Tensioning the belts on the X1, P1, A1 and H2D (oval circles, ringing or tension alert)
Guide based on the manufacturer's official documentation; usi3d has not yet verified it on a machine.
Technology: FDM · Brand: Bambu Lab · Symptoms: Loose belts, Ripples or echoes on the walls (ghosting), Shifted layers (layer shift) · Updated on 9 October 2026
Symptom
Circles come out oval, ringing or dimensional errors appear, the printer warns after calibration that a belt needs tensioning (the A1 asks through an HMS alert) or it detects lost steps and asks you to check for layer shifts (0300-800C).
Likely causes, from most to least likely
- A belt that has lost tension with use: the natural frequency of the system drops and vibration compensation gets worse.
- Belts with different tensions on each side, for example after cleaning the rods without equalising them.
- Tensioner screws overtightened by hand: it does not help and can damage parts.
- Old calibration: after tensioning or cleaning, the printer has not measured the resonance again.
Checks to tell which one it is
- Run the vibration calibration: the printer sweeps frequencies (a noise rising in pitch) and warns if the frequency has changed.
- On the X1 and P1, during homing both sides of the gantry should reach the front at the same time.
Before you start
Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.
Step-by-step fix
X1 and P1
Switch the printer off. Loosen (do not remove) the four tensioner screws at the back, move the toolhead back and forth several times (and the X axis along the Y axis), take it to the rear and tighten the four screws again: the tensioner spring sets the right tension. Do not overtighten them.
Check: The toolhead moves smoothly and calibration no longer asks for tensioning.
If that does not fix it: Check that the tensioners move when you press the belt next to the toolhead; if they do not, find out why before continuing.
A1: X belt
Raise the X axis to mid height, switch the printer off, loosen the tensioner screw at the back of the toolhead by one turn with the H2.0 key, move the toolhead side to side three times and tighten it again.
Check: The toolhead moves without play.
If that does not fix it: Repeat the process carefully.
A1: Y and Z belts
For Y, move the bed back, remove the small cap at the front of the base, loosen the two tensioner screws by one turn (do not remove them), move the bed back and forth three times and tighten. For Z, move the bed forward, loosen the two screws next to the right column by one turn, home the printer, move the X axis up and down once without the nozzle hitting anything and tighten.
Check: The axes move without jumps.
If that does not fix it: Do not remove the Y tensioner screws completely: the tensioner would have to be reassembled.
H2D
Switch the printer off. For the XY belts, loosen the four tensioner screws 1-2 turns, move the toolhead several times, take it to the rear aligned and tighten without overdoing it. For the Z belt, remove the glass top, tilt the printer with two people, loosen the tensioner screw, move the Z belt 3 to 5 times and tighten its fixing screw.
Check: With the printer upright again, the axes move without play.
If that does not fix it: If the belt is damaged, contact Bambu Lab support.
Calibrate afterwards
With the printer in its final position, switch it on and run the vibration calibration (vibration compensation or resonance frequency identification) from the screen or from Bambu Studio.
Check: Calibration finishes without alerts.
If that does not fix it: If it keeps asking for tensioning or layer shifts appear, contact Bambu Lab support.
Prevention
- On the X1 and P1, clean the carbon rods when you tension the belts: both change the resonance.
- Never grease the belts: they can slip and shift layers.
- Recalibrate after moving the printer or replacing parts.
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.
Printers it applies to
Bambu Lab X1 Carbon, X1, X1E, P1S, P1P, A1, H2D and H2D Pro.
Official sources
This guide summarises the official documentation linked here:
- X1/P1 Series Belt tensioning procedure · Bambu Lab
- A1 Belt Tensioning · Bambu Lab
- H2D Belt Tensioning Procedure · Bambu Lab
- Printer Calibration Guide · Bambu Lab
- Bambu Lab P1 series printer Maintenance Recommendation · Bambu Lab
- Error Code · Bambu Lab
This guide is general information: usi3d has summarised it from the official documentation linked here, and it may not match your model, its version or its firmware. If in doubt, follow the manual and the support of your printer's manufacturer. You decide what you do with your machine, and working on it may affect its warranty.