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Flat or Hollow Grind ???
- Thread starter Geoff
- Start date
- Joined
- Apr 27, 1999
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- 6,117
If you are cutting thin material (like a razor) or sticky resilient materials (like a scalpel) a hollow grind will approximate an edge-only blade and cut most effectively. It will also be the easiest to sharpen since less material needs to be removed when you sharpen. This makes hollow ground edges better for bragging (my knife shaves better than your knife) and hunting related tasks.
If you have a thin blade that is fully flat ground it will do as well as a hollow ground blade for the above tasks and has other advantages as well. The thin flat ground blade goes more evenly through thicker materials (think of how a box cutter goes through cardboard). A flat ground Swiss Army Knife also does a nicer job on cardboard than a lot of hollow ground premium folders. If your flat blade is thicker and narrow the angles get higher and performance drops and sharpening gets harder. In this configuration the hollow grind works comparably on thick materials and better thin materials.
For general purposes I prefer thin flat ground blades. For strength I like better alloys and wider blades. If I had to fit a fighting knife with a thick narrow blade I would want it hollow ground. If my hunting knife was over 1/8" thick I would prefer it hollow ground. For a chopping blade I would prefer a convex edge grind on a flat blade.
If you have a thin blade that is fully flat ground it will do as well as a hollow ground blade for the above tasks and has other advantages as well. The thin flat ground blade goes more evenly through thicker materials (think of how a box cutter goes through cardboard). A flat ground Swiss Army Knife also does a nicer job on cardboard than a lot of hollow ground premium folders. If your flat blade is thicker and narrow the angles get higher and performance drops and sharpening gets harder. In this configuration the hollow grind works comparably on thick materials and better thin materials.
For general purposes I prefer thin flat ground blades. For strength I like better alloys and wider blades. If I had to fit a fighting knife with a thick narrow blade I would want it hollow ground. If my hunting knife was over 1/8" thick I would prefer it hollow ground. For a chopping blade I would prefer a convex edge grind on a flat blade.
Buzzbait
Gold Member
- Joined
- Feb 25, 2001
- Messages
- 6,706
A couple more advantages of hollow grinds - Less steel equals less eight. Also, well made hollow grinds can be sharpened many times without a noticeable loss in cutting efficency. Extensive resharpening of a flat gorund blade will cause the thickess of the blade, behind the edge, to become thicker and thicker, with a resulting loss of cutting efficency.
- Joined
- Aug 2, 2002
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- 113
Never had a problem with my flat ground Caylpsos they are some cutting machines with their flat grind even though I've sharpened them alot. You will not go wrong with a flat ground knife!
- Joined
- Nov 29, 1998
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- 774
I have to go along with Captian Ron. The Calypso is a cutting machine as is the Military, Calypso Jr, Dragonfly, and Salsa, all flat ground.
- Joined
- Mar 28, 2001
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- 2,491
Number me among the Calypso fans. They do cut very well. But the fact is, any of the three major grinds, flat, hollow, and convex, work well if they are well executed.
Some just excel more at some tasks than others. Personally, if I could choose just one grind, I would have all my knives full-height convex ground.
Some just excel more at some tasks than others. Personally, if I could choose just one grind, I would have all my knives full-height convex ground.
Cliff Stamp
BANNED
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- Oct 5, 1998
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- 17,562
Buzzbait :
So can flat ground blades. I think it was Tom Mayo who first brought this sharpening aspect out on the forums. Specifically he was talking about very thick *sabre* flat ground blades. This is a very clear distinction. If the primary flat grind is very obtuse, then the edge will thicken significantly with sharpening as the rate of the thickening is proportional to the angle of the primary grind. On fully flat ground blades this angle is 2-4 degrees and thus you can take as much as 1/8" off the edge and still lose performance by a matter of a few percent.
Consider as well that on high end materials, this really isn't a concern. We are far beyond the days of 50 RC, 1045 steel blades. The amount of use it would take for example to wear this much edge off current hard and high alloy blade, 62 RC D2 for example, blade is considerable indeed. The only blades I have seen that have had this much wear induced were either heavily damaged on a regular basis (edge rusting, chipping etc.), or were very soft plain carbon steel and saw constant use on a butchers steel for many years (10+) .
Another excellent overview by Jeff, of which I have only to add, that if you are looking for the ultimate in low stress cutting ability hollow grinds are much more functional than flat grinds. If you flat grind all the way from the spine to the edge (puukko style), you can end up with a very efficient cutter, but if you hollow grind all the middle out, then the blade will not only cut slightly better, but will be *much* easier to sharpen. Few people make knives like this though, so it isn't a practical advantage when speaking of hollow vs flat in general.
One of the real utlity aspects of hollow grinds comes in combining them with other grinds on the same knife. A hard wood felling axe for example has a primary convex grind which forms the body of the axe, but has a significant hollow relief above the edge to increase penetreation.
-Cliff
So can flat ground blades. I think it was Tom Mayo who first brought this sharpening aspect out on the forums. Specifically he was talking about very thick *sabre* flat ground blades. This is a very clear distinction. If the primary flat grind is very obtuse, then the edge will thicken significantly with sharpening as the rate of the thickening is proportional to the angle of the primary grind. On fully flat ground blades this angle is 2-4 degrees and thus you can take as much as 1/8" off the edge and still lose performance by a matter of a few percent.
Consider as well that on high end materials, this really isn't a concern. We are far beyond the days of 50 RC, 1045 steel blades. The amount of use it would take for example to wear this much edge off current hard and high alloy blade, 62 RC D2 for example, blade is considerable indeed. The only blades I have seen that have had this much wear induced were either heavily damaged on a regular basis (edge rusting, chipping etc.), or were very soft plain carbon steel and saw constant use on a butchers steel for many years (10+) .
Another excellent overview by Jeff, of which I have only to add, that if you are looking for the ultimate in low stress cutting ability hollow grinds are much more functional than flat grinds. If you flat grind all the way from the spine to the edge (puukko style), you can end up with a very efficient cutter, but if you hollow grind all the middle out, then the blade will not only cut slightly better, but will be *much* easier to sharpen. Few people make knives like this though, so it isn't a practical advantage when speaking of hollow vs flat in general.
One of the real utlity aspects of hollow grinds comes in combining them with other grinds on the same knife. A hard wood felling axe for example has a primary convex grind which forms the body of the axe, but has a significant hollow relief above the edge to increase penetreation.
-Cliff