Convex Edged

The Convex Edge: Originally introduced more than 40 years ago by Hikari, produced the first of the new style of scissors (Japanese Style) that delivered unparalleled sharpness, accuracy and ease of use for the stylist. The convex outer edge and concave (hollow-ground) inner edge made this a cutting instrument far superior to the existing “German Style” shear with its beveled edge.

This new design represented a disruptive technological leap in scissors design. It also radically altered the landscape for hairdressing scissors sharpeners world wide.

Sharpeners using grinders could no longer effectively sharpen these new Japanese Style scissors. The next step in sharpening technology, the flat hone machine’s time had come.

Here is a video demonstration of how to sharpen a convex edge scissors on popular flat hone machine the Hira-To.

The Hira-To, like all flat hone machines, will do a reasonably good job on the convex edge depending on the skill of the sharpener.

Please notice, on any of the videos demonstrating scissors sharpening using a flat hone or water hone machine, from the old reliable Scimech to the  newer more advanced Rapid Edge machine the process demonstrated always shows the sharpener either holding the scissors blade in their hand or mounting it in some sort of clamp assembly. The next step is to lay the blade down on the pad and rock the blade back and forth (or convex) the blade.

Usually there are two – five pads used and there are additional sharpening or honing steps (often not shown) used to deburr the blade between passes on the machine.

The critical point is that rocking motion while the blade is in contact with the pad.

Here are two additional issues that need to be taken into account.

• Scissors have a designed in angle on the convex edge. If the rocking motion goes past that designed angle the scissors will not cut like new after no matter how sharp the “blade” is.
• Most Japanese Style scissors have an additional design feature. That is the 800 mm radius the slight curve in the blade from hilt to tip. This radius makes the scissors grip the hair earlier in the cutting motion therefore eliminating the problem of having hair push away as the scissors close.  Invariably flat hone machines, by design, cannot hold that radius or restore once it is removed.

The sharpeners are not at fault it is the equipment they use that creates the problem.

Before you get your Japanese Style Shears sharpened ask about the technology they use.