This file is designed to help you dial in your bed level so that you can get more reliable prints every time! This file and instructions can be used with just about any FDM 3D Printer but I'll reference the Ender3 since it is very common and that is what I am using.

About the model:
This model contains 6 concentric squares. The largest is 150x150mm and they step down in 10mm increments until the smallest square which is 100x100mm. Each square is .4mm wide and .4mm tall. The corners are rounded to prevent the machine from starting and stopping in the corners, which tends to deposit additional material that can be misinterpreted as needing adjustment.

Note: Patience is very important when it comes to calibration. Do not rush and make too many adjustments in a short period of time, you can end up chasing your tail this way. It is best to make a small adjustment then allow the printer to traverse 1-2 axes before making another adjustment. You will likely have to abort and restart the print many times during this process This process can take about 1hr.

1. Watch this generic bed leveling video for some basic tips and the paper drag test mentioned below. Ignore the parts about sending commands to adjust the bed height since we will be using the manual adjusters on the Ender3. https://www.youtube.com/watch?v=ED1Gxvw2Rmw

2. Perform the standard "paper drag" calibration to get to a "close" bed level. Do not get too carried away with trying to find the "right" amount of drag, just get it to where they all drag about the same amount. We will refine the calibration in the following steps.

3. Configure your slicer to use a "skirt", set it to 3-4 loops. This will slowly draw a perimeter around the print before it starts on the actual print. We will actually focus a lot on the skirt itself in this process so do not omit this step!

4. Slice and print the file. Run the machine with default settings.

5. Allow the machine to print the first loop of the skirt. If it sticks, Great! If not, make slight adjustments on the high/low points and try the print again until the first loop sticks.

6. With the first loop down, now you have a reference line to evaluate how your bed level adjustments affect the results on subsequent lines. You should be able to rub your finger over the printed line without it coming off the bed.

7. Allow the machine to continue printing the skirt lines. Most slicers will print skirt lines adjacent to the previous line so here you want to look at how well the lines merge. If there are small gaps between the skirt lines you need to raise the bed in those areas until the lines are clean and touching each other. If the lines are really smooshed together and rough, you need to lower the bed in those areas. Make very small adjustments one corner at a time. You may have to restart the print many times at this point in the process. Be patient.

8. As the lines are printed, observe the line widths on the four sides of the bed. As the head moves from the front to back or left to right you may notice the line tapers from wide (bed is too close) at one end to very narrow on the other (bed is too far). Make adjustments until all lines are clean, smooth, and the same width.

9. Once the print can be completed with all lines sticking well (not coming loose when you slide a finger over it) consider yourself calibrated!