Everyone needs a hardness tester.

[clavius]

Tony Foale is only partly correct with his claim to measure hardness with his (ingenious) device. What it does measure is the energy loss an elastic ball experiences when rebounding from a surface, since

KINETIC ENERGY = mass times VELOCITY squared

and velocity is what Tony's device measures.

<Other stuff snipped>

Wow, that is quite a reply. Holy cow.

So much to look at here. For starters, this device does not measure velocity as you assert, it measures the ratio of the initial and rebound velocities. That is a very different thing. That measure is a accepted by ASTM and similar standards bodies as a valid hardness test. Like any test, it has to be done properly and within the intended use or it will as you say report a "load of bull."

A Rockwell tester will not give useful measurements if used on "materials with directional properties, such as fibre re-enforced materials" as will a Vickers, Brinell or other similar tools, That is not what they were intended to do, and neither is this.

If you "measure the hardness of a THIN knife, with supports way away from the point of impact" or that "were supported by a sandbag" with a Rockwell tester you will not get valid results either. That does not make a Rockwell tester suspect, it means you are using it improperly.

As for the "speed of impact" example, Silly putty and steel are entirely different things that behave entirely differently. A steel ball placed on a steel sample will never be "swallowed by no more force than its own weight" no matter how long you wait. Silly putty is designed to behave exactly as you describe, and does, but that has zero bearing on what is being discussed here. The use of the ratio of velocities is specifically to take the absolute speed of impact out of the equation.

The design in no way "totally ignores the reality of the physical metallurgy of a real piece of metal, its composition and its internal structure from grain size and orientation, inclusion content, via dislocation density and orientation, down to chemical bonding." That test was defined near 50 years ago by a Swiss company that develops tools for materials testing. Google it. Tony did not define the test, he rather created a homebrew version of a tool to perform the test and it's a rather clever one at that.

"Again, be careful with what you conclude from using Tony's device. If you do Quality Assurance, and your customer has told you to use it, then do use it. But if you do process development, and you need to optimize both wear resistance ("my knife gets blunt so quickly") and fracture resistance ("the cutting edge chips"), I at least would stay far away from the gadget, as in that situation it is just a waste of time."

Did anyone suggest that this was an acceptable substitute for qualified testing in a commercial setting or for process development? I didn't see that. As for wear or fracture resistance, no hardness tester tells you that. Neither will a file. One needs to be careful what one concludes from ANY test or measurement. If one misapplies any test in the ways you describe for this one, the results will be suspect at the very best.

To recommend a $1580.00 tester from ebay as an alternative for a bunch of home shop folks on a homemade tools forum (It's right in the name) is a bit over the top, really. Now that I think of it, if one is doing process development or quality assurance work for customers, I would probably steer them away from buying their development and QA tools from ebay.