Calibration - STD DEV

[Underspec]

I was told at the PCDMIS training that anything under 0.015" STD DEV is ok. Where is everyone's max at? What is a good STD DEV to stay under? 0.015" seems high to me.

[craiger_ny]

in or mm? I hope that is mm!

[Matthew D. Hoedeman]

I would say MM, NOT INCHES ("). Nowayinhell would I accept 0.015" for the STD DEV for ANYTHING. You can basically double that value to get any of the 'shape' items, ROUNDNESS, SPHERE, FLAT, STRAIGHT, etc. (at least, it will be DANG close). So, I guess it depends on WHAT that STD DEV is for? CAlibration results? NO WAY! Alignment features on a fixture? NO WAY! A measured feature of a part, well, that will depend on the tolerance of the part.

[Underspec]

He might of been talking mm LOL. What do you usually go with?

[cmmguy]

That has to be MM. and that is a little high for MM for simple probes.

Although, how many of their trainers have real world experience?

[Underspec]

What do you guys consider limits as far as calibration goes?

[cmmguy]

On a Discovery, 5 microns on a good probe, and up to 17 microns on a bad probe.
Good= within the Renishaw guidelines of module
Bad = Not within the guidelines of the module

Star probe - forget them....

[Matthew D. Hoedeman]

I have my calibration STD DEV set to give me a warning if it is greater than 0.010mm (0.0004"). Only EVER happens if I miss a piece of crap on teh tool or tip.

[cmmguy]

sure wish i checked sheet metal....

[craiger_ny]

Star probe - forget them....

First time I've heard anyone else say that. Now I don't feel so bad. I get a big ration here for refusing to use one. everyone whose seen a picture of a CMM sees one of those being used so they think I should use it. There is one guy here that insists I use it instead of tip rotations (he is a Ziess guy). I still refuse. I don't know why that is the most requested thing here in a plant full of people that don't know jack about CMMs. They have their place but that place is not with most of today's hardware and certainly not with most of our tolerances that is for sure.

Craig

[cmmguy]

First time I've heard anyone else say that. Now I don't feel so bad. I get a big ration here for refusing to use one. everyone whose seen a picture of a CMM sees one of those being used so they think I should use it. There is one guy here that insists I use it instead of tip rotations (he is a Ziess guy). I still refuse. I don't know why that is the most requested thing here in a plant full of people that don't know jack about CMMs. They have their place but that place is not with most of today's hardware and certainly not with most of our tolerances that is for sure.

Craig

They work on the Zeiss head, they work very well on the SP600, they just down right suck on the TP20?

[Matthew D. Hoedeman]

sure wish i checked sheet metal....

What-you-talking-about, eh? This machine is 20 (or more) years old and yes, I check sheet metal. The machine (factory) specs are +/-0.0007" (linear, repeat, sqaure, etc., and I am still within them) and I use 1/2 of my machine spec as a limit for my calibration STD DEV. What gives? What does sheet metal have to do with that, huh?!

[#2#]

I never see anything over .0002 inches so that is my limit. If it comes up .0003, I clean the tip and the calibration sphere and run again. I've never had it come up .0003 after cleaning.

[Matthew D. Hoedeman]

I never see anything over .0002 inches so that is my limit. If it comes up .0003, I clean the tip and the calibration sphere and run again. I've never had it come up .0003 after cleaning.

Ya know, I never even look at the results of the calibration. IF it calibrates within the set tolerances (0.0004" STD DEV and 0.002" size) I never even bother, I just go on with what I am doing. If it pops-up a warning, then I will double check what I have done and do it over.

[cmmguy]

What-you-talking-about, eh? This machine is 20 (or more) years old and yes, I check sheet metal. The machine (factory) specs are +/-0.0007" (linear, repeat, sqaure, etc., and I am still within them) and I use 1/2 of my machine spec as a limit for my calibration STD DEV. What gives? What does sheet metal have to do with that, huh?!

PLUS OR MINUS???!!! Holy cow! j/k

What is the tightest tolerance on your worst sheet metal part?