A V-slot carriage should roll smoothly without rocking, binding or developing a repeating bump. This guide shows how to diagnose the fault, adjust the eccentric hardware and replace a worn POM wheel without losing the original spacer order.
In this guide
What the symptoms are telling you
Do not assume every rough axis needs a new wheel. A loose eccentric, over-tight adjustment, damaged bearing, dirty extrusion, misaligned bracket or incorrect belt tension can feel similar at first.
| Symptom | Likely checks |
|---|---|
| The carriage rocks when gently twisted | Check whether one or more wheels have lost contact, then inspect the eccentric adjustment and axle fasteners. |
| Movement is stiff across the whole rail | The eccentric may be too tight, the wheel stack may be clamped incorrectly, or the belt may be over-tensioned. |
| A bump repeats once per wheel revolution | Inspect the POM running surface for a flat spot, embedded debris or visible damage. |
| One section of the rail is tight | Clean the extrusion and check rail alignment before tightening the wheels further. |
| The wheel turns roughly off the machine | The bearing may be damaged or contaminated. Replace the wheel and bearing assembly if it does not rotate smoothly. |
Useful first test: power the printer off, let hot parts cool, and move the axis slowly through its full travel by hand. A fault that repeats at regular intervals points more strongly to a wheel or bearing than a fault at one fixed point on the rail.
Prepare the machine before adjustment
- Power off and unplug the printer. Let the nozzle and bed cool. Never work around a moving carriage or live heater wiring.
- Support the carriage or gantry. It must not drop, twist or load the remaining wheels when a fastener is loosened.
- Clean the contact surfaces. Wipe dust and filament debris from the V-slot extrusion and the wheel surfaces with a dry cloth.
- Check the full wheel set. Look for cracks, chips, uneven wear, flat spots and bearings that feel rough.
- Photograph the hardware. Record both sides of the wheel stack before removing anything. Printer models and aftermarket plates do not all use the same order.
Keep the original hardware order. Bolts, precision shims, straight spacers, eccentric spacers and locknuts each control alignment or clearance. A generic exploded diagram is not proof of the correct stack for your machine.
How to adjust an eccentric nut
An eccentric spacer has an off-centre bore. Rotating it moves that wheel slightly toward or away from the extrusion. The goal is to remove play while keeping the carriage free to roll. More pressure is not better.
- Find the adjustable wheel. Look for the hex-shaped eccentric spacer between a wheel and the carriage plate. Not every wheel is adjustable.
- Hold the axle hardware correctly. Use the tools that fit your machine so the bolt or locknut does not loosen unexpectedly.
- Turn the eccentric a small amount. Adjust a few degrees at a time, then gently test the carriage for play.
- Stop as soon as rocking is removed. The carriage should still travel smoothly from end to end without a tight section.
- Recheck after securing the fastener. Tightening can shift the setting. Test again before applying power.
If the carriage is already stiff, turn the eccentric in the direction that reduces wheel contact. Because the tight and loose directions depend on the eccentric's starting position, test the result rather than assuming clockwise always means tighter.
How to replace a worn V-slot wheel
- Confirm the replacement dimensions. Match the wheel profile, outside diameter, width, bearing bore and hardware clearance to the removed part.
- Replace one wheel at a time. This makes the remaining assembly a useful reference and reduces the chance of mixing spacers.
- Lay out parts in removal order. Keep each washer, shim and spacer facing the same way where orientation matters.
- Fit the new wheel without side loading it. Seat the bearing squarely on the axle hardware. Do not crush the POM or clamp the bearing so tightly that it cannot turn.
- Restore the photographed stack. Reassemble the exact machine-specific order, then secure the fastener.
- Set the eccentric contact. Remove play with the smallest useful adjustment and test the full travel again.
Final checks before the next print
- Move the carriage through its entire travel by hand. It should feel consistent from one end to the other.
- Gently check for rocking at several rail positions.
- Confirm every wheel rotates and stays seated in the extrusion profile.
- Inspect that cables and belt teeth are not trapped or rubbing.
- Set belt tension only after the carriage rolls freely. A tight belt cannot correct a badly adjusted wheel.
- Run the printer's normal homing procedure and watch the first movement closely before starting a print.
Troubleshooting after adjustment
| Problem after service | What to do next |
|---|---|
| Carriage still rocks | Check that the eccentric wheel is actually moving toward the rail and that no axle fastener or carriage plate is loose. |
| Carriage became harder to move | Back the eccentric off slightly. Then verify the spacer order and that the bearing is not clamped. |
| New wheel has a repeating bump | Clean the rail and wheel, then inspect for shipping damage or a mismatched profile. |
| Axis is smooth with the belt loose but rough when tensioned | Check pulley alignment and reduce excessive belt tension. Inspect the motor and idler path separately. |
| Only one rail position binds | Check the extrusion, frame alignment and bracket squareness before changing the eccentric again. |
Choose the right replacement wheel
The NZN 625ZZ POM V-slot wheel has a pre-installed 625ZZ bearing, an approximate 5mm bore, 24mm outside diameter and 10mm wheel width. It suits compatible Ender 3, CR-10 and similar assemblies where the profile and hardware arrangement match.
Model names alone are not enough. Manufacturers revise machines, and aftermarket carriages can use different wheel sizes or spacers. Compare the removed wheel and check the available clearance before ordering.
Frequently asked questions
Should every V-slot wheel be tight against the rail?
Each wheel should follow the rail without the carriage rocking, but excessive preload creates drag and wear. Use the eccentric adjustment only until play is removed.
Can I fix a flat spot by tightening the eccentric?
No. Extra pressure can make the bump worse and add bearing load. Clean and inspect the wheel first, then replace it if the running surface is permanently deformed.
Should I lubricate POM wheels?
Keep the wheel and extrusion clean and dry unless your printer manufacturer specifies otherwise. Oil attracts dust and does not repair a damaged bearing or wheel surface.
Do I need to replace all the wheels at once?
Not automatically. Replace any wheel that is damaged, rough or dimensionally mismatched. Inspect the whole set so one worn wheel is not hiding another problem.
Manufacturer guidance checked: Creality advises power-off cleaning and manual axis checks during maintenance and troubleshooting. OpenBuilds assembly documentation shows eccentric spacers as the fine adjustment point for V-wheel contact. Always give your exact printer manual priority where its hardware differs.
Creality maintenance guidance | Creality printer FAQs | OpenBuilds V-wheel assembly example
Make the carriage smooth before tightening the belt
Diagnose the mechanical drag first, preserve the original hardware order and make small eccentric adjustments. If the wheel or bearing is damaged, compare the dimensions and profile before replacing it.
View the 625ZZ POM V-slot wheel
