The Day I Realized the Print Was Wrong, Not the Part
I was running a batch of forty-two hydraulic cylinder barrels for a mining equipment customer. Each barrel was forged 4140 steel, 2 meters long, with a wall thickness of 25mm. The print called for a 100mm bore through the full length. After drilling the first five parts, I pulled the first one off the machine and set it up on the inspection bench. The bore came out at 100.5mm. The tolerance block on the print showed plus or minus 0.2mm on all bore dimensions. By my reading, the part was 0.3mm over the upper limit. I had drilled about thirty thousand bores up to that point in my career, and I knew a 0.3mm oversize condition on a 100mm bore usually meant the drill was cutting slightly over size due to guide bushing wear or a minor misalignment. I flagged the part and told the operator to stop the machine. ...