Who says you can't calibrate a steel rule!

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Wes Bucey

Quite Involved in Discussions
#2
Channeling Clinton:
It depends on what your definition of "calibrate" is.
mark (a gauge or instrument) with a standard scale of readings.


  • correlate the readings of (an instrument) with those of a standard in order to check the instrument's accuracy.

  • adjust (experimental results) to take external factors into account or to allow comparison with other data.

Does ALL calibration require adjustment? Or can "some" calibration merely be a process of affirming or denying whether the instrument is within its stated tolerances? Perhaps something as simple as saying this is no longer meeting one tolerance class, but may meet a lesser class of tolerances. Here's an example of thread tolerances to get an idea that a gage, for instance, "could" gradually move down in class as it wears.
Tolerance classes

A classification system exists for ease of manufacture and interchangeability of fabricated threaded items. Most (but certainly not all) threaded items are made to a classification standard called the Unified Screw Thread Standard Series. This system is analogous to the fits used with assembled parts.
Classes 1A, 2A, 3A apply to external threads; Classes 1B, 2B, 3B apply to internal threads.
Class 1 threads are loosely fitting threads intended for ease of assembly or use in a dirty environment.
Class 2 threads are the most common. They are designed to maximize strength considering typical machine shop capability and machine practice.
Class 3 threads are used for closer tolerances.
Thread class refers to the acceptable range of pitch diameter for any given thread. The pitch diameter is indicated as Dp in the figure shown above. There are several methods that are used to measure the pitch diameter. The most common method used in production is by way of a Go/no go gauge.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#3
My definition of calibrate is very simple: Verify a measurement system against a standard to assure its accuracy.

Adjustment is not calibration, only an option to react to an out of calibration condition. If you can adjust, fine - do so. If not, pitch it or "reclassify" it.

Gotta love definitions. When its all said and done, they are not very definitive.
 

David-D

Involved In Discussions
#4
I think advocating for not calibrating really misses the critical point on what that calibration is buying you. It is providing book-ends in the measurements made between those calibration points, and thus the acceptance and rejection decisions, were accurate. I'm always scheptical of when organizations buy a new, calibrated gage and then rather than get it calibrated, they dispose of it and buy a new one. I understand that is often cheaper (ex. Set of pin gages) but there isn't any closure on the gages.

David
 
#5
I don't think the thread is about advocating for/against calibration. It's more a case of whether a steel rule SHOULD be calibrated compared to simply being verified. Knowing how far "off" a steel rule is, for most uses isn't really necessary and it's likely not the right tool, if you do need to know.
 

Steve Prevette

Deming Disciple
Staff member
Super Moderator
#7
In my past life with a calibration program, we would have referred to the test on the steel rule as a "calibration check".

Generally, if a steel rule were to fail its cal check, the only remedy is to dispose of it and buy a new one, I would suppose, unless there were a special case like I could sand some off the end . . .
 

Marc

Hunkered Down for the Duration
Staff member
Admin
#8
You can calibrate gauge blocks. You just have to have the right tools. :D
Yeah, but only if the block has "grown" which will not help because wear is usually the problem to begin with. Of course one could make a "new" smaller gage block.

With regard to the thread topic this is along the lines of "calibration" of a glass bulb thermometer. There is nothing to "adjust".
 
S

silentrunning

#9
The on line dictionary defines calibration as:

1: to ascertain the caliber of
2: to determine, rectify, or mark the graduations of
3: to standardize by determining the deviation from a standard so as to
ascertain the proper correction factors
4: to adjust precisely for a particular function
5: to measure precisely; especially : to measure against a standard

I guess number 1,3 & 5 could apply. Number 2 & 4 might be a stretch for a steel ruler.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#10
I would rather calibrate a steel rule than try to "calibrate" this gage block... The only thing to wring is the neck of the guy who stored it wet.

Nobody ever said calibration had to be difficult...all you need is a gage and a standard (helps to have a controlled environment, but sounds like some folks don't even want to go there....) Standards at 10:1 or 4:1, depending on whose theories you subscribe to. If the gage matches the standard, you "win" - congrats! Champagne for everyone!
 

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