9 thoughts on “Has Anyone Else Ever Wondered What the Inside of a Board Shear or Guillotine Blade Looks Like if You Saw Through the Mild Steel, Grind the Cutting Edge and Break the Area Where They Are Joined Together?

  1. Jeff Peachey Post author

    I bought an old, damaged blade and am using a eighteen inch section of it for the blade of a scabbard plane I’m making.

  2. Ron Hock

    When I was making knives, I’d include a test piece with each batch that I hardened so I’d have one to break. When hardened properly, the inside of the steel should look like gray primer; so fine grained that the surface is just matte gray. If the steel had been overheated during the hardening cycle it would have easily visible, sparkly crystals in it. Those crystals are large grains that weaken the steel. So from your photo, it looks like the tool steel bit was properly heat treated. The answer to your question is, essentially, yes.

  3. peacay

    O/T: Jeff, I was wondering if you would please whitelist GoogleReader so that each of your posts shows up in full via rss, as they used to?
    (It’s no great inconvenience of course — I’ll visit here in the alternative — but it is a little timesaver being able to keep up via a feedreader for those of us that follow a LOT of people/sites)

  4. Tom Conroy

    Cool. From the bevel this looks more like a guillotine blade than a board shear blade; and it was learly laminated, not just given different hardnesses by heat treating. Any idea when it dated from, and where?

  5. Jeff Peachey Post author

    Yes, it is a guillotine blade. Board shears intended for cutting leather do have a pretty acute angle like this, though.
    The markings read “Mirro-Keen/ Patent Applied For/ Trade Mark SWW Co./ Percision/ Simond Worden White Co./ Dayton OH”

  6. Tom Conroy

    Date would seem to be 1929-1968. I found this in a catalog of the photo collection of the Dayton Metro Library: “It [a pocket knife] was manufactured by the Simon[d]s Worden White Company. A. A. Simonds Company was founded in Dayton in 1874 and renamed in 1929. Apparently went out of business in 1968.” See p. 50 of:


  7. Bill Minter

    Great Post!, especially with the comment from Ron Hock about proper hardening — he should know. I only learned about the inlaid hardened steel of our blades in the past 15 years. As I look at your photo, I wonder if your description of the “Mild steel, twisted to failure” would actually be hardened steel twisted to failure? And it appears that the “hardened steel, broken” is the step-portion of the inlay, if I am seeing it correctly. Nonetheless, very interesting. Thanks.

  8. Jeff Peachey Post author

    Humm. Maybe, but the hardened steel just snapped when I bent it 90 degrees or so, while what I assume to be the mild steel bent back and forth a number of times. Or are you thinking there are actually three stages/types of metal here: a hardened and unhardened part of high carbon steel, and the mild steel opposite the cutting edge?

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