If you are having trouble with your Z-axis, first make sure you have properly calibrated your Z-axis before moving onto the troubleshooting.

Extruder printing in midair

There are a few common causes of printing in midair. If your printer is printing in midair, the following are the most likely causes:

1. A connection issue in your limit switch
2. Missing Start Gcode

Z limit switch not connected properly

If you try homing Z in manual controls, the platform should rise. If it does not rise, but will lower when you press "Z+" then your limit switch is likely the issue. Follow the procedure here for limit switch troubleshooting.

Missing Start Gcode

If when you click "Start Job" the printer starts printing before doing the following moves, you are missing the default start Gcode:

1. Extruder head moves to back right corner
2. Extruder head moves to near center of platform
3. Platform raises to meet extruder
4. Print starts

Follow the guide for Setting your Start Gcode to add or modify start Gcode in your software.

Z axis binding

There are 3 main causes of Z-axis binding; lack of grease, improperly set trimpot, or a bent rail or lead screw.

Lack of Grease/Dirty Rails

If your platform binds or gets hung up at random points, you may need to clean and reapply grease to your rails and lead screw. Try not to use petroleum based greases as they may slowly degrade ABS parts.

Improperly Set Trimpot

Another cause of intermittent binding may be a trimpot set slightly too low. Follow the directions for reseting your trimpots.

Bent Rails/Lead Screw

If you have a bend rail or lead screw, you will likely notice that the binding always occurs in the same location along the axis. This video for Z-Axis disassembly and reassembly is a good guide for replacing either of the components.