Short lived edge from sharpmaker?

[omegaci]

Hi, new to the forum and sharpening. I am have a few questions about my sharpmaker 204 and would appreciate the help.
1)
I used to use a pull though ceramic sharpener for my henckles knives. It produced an acceptably sharp edge that lasted through a few cooking sessions. I often sharpened before every cooking session, but I didn't have to.

With the sharpmaker, using the medium rods only, I get a very sharp edge, but it dulls very quickly. I find I have to sharpen after every cutting session. I tried using only the 40 degree angle, the 40 and then the 30, and just the 30.
Am I doing something wrong?
Is it possible this steel can't hold the edge produced by the sharpmaker and it just gets knocked off?

2)
this is more of a you've been there and made that mistake question:
After going through steps 1,2 (medium corner then flat), I usually have a very sharp edge. But when I then use the fine stones, I have somehow dulled the knife. I noticed that the knife is always sharper after using the corner but sometimes with the medium and almost always with the fine flat sides, the knife is duller. I must be doing something wrong with the flats, but as far as I can tell I am using the same motion as I do with the corners. Are the flats super sensitive to angle? is there something specific I should be looking for?

[KSDbass]

I was having the dulling problem too, I could sharpen all the way up until I had to use the flat sides of the fine rods, and I'd dull it. The only advice I can give is to practice, and go slowly. I was doing 3-4 strokes a second, and I realized that was way too fast. Just take your time.

Also, what are you cutting with the problem knife? and what kind of steel is it?

[Michael Cook]

:spyder: Your touch is too heavy. As the edge gets sharper it gets thinner, you're rolling the edge more than dulling it. :spyder:

[eljay]

It could be a couple of things. It's definitely possible to have a burr coming out of the steel that feels sharp and may cut for a bit but gets knocked off fairly easily. You don't really have a healthy edge.

One concept worth knowing is that if the edge is currently, let's say at 35 degrees. If you start sharpening at 40 degrees you'll get the very, very edge sharp at 40 degrees (which is fine for a kitchen knife incidentally). If you sharpen at 30 degrees it's not even going to hit the edge. It's going to hit a bit higher up on a shoulder. With any luck somebody will post a diagram, but to see this you get a sharpie or other permanent market and darken up the edge of the blade. As you sharpen this will get removed first. If it's removing right on the edge, great. If it's removing a bit higher up and the edge is still black you'll need to use the most coarse stone you have and stick with it until you've reprofiled the blade. This may take some serious elbow grease - if you have a bunch of knives the diamond stones will help tremendously. (Use a very very light touch with these!)

One approach for a long lasting edge is the one combination you didn't mention - 30 and then 40. This gives the overall geometry at 30 degrees but right at the edge a more robust 40. You would then touch up with 40 and maybe every fourth sharpening go back to 30.

For kitchen knives I just use the darker stones. I like the edge that produces and it's fast. But I suspect the pressure explanation explains why the white ones are giving grief. Go slow and light.

[omegaci]

Thanks so much for the advice. I will try lighter and slower, and the 30 then 40 angle. the sharpie is a great idea. I also have a 10x loop I am going to bring home from work so I can really check out the edge. the medium really is enough for a kitchen knife that is going to be used on everything from chopping parsley (lots of slapping into the cutting board) to breaking down a chicken.

after I get the hang of this I am going to try to sharpen my global knife. I have read a bunch on here about the convex blade shape.

[yablanowitz]

One other thing to consider. You mentioned you used to use a pull-through sharpener. Those tend to leave micro-grooves in the steel parallel to the edge which can act as stress risers, weakening the edge. Those pull-throughs also tend to snag large carbides and break them out of the steel matrix rather than wearing them down to form the edge. I would say the first order of business would be a complete reprofile to remove any such grooves and get back to clean metal.

It can't be stressed enough that the pressure you use must be VERY light, especially when using the corners of the stones, which concentrate that pressure on a very small area of the edge. Too much pressure will bend the thin edge back and forth, just like bending a wire coat hanger back and forth. The edge will break away just like the coat hanger breaks after enough cycles.

[JBE]

For your first question, sounds like you're producing a "wire edge." Using lighter and lighter pressure as you go should solve this. You also may find that using a strop will help with this problem as well.

As for the second question, some steels just work better with the coarse edge produced by the medium stones, for example 440V. I would use the corners of the mediums (cleaned well before use) then follow with a good strop. For serious resharpening/re-profiling I would recommend using a diamond stone first; you can either pick up the diamond Sharpmaker rods or a good diamond bench stone (I recommend DMT) This combination has always produced excellent results for me on some of these harder steels. I suspect it has something to do with the size of the carbides in the steel and the way they perform with a "utility" edge vs. a "polished" edge but I'm no expert when it comes to that. It may also be that the fine stones aren't "aggresive" enough to remove metal from harder steels. YMMV.