Voron Trident and 2.4: A/B belts loose, too tight or uneven

Symptom

On a Voron Trident or 2.4 (CoreXY), the A and B belts have lost tension, are too tight or have different tensions. Prints show defects, parts wear early, there is belt dust next to a pulley, or the gantry does not travel straight.

Likely causes, from most to least likely

1. The belts have stretched: they give during their break-in period and lose tension.
2. A and B have different tensions: on CoreXY, tightening one also changes the other.
3. Too much tension: overtight belts also cause mechanical problems and wear out sooner.
4. A belt rubs on a pulley flange; dust next to the pulley gives it away and it leaves marks on prints.
5. On the 2.4, the gantry is out of square: the X axis is racked at the front but not at the back (or vice versa) and the Z belts rub the printed parts.
6. If a belt keeps losing tension, something along its path is badly assembled or damaged.

Checks to tell which one it is

• Measure each belt with a sound analysis app (Voron lists Sound Spectrum Analysis on iOS, Spectroid on Android or Gates Carbon Drive with the motorcycle option): pluck the span and read the lowest frequency.
• Compare A and B with the gantry in the same position: they should read practically the same frequency.
• Look for black belt dust next to the pulleys.
• On the 2.4, move the gantry back and forth in X by hand and watch whether the idlers get pinched or the X axis twists.

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

1. Tension A and B by frequency

   With the motors disabled, move the gantry forward until the X/Y joint idler centres are 150 mm from the front idler centres. Pluck that span and adjust the tensioners until the lowest frequency is about 110 Hz, the starting point Voron gives (the low end of the range, roughly 2 lb of tension). Adjust A and B in turns until they match.

   Check: After moving the gantry back a few centimetres and forward again, both belts still match and read close to 110 Hz.

   If that does not fix it: Check whether a belt rubs on a pulley (next step).

2. Stop the belt rubbing on pulleys

   If you see dust next to a pulley, the belt is rubbing its flange: find that pulley and fix the rubbing before printing again, because it leaves defects on prints.

   Check: No more belt dust appears after several prints.

   If that does not fix it: On the 2.4, check the gantry squaring (next step).

3. Square the 2.4 gantry

   Follow the V2 Gantry Squaring guide: disable only the A/B motors, fully release their belts, drop the lower Z joints so the gantry hangs on the belts, partly loosen the extrusion joints and align the parts until the Z joints fit without forcing. Tighten again, re-tension A and B to about 110 Hz over 15 cm and heat soak the chamber for at least an hour and a half.

   Check: The gantry moves without pinching the idlers and the X axis stays straight.

   If that does not fix it: Run QUAD_GANTRY_LEVEL 3 to 5 times and fully tighten the Z joints while the machine is still hot, as the guide says.

4. Tension the 2.4 Z belts

   Raise the gantry until the fixed side of each Z belt is 150 mm from its idler centres. Pluck, measure and adjust: Voron gives about 140 Hz as a starting point. Lower the gantry a few centimetres, raise it again and measure once more.

   Check: The four Z belts are reasonably tight and even.

   If that does not fix it: If a belt loosens again, check how it is fitted (next step).

5. A belt that keeps loosening

   If a belt loses tension again and again, do not just tighten it more: with the printer off, check the parts along its path (tensioners, belt clamps and screws) for anything loose or damaged.

   Check: The frequency stays stable between checks.

   If that does not fix it: Replace the damaged part and tension again from the first step.

Prevention

• Check the tension from time to time, especially in the first weeks: belts stretch during break-in.
• Always tension A and B together and measure again after moving the gantry.
• At every maintenance, look for belt dust next to the pulleys.

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.

Tell the AI about your case

Printers it applies to

Voron Trident and 2.4.

Official sources

This guide summarises the official documentation linked here:

• Secondary Printer Tuning · Voron Design
• V2 Gantry Squaring · Voron Design
• Maintenance Guide · Voron Design
• Initial Startup · Voron Design