Three-facet grind vs hollow grind

[B B]

Would anyone be able to tell me why hair shaper blades tend to use a three-facet grind instead of a more traditional one, like 1/4 hollow or full hollow? I see it a lot in reference to medical or surgical settings, whereas industrial blades (unfit for shaving) may use only one or two facets.

What gives?

 

[bluesman 7]

Just a guess, but it probably is to provide rigidity.

 

[Slash McCoy]

On the scale and with the material used, it makes a better edge with simpler manufacturing methods. A compound bevel has advantages. The apex is stronger. The relieved shoulders reduce sticking and dragging, and help with cutting power. Add a bit of teflon and/or a thin coating of platinum or whatever, and you get a very efficient blade for a very low cost, cheap enough to use a few times and throw away. It is also a way to create an edge that does not respond all that well to stropping. The hollowground razor depends heavily on steel quality and individual honing and stropping. It costs too much to make such a blade, even with mass production methods, to just use it a week or so and discard it. It must be maintained and used for years, at least, and not mere days.

 

[stone and strop]

Would anyone be able to tell me why hair shaper blades tend to use a three-facet grind instead of a more traditional one, like 1/4 hollow or full hollow? I see it a lot in reference to medical or surgical settings, whereas industrial blades (unfit for shaving) may use only one or two facets.

What gives?

When you are referring to hair shaper blades I assume you mean DE blades?
My guess would be for speed and cost savings.
I don't think the final edge would be significantly stouter in comparison. DE initial bevels are pretty low, each subsequent bevel being a little more obtuse finishing at the desired angle.
Progressively moving an edge along will always lead to a better finished product IMO.
To grind a single bevel to such a refined level with machinery would generate significant more heat. It would also be much more wear on a superfine hone as opposed to a micro bevel pass.
Many times industrial edges are still final honed by hand.

 

[B B]

When you are referring to hair shaper blades I assume you mean DE blades?

No, just the 2.25" single-edge hair shaper blades, like for Weck Sextoblades.

 

[B B]

On the scale and with the material used, it makes a better edge with simpler manufacturing methods. A compound bevel has advantages. The apex is stronger. The relieved shoulders reduce sticking and dragging, and help with cutting power. Add a bit of teflon and/or a thin coating of platinum or whatever, and you get a very efficient blade for a very low cost, cheap enough to use a few times and throw away. It is also a way to create an edge that does not respond all that well to stropping. The hollowground razor depends heavily on steel quality and individual honing and stropping. It costs too much to make such a blade, even with mass production methods, to just use it a week or so and discard it. It must be maintained and used for years, at least, and not mere days.

Thank you! Concisely put!