Edge retention,sharpening

M

mordi

Joined
Aug 12, 2007
Messages
137
I need some help with getting better edge retention.I sharpen kitchen knives
part time 50>100 per week.My basic method is 19 deg on Edge Pro 220 stone and up for finish,then a micro bevel 20 deg Sharpmaker and then afew strokes on a ceramic steel.The basic knives in my area are Icel, Sico ,Arcos all lower end europian. The Biggest problem I have is with knives that have previously been sharpened with a convex grind ussing power tools {high heat}. The new edge can detriorate within a day.Any tips would be great. I have spoken with Ben Dale afew times on this subject and he is O.K. with my methods.
 
get a benchstone, hold the blade perpendicular to the surface, and cut off the edge completely. This will get rid of the damaged steel. I'd personally drop the angle of the relief, somewhere around 15. Should help the blades cut better after the micro wears, which I guess happens faster with the cheaper kitchen brands. Hard to make a blanket suggestion for different brands and different profiles/uses.
 
Well, I fear the obvious solution is one that isn't overly helpful: Higher quality knives will offer greater edgeholding (for example the Shun or Al Mar VG-10 series). On the knives, on which you suspect a burned edge. Take that Edgepro 220 stone and grind off about 1 mm off the edge before applying a final edge. That should remove the burned and fatigued material.
 
I would say your approach is the optimum. The suggestion to remove the fatigued edge is a good one. Two additional suggestions:
1. The users should learn to steel. That works well for knives like these with edges that deform easily.
2. Cover the kitchen prep area with poly cutting boards. One cut into a metal or glass surface will undo all effort spent sharpening.

After this....the rest is just job security. The owner will need to weigh the cost of better knives against your fee for frequently sharpening the cheeper ones.
 
Ben Dover said:
Why not get a belt sander and retain the vastly superior convex edge???:confused:
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Ben I have a belt sander 1*32 vertical. I have 2 problems with it ,1 keeping a correct angle for the length of the knife ,2 over heating.I use the belt for redoing badly chipped blades and removing bolsters.
 
mordi. i used to sharpen knives for a few places when i was able to travel using a set of cardboard wheels. when used properly you can sharpen the knives in no time at all and without damaging the blade. i have 3 short video's showing how quick it is to work up a burr and how to hold the blade to the wheel. stevebot, a member here sells the (good) wheels at a discount to members and has a few books on sharpening knives one named sharpening made easy. i have used these wheels for 16 years and wouldnt change for anything. i used to have an ez sharp which was similar to a lansky to work up a burr then finish off the edge with a ceramic stick to get a shaving sharp edge. now i can get the same edge in just a few minutes compared to some knives which could take a half hour or longer.
 
me2 said:
Why is it vastly superior?
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Well, in my experience, they cut much better and hold an edge longer. And if you maintain them, you only need to use a strop, or at worst, a 15 micron belt for 2 or 3 passes to touch up the edge.

Overheating is caused by improper technique. After one of two passes, I dip the blade in water, and wipe on a shop towel.

I can sharpen a quality steel blade (like D2) in 5 minutes on the belt sander, to hair-popping, that would take an hour on stones.

Ben
 
Ben Dover said:
Well, in my experience, they cut much better and hold an edge longer. And if you maintain them, you only need to use a strop, or at worst, a 15 micron belt for 2 or 3 passes to touch up the edge.
Click to expand...

Perhaps another thread is in order. Are you sure the increased cutting is only from the convex edge, and not from a higher polish, thinner edge angle or other such advantage? IME, convexing a knife typically lowers the edge angle, increasing cutting ability. It seems covex edges tend to be more highly polished also. At least this was my experience when I convexed the blades of my Old Timer. Is it more difficult to maintain flat edges so that they only need a stropping or light pass on fine abrasive?
 
I use stones and strop my edges to maintain them. multiple bevels do the same thing as convexing. AFAIK, you're right, the act of convexing just thins the edge, which is where the advantage is gained.
 
Not to say anything against the advantages of a belt sander, but I have rebeveled a S30V blade in about half-an-hour on stones and that was before I got the DMT XXC. To spend one hour sharpening a blade of any steel on stones I would consider quite excessive.

Of course if you are playing around and are trying to gain the last bit of sharpness, nothing is excessive :D, but I don't think that is a fair comparison of one technique versus another.
 
Ben Dover said:
I can sharpen a quality steel blade (like D2) in 5 minutes on the belt sander, to hair-popping, that would take an hour on stones.

Ben
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I can do the same in minutes on benchstones with a microbevel. That includes swapping stones in the stoneholder I have and checking the edge under magnification for burring (the knife will be tree topping at this point). When I add in lapping films for really polished edges that easily whittle hair I may have 10 minutes, max into getting that edge. If it was one of my Krein regrinds it would take even less time. Again, this is using a microbevel, full bevel sharpening would take longer. Though, even with full bevel sharpening it shouldn't take anywhere near an hour. I rebevelled CPM D2 and ZDP 189 by about 4-5 degrees per side in only a few minutes on the DMT D8XX, and it doesn't take that long to remove the scratches with the DMT coarse and fine stones and have a good working edge on the knife that shaves very nicely.

Mike
 
gunmike1 said:
I can do the same in minutes on benchstones with a microbevel. That includes swapping stones in the stoneholder I have and checking the edge under magnification for burring (the knife will be tree topping at this point). When I add in lapping films for really polished edges that easily whittle hair I may have 10 minutes, max into getting that edge. If it was one of my Krein regrinds it would take even less time. Again, this is using a microbevel, full bevel sharpening would take longer. Though, even with full bevel sharpening it shouldn't take anywhere near an hour. I rebevelled CPM D2 and ZDP 189 by about 4-5 degrees per side in only a few minutes on the DMT D8XX, and it doesn't take that long to remove the scratches with the DMT coarse and fine stones and have a good working edge on the knife that shaves very nicely.

Mike
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If you can do all that free hand with a stone, then my hat is off to you, sir! you are truly talented!:)
 
me2 said:
Perhaps another thread is in order. Are you sure the increased cutting is only from the convex edge, and not from a higher polish, thinner edge angle or other such advantage? IME, convexing a knife typically lowers the edge angle, increasing cutting ability. It seems covex edges tend to be more highly polished also. At least this was my experience when I convexed the blades of my Old Timer. Is it more difficult to maintain flat edges so that they only need a stropping or light pass on fine abrasive?
Click to expand...

I honestly haven't the faintest idea why convexing works so well. All I know is that it works for me! :):D:)
 
Richard j Thanks for your info .I thought that stevebot usses aTormek and then a paper weel.Curently I work in clients kitchens so I could use 1 more machine as a backup to my primary Edge Pro .
 
Ben Dover said:
If you can do all that free hand with a stone, then my hat is off to you, sir! you are truly talented!:)
Click to expand...

Maybe 10 passes per side (5 or so on a really thin regrind) is all it takes to sharpen a microbevel on a knife at each grit. I don't see where that makes me talented, it just means that I can work a tiny amount of steel in a relatively short time on benchstones. Belt sanders will always be faster for full bevel sharpening and rebevelling (they remove metal WAY faster than you can on a stone), and especially reprofiling the primary grind, but microbevel sharpening can get full sharpness back in a short period of time. Certainly much less than an hour.

Mike
 
Hi Mordi,

I often sharpen 50 to 100 knives in a day. These knives at a local charity soup kitchen have been abused for months or years between sharpenings.

I would use a belt sander (carefully to avoid high heat) and reprofile the blades to around 12 degrees per side. Then I would put on the final edge using your manual technique at 15 degrees (Spyderco "30-degree" slots). Contrary to common misconception a kitchen knife ground at a higher angle gets dull faster than one ground at a lower angle. I suspect that the "convex" grind on some knives was effectively a higher angle grind.

If a cheap belt sander is not available I would use a long smooth file for reprofiling to the lower angle. This will work quickly if your blades are cheap and soft or if their heat treatment has been compromised by over heating.
 
Jeff Thanks for the info. do you do 12 deg. freehand or is there a method to guide or chek an angle while sanding:
 
I do my profiling freehand. All I am really trying to do is create an angle that is significantly lower than the 15 degree Sharpmaker fixture. I go as low as I can conveniently do it. When I am doing 50 really dull knives I do them assembly-line style. I do all the left sides with 120 grit, then I do all the right sides with 120 grit. I switch belts to 220 and do all the left sides then all the right sides. I switch to 400 grit and do all the left sides then all the right sides. Finally I switch to 600 grit and do each blade alternating left-right-left-right to reduce the edge burr. I work with wide belts that allow me to hone edge-first. This is to reduce the burr and reduce heat build-up in the apex of the edge.

My assembly line approach allows the blades to cool between passes and I am careful not to overheat the edges. I let the belt do the work, I don't apply high pressure. I hold the blade with my bare fingers so I can feel if the blade is starting to heat up. I go light and slow near the tip which is the easiest part to overheat. I am more and more careful as the edge gets thinner. It is the thinnest and narrowest part of the edge that heats up the quickest.
 
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