We’ve all done it. You check a bore, an OD, or any feature, make your adjustment, push start and experience that sinking sensation in your gut as you go to check the result. It’s bad. It’s out of tolerance. If you’re lucky, you just have to adjust and cut it again. If you’re really unlucky, you crash the machine and the rest of your day is spent trying to recover.
It likely happens far more regularly early in your career, but even the most seasoned machinist never completely escapes the haunting dread of “fat fingering” an offset, rushing just a little bit and missing that one zero that makes the difference between .0005 and .005, or (oh no!) just dropping the decimal point entirely. My personal biggest nightmares are the dreaded math errors, or the “wrong direction” offset. In the machinist world of +/-.0005 there isn’t room for errors like this, and no one wants to be the person who just blew up the brand new cutter, scrapped a part, and cost hours of maintenance and down time recovering from a crash.
There are ways to decrease the likelihood of these varieties of mistakes, and they go far beyond the normal “pay more attention.” A lot of modern machine controls feature a calculator built into the offset page that not only eliminate the math errors, but also allow you to see the before and after prior to you saving over the previous offset. I worked with a gentleman for many years who kept a notebook at his machine and wrote down the before and after for literally every single offset he made just so he could verify it twice before pushing start.
Recently, while working on a production style job, I started using a Post-It note to write down my first known good offset, and stuck it directly on my machine monitor. As I sized in each subsequent part, I was able to just look at the note and know I was near my previous target. It felt redundant, it felt a little silly, but it also saved me from scrapping a part when I got distracted by a late night shipment and fat fingered the offset .0065 inches instead of .005 when I finally returned to my machine.
Staying focused, especially when running a tedious, boring, repetitive job, is one of the unsung and under-rated aspects of good machinists that don’t get recognized enough. That said, little tips and tricks like those listed above can help even the most average of us avoid the scrap, crashes, and stress that comes with the simple offset mistakes that happen in machining every single day.