CMM - datum and ring gauge

Question

CMM - datum and ring gauge

dogbural (Aerospace)

(OP)

24 Jul 23 14:02

Hi,

Our supplier machined and measured a shaft that require high precision accuracy.

What they said is that they used plug/ring gauge as the zero value of CMM. And the gauge is calibrated as below

Under D1564, nominal value : 60.001mm, measured value : 60.0031mm

At the end, when we measured the sample, they are out of tolerance. Nominal shaft OD 60mm, but measured out of upper limit.

Question is that
Q1. What is zero value of CMM using ring gauge? Is it a setup of datum?
Q2. with measure value of 60.0031mm of ring gauge, will it derive an incorrect measurment?

BrianE22 (Specifier/Regulator) · Answer 1 · 2023-07-24 15:06:43

First question: Can you really measure to .0001 mm with a CMM? It must be CNC? In a temperature controlled environment?

IRstuff (Aerospace) · Answer 2 · 2023-07-24 17:20:59

Is there some reason you don't want to share the somewhat critical information about your tolerance limits?

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dogbural (Aerospace) · Answer 3 · 2023-07-25 01:25:44

Attached an example

bearing tolerance in red box and the remaining the shaft tolerance

I do not have much experience on measuring.
It seems they can measure 0.0001mm with a CMM, machine itself seems capable of it, even 0.00001mm as well.

https://files.engineering.com/getfile.aspx?folder=e5655b08-b105-4b9e-a16c-1

IRstuff (Aerospace) · Answer 4 · 2023-07-25 04:26:54

Quote:
What they said is that they used plug/ring gauge as the zero value of CMM. And the gauge is calibrated as below

Under D1564, nominal value : 60.001mm, measured value : 60.0031mm

OK, so what exactly does "gauge is calibrated as below" mean? How much above 60 mm was your measurement? What did they measure it to be?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

BrianE22 (Specifier/Regulator) · Answer 5 · 2023-07-25 13:35:14

Send the gauge out for calibration (to a shop both you and your customer agree to). It will still be an argument about semantics but at least you'll have a number for the gauge you can trust. I'm not sure what you mean by "datum" in your first question. Are you talking about using the spherical ball your CMM probably has for calibration of the probe or using the measured gauge diameter for calibration? The way the wording seems to me your customer wants you to used the measured reading of the gauge they supplied as the calibrated "zero".

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CMM - datum and ring gauge