No, you dont need to as it saves the mesh, if you change the tool head or the bed plate you would need to do it but otherwise you just leave it, turn it on and print and then turn it off. I keep a record of the mesh using the bed visualizer plugin on Octoprint or the UBL mesh editor.
You also need to level it with the tool head hot and the bed heated as well, this is now available in the software. Manual calibration with the card at each point will usually be better than the automatic calibration. if you calibrate with a cold nozzle it may have some filament on it affecting the drag on the card and throwing out the grid.
The sensor is a Hall effect device that uses magnetism to work. Under normal conditions you should be using the supplied steel Snapmaker printing bed, That would also act as a shield, keeping the two magnetised parts apart. but I suppose if you are not then You’ve nothing shielding the magnetism of the hall effect sensor from the magnetism of very bottom heated part.
That is not correct. It works similar to a metal detector that you use to fin things in the ground. One coil emits a signal, the other coil detects a signal, and the range is only a few millimeters.
I used to calibrate every time just about. I wasn’t as worried about the power off, knew it tried (early firmware and software had issues) to maintain the calibration grid, for me it was more thinking removal/flex/replace of the spring plate was likely to mess it up, I was putting too much ‘set’ into it or something. Plus all my history before SM was with a really really (really!) old school machine with the 3 spring-loaded allen bolts to manually bed level, that just always required fiddling because the structural parts were half laser cut ply that warped with temperature and humidity changes day to day. (Rest in pieces, my old Solidoodle V2 “Pro” (<-hah on that last part!) )
I don’t know when but at some point I just started trusting. Now I only calibrate after either totally trading between or flipping faces on the print plate, or swapping tool heads (between lasering and printing) or replacing nozzles and/or hotend.
At this point I’ve owned the A250 since Kickstarter receipt and have only recently swapped to the ‘upgraded’ print head from my original…but never replaced a proximity sensor aside from that effectively. (My original print head probably still works if I clean it out to keep as a backup, I just got lazy and swapped to the upgrade I’ve had sitting on the sidelines from a discount offer purchase after a self-induced clog – 100% infill with any pattern that ‘crosses over itself’ too much just scrapes too much crap back into the nozzle, dumb mistake on my part…)