Belt and chain mechanical issues

Loose belts, worn chains, and mechanical play in the motion system show up as print quality issues — layer shifts, rounded corners, ringing, dimensional inaccuracy. Reported across 24+ customer cases, with a clear correlation to machine age (issues start to surface 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)
• After tightening: customer reports “everything is fine again”

Possible causes

1. Belts loosened over time — the most common after months of use
2. Pulley grub screws backed out — pulley spins on the motor shaft instead of driving the belt
3. Idler bearings worn — clicking / clunking sound during fast moves
4. Z lead screws unlubricated — squeaking, sometimes louder during bed leveling
5. Frame bolts loose — rare but possible after shipping or relocation

Diagnosis

Step 1 — Listen

• Clicking / clunking during XY → bearings or loose belt
• Squeaking during Z → unlubricated lead screws
• Knocking on direction changes → loose pulley grub screw

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
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 — Pulley grub screws

1. With the machine off, mark the pulley and motor shaft with a pen
2. Manually move the affected axis
3. If the pulley rotates relative to the shaft (mark moves) → grub screw is loose

Step 4 — Visual inspection

• Look for fraying, missing teeth, cracks on belts
• Inspect belt rubber carefully: if the white rubber casing is worn through, you may see fine steel wires protruding from the surface — this belt must be replaced immediately regardless of felt tension
• Look for play in the idler bearings (push laterally on the idler)
• Check Z lead screws for old / dried grease

Step 5 — 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

Re-securing pulley grub screws

1. Power off the printer
2. Loosen the pulley grub screw
3. Slide the pulley to the correct position on the motor shaft (typically against the flat of the shaft)
4. Apply threadlocker (medium strength, blue) to the grub screw
5. Tighten firmly against the flat
6. Confirm by hand-rotating that the pulley drives the belt without slipping

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.

X axis chain — shortening when tensioner is maxed out

The X axis uses a chain drive (not a belt). It has a tensioner knob, but this has a limited range. If the knob is fully tightened but the chain is still loose (jumps off the pulley during fast moves), the chain itself must be physically shortened:

1. Power off the machine
2. Release the tensioner knob completely
3. Cut the cable ties holding the chain
4. Remove exactly 6 chain links (~1 cm shorter)
5. Reconnect the chain ends
6. Secure with new cable ties
7. Re-engage the tensioner knob
8. Test by hand-moving the X axis end-to-end — chain should feel firm and not jump

Note

Signs the chain jumped the pulley: unusual sound during X moves, layer shift primarily in X direction, or the motor stalls on fast moves.

Replacing worn parts

• Frayed belt → replace (Ginger Additive spare)
• Worn idler bearing → replace (off-the-shelf size, Ginger Additive can advise)
• Cracked pulley → replace

Recommended periodic maintenance

Interval	Task
Monthly	Check belt tension by hand
Monthly	Listen for clicking / squeaking during operation
Every 6 months	Inspect belt teeth visually for wear
Every 6 months	Re-grease Z lead screws
Every year	Full mechanical check — belts, pulleys, idlers, frame bolts

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

• Pattern observed across 24+ customer cases
• Strong correlation with machine age — first reports usually after 6+ 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
• Belt tensioning