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[–] lipids 0 points 2 points (+2|-0) ago 

No wonder those machines are so damn expensive.

Since you would know, how long between recertifications? I'm sure their tolerances aren't perfect forever.

[–] screamingrubberband [S] 0 points 2 points (+2|-0) ago 

That is a loaded question... I work for a division of a machine-tool OEM, but am not too involved in the 'normal' machine sales. Our machines have thermal expansion checks in the ballscrews, and some level of automatic backlash compensation. Both of these are in the background and are beyond what the control adjusts. Because of that, our service techs mostly replace worn-out motors and seals and boards, but will rarely also rebuild spindles and re-finish/scrape bedways.

Our division typically sells machines that are single-part specific for high-volume runs (automotive, aerospace... like that) with custom workholding and automatic offsetting from a part-specific custom in-process gage. One of our customers has seven machines in production for going on eight years, making 80-lb cast iron housings. The same 2 parts over and over and over. Our service department has been called there one time to perform a ball-bar test on each machine just as a part of the customer's preventative maintenance schedule. They were all within 5 microns except the vertical that drills the fastening holes for a bearing cap (2 per housing); it has drilled and tapped the same four holes in the same location so many times that there is a 15 micron step in the bedways near the edge of the table opposite the tool changer because the machine has NEVER traveled there.

So... almost never!

[–] lipids ago 

Thanks for the reply. Interesting stuff.

[–] bbqchipz ago  (edited ago)

Another interesting thing to note, that when you re-setup a cnc machine to do say like 30 different jobs in a year, alot of the time when you're setting up a job you're actually basically re-certifying and telling the cnc machine where it's supposed to work anyway. I work in shop that does some very precise work, and some of the cnc machines are only starting to show their 30+ years of age because they can't get replacement parts for the things wearing out in them.