bed auto leveling… I seem to have it set up and working… in that it moves around and takes some points around the bed when i run a G29… but then i jog the printer sideways and the print head hit the bed… once you have run the G29… should it not move the Z up and down when you jog the X Y to keep the head the same distance off the bed?? Whats the story? Thanks for the help again guys.
Are you doing anything after the G29? Like a G28 home?
No
The auto-level theory is sound, but it does assume that the build plate is perfectly flat.
For my Printrbot, the G29 program samples the height at 3 points and computes the plane defined by those 3 points.
But, if the actual plate is warped, bowed or curved in any way then the computed plane is a poor approximation.
To see how bad your plate is, Run G29 to auto-level, then set your extruder height to about 10mm, and move the extruder around on the X-Y axes and execute the G30 program for many points, and keep track of the actual heights reported at each X-Y location.
The G30 program is a spot-test program that reports the travel distance required for the Z probe to trigger.
This will give you a 3D profile of the actual build plate. I am guessing that your plate is warped upwards away from the G29 sample points, and this means your extruder can collide with the plate in some places.
In my case, the build plate was very low at the back-right edge, so then I used spring washers to twist it back and then it became very close to truly flat.
If your plate is very badly warped, it’s probably best to ask for a replacement under warranty.