grit thoughts

[Ken S]

Much praise has been posted about the benefits of superabrasive wheels, both diamond and CBN. The diameters do not decrease with wear and they never need truing. While these are indeed formidable advantages, the praise chorus often overlooks a notable constraint. These marvelous wheels are single grit. Standard advice given to new users is often to purchase three diamond wheels or four or more CBN wheels. We are starting to see conflicting advice given to new users who want to purchase only one wheel due to budgetary constraints. Purchasing a set of superabrasive wheels can easily double the investment in a T8. What to do?

Our late very innovative member, Wootz (Vadim of Knife Grinders), did the preliminary work on a solution. Tragically, his death cut short the development of his ideas. One of his most promising ideas was the use of diamond plates for grading the SG and SB grinding wheels. While still not universally known or accepted, we now know that the concept of using the stone grader to change the grit from 220 to 1000 (only) was an oversimplification. For years, the concept of "600 grit" has been gradually entering the conversation. "600 grit" is a grit somewhere between 220 and 1000, a medium grit somewhere between 220 and 1000, as opposed to an exact number.

Wootz also introduced the idea that using a 1000 grit diamond plate to grade the SG could produce a grit similar to 1500 grit.  Wootz also introduced using the 80 grit diamond plate to set the SB wheel to coarse without having some grains standing proud. Wootz left us some interesting ares to further develop.

I do not mean to minimize the importance of the stone grader. For the many years when the SG was the only available grinding wheel, the stone grader provided a way for the Super Grind (SG wheel) to also grind like the finer (smoother finish) discontinued natural sandstone grinding wheel.

My question for my fellow forum members is have we explored the limits of the grading potential of the SG and SB wheels? If, as Wootz said, a 1000 grit diamond plate will produce 1500 grit with the SG, will a 2000 grit plate produce an even finer grit? Or, is a 1000 grit the maximum for making the SG finer? What about varying grits with the SB or intermediate grits with either the SG or SB?

I recently ordered half a dozen diamond plates in various grits from 80 to 2000 from Amazon. At around $10 US each, they were not expensive. Three or four would provide the average Tormek home user with plenty of versatility at a fraction of the cost of a set of superabrasive wheels.

I welcome your thoughts.

Ken

[RichColvin]

Ken,

I am eagerly awaiting your testing results!

Rich

[Ken S]

Rich,

Thinking about how to do these tests, I plan to use my dozen identical 3/4" Irwin Blue Chip chisels. The chisel bevels are much larger and easily to see than knife bevels. For closer inspection, I can use my machinist's loupe. I can use masking tape on the handles to identify which chisel is which grit. As I already have these chisels, no extra cost will be involved.

My gut feeling is that trying to use half a dozen different grits may prove cumbersome. One or possibly two middle grits may prove useful.

I presently have an unusual amount of family commitments, so results may take a while to complete. In the meantime, I welcome comments and test results from other members.

Ken

[RickKrung]

What is the question you are attempting to answer, specifically a clear, concise hypothesis statement?  How will you use these diamond plates and how will you distinguish differences?  How many times will you repeat the tests, that is number of replications? How will you eliminate untested variables?  What about adequate separation of trials to be sure a difference, if real, can be discerned. 

I sure don't expect a rigorous statistical approach, but you need to have some clearly defined objectives and procedures, particularly with so many variables (number of grits). 

[RichColvin]

I think it would be great to have side-by-side comparison photos.  I believe that you have a microscope with a photo capability.  I can imagine comparing the photos of (for example):

• Chisel ground on an SG grindstone graded using a (600 grit?) diamond plate vs
• Same chisel ground on a DF grinding wheel.  

If you want to do the tests and send me the pictures of the various grinds, I'll put everything together for you. 

[Ken S]

Good thoughts, Rich and Rick.

I hope to test for the practical limits of grit changing. The stone grader goes back to the days when the SG-250 was the only wheel available. I have long felt that the 220 and 1000 numbers were arbitrary and certainly not "digital" (either/or).

I purchased six diamond plates with grit ratings from 80 to 2000 from Amazon. The last plate finally arrived today. A logical place to start seems to be with the scratch pattern of the fine side of the stone grader on the bevel of one of my test chisels, what Tormek calls "1000 grit". I have no way of accurately testing grit number, nor do I especially care. The Tormek method of using the fine side of the stone grader will be my
designated fine grit.

Using Wootz' three times the diamond grit to determine the stone grit formula, I will start with one of the middle grit plates and determine which plate approximates the stone grader "1000 grit". Then I progress one at a time through the finer grits. I expect to reach a point where a finer grit no longer produces a finer grit on the grinding wheel. The finest diamond wheel which produces a grit change on the grinding wheel will become the fine grit limit with the SG wheel.

If my 2000 grit diamond plate produces any change in fineness of the grinding wheel, I will order a 3000 grit diamond plate. (After I ordered my diamond plates, I became aware of the 3000 grit plates.)

I will then perform these same fine grit limit tests with the SB and SJ wheels.

I would like to make two points clear: First, I do not consider this level of attention practical for most knives. I think it might possibly make sense for one's best clients and knives. Atthis point, it is only a possibility, not a certainty. Second, I have no intention of being critical of Tormek for sticking with the stone grader. Tormek has knowledge and experience leagues beyond mine.

This initial test will give me an idea if further tests are practical. My shop time is very limited. Please be patient. I will post results when they are available.

Ken

[John Hancock Sr]

I have long felt that the 220 and 1000 numbers were arbitrary and certainly not "digital" (either/or).

As you are probably aware the grit system is best described as "it depends". What the actual number means depends on which standard you are using and even then it is a range, not a fixed number. Assuming that the maker complies with whatever standard they are using the particle size will be within a specified range.

And to be blunt we are really talking about creating an apex. In the vast majority of applications so long as the apex is clean and consistent the tool will perform more than adequately, even if some scratches have been left behind.

[3D Anvil]

The main reason I use CBN wheels is because I primarily sharpen super steels with high vanadium carbide content.  It's possible to sharpen such knives with the SG, but not ideal as the abrasive in the wheel is softer than the carbides in the blades.

[John Hancock Sr]

but not ideal as the abrasive in the wheel is softer than the carbides in the blades.

Yes. A pretty basic principal in sharpening. Sharpening is in its most basic form scratching to remove material in order to create an edge. The finer the scratches the more refined the edge. De-burring is, again scratching away at the burr to remove it leaving a clean edge. In order to create the scritches you must use a harder material for the abrasive in order to scratch the softer material being sharpened.

In practice I found that I was glazing the SG wheel with harder steels which quickly rendered it ineffective.