Case note: a slewing ring with no drawing and no supplier

The crane was nineteen years old and the slewing ring had been obsolete for nine. The original maker had been absorbed twice. There was no drawing, no catalogue entry, and no equivalent in any standard range — slewing rings are made to the application, not to a size table.

The commercial alternative was a crane rebuild, quoted at several times the cost of a ring with a much longer downtime. The technical alternative was to reverse-engineer the part from the worn original — which is possible, but only if the wear is understood rather than copied.

1. Measure in place. Mounting bolt pattern, pitch circle, overall diameter and height, and the gear module and tooth count, recorded before removal.
2. Measure on the bench. Raceway diameters, ball or roller size, section, seal grooves and lubrication ports — with the wear allowance noted rather than averaged away.
3. Produce a drawing. Dimensions, tolerances, material, heat treatment, clearance, gear data and marking, issued for approval.
4. Approve and manufacture. Rings turned, heat treated, ground and assembled; gear cut to the measured module.
5. Verify. Dimensional report against the approved drawing, plus a runout check on the assembled ring.

A worn raceway is not the original raceway. If it is measured at the worn surface, the replacement is made to the worn geometry — with the clearance already opened and the section already reduced. The measurements have to be taken on unworn references: the mounting faces, the gear teeth away from the pitch line, the seal grooves. That distinction is the difference between a part that fits and a part that lasts.