A seam welding wheel is consumed on a wear cycle, and the machine it mounts on is fixed capital that outlives dozens of wheels. That asymmetry is what makes wheel tolerances a production question rather than a drawing formality: every replacement must fit the same shaft, track the same seam, and weld to the same schedule — ideally with no fitting, shimming, or debugging at changeover. Two tolerances do most of that work: bore and runout.
The drop-on test
The practical standard for a replacement wheel is simple: it goes onto the shaft, the key seats, the wheel runs true at line speed, and the first seam is in tolerance. When that happens, changeover is minutes. When it does not — bore tight, runout visible, wheel hunting on the strip — the maintenance team spends a shift chasing a problem the wheel manufacturer created.
Seam wheels are replaced often enough that “drop-on” is not a luxury. It is the difference between wheels being routine consumables and wheels being recurring projects.
Bore H7: the fit that carries everything
We cut every wheel bore to H7 as standard, with keyed bores machined to drawing. H7 is a widely used ISO hole-basis tolerance class that gives a close, precise location fit — for a bore this typically means a few hundredths of a millimetre of tolerance band around nominal, tightened as the bore size grows.
Why it matters on a seam welder:
- Current path. Thousands of amps pass through the bore-shaft contact on gear-driven wheels. A loose bore raises contact resistance and heats the shaft; a slivered fit every changeover adds up.
- Concentricity. The bore is the datum from which the OD and face are machined. If the bore fit is sloppy, nothing downstream of it can be true.
- Keyway alignment. On keyed, gear-driven wheels, the keyway position relative to the bore is what transfers drive torque. An off-position keyway loads the key edges instead of the face and chews both.
H7 is also what makes repeat ordering safe: because every wheel is cut to the same bore class from the same datum, wheel number twenty fits exactly like wheel number one.
Runout 0.02 mm: the number that stops the hunting
Runout — how far the wheel’s outside face wanders from true rotation — is where weld quality is won or lost. A wheel with excessive runout does not weld a seam; it welds a series of overlapping spots with a periodically varying gap. On the strip this shows up as:
- Seam chatter — a visible periodic ripple and width variation along the weld.
- Nugget inconsistency — penetration wandering as the effective gap and force cycle with each revolution.
- Accelerated wear — the face takes impact loading every revolution instead of smooth rolling contact, so the profile degrades faster and unevenly.
At 0.02 mm runout, the variation at the contact is small enough that the schedule holds across the full revolution — and across the full wear life of the wheel. Holding it requires the whole machining chain to be honest: bore, OD and face all cut from consistent datums, and the wheel balanced before packing. Balance matters at line speed for the same reason — an unbalanced wheel shows up as chatter long before it shows up as wear.
The rest of the tolerance package
Bore and runout sit inside a complete set of dimensions we hold on every wheel:
| Dimension | Tolerance |
|---|---|
| OD | 0/+0.5 mm |
| Thickness | ±0.1 mm |
| Bore | H7 (keyed bores to drawing) |
| Runout | 0.02 mm |
OD is specified 0/+0.5 mm so a new wheel is always at or above nominal — your arm geometry and seam position are set up for nominal, and the wheel wears into the running position. Thickness at ±0.1 mm keeps the wheel tracking in the arm without lateral shimming.
Ask for the paperwork
For automotive and food-can lines running incoming inspection, we include dimensional inspection records per wheel — bore, OD, runout and thickness — against the drawing revision you hold, and third-party stamped reports to ASTM B702 are available when your quality system wants an external certificate.
Get a quote
Whether you have a drawing or just a worn wheel, send it over — we will match bore, OD and profile so the replacement drops straight on. Request a quote: standard lead time 10–14 days, no minimum order.