Batch Repeatability: 5 Units of Surveying Instrument Base Plate to One Standard

How we held consistent results across a 5-unit batch of an aluminium base plate carrying tribrach threads and levelling feet: the controls on tooling, offsets and inspection that keep the first part and the last part the same.

The order

The customer released an aluminium base plate carrying tribrach threads and levelling feet in a batch of 5 units, with the whole quantity needed before their own line stopped.

Every part had to meet thread accuracy to 5/8-11 with mounting faces flat within 0.02 mm, and partial delivery was not an option, so consistency mattered more than raw speed.

Sources of variation

Across a batch of this size the variation sources are tool wear, thermal drift, fixture cleanliness and material differences between blanks.

Rather than compensating blindly, we separated them: tool wear by part count, thermal drift by warm-up cycles and coolant control.

Controls during the run

The critical features were probed in cycle at intervals, tool life was counted against a fixed replacement number, and parts were taken out for full inspection at set intervals across the batch.

Every measurement was recorded against its serial number, so a trend could be seen while there was still time to react.

Results across the batch

All 5 parts met the drawing, and the measured spread on the critical characteristic stayed well inside the tolerance band from the first piece to the last.

Scrap across the batch was 0.5 per cent, almost all of it from the first setup rather than from the running process.

What the customer received

The batch shipped with a full inspection report, material certificates and photographs of the packing.

The adjusted process is now the reference for the next release, which is how repeat orders get easier rather than starting from zero.

Summary

The figures quoted in this case come from the inspection reports supplied with the shipment rather than from the quotation stage.