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Knife dulls overnight after sharpening - grepper - 08-10-2018

This is the knife:
 
https://www.amazon.com/Victorinox-Fibrox-Chefs-Knife-5-Inch/dp/B000QCLEFC
 
I ground it at about 15° (dps) on my Kally with a 150 grit Cubitron belt.  The 150 Cubitron is my go to belt for general use knife sharpening.  It is very fast, and especially considering I use a light touch when sharpening they seem to last a very, very long time.  I've been using the same belt for a long time now and it seems like new.  Pretty amazing.  Additionally, the 150 grit produces just the toothy edge I’m looking for.
 
I ground on alternate sides until I noticed a barely visible burr forming on one side of the blade.  I continued grinding on the opposite side as the burr until the very small, barely visible with careful examination under a good light burr formed evenly along the entire length of the blade.  Then I ground the other side in the same manner. 
 
My new method of deburring is to use a very fine Scotch-Brite belt.  It is by far the quickest method I’ve ever found, and does a most excellently complete job of removing burr without smoothing the toothy edge.
 
To deburr, alternating sides I did four passes each side with the S-B belt.  I could still see some little flecks of burr, so I ran my fingernail at 45° down each side of the edge and the burr sprinkled off the edge like tinsel rain.
 
Then I did one swipe on each side of the blade with the rough side of a clean leather belt on the Kally, wiped the blade a few times on my jeans against the top of my thigh to clean off any loose crud and took four sharpness reading from handle to tip:
 
110, 130, 110, 125
 
Now here is the interesting part.  I put the knife in one of those flat in-drawer knife blocks overnight.  The knife was not used it just sat in the drawer overnight.  The next day, today, I removed it and checked the sharpness.  The readings were:
 
160, 150, 150, 175
 
That’s a maximum 50 point reduction in sharpness from just sitting in a drawer overnight.  Without real proof, I suspect this sharpness reduction is due to a lesser extent oxidation but mostly from metal memory as the extremely thin toothy edge returned to whatever position it was in after the tortuous micro heating, tearing at the steel and bending that happened during grinding.
 
So, I did one pass each side of the blade using the rough side of the leather belt on the Kally, wiped it clean on my jeans and took four readings from handle to tip:
 
125, 110, 105, 100

Here is a picture of the edge:

[attachment=720]

 My best guess is that the one swipe on each side of the blade with the leather belt straightened the edge.
 
You may be thinking this is just a fluke.  Well, consider this:
 
The same day I sharpened the Victorinox I sharpened an 8” Calphalon chef’s knife.  It’s a nothing special, big, heavy blade with a full tang that is 1/8” wide at the spine and tapers to the edge.
https://www.kmart.com/calphalon-classic-traditional-8-8221-chef-s-knife/p-00860553000P
 
Unfortunately I didn’t write down all the numbers documenting the saga but I did when I had finished sharpening and pretty accurately remember the rest.  I also noted the final sharpness numbers after checking it today.  So the first and final numbers are completely accurate.
 
I sharpened it using the same method as the Victorinox.  After sharpening the readings were:
 
95, 85, 115, 105
 
After sitting in the drawer next to the Victorinox overnight, the reading were all between
 
125 – 185
 
That’s up to a 100 point lower sharpness reading!  So today, as on the Victorinox, I did one swipe each side with the leather belt on the Kally and the readings were:
 
110, 130, 110, 125
 
So…, Hey Kids!  Try this at home!  Get a blade as sharp as you can, take four sharpness readings along the edge from handle to tip and let it sit for 24 hours or so.  The next day do another four sharpness readings.  Let us know your results!


RE: Knife dulls overnight after sharpening - Ken S - 08-11-2018

Grepper,

Your innovative work never fails to amaze.

As you know, my sharpening background for the last nine years is primarily Tormekcentric. (I love being able to make up works in my old age.  :Smile   Anyway, here is a link to a garden variety in drawer knife block:

https://www.amazon.com/Included-Pointing-Sharpener-Noble-Organizer/dp/B01DG45HOU/ref=asc_df_B01DG45HOU/?tag=hyprod-20&linkCode=df0&hvadid=198060092138&hvpos=1o2&hvnetw=g&hvrand=831307438063288094&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9014861&hvtargid=pla-348447272380&psc=1

Notice how the knife blades all have their sharp edges pointing downward where the evil forces of gravity compress the edges against the bottom of the block. Several years ago, one of the Tormek support staff advised me that he had instructed his children never to put a knife back in the block resting on the edge. Ever since then, all of the knives in my knife block have the sharp edge facing upward. The slots of my knife block all have wood covering the tops; the upward orientation is safe.  This means that the sharpened edges onlt come in contact with air. (I had to abandon my efforts to make the kitchen an anaroid environment due to my wife's complaints that it interfered with using the gas range and made breathing difficult, a small price to pay for sharp knives.)

I don't know how much effect the orientation of the knives in the block has on sharpness. My guess is that any contact of the edge with the block beneath it would be a negative impact. I am currently running some unofficial tests of Tormek's new diamond grinding wheels. I will incorporate your suggested BESS overnight readings with both edge on up and edge on down storage. (Sorry, Mike, the devil made me made that bad pun.  Sad

Ken


RE: Knife dulls overnight after sharpening - Jan - 08-11-2018

Mr. Grepper, thanks for sharing your very interesting results. Smile 

The term memory metal or shape-memory alloy is used for material which returns to initial shape when heated. Most often used are nickel-titanium alloys which undergo reversible transition between martensite and austenite phases.

In carbon steels this process is not reversible and for this reason steels do not have the memory properties.

In my opinion relaxation of residual stress, induced through the mechanisms you have mentioned, would also be able to explain the deformation component of an edge dulling.

Jan


RE: Knife dulls overnight after sharpening - KnifeGrinders - 08-11-2018

I like Ken's pun of edge on down and moreover so because it really is a bad pun to make on the Edge On Up forum Big Grin
As Grepper and Mike B. I used to attribute the post-sharpening sharpness worsening to "metal memory", but now we have the above Jan's comment.

My most systematic observations have been done on Victorinox SWIBO knives, of similar to Grepper's stainless steel - carbon content 0.5% HRC 56-58.
The minimal worsening we've seen in 24 hours is 5 BESS, which we attribute to oxidation of this steel, so anything over that is attributed to this phenomenon.

An example set of our data will follow, but what I want to say is that no matter what sharpening and deburring method is used, this post-sharpening sharpness worsening does develop.
The sharpness worsening can be seen as soon as 1 hour later, and it takes only 12-17 hours for the worsening to develop fully; in a day or 2 we saw slight variation of sharpness in both directions - as compared to that measured 12-17 hours later it may worsen or (paradoxically) improve by 10-20 BESS.

The below Victorinox SWIBO knives were all sharpened at 20 dps (40 degrees included), edge set on Tormek using a #1000 CBN wheel, then deburred on paper wheels, first with 5 microns diamond paste, and finishing on a paper wheel with 0.5 micron diamond paste at the exact edge angle.

INITIAL SHARPNESS (BESS) - LATER SHARPNESS (BESS) - WORSENING BY (BESS)
100 - in 10 hours 130 - by 30
85 - in 10 hours 110 - by 25
85 - in 12 hours 135 - by 50
75 - in 17 hours 120 - by 45
65 - in 17 hours 125 - by 60
90 - in 24 hours 120 - by 30
85 - in 24 hours 110 - by 25
85 - in 24 hours 90 - by 5 << this we attribute to pure oxidation

Average worsening in 10 hours = 28 BESS
Average worsening in 12-17 hours = 52 BESS
Average worsening in 24 hours = 28 BESS

Example timing of sharpness worsening:
initial 55 BESS > in 1 hour 85 > in 12 hours 105 > in 2 days 115 BESS

The phenomenon is not edge angle related - we've seen similar loss of sharpness on edges sharpened at 20, 17, 15 and 12 dps.
Neither is it steel related - it happens to stainless and carbon knives, conventional and powder, mainstream and high-end, hardness from 54 to 70 HRC.
Neither sharpening method related - it happens to knives sharpened on bench stones, with Edge Pro etc, on wheel and belt sharpeners.

Cure, simlarly to Grepper's, is stropping.
When the stropping is done with CHROMOX or 0.25/0.5 micron diamonds at a little higher than the edge angle, the subsequent sharpness worsening in 24 hours is less pronounced, about half of what we've seen above or less; a few times I saw no worsening at all.

So where we are at the moment?
We know that the edge sharpness will worsen after sharpening, and we know it is due to something happening in the very apex.
We also know how to fix it when it happens.

Next is to find out how we can prevent this from happening - is there something we can finish our sharpening session with that would minimise the subsequent sharpness worsening?
I know it is possible as it happened to my knives several times, but I didn't catch what I did differently. We saw sharpness worsening only by 10 BESS over 24 hours in the meat plant - it was a planned test and I remember my surprise. Looking at the results of the last two sharpness contests we had in Australia, I see a knife which sharpness was recorded and has worsened only by 15 BESS over 4 months, the knifemaker assures he hasn't done anything to the knife since the previous show.


RE: Knife dulls overnight after sharpening - EOU - 08-11-2018

Isn't this interesting stuff? We first noticed the phenomena back when the frame of the prototype KN100 used to look like this as opposed to this. 

                                               [attachment=721]

Knives left in the test apparatus that had tested 200 in the evening tested 30 - 60 points higher in the morning. We attributed the change to what we referred to as "metal memory"  and/or oxidation. We know that an uncoated, brand new razor blade left out of it's wrapper overnight will measure 10-15 points higher the next morning. We attribute that change to oxidation. We've coated knife edges with oil and left them out overnight and they still deteriorate in sharpness. We called that "metal memory". We did a little research on the subject just a few minutes ago and have to agree that "metal memory" may not be the most correct engineering term for what we seem to be witnessing here. Perhaps "relaxation" is a more appropriate term. We do sense with the problem that elements of the edge emerged from the grinding process in a particular orientation and that they seem to be trying to get back to where they came from. Perhaps that's all just balderdash and someday we'll learn that it is all due to oxidation or some other "yet to be discovered" phenomena but that's where we are for the time being.

We do know that it is an issue for our BESS Partners (the people who attach BESS numbers to sharpened products). They leave the BESS Partner's factory at 200 and arrive at the customer's location at 240. Always higher and never lower. As always, a little stropping or similar exercise and the edge returns to it's original sharpness level. Just like so many other things that we have discovered about edges through sharpness testing, this just seems to be how it is in the world of edges and as KG suggests "We know that the edge sharpness will worsen after sharpening, and we know it is due to something happening in the very apex. We also know how to fix it when it happens."

Thanks to Grepper for uncovering and then disclosing his findings. In our opinion, this kind of work is one of the real values of edge sharpness testing. In all this though Ken turns out to be, as usual,  the most percipient. He is the first to decipher the subliminal message buried in the Edge On Up company name...never store your knives edge down, always edge up.


RE: Knife dulls overnight after sharpening - Edgepal - 08-11-2018

All blank newley sharpened edges oxidate in contact with air. When they have oxidate the edge have got a protecting layer of "something" and the oxidation ends.

This layer of oxidation protect the edge from contact with air and the layer is hard and do not where away when the knife are used in soft materials as meat, fish, wet fresh wood and so on - but where away after some time when the edge work in hard dry materials.

In my mind as a traditionalist, this is not a problem becouse my edges are very seldome "razor sharp", they are just as sharp they need to be for its purpouse.

For people that allways use razor sharp edges this can be a problem.
Barbers that shave with a razor start every shaving with to strop the razor = they know the problem = the best result come when the edge is stropped just before sharpening.

My experiance of barbers understanding av edges on scissors is not the best... Barbers are the last group of people that not can sharpen their own edged tools (scissors) but they have been able to shatpen their razors for thousends of years.

The producers of scissors competitate with "super edges in super steel" in adverticing - but in reality they use very high edge angles..

A steel cutters edge holds 90 degrees to hold.
A splitting axe edge holds 45 degrees to hold splitting wood
A knife holds 22 degree to hold slicing wood along the wood fibers
A razor hold 11 degrees to hold slicing of facial hair.

As you se the degrees above change with 50 percent in each step when the material get softer.

A barber scissor can hold 11 degree and make a perfect job in hair - IF te barber could sharpen the scissor - but the barbers can not - so today there is high angles on barber scissors.

High angles needs more force and pressure of the barbers fingers.

A man with a spade that dig in the ground makes about 2000 heavy move with the spade per day. A man that sit in a Office and type on a kayboard makes about 200.000 movements with his fingers per day. They both use up the same amount of energy per day.

Translate this ro a barber with a 11 degree scissor edge compare to the same barber with a 75 degree scissor edge. The 11 degree scissor edge makes him less tierd becouse he use less energy with his scissor hand compare with if he use a edge in 75 degrees.

butchers knows it also, the steel, or strop their knifes the first thing in the morning before they starts to work.

It would be very interesting to know exactly what it is I have named "oxidation". I think it is oxidation , it is logical - but I do not KNOW if it is oxidation.

I do not belive in steel "memory" - but I jave been wrong before... Smile (why shall steel have memory when I have not)...

Thomas


RE: Knife dulls overnight after sharpening - grepper - 08-11-2018

The Victorinox has once again enjoyed a relaxing (thanks for the clarification Mr. Jan) 24 hours in the drawer overnight.  Just for grins I’ll take another set of measurements later today.

It should also be noted that by design I create very toothy edges and there will be some variation in sharpness readings simply because the edge is so uneven and the test media is of very small diameter.  Overall however I think that four readings along the edge provide an acceptable understanding of what is happening at the edge.

Thanks for the additional info Mr. KG. You answered some questions I had before I asked.

Considering how much a few chops of a carrot will dull an edge, from a practical point of view the overnight degradation of sharpness does not matter much.  It's interesting nonetheless.

I have another solution to the problem.  I'm simply going to set the Space-time Continuum (TPC) dial (Time Passage Control) on my knife storage drawer to the "inhibit" position.


RE: Knife dulls overnight after sharpening - grepper - 08-11-2018

So, the Victorinox spend another 24 hours relaxing in the drawer.  I pulled it out and tested from handle to tip:
135, 140,130, 105

After one pass each side of blade with the leather belt on the Kally:
120, 100, 100, 105

In summary over two days:

First sharpening: 110, 130, 110, 125
After overnight : 160, 150, 150, 175
After stropping : 125, 110, 105, 100
Overnight #2   : 135, 140, 130, 105
After stropping : 120, 100, 100, 105

I made no attempt to test in exactly the same places on the blade as that is next to impossible so some variation is expected.  However, this provides a good general picture of increasing sharpness readings from a blade relaxing in a drawer overnight, and how as Mr. KG noted stropping restores the original sharpness.  

I assume this is mostly due to the edge changing shape rather than oxidation.  I would think that oxidation alone of the stainless steel blade would not cause such a large increase in sharpness numbers.

FWIW: The blade sat in the in-drawer flat knife block edge down with the blade resting on a flat wood surface.  However, due to the shape of the blade, only the part near the handle touches the wood.  The rest of the blade is hanging in air.  

I would think that edge up or down would make little difference.  But, we are talking about very thin steel at the edge so maybe, possible it may make some small difference.  That said, I'm not going to worry about it.  Slicing one carrot will instantly have far more impact on the edge than sitting edge up or down in the knife block.


RE: Knife dulls overnight after sharpening - KnifeGrinders - 08-12-2018

Oxidation is responsible for loss in sharpness by 5-10 BESS in the Victorinox/SWIBO stainless steel.
Effect of oxidation on sharpness >>

Grepper's sharpness numbers tell us that the clean leather not only straightens the apex, but also removes the oxidation, and the edge again scores the same as immediately after sharpening.
We've seen the same, for example:
Initial Sharpness 92 BESS > in 24 hours 100 BESS > after 2 strokes on a clean leather hanging strop 94 BESS.

I believe I've found out how to beat this post-sharpening sharpness loss phenomenon.
We already had indicators that higher-angle finish mitigates it, I only had to find the right combination. I shan't trouble you with the details - for SWIBO the following works.

The below Victorinox SWIBO knives were sharpened at 12 dps (24 degrees included), edge set on Tormek using a #1000 CBN wheel, then deburred on paper wheels, first with 5 microns diamond paste at a +1.2 dps higher angle, i.e. at 13.2 dps, and finished on a paper wheel with 0.5 micron diamond paste at +0.4 degree higher angle i.e. at 12.4 dps.

This higher-angle deburring resulted in about 10 BESS worse edge sharpness as compared to when finished at the exact edge angle ("initial sharpness"), but with little to none post-sharpening sharpness loss.

Initial Sharpness (BESS) - EDGE SEALING - Sharpness in 24 hours (BESS)
95 - none - 97
103 - Lanox MX4 spray - 99
93 - Tuf-Glide - 98

Edge sealing with the Lanox MX-4 has completely prevented oxidation as seen by the BESS scores, while the Tuf-Glide not.
Lanox MX4 is an Australian lanonlin-based heavy duty anti-corrosion lubricant, made by INOX, they have a sales branch in the USA.


RE: Knife dulls overnight after sharpening - Jan - 08-12-2018

(08-11-2018, 07:55 PM)grepper Wrote: So, the Victorinox spend another 24 hours relaxing in the drawer.  I pulled it out and tested from handle to tip:
135, 140,130, 105

After one pass each side of blade with the leather belt on the Kally:
120, 100, 100, 105

In summary over two days:

First sharpening: 110, 130, 110, 125
After overnight : 160, 150, 150, 175
After stropping : 125, 110, 105, 100
Overnight #2   : 135, 140, 130, 105
After stropping : 120, 100, 100, 105

Mr. Grepper thanks again for posting very interesting sharpness data. Smile

When I was thinking about your recent results the following interpretation occurred to me.
Average sharpness drop over the first night after sharpening was 40 gf, while the sharpness drop of the stropped edge over the second night was less than 20 gf. I consider it as a statistically significant difference.

My hypothesis interprets the sharpness drop over the first night as an edge misalignment caused by the relaxation of major part of residual stresses in the edge after sharpening. Stropping after the first night probably does not generate additional residual stress in the edge and so the smaller sharpness drop over the second night can be interpreted as relaxation of the minor part of the remained residual stresses generated by the initial sharpening.  

Jan

P.S.: A short general consideration (not fully relevant to overnight knife dulling)

Residual stresses which resides inside the sharpened blade after removing all applied forces may be compressive (pushing the steel together) or tensile (pulling the steel apart).
[attachment=722]
Residual stresses acting over long distances are called macro-stresses while residual stresses existing inside a steel grains (or between grains) are called micro-stresses. In my understanding the overnight dulling may be caused by relaxed micro-stresses.

When a knife blade is bent, tensile and compressive stresses are generated in the blade.

When the bent blade does not spring back, we know that some atomic bonds were broken. However not all bonds were broken, and in some regions we still have not broken bonds which remain stressed. Those bonds are stacked because they are not stressed enough to brake and also not strong enough to spring the blade back. Generally more atomic bonds are broken in the tensioned regions than in the compressed ones.

The fighting between regions in compression and tension is what I understand under the term residual stress.