Check the gauge before you trust the curve

The curve on the Lat Krabang bench dropped on a Tuesday and stayed low. The supervisor had already called the toolroom. Malee asked for ten minutes with the dial indicator before anyone pulled the fixture. The same metal coupon, measured five times by the inspector who had written the Tuesday column, wandered by more than the shift the curve was accusing the process of.

A small check, done on the piece you already have

Pick one piece that will not be reworked while you do this. Ask the inspector who writes the column to measure it five times, putting the tool down between tries. Write the five readings. If those five move as much as the 'shift' on the chart, the chart is not ready to brief. The gauge, the fixture, or the way the piece is seated is in the picture.

At that bench the indicator's plunger was sticky with a film of oil. After it was cleaned, the Tuesday parts were measured again. They sat where Monday had sat. The toolroom visit was cancelled. The folio's note was two lines: the curve was the gauge, and the parts were not re-sorted.

When the repeat is quiet

If the five repeats sit tightly and the chart still jumps, then look at the process: a die change, a new lot of material, a different inspector. The repeat check does not explain the line. It only stops a dirty gauge from wearing the costume of a process change. We do this before a capability briefing is inked. A briefing that skips it can send a plant to adjust a press that was already fine.