There's been some debate here about what the CMM is capable of measuring to when it comes to the 10:1 rule. Obviously we can change the resolution on the dimensions we want reported way out. What number do you guys reference for this?
First, look up the machine's Uncertainty spec on it's calibration report.
Note it's an uncertainty per-unit-of-measurement (usually meter?), so you have to math how much uncertainty for X length of measurement.
That had better waayyyy under 1/10th of your tightest tolerances.
Next, run some tests where you measure ring gauges and/or qual sphere over and over again in different positions with common stylus builds.
I like to dump the data to Excel for this, then crunch it for Range and Standard Deviation.
That will give you some realistic idea of how much uncertainty your machine is delivering, and is a good way to spot failing wrist/probe/stylus equipment too.
If that's over a tenth of your print tolerances, it's time to explain to mgmt that if they want to continue to bid on those kind of prints then they need to buy a better CMM, rarely a fun conversation.
Never report more decimal places than the machine's realistic uncertainty. It's typical to match or go one decimal place more than the print.
The CMM isn't a godlike purveyor of molecules, it's an industrial measuring machine - probably good to a couple microns.
First, look up the machine's Uncertainty spec on it's calibration report.
Note it's an uncertainty per-unit-of-measurement (usually meter?), so you have to math how much uncertainty for X length of measurement.
That had better waayyyy under 1/10th of your tightest tolerances.
Next, run some tests where you measure ring gauges and/or qual sphere over and over again in different positions with common stylus builds.
I like to dump the data to Excel for this, then crunch it for Range and Standard Deviation.
That will give you some realistic idea of how much uncertainty your machine is delivering, and is a good way to spot failing wrist/probe/stylus equipment too.
If that's over a tenth of your print tolerances, it's time to explain to mgmt that if they want to continue to bid on those kind of prints then they need to buy a better CMM, rarely a fun conversation.
Never report more decimal places than the machine's realistic uncertainty. It's typical to match or go one decimal place more than the print.
The CMM isn't a godlike purveyor of molecules, it's an industrial measuring machine - probably good to a couple microns.
