Grit drifting

[BradGE]

Hi All,

This is perhaps a silly question and could only really get asked amongst Tormek junkies. The question came to me because I realised after using the stone grader and then grinding a knife the stone is wearing away, and so presumably the grit is changing.  If graded to 250 then presumably the grit goes up, and if you've graded to 1000 the grit would go down.  Presumably then if one kept going for long enough in those two situation the stone would eventually reach some sort of equilibrium.  I'm sure it depends on what is being ground by the stone, but lets say for a stainless steel knife, where would the settling point be? 

All the best,

Brad

[cbwx34]

Hi All,

This is perhaps a silly question and could only really get asked amongst Tormek junkies. The question came to me because I realised after using the stone grader and then grinding a knife the stone is wearing away, and so presumably the grit is changing.  If graded to 250 then presumably the grit goes up, and if you've graded to 1000 the grit would go down.  Presumably then if one kept going for long enough in those two situation the stone would eventually reach some sort of equilibrium.  I'm sure it depends on what is being ground by the stone, but lets say for a stainless steel knife, where would the settling point be? 

All the best,

Brad

Not silly at all, and you are correct.  Some refer to it as the stone's "natural state"... where, if the stone grader isn't used, the stone ends up somewhere in-between the 2 grits you mention.  I don't think a specific number is given... but 600g give or take would be the ballpark IMO.

Good observation!

[John_B]

I often start my sharpening of previously sharpened knives using this "natural" state. I use the coarse grader or truing jig when I an changing the angle or removing damaged areas.

[Ken S]

Brad,

CB is correct; you are asking a very good question. The original Tormek grinding wheels were natural stone mined on a Swedish island. They are finer grit than today's manmade aluminum oxide SG grinding wheels. For a while, one could choose between the finer grit natural stones and the faster cutting manmade stones. Tormek's solution for this was to introduce the stone grader, which made the SG perform like a finer grit stone when desired. This practical method actually works well. Introducing the graded fine step between the graded coarse step and the leather honing wheel will produce  more polished edges with smaller scratches. It accomplishes this with minimal wear to the grinding wheel, a moderate amount of time, and without the expense of purchasing a second grinding wheel and either purchasing a second Tormek or redesigning the Tormek to work with two grinding wheels.

Frankly, I look at Tormek's grit numbers as approximate guidelines rather than hard numbers. I have no problem with this; they are useful guidelines. I only achieve full coarseness with the SG immediately after using the truing tool. This coarseness is short lived. If I want a coarse grind, I will use the 360 grit diamond wheel. The "220" grit SG dressed coarse is no match for the "360" grit diamond wheel. These are field observations; I suspect that the diamond cutting surfaces are sharper and harder.

I ran a test with the SG and the fine side side of the stone grader. With a longer time than the recommended twenty to thirty seconds, the surface of the grinding wheel felt smoother. The stone grader is capable of producing middle grits, not just 220 and 1000. I call it analog rather than digital.

My mentor uses the "natural state" of the wheel for very good reasons. For many years, he worked the farmers market circuit, sharpening over a hundred knives, scissors and garden tools on a very busy Saturday morning. As an efficiency expedient, he set the initial bevel with the natural state Tormek wheel, and then did the finer grinding and then honing using higher speed paper wheels.

I asked him if he could do the entire process with just a Tormek. He said yes, but that it would take longer. For most of us, me included, that time constraint would not be a problem. I like the cost efficiency of being able to sharpen knives with one Tormek and one grinding wheel.

The choice of grinding wheel and grits is always a balancing act. Diamond and CBN wheels offer greater longevity and constant diameter with no need for truing and dressing. They are also single grit and cannot be trued if the wheel goes out of true. Conventional grinding wheels wear down with use, but can be trued more accurately. They can be used with a variety of grits with the stone grader.

Skilled sharpeners use both techniques.

Ken