Shaft Inspection

Look up "coefficient of thermal expansion" for the material. Inspection temperature should be specified, or at least noted. You can't keep things from expanding and contracting due to temp variations.

Have you been in this business a long time? What, exactly, was your measurement and what was theirs? Did you both note the temperature during the test?

When I measured the shaft in UAE at 30'c the measurement reading was 997.10, when they inspected in Europe at 20'c the measurement is 996.92 length. Please send me the calculation for EN 19 Material. My friend has given the coefficient of thermal expansion for the above material is 1.23E-05 per length.

Please send me the calculation. Thanks in advance

1.23E-05 per length per degree centigrade.

1.23E-05 per length per kelvin temperature

The difference between Celsius and Kelvin is just a shift of the zero level.

"The tolerance of the shaft is +/- 0.06MM for 1 Metere"

In the above, either you are stating a general tolerance, or (if nominal dimension is indeed 1000) you have missed the dimension by a few mm. Whatever the case, your dispute with the european inspector is pointless:

1) If indeed a general tolerance, I doubt that a -0.12mm difference=997.10*(20-30)*1.23E-5, which would bring your measurement to 996.98@20degC and therefore within +0.06 from the european measurement, would so much change functionality, that it would be unacceptable. Shaft lengths (especially with long shafts) are never (or should never be) critical functional dimensions... So I'd guess it should be acceptable as is.

2) If an explicit tolerance, then you've missed the 1000 by a few mm. It's not the temperature's fault. But I'm betting on #1.

My suggestion: tell the inspector to lighten up. And by all means follow the previous thread suggestions for your future measurements (temp equillibrium, instrument calibration & certification etc).

BTW, to measure a X.XX tolerance, you should best be using an instrument with an accuracy better by 1 order of magnitude, i.e. 0.00X. All FARO-arms achieve something like 0.02 at best, at least as far as I know. Therefore they are mostly not proper QC instruments, more like assembly aides...

Cheers

Good answer.

Make sure next time to measure the length using the customers ambient temperature.

or get a better measurement device

The calibration certificate, if you have one, will also state the temperature at which it is calibrated. All measurements are only valid at that temperature.

Usually for tool room the standard inspection room is maintained at some standard temperature and standard (dust free) atmosphere condition . ( I do not remeber the standard temperature.)

All the measuring tools, gauges , surface plate etc. are kept inside the inspection room.These instruments are different from the instruments used in shop floor. The job to be inspected is kept at least 24 hrs. before the isnpection time in the inspection room so that it achieves the standard temperature.

Then the mesurement is done.

D.N.Shenoy

20 deg C (and that was the european measurement procedure)

This is the temperature (along with the dust free you said, ensured by the double door, air curtan and shoe change) that is done at our CMMs as well as calibration centers

Additionally the few hours are required for the temperature stabilisation.

But after all this I get a basic doubt.

I make a component - of course measure during processing, get it OK. Then my own (assume that not the EU but my Faro arm has rejected it)

This goes against the quality concept of doing it right the first time.

In fact we do face this problem, and with the experimentation addressed it.

Rough the criticals (with very low allowance) , and then the non criticals, with coolant, enough to stabilise the temperature through coolant and tima gap.

Under this condition, make the component a bit Oversize (as a part of the correlation exercise at our place) - by a fixed amount based on the size.

In these condition almost all the components (made over size on the machine) pass through the final inspection out of machine under standard condition.

This was the result of quite a bit of headache and head butt. Since the operator has to machine it, he makes to size on machine, (some times he did get it inspected on machine) and then the inspector rejects or writes rework when it is off machine.

In fact in about 500 mm or so, it was losing 0.05mm as I remember after all these precautions (finish allowance only 0.5mm on tool point)

At the base of the Faro arm, there will be a sticker with the serial number, model number, etc. On that sticker is the certification date and the certification accuracy. Our Faro Silver arm, circa 2001 is only accurate to +/- .076mm.

His first mistake was using a Faro-Arm. The ones I've seen could be calibrated with a yard stick. Next time, beg, borrow, or steal a decent CMM like a Zeiss, allow your product to normalize to ambient and measure. At + or - .06mm / meter, a good vernier caliper and competent inspector would be good enough to give you figures for conversion, but Faro-Arms are best used as weighty objects to hold the floor down.