Sharp enough or too sharp?

J

Johan

Joined
Oct 12, 1999
Messages
631
I'm pretty picky about the edge on my knives. My usual test is slicing cigarette papers up and push shaving. I use the Spyderco 204 set to 30 degrees for my edges. I first worried that this might be too steep, but the edges seemed to hold up well. This morning I was hastily making a big cardboard box smaller. I used my BM 750 to cut all around the box to make it shorter and then in half to make it lower. Towards the end the cardboard was buckling and the knife could no longer cut ciragette papers (regular paper was ok)nor shave hair. The cardboard was about 3/8" thick and I figure I cut about 150" of it. My question is: Do you think I had too ssteep an angle causing the edge to break down prematurely, or was this just natural considering the density and amount of cardboard cut? Thanks in advance for your input.

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"Better to reign in Hell, than serve in Heav'n"
John Milton
There are only two types of people; those who understand this, and those who think they do.
 
The thing to remember when your cutting thick cardboard is it's not just paper your cutting but also glue's and resin's to it's not a matter of the angle your bevel is I use about 27 to 28 on mine your cutting alot of stuff even though it doesn't seem like it sharpen it up and give it another chance .
 
You bet. Cardboard boxes are very hard on knives. We tend to use carbon steel edged Schrade Old Timers at Knife Outlet for box cutting duties. I find that my personal knives with stainless steel blades tend to need sharpening every time after a day at the office with carboard boxes.

Yes, I think 30 degrees (actually 15 degrees since you should count only one side of the edge) is a little steep for pocket knives. Fine for some kitchen slicers. I'd recommend 20 degrees (40 by your measurement) as a better choice for most pocketknives. My pocket knives sharpened to about 20 degrees will slice up paper with nary a problem. Since I don't smoke, I need to limit my tests to newprint. Take care.


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Fred
Knife Outlet
http://www.knifeoutlet.com


 
I can't say if your bevel is optimal for cardboard or not. It doesn't surprise me that it could get dull on cardboard.

There are a variety of things that could have happened, you abraded some material off the edge, you rolled-over the edge a little, or you just got the edge coated with resins.

Try some experiments:
1. Clean the edge with a solvent like paint thinner and see if it shaves. If the answer is yes, you just got it dirty.
2. Try steeling the blade a moderate amount with a smooth steel and see if it shaves. If the answer is yes you rolled the edge and you might want to use a little bit higher bevel on your edge.
If neither of the above helps, you abraded your edge and a different bevel would not have helped much. There would not be a great difference in the amount of material abraded from a slightly thicker bevel. The edge gets shorter faster with a thin edge, but it gets wider faster with a thick edge. For a moderately hard material like cardboard I think the effects would sort of balance. If you hit something extra hard a higher bevel would help both abrasion and rolling.

My take is that if I can easily strop or steel the edge back to sharpness, it is not too sharp.
 
Thanks for all the advice and opinions. I took a close look at the cardboard and it's actually three sheets of regular cardboard glued together. So I'd say there was a lot of abrasive particles to cut through. I resharpened the knife (steeling didn't help too much) in a couple of minutes. The next time I do this (probably tomorrow as a test) I'll clean the edge and see if that helps. And Fred, I don't smoke I just buy the papers -I'm sure the guy at the corner store thinks I'm doing drugs
smile.gif


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"Better to reign in Hell, than serve in Heav'n"
John Milton
There are only two types of people; those who understand this, and those who think they do.
 
The amount of wear is also high dependent on the speed and force you use to cut the cardboard. As Jeff noted while a thicker edge may prevent rolling (and protect against impacts but that is not relevant here) it will not do a lot for wear. It will in fact probably just make the blade perform worse because now you will have to use more force to push the blade through the cardboard.

-Cliff
 
On using Old Timers for cutting boxes - do they seem to do any better than other carbon steel knives, and/or is it because they're readily available and work well enough ?
 
you may want to try an m-2 knife, just make sure you daon't bring the bevel back to far, it'll definetly hold an edge longer. i'm getting some m-2 barstock that i'm gonna make small knives from, i don't sell knives though, but i can test it out see how long it lasts on cardboard.
 
Hey!!

Too sharp?? 2Sharp...hmmmm....

;-D
Take care and be well!/Jonas aka 2Sharp

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"May all your detonations be expected"

 
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