FFG VS FG
- This topic has 7 replies, 5 voices, and was last updated 11/28/2017 at 5:39 am by
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Hi MarcH, I’ll take a stab at this. I’m not sure people use consistent definitions of FG and FFG. There are just too many possible variations of knife design to fit neatly into those categories without some gray areas.
But by one definition, FFG is a special case, or a subset of a FG, where the profile taper begins at the spine and continues down to the edge (and it may be a linear taper or it may have some curve to it).
There are other subsets of FG, where the profile taper begins below the spine (closer to the edge) with a distinct break-point, and people give those different names depending on how far down the profile taper begins. But in those cases, the portion from the spine to where the profile taper begins is (often but probably not always) a constant thickness.
So by this definition, there is a difference between FFG (which would have some profile taper within the vise jaws) and the other forms of FG where the taper begins lower. For this definition of FG, the portion within the clamp jaws does not have a profile taper.
This didn’t really answer your question definitively, but it’s one possible answer. On top of all the above (and I know you already know this so I’m just mentioning it for completeness), any given knife could also have distal tapering heel to tip, but even in those cases, the distal tapering at the spine may be a linear taper over the full length, or the spine may be a constant thickness (i.e. no distal taper) until ~ 50% of the length and only tapers from there toward the tip. But it doesn’t usually have the clear break-point that you see in profile tapers that begin somewhere in the middle.
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Thanks Graphite. My post was more rhetorical.
Don’t they clamp in exactly the same manner? What is the difference in how we clamp just any knife VS how we clamp a flat ground or FFG knife? Is the process or procedure different?
Irrespective of what the knife’s shape, size or style, I attempt to apply the same clamping technique and procedure to all of them. In order to apply an even bevel down the entire knife length with the least amount of profile change and metal removal. Only when I can’t do this, do I find alternatives or employ adapters like the L.A.A. or the Tormek Jig.
Marc
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Hi Marc, re: “Irrespective of what the knife’s shape, size or style, I attempt to apply the same clamping technique and procedure to all of them.”
I must be confused. What is the purpose of the tension adjustment lever if it’s not to apply knife-specific tension based on the shape/size/style of the knife?
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Absolutely, Graphite, you are correct.
The tension control allows you to adjust the starting place on the jaws. If you look at the jaws as you turn the tension adjuster from (-) to (+) the space between the jaws closes smaller to the (+), (i.e., more tension). When you pivot or rotate the lever arm to close and lock the jaws, it has the same throw, the same amount of cam movement, from open, to the left position, to closed or locked, fully to the right position, irrespective of the tension controls position or setting. If you adjust the tension more towards the (+), tighter, when the lever arm is moved to the full lock position, full throw, the cam moves the same amount, which in turn, moves the jaw the same amount and all the jaws can do is squeeze harder/tighter on the knife. The flexibility in the metal jaws allows for this compression. The split jaws allows for this compression to be distributed more evenly down a distal tapered blade.
I place or orient the knife in the vice, the same, no matter, what shape or size or style knife I sharpen, in a manner that provides the best application of an even bevel down the entire length of the knife with the least amount of metal removal, while avoiding the need to move the knife during the sharpening process. I do utilize the tension adjustment to allow for the tightness in clamping force necessary to hold a knife in that position securely, only when it is necessary to make this tension adjustment.
That being said, what I’m really asking, “Am I missing something or over simplifying this?” Do others, of you, do this differently, (i.e., clamp knives differently), for different shaped, sizes or styles of knives? Have you found a different or specific clamping method or technique that works better for a specific kind of knife?
Marc
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Knives that feature a flat area near the spine (such as sabre and hollow ground knives) tend to be easier to clamp. They don’t have a tendency to cant to one side of the jaws (requiring additional adjustments to the angle settings in order to get a symmetrical bevel) and they can be clamped firmly without slipping in the jaws. Knives that are described as fully flat ground lack a flat spot to clamp and can be more difficult to clamp securely. The steeper the grind, the more likely they will be difficult to clamp. Have you ever tried to clamp a spear point knife? Those things literally slip right out of the clamp.
There are several ways to clamp an FFG blade in a pre-Gen3 vise. Some use tape or chamois to fill in the gaps at the vise jaws, trying to find a reasonably vertical position. I always clamped the blade with the left face flat against the left jaw. I then canted the right jaw to clamp it flat against the opposite face. This left the blade canted to the left. I’d measure the degree of cant and subtract it from the left angle and add it to the right.
If you can’t measure the degree of cant from the blade, measure the change in the angle of the right jaw. The angle of cant is one-half of this angle change if the right jaw is in fact clamped flat against the right side of the blade.
The Gen 3 vise is designed so that it only clamps with the faces of the blade uniformly displaced from vertical.
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Regarding the difference between FFG and FG knives I tend to agree with Graphite.
But by one definition, FFG is a special case, or a subset of a FG, where the profile taper begins at the spine and continues down to the edge (and it may be a linear taper or it may have some curve to it).
There are other subsets of FG, where the profile taper begins below the spine (closer to the edge) with a distinct break-point, and people give those different names depending on how far down the profile taper begins. But in those cases, the portion from the spine to where the profile taper begins is (often but probably not always) a constant thickness.
Many tips have been given already on how to clamp them. I always use a piece of chamois, which works fine for me, but I think Tom’s method also works very well (and may be even more accurate).
Molecule Polishing: my blog about sharpening with the Wicked Edge
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