HOW TO LEVEL YOUR 3D PRINTER BED

Levelling - more accurately, tramming - aligns your build plate so the nozzle stays the same distance from the surface as it travels in X and Y. A bed that's tilted by even 0.2 mm across its width will have under-extruded lines on one side and over-squished lines on the other - first layer adhesion breaks down on the high side, elephant foot appears on the low side. Auto bed levelling (BLTouch, CR-Touch, Bambu's MicroLidar, Prusa's mesh sensor) corrects for tilt digitally by adjusting Z height per XY position during printing. It's powerful but doesn't replace physical levelling - if your bed has 1+ mm of physical tilt, the firmware works hard to compensate every move and the print suffers. Get the physical level right first, then let auto-levelling smooth out the residual variation.

Manual paper-drag levelling: Ender 3 / CR-10 / Sovol stock, any printer with adjustable bed corners and no auto-levelling sensor. Re-do after any physical move, every 20-30 prints, or whenever first-layer quality drifts. Auto bed levelling: any printer equipped with a sensor. Run a fresh mesh after physical move, after any bed surface change (PEI swap, glass plate), or every 50 prints. Run after the bed is at print temperature - thermal expansion shifts the surface. Don't bother re-levelling when: the printer hasn't moved, no hardware has changed, and first-layer adhesion is still good.

Manual (paper-drag) method: 1. Heat the bed to print temp (PLA 60C). Skip this and you're levelling against a cold surface that will warp when heated. 2. Home the printer (`G28`). 3. Disable steppers (`M84`) so you can move the print head by hand. 4. Place a sheet of regular printer paper between nozzle and bed at one corner. Move the print head to that corner. 5. Adjust the bed-levelling knob until the paper drags with light friction - you can pull it but it catches on the nozzle. 6. Repeat at the other 3 corners, then once in the centre. 7. Re-check all 5 points - adjusting one corner shifts the others. Iterate until all 5 points have the same paper-drag friction. Auto bed levelling (BLTouch / CR-Touch / Bambu / Prusa): 1. Heat the bed to print temp. 2. Run a fresh probe mesh. Marlin: `G29` (after `G28`). Klipper: `BED_MESH_CALIBRATE`. Bambu/Prusa: built-in 'Auto bed levelling' from menu. 3. Inspect the mesh deviation. Most printers show min/max Z values. If the range is more than 0.4 mm, the bed itself is physically tilted or warped - tighten bed-mounting screws or replace the plate before relying on the mesh. 4. Save the mesh. Marlin: `M500` after `M420 S1`. Klipper: `BED_MESH_PROFILE SAVE=default`. Bambu/Prusa: auto-saved. 5. Set Z-offset. Auto-levelling sets the relative shape; Z-offset sets the absolute height. Run a first-layer test square after levelling and adjust Z-offset live.

Levelling cold. Heat the bed first - thermal expansion is real and matters. Levelling at the four corners but not the centre. A bowl-shaped or domed bed levels fine at corners and is way off in the middle. Trusting auto-levelling on a physically warped bed. Auto-levelling can correct ~0.4 mm of tilt cleanly; beyond that, prints have visible Z bands. Fix the physical bed. Skipping Z-offset adjustment after auto-levelling. Auto-mesh defines the shape; Z-offset defines the height. You need both. Using thick paper or a feeler gauge instead of regular printer paper. Standard printer paper is ~0.1 mm thick. Thicker materials throw off your reference Z height.

After levelling, dial in Z-offset with the live first-layer test. For first-layer problems that levelling doesn't fix, see the first-layer-not-sticking guide. For Z-banding patterns that survive levelling, that's a mechanical Z-axis issue.