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Field Book · Chapter 7 of 8 · Control plan and reaction plan

Lock It In

Write the control plan row that catches drift early: chart limits, an early warning input, the signals, and a reaction plan with a trigger, owners and the authority to stop.

By Chris Martin, quality manager. 2 minute read. Free, no signup.

Fixing today is not enough. Write the control plan row that catches the next drift early: the chart with its control limits, an early warning input such as coolant temperature, the signals that trip it, and a reaction plan that names who stops the machine, who is called, and what must be true to restart. Here the plan trips 0.0116 mm inside the tolerance, while every part is still good.

The condenser filter is cleaned, the chiller is reset, and the coolant is back at 21 degrees. That fixes today. The next drift will come from somewhere else, and the way to be ready is to write the row that catches it early.

What the control plan row holds

  • Characteristic: shaft SH-3306 outside diameter, 24.000 plus or minus 0.020.
  • Method and frequency: X-bar and R chart, five consecutive pieces every 20 minutes, with the control limits drawn on the chart: upper 24.0084, lower 23.9996, range limit 0.0162.
  • Early warning item: coolant temperature at the lathe, read every hour, limit 25 degrees C. On the day, the coolant crossed 25 a little before 11:00.
  • Signals: one mean beyond a control limit, eight in a row on one side of the center line, or coolant above 25.

The reaction plan

The plan must say who does what and how fast, with the authority to stop written into it:

  1. The operator stops the lathe and red tags everything made since the last good check.
  2. The operator calls the shift lead, who sends a quality alert.
  3. Maintenance checks the chiller and the coolant before the lathe restarts.
  4. The lathe restarts only after a five piece check shows the mean back inside the limits.

Notice where the trigger sits. A mean above 24.0084 trips the plan, which is 0.0116 inside the upper tolerance of 24.020. The plan catches the drift while every part is still good.

The fixes behind it: the chiller goes on the weekly preventive maintenance list, the filter is cleaned weekly, and the chiller alarm gets a light at the lathe.

Read more: how to write a control plan and a control plan example.

The mistake to avoid

A reaction plan that says "notify supervisor." That is a phone call, not a plan. Write the trigger, the first three actions, who owns each one, and who can stop the machine.

ON THE FLOOR MONDAY
  • Pick one control plan row and read its reaction plan.
  • Check it names a trigger, an owner and who can stop the machine.
  • If it says "notify supervisor," rewrite it this week.

Open the printable Monday Board

Want every tool on this trail in one purchase? The Process Trail Bundle has all 13.

The part, the machine, the shift and every number in this book (shaft SH-3306 on Lathe 3) are a made-up example. The tool sidebars show ShopFloorOps tools, which I make and sell. Every chapter teaches the step itself, so you can use your own forms. New to a term? See the quality glossary.