Re: Hardness tester wanted

Harold and Susan Vordos wrote:


"Sevenhundred Elves" <sevenhundred@xxxxxxxxxxxxx> wrote in message
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Harold and Susan Vordos wrote:


<clutch@xxxxxxxxx> wrote in message
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"Tom Gardner" <tom(nospam)@ohiobrush.com> wrote:

Does anybody have a hardness tester laying around? Gunner has five or
six
I'd bet! (encased with rust maybe, but...)


Enco has a new one for 800 bucks iirc.

Wes

That's why I bought the old Wilson. They're quite proud of those things
when
they're new. I always wanted one, but couldn't justify the cost.
Getting one cheaply from ebay made it a reasonable acquisition. I
didn't
mind the rebuild, and had more than enough material on hand to make the
components. Truth be known, it was a fun job. I rarely comment on
machining being fun. The shine went off that for me years ago.

Harold

I have been thinking of making (or rather applying, for there is no
actual "making" involved) my own hardness tester for a cost of something
like zero.

This is how I figure:

IIRC, at least one of the different hardness tests is designed around
measuring the size of the impression made by a sphere, (help me with
their names please).

Instead of applying a precise force for a precise length of time, my
idea is that if I have a piece of steel with known hardness, and another
that is unknown, I put them both in a vise with a ball bearing between
them. Then squeeze hard. Now the pieces obviously get indented with the
same force and for the same length of time.

So I have get impressions, one in the unknown material, and one in the
known. Now I reason that the relative sizes of the impressions must
surely be proportional to the relative hardnesses of the materials.

Do you think this idea would work as I think it might? If it does, what
should I measure, the areas or the diameters of the circular indents?

S

In a sense, that's how a hardness tester works, but in the case of the
Wilson, it measures the depth of penetration, not the diameter.

Yeah, your idea would work, but I have serious doubts about the ability to
read the results and translate them to useful information with a reliable
degree of precision.

Harold

Well, I was thinking of buying a loupe with a scale, the kind
seamstresses use to count threads, to measure the diameters of the
indentations but perhaps you are right, and it would still be too hard
to see the exact edge.

Also, since you say it is the depth of penetration that's important,
perhaps I should measure that instead. I imagine it would go like this:

1. Measure the thickness of the unknown material before testing with a
micrometer. Call the result U1.

2. Take the same measure of the reference material. Call the result of
that measure R1.

3. Press together in vise.

4. Measure the diameter of ball bearing. Call that B. (Here I assume
that it won't be deformed, but in real life I'd have to verify that)

5. Leave the ball bearing in the indentation it made during the test and
measure the combined thickness of the unknown material and the ball
bearing (sitting in the little pit it made) with the same micrometer.
Call that combined measure Cu.

6. Do the same with the ball bearing and the reference material. Call
that combined measure Cr.

7. Calculate the depth of penetration in the unknown material,
Pu=U1+B-Cu

8. Calculate the depth of penetration in the reference material,
Pr=R1+B-Cr

9. The ratio of the hardnesses would then be Hu/Hr=Pu/Pr, so the unknown
hardness would be Hu=Hr*Pu/Pr

All of the above assumes there is a linear relation between hardness and
depth of penetration, which I somehow doubt, because of the spherical
shape of the ball bearing. In real life, if one was determined to get
some accuracy out of this method, I guess one could experimentally
produce some tables of factors to multiply with, or perhaps it could be
calculated theoretically.

Yet, in spite of all this, I still have this image in my mind from
reading about hardness testing with a sphere long ago, that what should
actually be measured was the size of the indentation, either its area or
its diameter.

Well, luckily, I don't really need to measure any hardness, at least not
right now.

S.
.

Relevant Pages

  • Re: Changing over to ceramic bearings.
    ... "Materials Science and Engineering." ... and I get the concepts of hardness and fracture toughness. ... modulus, the "height" of the line, the strength. ... Callister also says that yield and hardness are related in metals, but says nothing of the sort for ceramics. ...
    (rec.bicycles.tech)
  • Re: Changing over to ceramic bearings.
    ... "Materials Science and Engineering." ... and I get the concepts of hardness and fracture toughness. ... modulus, the "height" of the line, the strength. ... Callister also says that yield and hardness are related in metals, but says nothing of the sort for ceramics. ...
    (rec.bicycles.tech)
  • Re: Hardness tester wanted
    ... Enco has a new one for 800 bucks iirc. ... at least one of the different hardness tests is designed around ... So I have get impressions, one in the unknown material, and one in the ... surely be proportional to the relative hardnesses of the materials. ...
    (rec.crafts.metalworking)
  • How to calculate hardness
    ... When it comes to measuring the "hardness" of a material, most tests are distinctly low-tech and basically involve pressing a diamond tip into the surface and measuring the size of the dent produced. ... The results, obtained from first-principles calculations alone, agree well with experimental data and could help scientists make harder materials (Phys. ...
    (sci.physics)