Bed Leveling - Exact or Tolerance?

Does the Bed have to be exactly level in all corners or is there some kind of tolerance? What is the best reference point from the bed to measure from? I am thinking that one of the reasons my ABS parts come up on one side could be that my bed is not level enough. Thanks for your help.

Mike

It has to be level to within small part of the layer height. With say 0.4mm layers it should be better than about 0.05mm.

I move the nozzle over each of the four corners and level them. I have to repeat that several times as each adjustment tends to affect the others when there are four points to adjust on a PCB bed. It is much easier with three points on a stiff aluminium bed.

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[www.hydraraptor.blogspot.com]

This part helps with leveling and saves plastic:

[www.thingiverse.com]

I use a feeler gauge to level the bed to my base layer height. I find that moving the head as close as possible to the adjuster screw, rather than out to the corner of the bed minimizes the back-and forth of adjusting (less lever effect from the interaction of the other three adjuster screws).

I use the same method as billmi but I use a sheet of printer paper which in the USA is just shy if 0.1 mm. I adjust the height so that I can feel a slight resistance when I push and pull the paper. If the bed is really off, then rolling a round rod is safer to avoid crashing the nozzle into the bed.