User Error. What am I doing Wrong?

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Brocket21

Joined
Dec 19, 2010
Messages
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So I bought a blue M390 PM2 and I have seen YouTube videos where guys can cut for days on cardboard, rope and other abrasives and afterwards the knife will still shave hair. I can get mine shaving sharp with the coarse and fine stones on the Sharpmaker by following all the recommended techniques from Sal's video. We have been buying a bunch of furniture after moving and every week a couple of new large and worn cardboard boxes need to be cut up to fit in the recycle bin. After cutting up two boxes using the seams as a guide, the knife loses it hair shaving edge and feels almost dull. I have had to resharpen three or four times in the last couple of weeks and have cut up probably a total of ten boxes. Am I just putting a bad wire edge on the knife? Any ideas on what I might be doing wrong? I was under the impression that M390 could cut cardboard for a long time and still stay razor sharp. Thanks.:D
 
Unfortunately, not all cardboard is equal. There are some pretty abrasive ingredients in cardboard, including:
Metal
Dirt
Wood
As far as the edge not holding, I'm not sure I understand. What sharpening method are you using? How steepi s tour angle? Are you knocking the burr off the blade?
 
Losing hair shaving after two large boxes doesn't seem too bad. No knife maintains a razor edge against cardboard, and sharpness loss is very fast at first for any steel.
 
Rev,

I am using the 40 degree angle. Starting with the corners and then moving to the flat sides of the stones. I think this whole process is knocking the burr off but I am not sure? The very last bit of the edge does look pretty thin when I hold it up to the light. Thanks for the help.
 
RevDevil said:
Unfortunately, not all cardboard is equal. There are some pretty abrasive ingredients in cardboard, including:
Metal
Dirt
Wood
As far as the edge not holding, I'm not sure I understand. What sharpening method are you using? How steepi s tour angle? Are you knocking the burr off the blade?
Click to expand...

Rev. The cardboard I am cutting is pretty well worn and flexy so it is not crisp. It buckles a bit under cutting pressure, making it really tough to get through.
 
hardheart said:
Losing hair shaving after two large boxes doesn't seem too bad. No knife maintains a razor edge against cardboard, and sharpness loss is very fast at first for any steel.
Click to expand...

Thanks. Maybe my expectation is unreasonable for any steel.
 
When my knife feels like it has lost it's edge I cut phone book paper. I am usually surprised how sharp it is.
 
Hehe is a trick when you feel the edge getting dull. Strop it on that same cardboard you are cutting. Old cardboard can be extremely abrasive.
 
Cardboard is an edge killer. That's for sure. If you put a good edge on the first time, you shouldn't have to keep sharpening it. You should just be able to strop it and get it right back to sharp. I don't know what to expect from super steels either. For the price, you would expect it to last way longer than some cheapo steel. I think that's why I've tried to buy a knife in every steel I could find.
 
Paper, unfinished...without gloss coatings, etc...is abrasive. Working in a paper mill we can easily wear the tip down on a razor blade utility knife within a minute slabbing off layers of paper on a roll...the more coarse the paper the faster and easier it wears. We also go through our belt knives fairly quickly because they wear down so quickly...and the constant resharpening on the crappy dry stones we are provided.
Dulling a blade while cutting cardboard...just paper and not very good paper as it is designed to be just a box...corrugated at that is very rough on a knife blade.
Paper is not just paper. Remember it is made from wood...wood pulp...often mixed with a variety of recycled materials as well as "clay", latex, etc. Plus the stuff is generally coated with more clay, starches, etc.

If you open a lot of boxes on a daily basis, expect to have to touch up and perhaps sharpen your knife on a more regular basis.
 
I think OP is asking if his experience for this paricular knife and steel is reasonable or he has a lemon.

Have no M390 blade experience, I can't tell. I know that my shaving sharp (I do shave with my knives) of 8Cr13MoV or 9Cr will lose it's shaving ability (30 inclusive, convexed) after cutting up a pizza box (into approx 3" long strips, similar to Ankerson's cardboard test in his EDC video). I would expect M390 to hold up better, but not sure how much.
 
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