08-11-2018, 04:27 AM
(This post was last modified: 08-11-2018, 10:04 AM by KnifeGrinders.)
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 
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.
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.
http://knifeGrinders.com.au