Calibrating torque wrenches, was dist. rattle

[Bernie Benz]

> From: auditude at cox.net
> 
> Bernie,
> 
> Well, maybe we're used to different terms.  To me, when something is
> calibrated, it is reset
> against the standard.  Something is changed to bring it within the tolerances.
A calibration is the quantification of the error characteristic over a
defined range, and does not imply a scale change to bring the indicated
within a given percentage of the actual.
> 
> Like with some video cameras you do some kind of calibration setup against
> something
> white before you use it (don't know if that's current technology).  Or when I
> look down at the
> bathroom scale with nothing on it and it shows 4 pounds, when I reset it to
> zero before using
> it, to me that is calibrating the scale in a way.
A zero adjustment is a trivial part of a calibration.  If the response error
is linear relative to the indicated scale, i.e. reads 10% high for all
readings over the range, one has a simple to apply calibration, or
correction factor.  Such is not always the case, requiring a more complex
correction formula or look up table.  The indicated reading is less than
accurate until corrected per the current calibration table.  The scale
numbers may be meaningless, 1 to 10, until the correction factor is applied,
i.e. 10.5 ft lbs per division.

>  This is different to me  than putting on a 5
> pound weight to verify that it measures 5 pounds, and therefore requiring no
> adjustment at
> all.  The words I use in that instance is a calibration check, altho' I'm not
> asserting that it is
> the correct or best term to use.
> 
> Altho' it's not necessarily a technical definition, we can look to trusty
> dictionary.com to see if
> it helps.
> 
> http://dictionary.reference.com/search?q=calibrate
> 
> cal·i·brate     P   Pronunciation Key  (kl-brt)
> tr.v. cal·i·brat·ed, cal·i·brat·ing, cal·i·brates
> 1. To check, adjust, or determine by comparison with a standard (the
> graduations of a
> quantitative measuring instrument): calibrate a thermometer.
> 2. To determine the caliber of (a tube).
> 3. To make corrections in; adjust: calibrated the polling procedures to ensure
> objectivity.
> 
> I'm using either the "adjust" portion of definition 1. or definition 3.  It
> sounds like you are
> referring to just the "checking/determination" portion of definition 1.
> 
> Or maybe you are using the same definition as I am, but you haven't yet
> described what you
> Do Yourself when the wrench doesn't repeat the correction measurement against
> the
> standard?  I guess with a pointer style you can maybe bend the pointer, but
> with a click type
> I wouldn't know what to do.
> 
> If the report that came back with my torque wrench showed that it was as
> effective when I
> got it back as it was when I dropped it off, then for sure I wouldn't think it
> was worth the
> money.  But since they changed something in it or about it to make it more
> effective, and I
> don't yet know how to Do That Myself, I figure it was worth it.
If one does not know what he has paid for, it most probably was not worth
the price.

Bernie
> 
> Cheers,
> 
> Ken
> 
> On 27 Jan 2004 at 19:38, Bernie Benz wrote:
> 
>> 
>>> From: auditude at cox.net
>>> 
>>> Is there a DIY calibration, versus calibration checking?
>>> 
>>> Ken,
>> 
>> What's the diff, Ken?  A check or calibration is only a repeatability check
>> on the previous calibration.  I do it before every use (once every 2 or 3
>> years, if I need the wrench and can find it).  DYI is pretty simple.
>> Torque = force x the quadature lever arm length.
>> 
>> Bernie
>> 
> 
>