sharpening error-- what went wrong?

[Josh Feltman]

Ok, I had my Benchmade 942 pretty sharp on my sharmaker-- effortless pushcuts through a variety of paper types, shaving hair off my arm without touching the skin, and then last night i decided to strop it a bit on the back of a notebook to see if I could improve the edge. Well, instead of improving it, it seems to have ruined it-- totally dull. I had to start over from scratch. I started with the medium stones, got a burr on both sides, ground it off, moved to the fine stones, and ended up with a tiny burr that took forever to remove. For some reason, I just couldn't get it sharp, so finally, out of frustration, i went back to the medium stones and started over. Got a decent edge finally, but nowhere near what I had before. I thought that I might have had a wire edge that the stropping removed, leaving me with a dull edge, but the edge had been very durable before that. Any thoughts on what I did wrong and what I can do to get the edge back to its former glory?
--Josh

 

[gadgetman]

The same sort of thing happened to me with a couple of soft steel kitchen knives. I just couldn't get them sharp! I finally decided that I would have to reprofile the edge on a DMT bench stone before using the sharpmaker. That definately did the trick. The whole experience was strange because I had sharpened a third knife with just the sharpmaker, though that one was a higher quality steel.

 

[Jeff Clark]

I believe there are a couple sources of your problem.

First I would guess that your notebook was rather soft and more abrasive than you would expect and/or you were holding the knife up at too high an angle and/or the notebook was inadequately supported and sagged down in the middle as you stropped. A good strop would be relatively hard and flat to not wrap-around the edge as you worked. You would strop flat on the edge to not reduce your edge angle. End result is that you were slightly rounding your edge rather than aligning and polishing the edge.

What is likely a bigger problem is the hardness of your 154CM / ATS-34 type alloy did not match well with your stropping. The high molybdenum content gives a bunch of carbides that are not cut at all by your stropping. All you do is round these carbides and fill the space between them with iron that you have pushed around with the strop. Steels that are above 60RC and have things like molybdenum don't strop well.

At this point you may want a harder hone to work with to cut your hard carbides. An extra-fine diamond hone might be a good thing and then finish with a few strokes on your sharpmaker. I have better luck using a smooth steel on these hard alloys rather than stropping on leather or other compliant media. I only strop a few strokes at most and then finish on my ceramic rods. I rough all these down with diamond abrasives first.



[This message has been edited by Jeff Clark (edited 05-18-2001).]