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The most important skill in 3D printing

If your first layer sticks evenly, prints succeed. If it does not, they fail. Bed leveling sets the nozzle the perfect distance from the bed - about the thickness of a sheet of paper - across all four corners. This page takes your time and patience, but it is the skill that makes everything else work.
You will need a sheet of printer paper and the SD card (in the white flash-drive reader from the parts bag). Get the bed-leveling G-code files onto the card first (see the note below).

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Download the leveling files

Copy these three files onto your microSD card before you start. Use M1 if you have an 8-bit board (older Ender 3) or M2 if you have a 32-bit board (Ender 3 V2 / newer) - if unsure, try M2 first.

STEM_M1_bed_level

Leveling routine for 8-bit Ender 3 boards (M0 pause).

STEM_M2_bed_level

Leveling routine for 32-bit Ender 3 boards (M25 pause).

STEM_bed_level_print

The squares test print you run after leveling.

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Insert the SD card

1

Get the leveling files onto the card

Pull the microSD card from the flash-drive reader. Use the reader’s USB end to copy the bed-leveling G-code files (STEM_M1, STEM_M2, and STEM_bed_level_print) onto the card from your computer. Do not lose this tiny card.
2

Insert it into the printer

Push the microSD card into the slot on the front of the printer, contacts facing down, until it clicks.

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How the leveling knobs work

Under each corner of the bed is a large knob on a screw. This is the key relationship:

Loosen = bed rises

Loosening a knob raises that corner of the bed up toward the nozzle.

Tighten = bed lowers

Tightening a knob pulls that corner of the bed down away from the nozzle.
Diagram showing loosening a leveling knob raises the bed and tightening lowers it

Loosen to raise the bed, tighten to lower it - the core relationship of leveling

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Start from a raised bed

1

Lower all four knobs fully

At each corner, spin the knob so the bed rises as high as it goes (the screw nearly disappears). Keep a finger under the screw so the knob does not fall off. Do all four corners.

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Run the leveling routine

1

Open the leveling file

On the LCD, click the knob to open the menu. Go to Print from TF card → STEM_M2 bed level → Print. The printer homes itself using the limit switches, then pauses.
2

Resume to the first corner

Select Resume. The nozzle moves to the front-left corner.
3

Do the paper test

Slide a sheet of paper between the nozzle and bed. Tighten that corner’s knob (which lowers the bed) until the paper slides with a light scratch - a “4 out of 10” of resistance. Not free (too far), not ripping (too close).
4

Move corner to corner

Click the knob to advance the nozzle to each corner in turn - front-left, back-left, back-right, front-right - and repeat the paper test at each. Aim for the same feel at every corner.
Diagram of the four-corner leveling order across the print bed with a center check

Work the corners in order, then check the center

5

Check the center, then do a second pass

The routine sends you to the center to check, then back around all four corners. Leveling one corner slightly un-levels others, so a second full pass fine-tunes everything.

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The paper-test feel

Diagram of the paper test resistance scale from too far to too close

The nozzle should pinch the paper with a light, even scratch - not free, not ripping

Consistency matters more than perfection. The goal is the exact same light scratch at every corner. The second pass is where it comes together - do not skip it.
The SD card is seated, you have completed two full passes of the paper test, and all four corners plus the center have the same light-scratch feel. You are ready for a test print.

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Up next

Time to prove it works - run the print bed test and read the results.