Belt and pulley mechanical issues

Loose belts, worn idler pulleys and mechanical play in the motion system show up as print quality issues — layer shifts, rounded corners, ringing, dimensional inaccuracy. They correlate with machine age, surfacing after several months of continuous use.

Symptoms

• Layer shift — layers offset visibly during a print, geometry skewed
• Rounded corners that should be sharp
• Ringing / ghosting on vertical surfaces (echo of corners)
• Dimensional inaccuracy — printed parts not matching CAD dimensions
• Clicking / clunking sounds during XY moves or homing
• Squeaking during Z moves (separate issue — see Z screws below)
• All of it stops the moment the belt is brought back to tension

Possible causes

1. Belts loosened over time — the most common after months of use
2. Idler pulley bearing worn — the bearing inside a free-running pulley is the real wear item; clicking or clunking during fast moves
3. Z lead screws unlubricated — squeaking, sometimes louder during bed leveling
4. Frame bolts loose — rare but possible after shipping or relocation

Diagnosis

Step 1 — Listen

• Clicking / clunking during XY → idler bearing or loose belt
• Squeaking during Z → unlubricated lead screws

Step 2 — Belt tension check

With the machine off:

1. Press a finger on each belt mid-span
2. The belt should feel firm — like a guitar string at moderate tension. There is no torque figure or frequency to hit: tension is set by feel
3. If you can deflect it more than a few millimeters with light pressure → too loose
4. Compare both X and Y belts — they should feel similar

Step 3 — Visual inspection

• Look for fraying, missing teeth, cracks on belts
• Inspect the belt body carefully: if the casing is worn through and you can see the reinforcing cords protruding, replace the belt immediately regardless of how the tension feels. On older machines these are fine steel wires — that fraying is exactly why current belts use fibreglass instead
• Look for play in the idler bearings (push laterally on the idler)
• Check Z lead screws for old / dried grease

Step 4 — Hand-move friction test

With the machine off, grasp the extruder carriage and slide it slowly along each axis by hand. You should feel only light, even resistance from the motor magnets. Any roughness, binding, or sticking at specific points indicates:

• Dirty or dry linear rails → lubricate (see below)
• Loose frame bolt or deformed carriage
• Foreign object (pellet, debris) in the rail

A machine producing Y-axis layer shifts and making grinding noises that still prints well is usually a linear rail lubrication issue, not a belt or motor problem.

Fix

Tightening belts

1. Power off the printer
2. Locate the belt tensioner for the affected axis (typically a screw or eccentric on one of the idler ends)
3. Tighten in small increments — about 1/4 turn at a time
4. After each adjustment, hand-move the axis end to end:
   • Should feel smooth, no binding, no jumping
   • Belt should not deflect more than a few millimeters at mid-span
5. Don’t over-tighten — too tight wears the bearings and motor

Lubricating linear rails (XY)

If the hand-move test reveals friction or grinding on XY:

1. Power off
2. Apply linear rail oil (ISO VG32 or equivalent machine oil — not WD-40, not grease) to the carriages along the rail
3. Slide the carriage end-to-end 10–15 times to distribute oil inside the ball bearings
4. Wipe excess oil from the rail surface
5. Re-test by hand — movement should be smooth throughout

Note

Do NOT apply grease to linear rails (it attracts pellet dust and clogs the bearings). Use only thin, clean rail oil.

Temporary acceleration reduction while diagnosing

If the machine is showing intermittent layer shifts and you need to keep printing while investigating, reducing travel acceleration (moves where the nozzle is not extruding) can eliminate the symptom temporarily without changing print time. Do this via the G1OS Mainsail dashboard and restore the original value once the mechanical issue is resolved.

Lubricating Z lead screws

If Z is squeaking:

1. Power off
2. Apply a solid screw grease (lithium-based or PTFE-based) to the Z lead screws
3. Move Z up and down a few times to spread the grease
4. Wipe excess off the linear rails (don’t get grease on the rails — they need a different lubricant)

Note

Solid grease, not spray. Spray oils evaporate and need frequent reapplication. Some customers use white lithium grease tubes, which work well.

Replacing worn parts

• Frayed belt → replace (Ginger Additive spare). Use the fibreglass-reinforced GT2, not a steel-corded one — steel cords fray on the G1’s small pulleys, which is why the machine moved away from them
• Worn idler pulley → replace. What actually wears is the bearing inside the free-running pulley. The pulleys on the motor shafts are held by a key plus a grub screw and do not slip
• Cracked pulley → replace

Routine maintenance

The motion system is one of the parts that does need regular attention — belts and idler pulleys are the machine’s main moving parts.

• Belt tension on X and both Y belts
• Belt condition — check the cords, not only the teeth
• Idler pulleys — the free-running ones; the pulleys clamped to the motor shafts are not the ones that wear
• Z lead screws — re-grease roughly every 4 months, see Z lead screws

How to prevent

• Don’t over-tighten belts — adds strain and shortens life
• Avoid leaving the machine sitting unused for very long periods (lubricants migrate)
• After moving the machine, re-check belt tension and frame bolts
• Listen for new sounds — they’re early warnings

Notes

• Strong correlation with machine age — first reports usually after several months of use
• Customers often resolve this themselves once given a one-line tip (“check belt tension”), so a clear short answer is high-value
• Z squeaking is often misdiagnosed as a motor or driver issue — it’s almost always lubrication

Related notes

• Belts and pulleys
• Z lead screws
• Linear rails
• Frame
• Lubricating linear rails