Subject: Re: Quick hardness tester?

From: [email-masked] (KLM)
Date: 21 Nov 1994 16:24:05 GMT

James Kirkpatrick <[email-masked]> wrote:
>
>I wonder if this wouldn't cause problems on two accounts.  First, there is
>bound to be some squashing of the ball.  This is probably taken into account
>in the definition of RC, assuming that it is specified as the *depth* of
>indentation caused by a ball of specific construction.  Measuring the
>diameter of the dent violates the specification if it specifies depth,
>and assumes perfect rigidity.  You'd probably end up with a hardness
>lower than actual because the ball squashes and causes a larger rim
>diameter than ideal.
>
>Second, I wonder if the rim of the indentation would be distinct enough
>to measure accurately.  A small imprecision in the measurement might
>translate to a large imprecision in calculated hardness.
>

Two points for insight! The measure-width-of-depression bit is exactly how
brinell testing works. It's upper useful limit is indeed where the ball
begins to deflect. Brinell uses a hardened steel ball, so hopefully
the carbide would help there. But the real problem with **cheap** brinell
testing is the need for the scope - they aren't cheap. And, even a carbide
ball may have problems at RC65 or whatever.

Thanks to the fellow who suggested the split beam: otherwise, the deflection
would have exceeded the limited range of the indicator.

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From: [email-masked] (Clive Washington)
Date: Tue, 22 Nov 1994 13:31:09 +0000

In article <[email-masked]>, [email-masked] (KLM)

> >translate to a large imprecision in calculated hardness.

Yes, this might be a problem.  I expect you'd have to use a
polished specimen, since for the method to work, the surface
has to be flat and smooth, compared to the size of the ball and dent.
-- 
!!!According to my contract, this place owns my opinions!!!

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From: [email-masked]
Date: 19 Nov 1994 20:15:43 GMT

Whoops, put the pivot in the wrong place on my last post--I meant

                                                        tenths indicator

   ================================================================
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         c                                                       ]
      sample                                                  weights

                      ...when I sit down to write
Don Holly             my intentions are always blameless however deplorable
                      the ultimate effect of the act may turn out to be.
                                           --Joseph Conrad

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From: [email-masked] (James Kirkpatrick)
Date: 20 Nov 94 23:26:10 MST

In article <[email-masked]>, [email-masked] (Clive Washington) writes:

|>You would need a very rigid beam.  Most of the deflection you measured
|>would be flexing in the beam.
|>
|>I think a better bet would be to load the ball using a lever arrangement
|>as you suggest, then measure the diameter of the dent using a 50x graticule
|>tester (a pocket microscope with a calibration scale).  This has the
|>advantage that a shallow dent is relatively wide, due to the ball
|>curvature.  A bit of simple trig. then gives the dent depth.

Just more speculation.

Jim