How sharp is sharp?

[Ken S]

Fascinating post, Grepper.

I think a Catra machine should be part of the kit of every serious Compleat sharpener. Older members of the forum may have enough equity in their homes to get a home equity loan for one. Steve has mentioned the Catra in conversation. I don't recall the exact price, but several thousand US dollars sounds familiar. Having one would give you significant bragging rights at the farmers' market!

On a more practical level, the basic Edge On Up tester may be purchased complete for seventy nine US dollars. The more sophisticated PT-50 tester is only one hundred thirty nine dollars. Either of these testers will allow a Tormek user to test his edges with good accuracy. BESS may not yet be the accepted standard for the engineering/scientific community. I am quite comfortable with a measurement which is understandable, consistent and repeatable with the sharpening community.

Among my collection of machinist tools, I have a kit of surface samples. These are several small pieces of steel ground to different known and accepted degrees of surface smoothness. These are held up to a machined piece to see if it is of matching smoothness to the blueprint. The engineer determines the smoothness required. Matching the smoothness is important because the product must both meet the needs and be cost efficient. Spending the extra production time to produce parts machined beyond their needs adds to the cost, but not to the practical quality. Size tolerances are the same way. Thread clearance tolerances depend on the application. Working to closer tolerance than is necessary adds to the cost without necessarily adding to quality beyond the machinist's pride.

While we seem to enjoy cutting paper and shaving our arm hairs, BESS gives us a more organized, consistent method of measuring practical sharpness at a price the average sharpener can afford. BESS has the same range of utility as the kenjig. The kenjig is designed both for the busy farmers' market sharpener who must work efficiently and has great skill AND for the beginner who is learning. BESS can also do both. It provides the skilled sharpener with quick repeatable data demonstrating the sharpness of his edges. It can also assist the very beginner sharpener (what Charles Hayward, the famous British woodworker, would call "the veriest tyro") with a readily mastered method of gaging his progress. In my opinion, that's a very useful niche.

Ken

[Herman Trivilino]

Each BESS unit corresponds to 0.01N (1 centinewton) of applied force.

Ahhh ... Thanks for that. All I needed to know. So speaking properly, it's a force not a pressure.

[Jan]

Yes Herman you are correct, the measured quantity is a force, however the pressure/stress at the edge is of crucial importance. 

At the initial stage the edge elastically deflects the surface of the test media. Then, at a critical contact stress, the edge penetrates the surface of the test media. The force necessary to reach the critical contact stress is a measure of sharpness.

When the knife edge is blunt, then the elastic deflection is much greater and the critical stress for the media penetration may or may not be reached. This depends on the size of the applied force.

Jan

[SharpenADullWitt]

Fascinating post, Grepper.

I think a Catra machine should be part of the kit of every serious Compleat sharpener. Older members of the forum may have enough equity in their homes to get a home equity loan for one.

Uhm, yeah

Define serious! Define compleat, then complete?
Is this a commercial sharpener?  High end  hobbiest with an ego, or what?
What is the target audience they cater to?  Does the target audience understand the scale or what the measurements reflect?  Does the customer tell them how to sharpen?  (I want it at this scale, because I use it for x aka the toothy tomato argument)
One of us, who is middle aged, with a paid off home, thinks this is more of an ego trip, that provides seriously questionable value, at best.  At worst, it is you trying to get into our pockets and spend our money (and wondering if you have stock in the company)!

[Ken S]

Lighten up, amigo. I was being facetious. "Compleat" usually refers to someone with an irrational sense of completness. In reply one of this topic, Steve states a price of $12,000 US for a Catra. I am not questioning the value of a Catra. If this fits your ego and wallet, go for it! Both my ego and wallet are considerably smaller. My curiosity and wallet can swing the hundred and forty dollars for an Edge On Up PT-50, but certainlu not a  Catra.

Ken

[SharpenADullWitt]

One problem with just text, and part of the reason smiley's were invented, it is SO hard to tell someones tone, just by what they right.   IMHE, it is told by what is going on to the reader and the mood they are in.  (in my case, just having someone recently "oh, lets spend your money, you won't mind")
The money in the range you say is affordable, to me would be better spent on Steve's video's then a tester at this point, however lots of expenses are currently happening and delaying "fun" time.

[Ken S]

SADW,

You are correct; my humor can sometimes be too subtle. Sorry about that. 

I agree. I would make Steve's Sharpening School DVD a priority purchase. Training first. An edge tester can follow. By the way, Steve's video has the best section I have seen on conventional edge testing (thumbnail and various paper tricks).

I am gradually adjusting to the smiley faces.

Ken

[stevebot]

There are two lesser known sharpness tests on the video.
Just a reminder, that is on section that is available free at
https://www.youtube.com/watch?v=rzWdpjyDZKM

[stevebot]

I do not often test a customers knives but rely on a consistent method to give consistent results. Some would say ritualistic. But yesterday a friend brought 4 knives over and I had the time, so I tested. When I saw the results of my regular sharpening I decided to add an extra stropping step.

As delivered BESS 600 to 1000 grams
First sharpening BESS 250 to 300 grams
Second sharpening BESS 175 to 225 grams

For reference, a new double edge razor BESS 50 grams
The Rabbi's knife, sharpened by me, BESS 100 grams

For the curious, this differs from my regular sharpening as follows:
German edges - 18 primary, 24 secondary at fine ceramic grit
Above, same plus a stropping
Japanese knives - 15 primary, stropped; as was the Rabbi's knife.

[Ken S]

Interesting, Steve. Would you elaborate about the first and second sharpenings?

How would the rabbi's knife compare with a scalpel?

I have been kicking around an idea in the back of my head. I want to try using the SG-200 standard wheel of my T4 followed by the T7 with the SJ-250 Japanese wheel. I believe the radius difference in the wheels would give a similar primary and secondary bevel effect, the finer wheel being set to only polish the every edge, not the entire bevel. Thoughts?

Ken

[Jan]

I have been kicking around an idea in the back of my head. I want to try using the SG-200 standard wheel of my T4 followed by the T7 with the SJ-250 Japanese wheel. I believe the radius difference in the wheels would give a similar primary and secondary bevel effect, the finer wheel being set to only polish the every edge, not the entire bevel. Thoughts?

Ken

Ken, you are very inventive! 

All will depend on the edge angle setting for the SG-200 and the edge angle setting for the SJ-250 grindstone. The radius difference in the grindstones itself cannot be reason for grinding primary and secondary bevel.

Please let me know the result of your experiment.

Jan

[Ken S]

Jan,

Thanks for your encouragement. So many times my "inventiveness" is merely utilizing existing ideas in different ways. The kenjig is the combination of a twist on the wooden spacer block method from the handbook and the projection stops as seen in the TTS-100. The idea of combining the T4 and T7 to grind a bevel and polish just the extreme edge is one hundred percent lifted from Steve's Sharpening School DVD.

I will post the results. I am getting quite a backlog of projects. I have long believed that the Tormek is a versatile machine capable of many variations in technique.

I will have to actually grind to absorb the effect of different radii.

Ken

[WolfY]

I want to try using the SG-200 standard wheel of my T4 followed by the T7 with the SJ-250 Japanese wheel. I believe the radius difference in the wheels would give a similar primary and secondary bevel effect, the finer wheel being set to only polish the every edge, not the entire bevel. Thoughts?

Ken

I've used the SJ250 (250mm) after using the very little worn SG250 (245mm) and you can already see that the SJ250 would leave the middle of the cutting edge untouched. With higher pressure it will "clean" all the edge.
So on first thought using the SG200 first IMO would be to big different. On second thought it could be a nice effect and worth trying.

As for the KN-100 I think it's getting too academic for chefs knifes (my working volume), and I, by practice always test with thin newspaper page. It gives me 2 indications.
1. If there is still some burr (even microscopic) somewhere along the edge.
2. I can feel how sharp the edge is by feeling how easy and smooth it cuts the paper.

Many times you can see ppl cutting printers paper with fast and forceful movement. It is by far more edge sharpness proof to do it slowly and controlled. Anyway customers are getting very impressed by the fast cutting movements to show how sharp the knives are after the sharpening session. But they get more impressed doing it slowly and with waves cut on the paper.

[Ken S]

Interesting thoughts, WolfY. I suspect you may be right about the radius difference, however, I will run the test to verify.

I agree the KN-100 is a bit academic for many sharpeners. However, the two latest edgeonup.com models are much more user friendly and practical for in the field. Your newspaper tests sound very useful, although, if I wasn't a very good sharpener, I would prefer heavy paper. It can mask a lot of dullness while still impressing the crowds!

Ken

[WolfY]

Your newspaper tests sound very useful, although, if I wasn't a very good sharpener, I would prefer heavy paper. It can mask a lot of dullness while still impressing the crowds!

As we are on Tormek forum, "if you were not a very good sharpener" you are not using Tormek, or have to practice little to become a good sharpener as you have the right tools. (not you in person )

I have the WE Gen3 Pro sharpener here as some clients asked for it. On 1000 grit you can't even get close to sharpness and sharpening time/result with it, compared to the Tormek. After they saw that, they got the Tormek. Also price wise it's unbeatable in favor to Tormek.
IMHO, WE have lots of errors that ppl don't know and not worth the money at all. Works OK on small pocket knifes and nice when compared to freehand sharpening on japanese stones. Other wise time and energy consuming with very bad price/result/time ratio.
This VDO shows a knife that was in condition that you couldn't cut yourself and the tip was bent after faling on the floor.
https://www.facebook.com/ultrasharpisrael/videos