saw plates old VS new

[Rob Streeper]

So, it seems that the steel is actually increasing in hardness as a function of hammering. Is that the message? That the testing supports the commonplace knowledge, that is a good thing. If there is more here than that you need to esplain it, there's just too much data and not enough information.

The steel is hardened, or appears to be hardened, in the areas adjacent to the hammering.

I made an interesting observation during the testing. When running tests on the hammered zones the needle on the tester stopped at a certain point under load (150kg). When the load was relieved the needle swung back up to indicate the hardness. In the non-hammered zones however the needle stopped at a somewhat lower reading than it did in hammered zones indicating that it penetrated the metal further than it did in the hammered zones and then when the load was released it came back to read harder than the hammered areas.

That's why I think the Bauschinger effect is in play here, there's a plastic compression zone (hammered) surrounded by an elastic zone (adjacent) under tension. So maybe, just maybe, Disston did start out with steel at ~52 C scale hardness and the hammering makes it appear that they are harder when in fact they are under Bauschinger / autofrettage tension. Bauschinger discovered this effect in 1881 (http://esaform2008.insa-lyon.fr/proc...4/p_Le_226.pdf). I wonder if one of Disston's sons read about it?

Nonetheless, I was able to produce hardness measurements approximating those I found on the Disston saws I tested under the handle, including apparent hardening in areas that were not hammered. Further those hardness values suggest the saws can't be file sharpened, but we all know that they can.

Too much data? https://www.youtube.com/watch?v=Q_UsmvtyxEI

[Tony Zaffuto]

What tester are you currently using and can you describe how the material is supported under the anvil?

[Rob Streeper]

What tester are you currently using and can you describe how the material is supported under the anvil?

The plate was directly and fully supported by the anvil. I used the 150 mm anvil that came with the tester. The free end of the blade was rested on a support to prevent deviations. The tester is a beam-style analog Rockwell B and C tester. It was calibrated with a three point calibration curve with three replicate measurements at each point. The calibration curve showed an R² value of 0.9965 indicating a linear response over the range of 27 to 62.

Here's the calibration data.Saw plate hammer hardening experiment instrument calibration curve 012015a_Page_2.jpg
This is what I mean when I say 'linear'.

Saw plate hammer hardening experiment instrument calibration curve 012015a_Page_1.jpg

[Rob Streeper]

I just noticed a calibration error, Excel likes to grab adjacent cells and it got ahold of a value I didn't specify. Corrected here.

Custom saw plate hardness measurements 012015a_Page_1.jpg

Custom saw plate hardness measurements 012015a_Page_2.jpgCustom saw plate hardness measurements 012015a_Page_3.jpg

[Stanley Covington]

Backsaws and handsaws are very different tools. It is ridiculously easy to make a decent backsaw. The flatness and straightness of the blade and shape, set and sharpness of the teeth are the critical points. But handsaws are not so forgiving, and are much more difficult to make. No one makes a handsaw nowadays that can hold a candle to the American handsaws pre-1950's. No one taper grinds, and no one hammer tensions. And the handles on Borg saws suck. The old Disston, Atkins, Jenkins, Bishop etc saws were made to satisfy men that used saws all day long, sharpened them themselves, and did not stint to pay several days wages for a good saw. I don't know how much you get paid, but that's a lot of money for a saw nowadays. The old saws are elegant, efficient, and still a bargain. Give them a try.

Stan

[Rob Streeper]

Backsaws and handsaws are very different tools. It is ridiculously easy to make a decent backsaw. The flatness and straightness of the blade and shape, set and sharpness of the teeth are the critical points. But handsaws are not so forgiving, and are much more difficult to make. No one makes a handsaw nowadays that can hold a candle to the American handsaws pre-1950's. No one taper grinds, and no one hammer tensions. And the handles on Borg saws suck. The old Disston, Atkins, Jenkins, Bishop etc saws were made to satisfy men that used saws all day long, sharpened them themselves, and did not stint to pay several days wages for a good saw. I don't know how much you get paid, but that's a lot of money for a saw nowadays. The old saws are elegant, efficient, and still a bargain. Give them a try.

Stan

Hi Stanley,

I agree with what you say about the classic handsaws. For me the first step in creating a handsaw is understanding the technical details of their manufacture. Sadly, much information seems to have been forgotten leaving me with the need to analyze the saws I can to try to reconstruct the techniques used.

Cheers,
Rob

[Rob Streeper]

I received the two saw blades from David. Here they are.

The leftmost blade is slightly bent concave as pictured, the right blade is slightly convex as pictured. The etched sides of both blades appear to be less rough than are the opposite sides.

saw blade pictures for testing_Page_1.jpgsaw blade pictures for testing_Page_2.jpgsaw blade pictures for testing_Page_3.jpg

Here's the smaller blade with the testing grid.

smaller blade with grid.jpg

And here's the grid on the larger blade.

larger blade with grid.jpg


Hardness measurements will be taken at the crossing point of each grid intersection with the following format long axis, short axis, Rockwell C scale hardness, Rc or HRC.

[Rob Streeper]

Okay, here's the data. These are first draft - I have not hand checked all of the input values. The corrections applied are as before, the first stage corrects for the offset of the instrument. The second stage adds about 2% to the values to compensate for roughness. These saws appear to be on the softer side, roughly Rc/HRC of 48-49 at the tooth line. Softer toward the spine. No real difference in hardness under the handle. More tomorrow.

Custom saw plate hardness measurements 012715a_Page_1.jpg

Custom saw plate hardness measurements 012715a_Page_2.jpg

[Rob Streeper]

Here's the calibration data. I'm having to move the instrument to use it so I recalibrate before each use.

012715 HRC calibration data and curve 012815a_Page_1.jpg012715 HRC calibration data and curve 012815a_Page_2.jpg

[Rob Streeper]

Here are some more corrections. I've changed the designation D7 to #7 per David's information. I also bolded those values taken in the areas under the handles and done some formatting. I still need to double check all values against my notes.

Custom saw plate hardness measurements 012815a_Page_1.jpg

Custom saw plate hardness measurements 012815a_Page_2.jpg

Custom saw plate hardness measurements 012815a_Page_3.jpg

[Rob Streeper]

Interesting editorial.

http://bos.sagepub.com/content/71/1/33.full.pdf+html