hollow grinding revisited

[Ken S]

Earlier this week, I had dinner with two old Tormek hands. This is a very rare treat for me. Among the various discussion topics was hollow grinding. We had at least three points of view on this. While trying to be fair to the other points, please be aware that this post will probably favor my thoughts.

The traditional Tormek view is that adding a secondary or micro bevel is unnecessary. Grinding with the Tormek is efficient that the labor saving micro bevel is not needed. In general, I agree with this.

Another viewpoint is using the Tormek to establish the bevel and then switching to flat bench stones to create the keener micro bevel, usually to 8000 grit.

A third view is to establish the primary bevel with the Tormek SG grinding wheel and then add a micro bevel using the Tormek SJ polishing wheel.

In my opinion, establishing the two reference points with a hollow grind to allow alignment of the blade on a flat stone does not reflect Tormek thinking. It can produce very sharp edges, and I have no doubt that many use this method. I think it also reflects both a lack of confidence in one's ability with the leather honing wheel and an addiction to grit numbers.

I am old enough to have been a charter subscriber to Fine Woodworking magazine in the early 1970s. One of the hot topics back then was hollow grinding. The majority of home shop grinders were six inch. A few were 1725 RPM. I recall a very few might have been seven inch. At the time, I purchased my set of three bench planes, lovely 1909 vintage Stanley Bedrocks, from an elderly carpenter who was the original owner. He proudly showed me how he had hollow ground the blades so that he could touch up the edges with a file.

Things have changed since then. I now sharpen plane blades with a Tormek with either  200 or 250mm wheel. This produces a hollow grind which is much less hollow than smaller diameter wheels. I do believe that much of today's thinking about hollow grinding is leftover from the small diameter dry grinding days decades ago. It does not reflect larger diameter Tormek grinding.

What about switching to bench stones for final finishing? Two experiences make me think this is unnecessary. The first occurred during one of my knife tests. I really leaned on the fine side of the stone grader with the SG-250 for a long time. To my surprise, the wheel felt smoother than ever before. It also cut very slowly. I had inadvertently been using a middle grit before.

The second experience was reading a post by Stig saying that he routinely used a very light touch for the finishing passes. I believe that if a sharpener used these two techniques, the need to use bench stones would be minimal. Combined with disciplined use of the leather honing wheel, I believe Tormek only edges can rival bench stones. I hope to purchase a USB microscope this summer to document these ideas. I presently have around eight 3/4" Irwin Blue Chip chisels for the tests. (I also have a set of Norton water stones from my pre-Tormek days.)

As I become very proficient with this technique and can document it better, I will compare it with finishing with the SJ-250.

Two factors to consider is the thickness of today's premium plane blades and the newer steels. All of my blades are old Stanley carbon steel. I hope others with experience with today's thicker blades will join in and post.

Ken

[Herman Trivilino]

Good points, Ken. The only thing I would add is that micro bevels are needed by folks who desire sharp edges and don't own a Tormek. These people may hire a sharpener to establish a hollow grind bevel using a Tormek, but then need to tune up the edges on a bench plane when necessary. This is rather like using a steel to tune up our kitchen knives in between Tormek sharpening sessions. I use my steel just about every time I reach for a kitchen knife, especially if the edge doesn't pass the fingernail test.

Can you tell us who your dinner companions were? I'm jealous!

[Ken S]

I remember those days (decades), Herman. I had a high speed dry grinder, however, I usually did all my sharpening with oil or water stones. (That was before flat diamond plates were available to restore India and Arkansas stones.) I welcomed micro bevels, although I welcomed the Tormek even more. I never paid anyone to sharpen to sharpen my chisels or planes.

I really like my ceramic "steel" for kitchen knives.

I suppose I am allowed to post the names of my two dinner companions. Rich Colvin, of our forum, lives in a suburb of Columbus. We have enjoyed "Tormek afternoons" a couple times. The other diner was a guy from Sweden who was in town for a Woodcraft meeting. He said his name was Stig. He knows a lot about Tormek. It was a great evening.

Ken

[Komitadjie]

Lucky duck!

I've actually used the hollow grind / microbevel that way myself, mostly because I can.  Give that edge just a couple more super-light passes on a high-grit waterstone (8k Snow White for me) and it puts an extra little bit of pop into the edge with basically no more effort at all. 

Do I need to?  Nah, that edge off the honing wheel is already sharp enough for any use short of eye surgery.  Do I do it anyway?  Heck yeah!

[Herman Trivilino]

Hand touch-ups are indeed a nice complement to sharpening with a Tormek. But only in some cases. Tools like chisels and mower blades,perhaps. But knives, not for me.

[Ken S]

Herman, I am pleased you have not forgotten your framing carpenter heritage. Perfection is nice, but so is being done by quitting time.

Ken

[Ken S]

Lucky duck!

I've actually used the hollow grind / microbevel that way myself, mostly because I can.  Give that edge just a couple more super-light passes on a high-grit waterstone (8k Snow White for me) and it puts an extra little bit of pop into the edge with basically no more effort at all. 

Do I need to?  Nah, that edge off the honing wheel is already sharp enough for any use short of eye surgery.  Do I do it anyway?  Heck yeah!

Komitadjie,

I applaud your willingness to go the extra mile with sharp edges. I have had similar thoughts. With me, in the back of my mind, I keep wondering whether my limitations with the Tormek are due to the machine itself or with my own level of technical skill. The old saying,"It's a poor craftsman who blames his tools" conyinues to haunt me.

Like many of us, I have studied the videos Jeff Farris made many years ago. Jeff demonstrated the Tormek for many years and became very skilled with it. My thought is if Jeff could do it, so can I, if I am willing to work hard enough.

Some Tormek skills have only developed with considerable effort for me. Case in point is using the truing tool. Like most new users, I delayed using it, not wanting to waste "my precious, expensive grinding wheel". I became very frustrated with the blackstone glazing while reshaping a turning gouge. I resorted to very frequent retruing (restoring) the wheel. I had to do enough of it to become fluent with the truing tool. I have since become a believer in frequent, light retruing. Those of you who, like I did, have not retrued your grinding wheel, or do so infrequently, may not realize the cutting potential of your Tormek.

I had a similar experience with the stone grader. These experiences have bumped my technique closer to full proficiency with the Tormek. This growth is ongoing.

Hang in there; do not settle for less than you can be.

Ken

[Komitadjie]

I really would like a SEM or something similar so I could properly evaluate the edge!  Technically, given the way I understand the SB stone to work, there *is* no way it can reach a scratch pattern as fine as an 8K stone by nature of the abrasive.  Now, that being said, I'm as far as possible from an expert with the stone and its structure! 

Certainly, for all working purposes, the edge straight off the honing wheel is sufficient for basically any use you'd put it to at all.  It gets into the "how do you define sharp" arguement, I think.  Are we talking perfection of edge linearity?  Minimum scratch pattern?  Minimum apex?  Easiest cutting of a given material?  I've heard that argument run around about a million times.  I generally base my personal comparisons on the result of BESS testing, just for a baseline.  I should really get some numbers for my Tormek edges, come to think of it! 

[Herman Trivilino]

You can create a perfect edge that gets a high score, has a polished bevel, and cuts through paper to impress observers. But as soon you you start using that knife it quickly becomes dull. Sometimes you need a more blunt edge angle so it'll stand up to everyday use, or a toothy edge to slice tomatoes.

The nice thing about a Tormek is you can adjust all these variables to your liking so that each of your knives suits your own purposes and preferences.

[Komitadjie]

Oh, I've played with the variables, and still do!  I just like the BESS as a basic way to compare one edge to another in my own sharpening.  Nothing like a standard to test to! 

I tend to go highly polished edges, with as acute of a bevel as the knife can hold.  I've had fine luck with tomatoes and a polished edge, as long as I've got the edge polished and acute ENOUGH.

[Ken S]

Another vote for BESS standardization of sharpness measurement. I think measuring edge sharpness is the first part. The hard (and interesting) part is in developing a feel for interpreting those numbers for your own use.

Keep on exploring!

Ken

[Komitadjie]

Well, and then determining the factors that make that particular blade work the best in the *exact* use you are sharpening it for.  Pure sharpness means nothing if the edge won't withstand the abuse you throw at it, etc. 

[grepper]

Plus 1 for the BESS sharpness standard.

The first instrument that I purchased to help me to understand sharpening was a USB microscope.  There is nothing like being able to get a good look at the edge of a blade to see burrs and the scratch pattern of different abrasive grits. 

Then I got a PT50B (BESS) sharpness tester.  The two instruments combined are amazing.  If a blade is for some reason not testing as sharp as I think it should be or is super sharp for that matter, I can check it under the microscope and see why.  With the sharpness tester I not only know how sharp a blade is but can also put a standardized number on the level of sharpness that can be communicated to others.  With a microscope I can understand why.  Very cool stuff!

I'd love to have a nice tabletop SEM, but it would stress my discretionary income just a bit. 

[Ken S]

Good points, gentlemen. I'm an old chisel guy. I first bought my Tormek to sharpen chisels. They remain my favorite tool to sharpen. I believe learning to sharpen chisels is "the great teacher" in learning to use the Tormek. Sharpening the straight, good sized single bevel is easy enough in itself to allow "the veriest tyro" ( I love that old British term for beginner) to be aware of the sound and feel of using the Tormek.

In my opinion, getting the bevel sharp with the grinding wheel graded coarse is both the labor intensive and easiest part. The last few light strokes with a 4000 or 8000 grit stone or wheel graded fine and then the leather honing wheel are the less physically demanding part.

In my case, I was content to remain in the comfort of continuing to finish with Arkansas stones or water stones. These were decades long friends. I was almost content, but I felt I had made this decision with bias. To decide fairly, I should have had equal skill with either method. I felt I had not fully learned how to finish with the Tormek. I took the time to practice finishing until I became proficient. Now I am equally comfortable with  either method. I generally finish with the Tormek. I would feel just as at home with my water or oil stones.

I do not advocate one method over the other. You should use whichever technique is more comfortable for you, or a combination. I do believe that we owe it to ourselves to make that decision based on being skilled with all choices.

Grepper, as you and the forum know, I have been excited about using BESS testing for some time. It quantifies sharpness with repeatable numbers. I am stepping things up a notch. Sometime this very day, my mail carrier will deliver the Celestron 5mp Pro USB microscope I ordered on your suggestion (badgering?      )  [like yours] I procrastinated too long. I will use it in conjunction with my 10x LED handheld magnifier, another suggestion from a friend.

This may seem like overkill, however, I believe it will intensify my visual acuity with examining my edges, my actual edges, and deepen my knowledge of sharpening. With coaching and encouragement from you, plus some trial and error work, I am finally comfortable posting photos on the forum.

I look forward to future dialogue; we have some new and useful tools.

Ken

[Ken S]

ps

My original intent is purchasing the USB microscope was to donate it to my grandchildren's school. It is a delightful learning environment that operates on a shoestring budget. I could borrow the microscope on weekends.

I believe that plan will change very soon. The school will still have the microscope, however, the next time my budget refills I suspect I will be ordering a second unit for my shop. I watched a video of a guy who incorporated it into the flow of his sharpening. He would grind and look, then grind again if necessary. This seems a more efficient work method to me than just having a post work inspection area. Rich Colvin has a tablet in place on the wall next to his Tormek. He is compiling a sharpening handbook which will be a vsluable reference. Pairing this tablet and reference with a USB microscope would be a powerful and efficient combination.

I look forward to future posdibilities.
Ken