Um, er . . . . Absolutely!
I suppose there are instances where a shop does no "close" tolerance work, and has a CMM becasue a customer requires it, that kinda thang. However . . .
A sphere not only "grows" over time, it also loses it's "perfect" form. It's not unusual for a calib sphere's Form to change by several 10ths over the course of a year or two.
But isn't the issue really . . . . "Is my sphere any good??" Not "Will I be questioned or rejected in an audit?"
The cost of having a sphere inspected and certified is about $50. Hmmmm.
You're running a machine that cost the company around $100K. You expect reliable data from the machine. Right?
Spend the $50.
In my experience, this is a "possible" proceedured you might consider.
Spend a few bucks, and buy a 2nd calib sphere. (Assuming you've had one already for let's say a year or more) Put the new sphere into service. By ser. no., etc. So it's in your quality system.
Send the old one to a lab, get it recertified. Then put it away for a year. (Dip it in the protective "goop" is you need to, and put it in a well controlled temp environment till next year.)
Next year, send the newer one to be recertified. Put the old one back into the system.
Alternate each year. It'll only cost ya about $50 a year! :mg:
One other point to consider . . . What is the "climate" in your CMM area? If the temp/humidity is closely maintained, you'll have less of an issue. Why?
Because that sphere expands and contracts with the slightest temp change. And being a sphere, the molecules don't always "go back" to exactly where they were when at optemp.
FYI: I know if i were to ask 500 "savvy" people what the temp variation of a CMM room should be, I'd get over 99% telling me it had to be within 4 degrees. Well . . .
That might be true for "inspection rooms", etc. That's the allowable, acceptible temp range for measuring parts. And the tem can vary that 4 degrees over the course of any day. But . . .
For a CMM to function properly . . . . repeat perfectly . . . . Stay "in tune" . . . all of it's "parts" working correctly, the total amount of acceptible temp variation is . . . .
0.7 (7 10ths) of a degree over any 8 hour period!
If you machine/room, etc. varies more than that, best guess is . . . . if you do close tolerance work . . . . Spend the $50!
