Here is a procedure to ensure a good starting bed level for your Taz:
- Check both Z leadscrews at the top where they enter the upper 608zz bearing. Both leadscrews should be all the way up and flush with the top center of the bearing as viewed from the top of the machine.
- with the machine off and the motors unplugged, measure the distance from the bottom of the Z leadscrew nut to the top of the lower Z leadscrew 608zz bearing. The distance should be identical on both sides. If they are not identical, manually turn one leadscrew on one side until they are identical.
- check the distance from the printed corner bed mounts to the aluminum bed mount plate. The distance from the bottom of each corner mount to the top of the mount plate should be the same initially, and the corner mounts should be parallel to the heated bed. It is possible for them to work loose at an angle, or to come un anchored from the bed but still attached by weight. If you have different heights at this point, reset them all to the height of the mount closest to the bed mount plate for now. This will ensure the mount is further from the nozzle, not closer to it when we start the printer back up here in a minute. THe nozzle expands thermally, it is important to level with the nozzle at full expansion for best results
- Turn the printer on, and heat it to normal operating temperature (bed and nozzle) Now wait a full 3 minutes.
- With the printer at temperature, locate a thin metal plate (about the thickness of a business card). The gauge that ships with the printer works well for this. Now move the nozzle to each corner of the heated bed, and use that gauge to carefully and without burning yourself adjust the corner of the heated bed until the nozzle is just touching the top of the gauge and the gauge is touching the top of the heated bed. Repeat this process on all four corners. Adjust the Z height adjustment target as needed to get the initial height for the first corner. Turning the cap head screws in the corner clockwise lowers the corner closer to the bed, counterclockwise raises it.
At this point all 4 corners of the bed should be at the same height relative to the nozzle. Now print the bed level test pattern gcode (on the SD card or available at download.lulzbot.com) and see if you get a good adhesion pattern that is consistant. Adjust the Z height screw up or down as needed. If after leveling you find this height drifts rapidly, consider applying a small amount of some elmers white glue or blue Loctite to the threads of the height adjuster (NOT red Loctite!) this will make it more difficult for that adjustment screw to turn accidentally.
If it continues to be a problem, take a look at the Micrometer endstop target modification.
Hope that helps!
If you find you have inconsistent results with the leveling, it is possible a portion of the frame is out of alignment, or the Z leadscrews on one side are out of alignment. There are additional fixes for that.