help - something's wrong with my edge

[spyken]

My SAK usually has a hair-popping sharp edge - high polish (I strop it on a loaded leather strop). BUT today, the blade simply wouldn't cut through a kerosene soaked nylon rope (actually a wick for an outdoor torch). I was so embarrassed as my knives are usually very sharp.

What went wrong? Are highly polish edges only good for push cutting dry paper, hair, envelopes?

Help!

 

[beluga]

Highly polish blade usually has less microserration. Perhaps, too much stropping that you've done removed the microserration completely. Try to sharpen your knife with fine or medium grit sharpener. You'll see the difference.

 

[DEA]

when cutting fibrous material i find serrated edges to be much more effective
beluga is probably right about the lack of microserrations

 

[WadeF]

Yup, the guys above have it right. Spending all that time on a strop is only good for one thing, shaving your face. If you want to cut rope finish with a rougher stone so you have some teeth on the edge to cut with.

 

[Jeff Clark]

I wouldn't maintain an edge solely with an ordinary loaded strop. As you guessed it will tend to give you a smooth edge that does not slice very agressively. The other problem is that most strops are not hard enough to insure a maximally acute edge if used repeatedly. An edge will tend to force a depression in the surface of a strop that is not extremely hard. There will be a tendency for the strop to round the edge slightly. You minimize this by using a hard strop and/or light stropping presure and by matching your stropping angle to your edge very accurately.

Usually you don't have all of these things taken care of when you strop so that slowly you get a more and more convex edge with a final edge vertex angle that is significantly bigger than you started out with. This effect is only at the last millimeter of edge and is hard to notice. If you do a few honing strokes with a medium-fine hone you will get rid of that rounding and add some microserrations that will dramatically improve the blades slicing ability. If frequently slice fibrous material finish try finishing with a medium grit hone.

If you are real fond of stropping try making a harder strop. Try gluing 240 grit Wet or Dry paper to a 3-inch by 12-inch piece of sheet metal. Make a base from a 12-inch length of 1x4 lumber with a couple 1x1 blocks across the top at the ends. Drill a couple 1/4 inch holes near each end of the sheet metal so that it can be screwed down to the blocks at both ends. You will use about number 8 deck screws and washers to hold the sheet metal across the blocks. You will put the screws a little extra close together to force the sheet metal to bow downwards slightly. You made the holes oversized and loosely screwed the metal down so that when you push down in the center of the sheet metal it will sag into a nice gentle arc. You will strop on this surface and get a nice accute convex edge that will never start to round.

 

[spyken]

thanks guys - yup, I think I stropped it too much. On looking at the edge again with a loupe, I realised that the edge is also rounded a bit, therefore blunting real quick. Just fixed it up this morning by using the grey ceramics on my sharpmaker. It still shaves but I think the grey ceramics induce micro-serrations, right?