Why do parts that passed inspection come back?
a walkthrough with stand-ins — a demonstration, not a finding · 10 certified links · outlined boxes are the roots · tap a claim to read it in full
Showing every action the room judged: it acts directly on 1 of the 3 root causes. It does not act directly on 2.
Quotes are won on price, so cycle times are cut to the bone → The oldest machine makes the tightest-tolerance partQuotes are won on price, so cycle times are cut to the bone → Operators are paid on parts per hourParts that pass our inspection fail the customer's → The customer's returns log and ours do not matchDeburring is done by whoever is free → Parts that pass our inspection fail the customer'sRework is not counted anywhere → Quotes are won on price, so cycle times are cut to the boneThe same operator runs the same machine for years and nobody checks the settings → The drawing on the floor is not the revision the customer orderedCustomers changed their inspection method and never told us → Coolant is changed when it smells, not on a scheduleCustomers changed their inspection method and never told us → Operators are paid on parts per hourTool wear is judged by ear → Deburring is done by whoever is freeRework is not counted anywhereRework is not countedanywherewhat the shown actions do to this root causeNO ACTION ACTS ON ITDIRECTLYThe same operator runs the same machine for years and nobody checks the settingsThe same operator runs thesame machine for years andnobody checks the settingsCustomers changed their inspection method and never told usCustomers changed theirinspection method and nevertold usTool wear is judged by earTool wear is judged by ear③what the shown actions do to this root causeREDUCED BY 1 ACTIONDeburring is done by whoever is freeDeburring is done bywhoever is freewhat the shown actions do to this root causeNO ACTION ACTS ON ITDIRECTLYCoolant is changed when it smells, not on a scheduleCoolant is changed when itsmells, not on a scheduleThe drawing on the floor is not the revision the customer orderedThe drawing on the floor isnot the revision thecustomer orderedQuotes are won on price, so cycle times are cut to the boneQuotes are won on price, socycle times are cut to theboneParts that pass our inspection fail the customer'sParts that pass ourinspection fail thecustomer'sOperators are paid on parts per hourOperators are paid on partsper hourThe oldest machine makes the tightest-tolerance partThe oldest machine makesthe tightest-tolerance partThe customer's returns log and ours do not matchThe customer's returns logand ours do not match
WHAT WAS PREDICTED TO FOLLOW
Each number on the map marks a root cause that action reduces.
① Ask each customer for their inspection method and gauge list, and keep it with the drawing
we expect: fewer parts come back once both sides measure them the same way
measured by: % of shipped parts returned as defective
due 23 Jan 2027
guesses: the room: 2.7 (median of 15, spread 1.5 to 5.5)
② Measure every returned part before it is remade, and log what was found
no prediction about this action yet
③ Pay on right-first-time parts, not parts per hour
no prediction about this action yet
A map from True Causes: a group’s judgement, not a measurement.