For the past 7 years we have had our Morso Blades hollow ground sharpened and I will admit havent given the subject much thought and been quite happy. I know Morso advise hollow ground sharpening.
However, the other evening I was talking to the boss of an engineering firm who specialises in this area. He sharpens on average 100 sets a week and for some reason he has started to be asked for flat ground instead of hollow ground.
One explanation given to him was that flat ground gives a much neater cut and that hollow ground actually weakens the blades. No maybe that is two explanations !!
What is consensus out there ???
MORSO Blades
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MORSO Blades
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I had my blades flat ground for about 16 years.
In the past year they have been hollow ground.
Maybe my senses aren't finely enough tuned, but I could not honestly tell the difference in use.
In the past year they have been hollow ground.
Maybe my senses aren't finely enough tuned, but I could not honestly tell the difference in use.
HOW Much!?
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We changed to flat grinding a couple of years ago and feel they last much longer.
I recently found this technical explanation on the Grumble by Baer Charlton which seems to make sense in the light on my own experience. Hope he doesn't mind my posting it here.
"Hollow grinding is done with a wheel milling across the face or perpendicular to the cutting edge. The result is a thinner blade at the working edge. That is why when your first slap them in the chopper, they cut like a surgeon's blade in butter. BTW scaples are also hollow ground; that is why they are also now "throw away after single use". Because they are rapidly useless. My surgeon nephew says he makes no more than one cut longer than 4" with a blade then pitches it. Skin is tough, but moulding is tougher.
"Flat" or "Table" grinding will heat the metal less in the sharpening thus leaving the ductal strength in the blade. Where the hollow is a rapid heat producing grit wheel that grinds away metal and produces a lot of heat. Enough to cause tempering of the leading edge, which is also now thinned below design thickness.
The cutting grind of a knife, chisel, or plane blade is about 25 degrees. Hollow grinding can reduce that angle to under 22 degrees, which dulls faster and becomes more brittle.
If a knife blade is hollow ground, a "micro angle" needs to be established at the working edge. The grind of the Micro angle should be greater than 25 degrees but not to exceed 30. This will add some strength to the working edge.
But with all that, the best is a Flat SLOW WET ground face that you should be able to see yourself in, both the grind angle, and on the flattened and polished back."
Case for the defence Morso?
Joe
I recently found this technical explanation on the Grumble by Baer Charlton which seems to make sense in the light on my own experience. Hope he doesn't mind my posting it here.
"Hollow grinding is done with a wheel milling across the face or perpendicular to the cutting edge. The result is a thinner blade at the working edge. That is why when your first slap them in the chopper, they cut like a surgeon's blade in butter. BTW scaples are also hollow ground; that is why they are also now "throw away after single use". Because they are rapidly useless. My surgeon nephew says he makes no more than one cut longer than 4" with a blade then pitches it. Skin is tough, but moulding is tougher.
"Flat" or "Table" grinding will heat the metal less in the sharpening thus leaving the ductal strength in the blade. Where the hollow is a rapid heat producing grit wheel that grinds away metal and produces a lot of heat. Enough to cause tempering of the leading edge, which is also now thinned below design thickness.
The cutting grind of a knife, chisel, or plane blade is about 25 degrees. Hollow grinding can reduce that angle to under 22 degrees, which dulls faster and becomes more brittle.
If a knife blade is hollow ground, a "micro angle" needs to be established at the working edge. The grind of the Micro angle should be greater than 25 degrees but not to exceed 30. This will add some strength to the working edge.
But with all that, the best is a Flat SLOW WET ground face that you should be able to see yourself in, both the grind angle, and on the flattened and polished back."
Case for the defence Morso?
Joe