Phrozen Sonic: the print does not stick to the build plate; calibrate (level) the Z axis with paper

Symptom

On a Phrozen Sonic, parts do not stay on the build plate or only stick in one area, and the build plate needs levelling to the LCD with the Z-axis calibration (Z-CALIB).

Likely causes, from most to least likely

1. The build plate is not level with the LCD and the Z-axis calibration has not been done.
2. The build plate screws were tightened unevenly or not fully (on the Sonic Mega 8K, if they are not tightened properly the calibration drifts with use).
3. Cured resin on the build plate or the LCD stops the plate from sitting properly.
4. With ACF film it was calibrated with a single sheet of paper: Phrozen says to use three A4 sheets with that film.
5. The bottom layer exposure is too short for the part to bond to the build plate.

Checks to tell which one it is

• After calibrating, tug the paper at all four corners: the resistance should be the same.
• Check that the build plate and LCD are clean, with no cured resin.
• Check which film your vat has (FEP, nFEP or ACF).

Before you start

Uncured resin irritates skin and eyes: wear nitrile gloves and safety glasses, ventilate the room and do not look at the UV light. Before taking anything apart or cleaning it, switch the printer off and unplug it, unless a step says otherwise. If in any doubt, stop and ask a professional.

Step-by-step fix

1. Prepare

   Wearing gloves, remove the UV cover and the vat and clear everything off the platform. Clean the build plate and LCD with alcohol (Phrozen uses 95 % sanitising alcohol; on the Sonic Mega 8K it suggests spraying it and waiting about 15 minutes to soften residue).

   Check: The build plate and LCD are clean with no residue.

   If that does not fix it: If resin remains, spray alcohol again, let it work for about 15 minutes and clean once more.

2. Calibrate the Sonic Mini 8K or Sonic Mighty 12K

   Loosen the 4 side screws on the build plate so it moves freely. Place an A4 sheet (about 0.07 to 0.10 mm) on the LCD, or three if you use ACF film. Run TOOLS → Z CALIB → NEXT (on the Mighty 12K, TOOLS → Z-axis Control → Z-CALIB). Wait 1 or 2 minutes for the plate to lower onto the paper, press it so it seats and, while holding it, gradually tighten the 4 screws diagonally (for example: top right, bottom left, top left, bottom right).

   Check: Tugging the paper at the four corners gives equal resistance; press DONE, wait for the plate to rise and remove the paper.

   If that does not fix it: If the resistance is not equal, loosen the screws and repeat the calibration.

3. Calibrate the Sonic Mega 8K

   Remove the handles, mount the plate aligned with the pins and secure it. Loosen the 4 small screws until they no longer protrude and, gradually, the 4 large ones (not too far: the plate could drop and damage the LCD). Place 3 to 5 A4 sheets cut in half on the LCD and run TOOLS → Z-CALIB → START. When it touches the LCD, hold it, tighten the small screws while tugging the paper and then the large ones in two rounds: first with the long side of the Allen key, then with the short side.

   Check: Paper resistance is equal at all four corners; raise the plate 30 mm before removing the paper and refit the handles.

   If that does not fix it: Do not overtighten the small screws: the calibration becomes inaccurate.

4. If it still does not stick

   Increase the bottom layer exposure time, as Phrozen suggests when models fail to attach to the build plate.

   Check: The part stays attached to the build plate.

   If that does not fix it: Contact Phrozen support with photos or videos of the problem.

Prevention

• Tighten the screws properly at the end of the calibration: if they are loose, the calibration drifts with use.
• With ACF film, always calibrate with three A4 sheets.
• Keep the build plate and LCD clean.

Still not fixed?

Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.

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Printers it applies to

Phrozen's resin printers: Sonic Mega 8K S, Sonic Mighty 8K, Sonic Mighty 12K and Sonic Mini 8K S.

Official sources

This guide summarises the official documentation linked here:

• [Sonic Mini 8K] Z-axis Calibration · Phrozen
• [Sonic Mighty 12K] Z-axis Calibration · Phrozen
• [Sonic Mega 8K] Z-axis Calibration · Phrozen