Rant: Spent 6 hours chasing a Z-axis drift that was just a loose setscrew

Ran a 40-tool production job last Tuesday and noticed my Z heights were shifting by 0.002" every 20 parts. After tearing down the spindle and checking the ball screw for 4 hours, I finally found a tiny 6mm setscrew on the coupling was barely finger tight. Has anyone else wasted a whole shift on something this stupid?

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pat_coleman2mo ago

Did you check the coupling first or go straight for the spindle like me?

2

jana_fox502mo ago

@pat_coleman I read an article in Modern Machine Shop about vibration analysis that mentioned loose setscrews as a common cause of intermittent Z issues. Something about the coupling acting like a slipping clutch under load. Took me two shifts to find a similar problem on a Haas VF2 last year. The setscrew was under the bellows so you couldnt see it without pulling the cover. My apprentice caught it by chance while cleaning. Made me feel like an idiot but its way more common than people admit. The article said something like 30 percent of positioning errors come from hardware that wasnt tightened properly during install.

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