Tronxy X3A Bed Leveling

Before making test prints, it's necessary to level the bed.  I tried several times, and read several websites, before I finally converged on the process that worked for me.  So without further ado, here's my bed-leveling process.

Compress the bed adjusting springs

Adjust the nuts on the corners of the print bed to compress the springs as far as possible.  Be careful not to over-compress them.  You will over-compress them if the Y-axis roller screws run into the bottom side of the heat bed.  This distorts the Y-axis table and causes slop.  If you get them too tight, just loosen them a little bit.

Adjust the Z-axis limit

By default, the printer wants to start at Z=0.  It's possible to use G-code to make a printer offset (and that's what I'll do once I have the auto-level sensor), but in the meantime it's easy to adjust the Z-axis limit and the print bed to make everything work well.  Here's the procedure:

1. Home all axes, using the buttons on the LCD panel.
2. Look at the end of the extrusion nozzle relative to the surface of the print bed.  Is it a few mm or more above the bed?  You'll need to lower the Z-axis limit switch.  It it at or below the level of the bed?  You'll need to raise the limit switch.  Is it 1-2 mm above the bed?  Your limit switch is just right.
3. To lower the Z-axis limit switch:
   1. Loosen the nut holding the switch in place.
   2. Slide the switch down.
   3. Use the LCD panel and buttons to lower the Z-axis. Get extruder nozzle 1-2 mm above the print bed (your eye is a sufficient measurement device).
   4. While watching the limit switch output on the display, slide the limit switch up until the display says the limit switch is closed.  Tighten the limit switch in the new position.
   5. Return to step 1 and see if the limit switch setting is correct.
4. To raise the Z-axis limit switch:Slide the switch down.
1. Use the LCD panel and buttons to raise the Z-axis. Get extruder nozzle 1-2 mm above the print bed (your eye is a sufficient measurement device).
2. Loosen the limit switch.
3. While watching the limit switch output on the display, slide the limit switch up until the display says the limit switch is closed.  Tighten the limit switch in the new position.
4. Return to step 1 and see if the limit switch setting is correct

Level the bed

Now you need to get the bed leveled and adjusted to the proper height.  Here's how I did it:

1. Use the LCD panel to preheat the bed and extruder.  I don't know how important this is, but some websites mention that thermal expansion can be an issue.
2. Use the LCD panel to move the Z-axis to a position of 0.12 mm.  This corresponds to the thickness of a typical sheet of paper.
3. Move the X and Y axes to position the extruder over one corner of the bed.
4. Place a sheet of paper between the bed and the extruder nozzle.  Loosen the bed adjusting screw to allow the bed to rise toward the nozzle, while moving the paper back and forth.  eventually, you will feel a slight drag as the nozzle makes contact with the paper.
5. Repeat steps 3 and 4 with each corner, and verify that the drag is the same at all locations on the bed.

Now you should be ready to print a test part.