First Impressions: 10” CBN 600 grit

[OBR]

Ken Rizzo from Wood Turners Wonders was kind enough to send me a 600 grit 10" CBN wheel for my T7 to test for sharpening knives. My plan was to try one to see if it would be a good replacement for the SB250 wheels that I've been using for my sharpening business. Each season I wear a 10" SB250 down to 7-1/2" by the time the market ends at X mass. I'm not complaining; each wheel will sharpen 1000+ knives during the season. However, the SB250's do go out of round quickly and require retruing back to a round shape every week and sometimes more. The big plus is that I never have use the grader to coarsen the SB250. I just keep it at the fine grit. I was hoping that a CBN would grind as effectively as the 250 and never go out of round or wear out.
   I picked up 6 dull knives from our local Habitat for Humanity store to run my first test. I ground 3 using my SB250 and ground the other 3 with the 10" CBN. I counted the number of passes for each grind and found that the 10" CBN took more passes to raise a burr and the burr was a little less distinct. It also took a little longer to buff the burrs off. I then used a BESS KN 100 to compare how sharp each knife was after buffing. The knives ground with the CBN averaged in the low 170's while the ones ground with the SB250 averaged 212. Not bat in in either case.
   I always thought that the SB250 trued fine was about 1000 grit. After my test today, I'm wondering if the SB250 isn't closer to 500 grit. I'm now starting to think that it would be better for me to get a 500 grit CBN??
   I plan on going back to Habitat for more test knives (they happily take them back sharpened). I'm also hoping that one of my ex-colleagues who is still teaching will let me use a microscope to take a closer look at the grinds.

Curt

[Ken S]

Well done, Curt! I appreciate your thoroughness and your evenness.

You have used your extensive knife sharpening experience as a testing backdrop.

You do not specifically mention it, however, I assume you allowed whatever break in time was needed for the CBN wheel.

I noticed a difference in performance between grinding into or away from the blade. Which way are you grinding? If you have been only grinding away, I would suggest trying grinding into to see if that might lower the number of passes necessary.

What grit would the next coarser wheel have? I have used 80 and 180 grit CBN wheels, both of which I consider too coarse for knives. A 360 or 400 grit wheel (not both) might be worth a try. A sharpener doing fewer knives might be happy with the 600 grit. In your case, with forty knives waiting, a coarser grit would be necessary.

Again, thanks for a well done report. Do continue to keep us posted.

Ken

[OBR]

Ken,

I understood that CBN wheels are more aggressive initially. I didn't know how long it would take to break in a wheel, but I assumed that the 600 CBN wheel would be so aggressive at the start that I would be ordering an 800 or 1000 grit CBN wheel for the upcoming season. Instead the new 600 CBN was less aggressive than my well worn SB250. Once the 600 grit CBN was broken in, sharpening knives would be even slower. We'll see how things go after I pick up some more Habitat knives and continue testing.

I've always sharpened knives grinding into the blade. I also discovered yesterday how much I appreciated the water pooling at the edge of the blade as SB250 is grinding into the knife. The amount of water at the edge acts as guide for how close I am to having having each blade side ground. With the CBN it was just sound and a guess. I'm sure I would adjust over time. I know that Ken at Wood Turners Wonders strongly advises against running the CBN's in water, so I won't try water with the test wheel that he sent.

Wood Turners Wonders do have a wide range of grits that are steps down from 600. Perhaps 500 or 400 would be the best choice for me. Your questions are helping me think through this potential purchase.

Thanks!

Curt

[Ken S]

Curt,

Your 600 grit wheel is acting differently than my 180 did. It cut ripping fast for a short time when brand new, and then settled down to how a 180 should act.

I found my CBN wheels worked well wet or dry. I found I need to use Honerite Gold solution with water with my steel wheels. I have not used aluminum wheels. As an old Tormeker, like you, I like wet sharpening. I would be curious to know the objections to wet grinding.


Wood Turners Wonders seems like a stand up outfit. I would keep working with them until you find a grit which works for you. You are certainly an experienced sharpener; you will recognize the correct grinding wheel when you find it.

Keep up the good reporting.

Ken

[grepper]

Curt-

Another thank you for your review!

I'm not quite as concerned about cutting speed as the finish of the edge.  I'm looking for a slightly toothy edge that will cut things like broccoli and tomato skin well without just riding on the surface.  Grapefruit rind is another good test material.  A super sharp polished edge works fine for a short time, but soon starts riding on the surface.

I've been trying to decide between a 400, 500 or 600 grit wheel, but they are too expensive to buy all three just for experimentation.

It would be interesting if you could test your 600 grit edges on some of the tough, smooth skin vegetables and fruits and see how they perform after a moderate amount of use.  I've found that is a actually a pretty good test for how well a particular grit finish is going to perform in general and kitchen use.

You might want to pick up a USB microscope.  They are inexpensive, ranging from $25.00 - $100.00 and are produce images that are very informative.  I would suggest a 5mp with 200X or more optical magnification.  Ignore the digital zoom numbers.  Digital zoom is meaningless as it is just the same as zooming in on an image in an image viewer.

My microscope and PT50B sharpness tester have become just part of how I sharpen.  A microscope and sharpness tester combined provides an amazing gestalt of empirical analysis of the edge.  Once you get use to that data, it's hard to believe sharpening is even possible without it.  Instead of just guessing what is going on, you can actually understand by measurement and observation.

The attached image, as well as the following links are some of my USB microscopy images:

https://forum.tormek.com/index.php?PHPSESSID=bsum39h9llrfedila1dig6tiq3&topic=3165.msg18073#msg18073
https://forum.tormek.com/index.php?PHPSESSID=g2oeq2479qc0cp6ab8qkrrd4i5&topic=3191.msg18467#msg18467
https://forum.tormek.com/index.php?PHPSESSID=nap2bgf53nbmoh4n6i0i9vupe0&topic=3190.msg18443#msg18443

Again, thanks for the review!  Please keep us informed of your further testing and experience.

[OBR]

While I wait for my USB microscope to arrive  , I did a little more experimentation with my T7 and the CBN 10" 600 grit Tornado from Woodturners Wonders. I mounted the CBN on my T7 and then put the water trough on. I wasn't planning on adding water to the trough but wanted to see how tight the fit was. I had heard it was a tight fit from an Australian turner. In order to screw the EzyLock nut on, I had to replace the thick Tormek washer that goes between the wheel and the bearing with a very thin washer. Even with the thin washer, the EzyLock just fit; and the CBN was very close to the motor housing. Even worse, I found it very difficult to get the water trough off. It took a lot of twisting and tugging to free the trough. This would not be a good situation for me at the end of a busy market.

When I measured the length of the axle hole in the SB250, it was slightly more than 1-3/4" (1-51/64" to be more precise). The CBN wheel axle hole was 2" long. When I contacted Ken at Woodturners Wonders, he said that the 10" Tornado CBN could be customized so the axle hub would be 1-3/4", but customizing does cost more. The 10" CBN wheels at D-Way are 1-1/2" wide but only come in two coarse grits (80 & 180). I haven't found any other 10" CBN options for the Tormek. I'm leaning toward a customized Tornado if I can settle on a grit.

[Ken S]

Curt,

I applaud your pioneer spirit. I think you have two solutions:

1) The custom sized wheel from Ken Rizza. I have heard good reports about his products, and I have absolutely no wish to sound overly critical. However, his wheel for the Tormek seems to have the same design problem as the third party conventional wheels, they are not designed to fit the Tormek. The Tormek made grinding wheels are 250mm diameter by 50mm wide. That is not the same as being ten inches in diameter or two inches wide. It is close, but not exact.

The other needed specification is the inset for the EZYlock or conventional nut on older shafts. Right, wrong, or otherwise, that is how Tormeks are designed. If a third party wants to sell grinding wheels for Tormeks, the dimensions and the inset need to be right.

Frankly, I do not see this being a major design problem. It does need to be done right. In fairness to the vendors, CBN wheels are primarily used with higher speed dry grinders.

When I corresponded with Ken, he was very helpful, and offered to make a custom sized wheel for my T4 if I would send him a dimensioned drawing. I do not fault his service or product. At this point, he seems to think in dry grinder ways, like most of the non Tormek suppliers (including the clone designers).

Ken Rizza is a new member of this forum. I believe his CBN wheels have the potential of being very useful tools for Tormek users, if designed to fit the Tormek. I mean my thoughts solely in the spirit of constructive criticism and hope they are interpreted positively.

Solution two is D-Way. Dave is starting to get into different grits, 360 and 600, if my memory serves. He was starting with the eight inch diameter by inch and a half width size. My 180 grit wheel in this size is a delight to use with my T4, and works as well as any 250mm wheel on the T7/8 when worn to an eight inch diameter. The D-Way wheels and reducing bushings fit the Tormeks very well as is. To my surprise, I did not find the slightly narrower width any constraint.

We have two excellent candidates for CBN wheels. Neither has quite locked in on the combined  target grit range and Tormek fit. Each has accomplished one part of the two part puzzle and both are reputable suppliers.

I hope that Tormek will eventually offer CBN wheels and in different grits. In my opinion, Tormek is the only company which really understands wet sharpening.

Ken

[OBR]

Ken,

Once the digital microscope and the K100 sharpness tester arrived, I've been able to take a closer look at whether a 10" CBN 600 grit wheel mounted to my T7 would be a good alternative to the SB250 that I've used for the last three years as I sharpen at our farmers' market. I managed to collect 22 knives to test. 4 of the 22 were identical 12" Victorinox butcher knives and 5 were Victorinox 5" boning knives,  so I could come closer to comparing identical knives. I could do my grinding with three different grits: 600 grit on the CBN, 180 grit using a Razor Sharp paper wheel, and the SB250 trued to the fine grit (whatever that is). During all my grinding I could look at the ground surfaces on the blades with the digital microscope, buff the burr off, look again through the microscope, and then finally test the sharpness. Doing this multiple times made me aware of how many ways I could come to the wrong conclusion.

When I used the digital microscope to examine the ground but unbuffed blades, the 180 grit paper wheel and the SB250 appeared to be very similar and to leave a coarser grit pattern than a blades ground by the Tornado CBN 600. The burrs created by the SB250 and the PW 180 were larger and much easier to detect while grinding. The CBN 600 left such a fine burr that it was hard to decide if a burr had been raised even after long grinding. Once the burr was buffed off in the honing, the 180 paper wheel and the SB250  had larger "teeth" along the edge. Made it slightly easier to cut a grapefruit. I didn't try to test how long blades would stay sharp.

Once deburred and buffed I moved the knives to the K100 sharpness tester. The honed knives took an average of 151 grams to break the test media with the scores ranging from 114 on a PW 180 ground knife to 214 on a knife ground with the CBN 600. All the knives except the 214 one passed my paper and left thumbnail tests. I also used a stopwatch to measure how long it took me to grind the 12" Victorinox butcher knives. The CBN 600 took twice as long to raise a burr, and the CBN 600 also took longer on other comparable knives.

I would have loved to try grinding with the CBN 600 in water, But Ken Rizzo did not think grinding in water was a good idea. Since he had kindly loaned me a new CBN for trail purposes, I didn't want to risk doing any damage to his new wheel. Instead I repackaged it and sent it back. I still really like the potential of a 10" CBN on my T7, but I'm left with the question: what grit would work well in my market sharpening enterprise? Ken only has 10" CBN at 600 grit in stock, but you can order 10" CBN at 400, or 200, but they wouldn't be test wheels. Once you decide, you would have to live with your choice. I do have some time to mull the options; the market starts at the end of May.

Curt

[Ken S]

Curt,

I am sorry that your well done reporting has been frustrating for you. At this point, I don't think we can definitively state if your problems are related to the CBN wheel itself or just the 600 grit b ing too fine. That is frustrating.

I was more fortunate than you with the wet or dry issue. The first wheel I tested was the D Way eight inch wheel I purchased. My first wet test was done very cautiously, and proved that plain water did allow both the steel wheel and the steel reducing bushing to rust. The wheel itself only rusted where the balancing holes were drilled. For the next test, where I had added the two loaner wheels from D Way, I was using Honerite Gold rust preventative additive. I was also fortunate that Dave had said the wheels could be used wet or dry.

Ken Rizzo had also written me that CBN wheels should only be used dry. He did not state the reasons for this. I am not sure if using the wheels wet actually causes a problem or if he felt the water bath was unnecessary. I experienced no overheating using the wheels dry. Being unnecessary for heat reduction is not the same as causing a problem.

Ken is a member of this forum. Perhaps he will post his thoughts.

Most of my testing has been self funded. In fact, I have purchased my three CBN wheels, two Norton wheels, six hundred grit wheels and four Tormek wheels. Normally I would purchase a three hundred sixty grit wheel. D Way now lists them in the eight inch diameter. That size is a match for the T four and works as well as any ten inch wheel worn to eight inches with the larger Tormeks. The cost saving with the right inch wheel will cover around a quarter of the cost of a T four. And, for the farmers market crowd, the T four is only half the weight to carry.

Curt, I will predict that at least one of us, probably both, will have a CBN wheel near three hundred sixty grit in the near future. As I stated earlier, I do not think either vendor has fined tuned his wheels yet for the Tormek. Both are primarily marketed for high speed grinders for turners. The D Way wheels fit both size Tormeks very well, however, the finer grits are only listed in the eight inch size. The Woodturners  Wonder wheels are really not ideally sized yet for Tormek.

I believe you will eventually find a useful CBN wheel for your knife sharpening. I do not think the present products are quite ready for prime time with knife sharpeners.

Do continue to keep us posted.

Ken

[larcal]

Curt,

Fascinated by your tests. Did you decide to try a lower grit CBN for this season?