Why does my vulcanized belt run off-centre after the joint is made?
Direct answer: In most cases the joint is the cause. A vulcanized belt steers itself toward the side that is tighter or thicker, so a joint cut at an angle to the belt edges, or a joint with a thickness step across the width, pulls the belt off-centre on every revolution. Square the joint and level the joint thickness before you touch the tracking guides.
Check in this order
- Joint squareness: measure from a straight reference edge to the joint line at both belt edges. A difference of more than 2 to 3 mm across a typical belt width is enough to steer it.
- Joint thickness: run a straight edge across the joint. A step of a few tenths of a millimetre on one side is enough to bias tracking.
- Belt edge straightness: sight along both edges. A belt that was slit with a camber will always drift, however the joint is made.
- Pulley and roller alignment: use a string line or laser across the pulley faces. Parallelism matters more than height.
- Take-up evenness: check that both sides of the take-up are at the same position. One side tighter pulls the belt over.
- Loading: confirm the product sits centred. A one-sided load will move any belt, jointed or not.
Match the symptom to the cause
| What you see | Likely cause | Action |
|---|---|---|
| Belt swings to the same side once per revolution | Skewed or stepped joint | Re-cut and re-joint, then recheck squareness |
| Slow steady drift with no rhythm | Pulley or roller misalignment, or belt camber | Align the frame, check both belt edges |
| Drift only when the load changes | Off-centre loading or uneven take-up | Centre the load, equalise the take-up |
| Drift appears when the belt warms up | Uneven splice stretch or uneven cover | Recheck the splice, confirm cover thickness |
| Belt climbs the pulley flange on one side | Crowned pulley worn or belt edge damaged | Inspect pulley crown and belt edges |
If the joint has to be remade
Cut back past the old joint on both ends, square the new cut against the belt edge, and confirm the belt is flat and stress-free before pressing. Measure the diagonal across the joint, not only the edge offset: diagonals catch a skew that an edge measurement can miss. After the joint cools, check thickness across the full width before the belt goes back on the machine.
Send photos of the joint and the drift
Email sales@goodlybelts.com photos of the joint from above, the belt edges and the pulley faces, plus the belt width and centre distance, or use the enquiry form. We will tell you whether the joint can be remade on site or the belt should be replaced.
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