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When manually calibrating my Rostock Max V2 I would bring the hotend and bed up to temp before setting the Z height. Should I do the same when autocalibrating the Artemis, or should I calibrate at room temperature with the hotend and bed turned off?

With my existing Duet conversions, I have a G28 and G32 in the "start" script of the slicer. This homes and calibrates before the print starts. Since the calibration is so quick, it doesn't cost you anything to run it every time. Just make sure you give the nozzle a quick swipe with a cloth as it's homing.

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I can't speak for the Artemis in particular. but for most delta printers:

1. Heating the bed may cause it to warp and/or expand a little. So any sort of bed probing is best done with the bed hot.

2. If the printer uses the nozzle as the probe, you need to make sure that there is no solidified plastic on the end of it. So the nozzle needs to be hot enough to melt the plastic. OTOH probing the bed with the nozzle at full printing temperature may not be good for the bed surface, depending on what it is (e.g. PEI). So I probe with the hot end at 190C.

So I did a little testing after work during the week and here is my conclusion (assumptions), at least for me:

Bed and Nozzle both on: This was what I was most interested in. I was unsure of the method due to the fact that heat causes things to expand. What I found that because the hot build plate is expanding with the clips holding it in place it is putting increasing pressure on the fsr contact points. This most likely in my opinion was one cause as to why I was getting inconsistent measurements and errors.

Bed and Nozzle both off and Bed off and Nozzle on: Oddly enough the results for these tests came out close enough that I feel comfortable calibrating with both off if necessary. I was able to get down to a calibration deviation of 0.00 using both methods and stopped worrying about cold vs hot calibration at that point.

I'm late to the party with this answer, but I did a bunch of testing and didn't find any significant amount of difference between hot and cold calibration. I calibrate with everything cold and haven't noticed any high or low spots. I did notice that if you heat soak the bed at a high temp (100+), eventually the FSR's get warm enough that they'll provide inconsistent results. For that reason I generally tell people to leave it cold when they calibrate.