Rockwell Hardness?

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Rockwell Hardness?

Postby Gavin Longrain » November 4th, 2016, 6:58 am

Has anyone got a Rockwell hardness tester? And what data do vintage and modern saws show for Hardness?
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Re: Rockwell Hardness?

Postby chancwj » March 28th, 2017, 7:46 am

I have access to a portable hardness tester at work. I haven't tried it on my saws, but I have brought in an adze, an axe and a few plane blades.

The results are a little hard to interpret. For example, most old tools have a carbon steel edge welded onto a mild steel body. These are the tools I look for and refurbish. I expect these to be hard at the cutting edge and soft in the body. Mostly, that's what I see with the hardness tester. But sometimes they're softer right at the cutting edge, or at least they appear to be. But they cut just fine. I used to think that someone had gotten the edge too hot on a grinder and softened it. But now I think it's got something to do with the way the tester works. For example, the adze head I recently tested showed off the scale low on the Rockwell C scale over most of the tool, increasing to around Rc35 about 1/2 inch back from the edge, but then decreasing to off the scale low again closer to the edge. I thought "Man, someone took the hardness out of this on the grinder. I guess I'll have to re-heat treat it." But then I sharpened it and used it for a week and it works just fine. Holds a good sharp edge.

I think our portable tester is rebound type tester.
https://en.wikipedia.org/wiki/Leeb_rebound_hardness_test
I suspect this method is unreliable for thin test specimens.

I'll try to bring my one man crosscut into work and test it. Are vintage saws differentially heat treated? I mean, did they have hardened teeth and softer blades?
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Re: Rockwell Hardness?

Postby chancwj » March 30th, 2017, 12:56 pm

I found a Rockwell hardness tester at work and brought my two saws in.
Before testing I ran the machine on a calibration platten that was supposed to be 40 on the Rockwell C scale.
The machine read 37. So maybe it's off a bit, but here's the results I got.

My one-man saw measured 54 on the back of the blade and 44 on a cutter tooth,
My two-man saw measured 52 on the back of the blade and 39 on a cutter tooth.

It's hard measuring thin pieces on a tester like this. I suspect that some of the reason why the teeth measured softer than the back is because the teeth have a pretty good set and that springiness as the machine mashes the tooth flat might make it look like a softer metal.

IMAG1283.jpg
The two saws I tested.


IMAG1287.jpg
The testing machine.
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Re: Rockwell Hardness?

Postby DucksinOR » March 30th, 2017, 5:18 pm

Last week I cut down a green Sequoia with my bucking saw. When I was done I noticed that the saw looked like it had blued from overheating, but then it dawned on me that Sequoia wood is rather acidic and that I had basically given it an acid bath that showed off the temper lines (it was in the tree for over 2 hours). The temper line followed the arc of teeth about 4ish inches back from the tip of the teeth with the widest part of the back of the saw not showing any temper colors. The saw is a champion tooth bucking that is crescent ground with no makers mark but the tooth patter suggest Simonds. I would post pictures but I doubt that I can photograph it.
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Re: Rockwell Hardness?

Postby Jim_Thode » March 30th, 2017, 8:11 pm

I would guess that the difference in measured hardness has more to do with the lack of support of the test sample rather then an actual difference in hardness between the back edge and the teeth side. Saws that I've seen that are broke show no difference in hardness and the same goes for saws that are bent. They seem to be the same hardness throughout. I'd guess that the only difference in harness may be due to filers tempering the rakers or cutters.

Here is a broken saw, it looks to be the same hardness through out.

Image

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