Coarse vs fine grind and edge retention

[grepper]

I've decided to change the way I sharpen.  I'm going to completely bail on the Tormek and simply sharpen using the rough side of the stone grader @ 6 dps.  That should do it!  Gotta love this stuff.

"In regards to the lower angle having increased edge retention the reasons are :

•   the 15 dps edge is already strong enough to resist rolling
•   there is no issue with carbide tear out or fracture in such low carbide steels
•   the higher angle concentrates forces around the edge
•   as the edge angle increases it takes less metal removed to increase the width of the apex

Thus increasing the edge angle does not offer a practical increase in strength and durability as it already is strong and durable enough to resist damage at 15 dps. The increased edge angle just makes the edge into a heavier wedge which actually thickens faster under a given amount of wear and the wear will be accelerated due to concentration of forces around the edge due to the higher angle."

http://www.cliffstamp.com/knives/reviews/angle_experiments.html

Well, this is amusing.  These guys actually sit around and do thousands of rope cuts.  Scroll down a little:
https://www.spyderco.com/forumII/viewtopic.php?t=65685&start=20

Some of the comments are funny! "can we smoke the hemp first.lol", "I use mine for ground cover, still have boxes full of it to dump out yet"

[grepper]

After reading Cliff Stamps's studies on edge finish vs edge retention, I've started to question some assumptions I have about sharpening. 

That being said, I thought I would pose this question:

With a kitchen knife for example, does a too sharp edge reduce edge retention?

Sharp, by definition, means thin.  It would make sense that a thinner edge would be more prone to wear, rolling and damage.

Onion other hand, a sharper edge requires less force to cut, therefore reducing force concentrated at the edge.  It would make sense this would increase edge retention.

For example, would a knife sharpened to BESS 50 (DE razor blade) have more or less edge retention than if it were sharpened to 150 (a sharper than average utility razor blade)?  According to the BESS folks, new high end cutlery is somewhere between about 250-350.

So, with a kitchen knife for example, does a too sharp reduce edge retention? 

Is there a happy medium?

Does anyone have an opinion on that?  Can you relate it to BESS numbers?

[Ken S]

One of the advantages of the Guillotine was that the heavier blade did not require frequent sharpening, thus allowing the use of less skilled, lower priced labor to operate. 

I was surprised with the BESS difference made by the leather honing wheel. When I sharpened a spindle turning gouge using just the 80 grit CBN wheel, the BESS reading was approximately 500. (This may approximate the sharper half of real world in use kitchen or pocket knives. ) Spending some time with the leather honing wheel and Tormek honing compound lowered the BESS reading of approx. 130. I say approximately because my technique is not yet well practiced with turning gouge testing. The difference in sharpness is obvious.

I think Grepper has introduced some interesting and usefyl questions, I look forward to many posts. (More in depth than this post, which has the constraint of being cut short br having to drive my grandchildren to school. More later........)

Ken

[Herman Trivilino]

Sharp, by definition, means thin.  It would make sense that a thinner edge would be more prone to wear, rolling and damage.

Another variable is the edge angle. You could, for example, make a very sharp edge at a very broad angle. Perhaps it would be as sharp as if it were ground at a smaller edge angle? But then it wouldn't hold up as well.

And the type of steel is another variable. Two otherwise identical knives made of different steel types will not perform the same at the same edge angle, and neither will they hold up the same.

I keep reminding myself of the lesson from Ron Hock (I hope I'm remembering it correctly):

When it comes to steel types you can have any two of these but only at the expense of the third:

1. Resistance to rust.
2. Sharpen-ability.
3. Edge retention.

Those of us with Tormeks may be more likely to let #2 be the weak one so we can have the other two. I say that because with access to an excellent means of sharpening we may not care as much about sharpen-ability. On the other hand, if you're an outdoorsman you may not always have your Tormek with you when you need it the most!

[grepper]

And, of course, it depends on how the blade is going to be used.  Some balance between steel hardness, sharpenability, and edge angel for the best performance in the environment that the blade is used in.

What I liked about this and the reason for the post is that for most everyday uses a toothy edge is more useful than a polished edge.  I was happy to see evidence that it may actually have superior edge retention.

I'm sure my tomatoes would feel quite differently, but I'm happy. 

[Ken S]

Grepper,

Topics like this remind me that "sharpness" is not just a simple, one size fits all concept.

Ken