Of course in could depend on the type of filament used it doesn't apply to ABS.
With a bed heater like mine (signature) I have never seen anything resembling burnt filament.
Warping is usually caused by uneven cooling from top to bottom or to rapid of cooling.

I have proof of this happening! on neutral ABS with long print and bed temp was only 90c. it caused edges to turn yellow brown and curl up/back and just over 3hrs into a 4.5 hr print it came loose. making it a waste of time and material. once I tuned bed down to 80c never had issue again. and thin layers are worce about this. the part that curled up about 1/4" was a corner of the filament cleaner/guide that holds chunk of foam inside and screws onto 2nd part through back hole of SD2 to feed filament through. it was like 50 layers thick down to like 12 layers thin and the hole thing finally peeled loose b4 finished so had to lower temp and reprint. so dont think it cant!
even a turkey that requires cooking at 350 degrees 'F' for hours per lbs will also cook or even burn if left at much lower temps for long enough time like Turkey Jerky.
there is no need to heat bed above temp needed to hold bottom layer from shrinking. so dont set at max temp b4 melting but min temp b4 shrinking loose from 1st layer adhesion which is a bit above 70c unless temp sensor is in wrong place for exact read. its like testing bath for baby ;^)