Do I need to worry about heat with a Ken Onion work Sharp?

HeavyHanded said:
Does anyone have the link to Roman Landes study where he discovered these extremely high localized temps? Every time I do a search all I get are more references back to it, but never the study itself. I've always been curious how one could distinguish between the temp of the edge at the micron level and the temp of any adjacent ground off swarf or even bits of abrasive for that matter. The tale of the burned eye - does not seem possible that a piece of metal that small produced by hand sharpening could retain that much heat traveling the 18 odd inches from the workpiece to the eye, and have enough heat energy left to overcome surface moisture and still burn the eye.

For myself I have never noticed any difference in edge retention based on dry, wet, or powered sharpening, at least none that was apparent relative to other considerations. A difference of 4-5 points Rockwell C generally makes a notable difference in edge holding, I'd think a loss of same for any reason would be fairly obvious.

Not that heat buildup isn't a concern, where there's smoke there's fire and powered sharpening needs to be approached with care in any event. But as pointed out in earlier responses - I've noticed a fair amount of heat generation while using various cutting tools, in some cases far more than I've ever detected while sharpening, even on powered equipment.
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It's probably somewhere in here... have fun lol
 
chiral.grolim said:
Very reasonable :thumbup: How low is the low speed?
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Took me a while to get back to this. Darex lists the WSKO as running from 1200 to 2800 SFM (Surface Feet per Minute). With the trigger pulled, that's probably pretty close. But there's a subtlety here: When you engages the lock and release the trigger, it doesn't stay at the depth you pulled it to. It "sags" down a bit and then hits the lock and stays there. At the lowest setting the difference is very easy to see/hear and I think it drops the speed by 1/3 to 1/2. So it's probably running 600 to 800 SFM (as a guess).

I can tell you, in practical terms, I can visibly and audibly slow the belt down by applying a bit of pressure with a blade when it's running at it's slowest speed. So it's running pretty slow. It's still just a bit too fast for really precise deburring, but it's WAY better than half or full speed.

Brian.
 
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This is an important discussion with many good points being made. Heat from friction is the enemy of any refined edge. When making the first or original set on a newly made knife using a 120 grit [new] belt is doable as long as the blade is kept cool. As the edge thins its paramount that heat from friction be avoided. It is the very apex itself thats the goal and contacts the object being cut; if it has been overheated in the process of sharpening, there is little purpose in continuing this technique. I set all first time edges using a 2 x 72 Pro-Cut belt machine with a VS DC 1 1/2 hp motor, it crawls along when set at its lowest setting. Even with this feature, once the edge starts to thin I switch to a diamond plate to refine the Apex and finish by removing the small wire using an ERU.
So whether its the heat coming from friction on paper wheels, which I don't use "at all" or the heat from heavy stropping, or that comes from using belts, it is all detrimental to the longevity of a cutting edge.

A belated happy 2015 to all of you, Fred
 
chiral.grolim said:
Yes, the ball is not rolling, the bevel is being dragged against the surface of the hone, and the contact is high = high coefficient of friction.


http://en.wikipedia.org/wiki/Friction#Coefficient_of_friction
COF wood:wood, which can be used to start a friction-fire by hand on relatively large/thick pieces of wood = 0.4
COF Metal:metal, which on a knife is at much smaller geometries than sticks being used to start a fire = 0.8
I admit I am not a physicist, but that suggests to me that sharpening and burnishing involve a lot of heat in the affected areas. If frictional heat were not in effect, you should be able to accomplish "burnishing" by simply pressing the hone on the bevel and lifting off again, no stroking or stropping required, correct? That is the "rolling ball" scenario.... but it doesn't work that way. Keep in mind that the surface of the bevel, even with the scratch-pattern, is quite robust with a thick geometry in those scratches, lots of supporting material that needs to be squashed and "smeared". What hardness is that martrix such that deformation is plastic rather than elastic, that the yield point can be exceeded on such thick geometry at high hardness? Why does it work?

The story Landes relates is a colleague sharpening on a ceramic V-stik set-up ... by hand ... being burnt. *shrug*
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If you're using a hone, you are definitely doing more grinding than burnishing. If you are using a loaded strop opposed to a bare leather one you are doing more grinding than burnishing - as in metal is being removed rather than pushed around by plastic deformation. As mentioned, I'm pretty sure there is little or no real heat generation when steeling with a smooth steel and this is more in line with the rolling ball scenario. However when it comes to worn out belts, plain leather, plain cork etc on powered equipment, we're dealing with a high degree of burnishing and definitely some heat generation as the velocity of the material is a greater factor than applied force when it comes to burnishing. Also of consideration is that most strops are treated with creams, oils, waxes etc that should all have some effect on friction generation.

The geometry of a scratch pattern is interesting stuff and maybe outside the current discussion. The outer edges of the scratch trough may not be as tough as the underlying matrix and likely already have undergone some level of plastic deformation as the abrasive gouged out its path. I can say with a lot of confidence that those scratch patterns can be burnished to effect fairly readily but maybe not so predictably in many cases. A sheet of copy paper over a Washboard will burnish most steels, even at RC in the upper 50s, and this without removing any steel. Scratching of satin polished steel on Kydex sheathes and holsters is also well documented. Again, I have no idea what temps are generated, but am very dubious of anything in the 1000s of degrees, but I do not have access to the gear needed to make that determination. I have seen nothing that would lead me to believe the RC is negatively effected in any event, in fact some mild burnishing seems to increase edge retention, at least on low carbide content steels.
 
Chris "Anagarika";14422172 said:
Martin,

This thread he started sometime back.http://www.bladeforums.com/forums/showthread.php/344902-Edges-and-Steels
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Thanks for the link, I'll have to take my time and read that through. A quick look already has me curious - he mentions D2 not exhibiting edge stability at 30* or less, yet my Bluncut D2 is holding up very well at about 24* inclusive, though I'm not beating tar out of it, I used it for everything when I first got my hands on it - including stuff I normally reach for a utility knife to deal with.
 
HeavyHanded said:
A last thought, shaving razors are sharpened on wheels with water, some of them used to use use a thin slurry on an iron wheel for the final pass, not sure what a modern shop uses.

Amazing that those scalpels are done in open air in the video link from pg1. I wonder if there's another unshown step that uses coolant in the process or the edge would be pretty poor if that one step was all there was to it. The scalpels I've seen, while still somewhat toothy, looked to have a secondary finish treatment along the cutting edge.
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I would be very very surprised if the scalpel blades were ground dry during actual production. What most folks who don't work in manufacturing don't really understand about "How It's Made" is that they do a lot of things differently when shooting with a camera than when doing actual work.

Most production machine tools, be they milling machines, lathes or grinders, use a serious amount of coolant at high pressure while working - the work being performed while these machines are actually producing work is mostly not visible because of the spray of coolant going everywhere. Some machines use cutting oil, some use a spray mister.

The point being, they shut these things off during filming or there would be nothing to see.
 
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