Setting the Z-Axis Home Position

Overview

The distance between the nozzle and the print surface is an extremly important factor in print quality and reliability. With the bed at the Z home position, the gap between the hot end nozzle and the top of the print surface should be 0.010 inches (0.3mm, or about 3 sheets of standard paper). If the gap is too small, the hot end nozzle will either contact the print surface or squish the first layer, potentially making your print difficult to remove from the bed. If the gap is too large, the first layer of plastic will not adhere to the print surface adequately and could lead to significant part failure and machine damage. This article will guide you through the process of setting the Z-axis home position for the ideal first layer height. 

Tools Needed: 

• GB3, GB3+, GBX, and Terabot
  • Z-Axis tool setter, or 0.010" (0.3mm) feeler gauge, or 3 sheets of standard paper
  • 8mm wrench
• GB2
  • 4mm Allen key
  • Calipers or micrometer
  • Z-Axis tool setter, or 0.010" (0.3mm) feeler gauge, or 3 sheets of standard paper
  •  

Instructions (GB3, GB3+, GBX, and Terabot):

If the bed and nozzles are not level, please consult the steps outlined in "Section B" of the Quick Start Guide for your specific 3D printer: Gigabot Quick Start Guides and in this article: Leveling nozzles for Dual Extrusion

If the bed and nozzles are level, you will adjust the Z-Axis home position adjustment bolt so that it contacts the upper Z limit switch at the right time point during the homing process. This screw is found on the front right corner of the bed frame as shown below:

Terabot:
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GB3+

Exabot:

This bolt is upside down, so turning it clockwise when viewed from above lowers the bolt, making it hit the limit switch later in the homing process, therefore bringing the bed closer to the nozzle. The future directional turns for the instructions will be assuming it is viewed from above.

****If you have an Exabot, please reverse these directions which are in bold below.****

Please proceed as follows:

Toolsetter method:

1. Select heat the bed to 60C and nozzles to 200C (If using GBX, just press "Preheat PLA all") without the enclosure on and leave for 1 hour. This allows the printer to thermally expand and reach it's steady-state position while heated.
2. To ensure the nozzle does not crash into the bed, turn the Z homing bolt counter-clockwise 4 rotations. This brings the bolt closer to the limit switch and therefore the bed further from the nozzle. If your hot ends are already far from the bed in the home position, you can skip this step.
3. Use the Viki to home the Z-Axis. This resets the Gigabot's Z home position
4. Go to move axis, then move the bed to 101.3mm for Gigabot (or the zero height of your tool setter minus 0.3mm), or 101.6mm for Terabot and Exabot (or the zero height of your tool setter)
5. Move the print head to the middle of the bed.
6. Place the touch off gauge in between the left hot end nozzle and the bed and analyze where the needle is:
   • If the needle is to the left of zero, the bed is too far from the nozzle. Turn the Z homing bolt clockwise to move it away from the limit switch. The bolt will travel 0.8mm per rotation, but err on fewer turns so that the nozzles do not risk crashing into the bed
   • If the needle is to the right of zero, the bed is too close to the nozzle. Turn the Z homing bolt counter-clockwise to move it towards the limit switch. The bolt will travel 0.8mm per rotation
7. Remove the tool setter from under the nozzle
8. Repeat steps 3 through 6 until your toolsetter needle reads zero, indicating that the nozzle and bed are the optimal distance away from the bed
9. Try a print and analyze the first layer.

Shim Stock Method:

Assuming the bed and nozzles are level, you will adjust the Z-Axis home screw so that it contacts the upper Z limit switch at the right time point during the homing process. This screw is found on the front right corner of the bed frame as shown below:

1. Select heat the bed to 60C and nozzles to 200C (If using GBX, just press "Preheat PLA all") without the enclosure on and leave for 1 hour. This allows the printer to thermally expand and reach it's steady-state position while heated.
2. To ensure the nozzle do not crash into the bed, turn the Z homing bolt counter-clockwise 4 rotations. This brings the bolt closer to the limit switch and therefore the bed further from the nozzle. If your hot ends are already far from the bed in the home position, you can skip this step.
3. Use the Viki to home the Z-Axis. This resets the Gigabot's Z home position.
4. Move the print head to the middle of the bed.
5. Place the 0.3mm or 0.01 inch shim stock in between the left hot end nozzle and the bed:
   • If the shim stock can slide freely between the bed and nozzle, the bed is too far from the nozzle. Turn the Z homing bolt clockwise to move it away from the limit switch. The bolt will travel 0.8mm per rotation, but err on fewer turns (or do partial turns when getting close to the shimstock) so that the nozzle does not risk crashing into the bed
   • If the shim stock can not slide freely between the bed and nozzle, the bed is too close to the nozzle. Turn the Z homing bolt counter-clockwise by a half turn to move it towards the limit switch. The bolt will travel 0.8mm per rotation
6. Repeat steps 3 through 6 until the shim stock has a slight friction when sliding between the nozzle and bed, indicating that the nozzle and bed are the optimal distance away from the bed
7. Try a print and analyze the first layer.

Let me know how this works out for you and if you have any questions!

GB2 Instructions: 

1. For GB2, adjust the Z home position using the Z-axis limit switch screw, found on the right rear corner of the bed frame. For GB3, the screw is located on the right front corner of the bed frame. Adjust this screw using a 4mm Allen key.
2. Ensure the M5 x 65 screw (M5 x 70 for GB3) is inserted into the Z-axis limit switch block with the head sticking up about 50mm above the block, and the lock nut (GB2 only) is tightened.
3. Position the extruder and hot end at the rear of its travel (Max Y position).
4. When homing the Z-axis, ensure the hot end does not come into contact with the bed. Manually move the print head to the very front or back of the machine so the nozzles are not above the bed. You can also manually stop the bed motion by triggering the Z-axis limit switch with your finger.
5. Using the Pronterface or Simplify3D control panel or the Viki, press the Home Z-axis button.
6. Adjusting the M5 x 65 (M5 x 70 for GB3), lowering the screw will raise the bed higher (closer to the nozzle), and raising the screw will lower the home position (further from the nozzle). Ensure the lock nut (GB2 only) is tightened after adjusting the limit switch screw.
7. One revolution of the screw will change the bed height 0.8mm (0.031").
8. Use a 0.010" feeler gauge or 3 sheets of paper to gauge the distance between the nozzle and the bed. Keep adjusted the screw and homing Z until there is slight friction on the feeler gauge or paper between the bed and nozzle.
9. The photo below provides a visual reference for what your first layer should look like. 

For GB3, the screw is located at the front right corner of the bed frame.

For initial calibration, please proceed to the next calibration step (Select Single or Dual depending on your extruder type): Single Extrusion Calibration | Dual Extrusion Calibration

Questions or concerns? Reach out to our support team at support@re:3D.org or open a support ticket.