edge to polished to cut well?

D

dfarm

Joined
Feb 21, 2008
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I use a set of paper wheels to sharpen all of my knives, and the seem to get plenty sharp, more than enough to make hair pop off of my arm. The problem I'm running into is that when I go to actually cut something, the edge wants to glide across the surface until it gets a start, then it cuts ok. The problem is most noticed on things like avocados and tomatoes with my kitchen knives, and zip ties and plastic bags with my folders.

Any recommendations to help me get my stuff cutting well?
 
The apex of the edge is likely a little rounded or blunt. That's where a slightly more 'toothy' edge often works, even if the apex isn't perfect (this describes the vast majority of typical kitchen knives, including those made for cutting tomatos). The teeth will compensate and keep cutting somewhat, if the edge is otherwise a little rounded or blunt. But, when the teeth go away, that imperfectly-apexed edge becomes immediately dull. A complete and cleanly-apexed edge cuts well at any edge finish, whether toothy or polished. So, focus on making the apex a little more pure, by more tightly controlling angle and not using too much pressure.

I don't use the wheels, but the above advice applies to any and all sharpening, by whatever method one chooses to use.


David
 
Make your finishing passes on the wheels a little quicker to preserve some of the 'tooth' from the grit wheel. As per above, you're either rounding the apex a touch, or grinding off every last bit of apex irregularities. Even well done, removing all the irregularities such as for a shaving razor, will result in an edge that gets very little benefit from drawing and will feel like its skating on items like you mention. It will cut better with static pressure, less so with a draw. There is no one type of edge (toothy vs polished) that will outperform all others on every task, so do a little experimenting and figure out what works best for most of your cutting needs.

Also, try to keep your inclusive edge angle fairly acute - 30 degrees or less. Cutting efficiency suffers considerably as you increase the inclusive angle. Make it as thin as the steel can handle without rolling, chipping, dulling too fast etc. For me, somewhere around 26 degrees works best for most applications.
 
dfarm said:
How can I tell if my apex is messed up, or my angle is wrong?
Click to expand...

Best way to tell, is to correlate how it's cutting with how the edge looks under good magnification (with BRIGHT light). It also helps greatly to use an example of a good or excellent cutting edge (if you have one that really impresses you) to compare, side by side with the knife you're sharpening, both in terms of cutting, and how the edge looks. At the most fundamental level, a 'good' cutting edge (as defined by one which cuts in obviously impressive fashion) will always, always look like a very clean & precise 'V' under magnification. The higher you can go in magnification, while still seeing a good-looking edge, the better. Bad edges will become glaringly obvious in their defects, when viewed at sufficiently high magnification. They really get ugly when viewed close-up. The best cutting edges will always look a little more impressive than mediocre edges under magnification. Look for a very crisp apex (the 'peak' of the 'V'), symmetry (even & balanced in shape) and irregularities on the edge itself (burrs, dents, etc.). If it doesn't look that pure (if it's rounded, flat on the apex, oddly shaped, asymmetrical, etc.), then it won't cut all that well either.

If the angle is 'wrong' as you say, it'll show up as either rounded (constantly varying the angle on every pass), or it'll have multiple bevels (perhaps one or more off-angle passes, after having previously been on track). OR, if there's an angle mis-match between sides, it'll look off-centered or asymmetrical.

And while sharpening, the easiest and most obvious indicator that the apex has been reached will be the formation of a burr along the entire length of the cutting edge. Even then, it's never a bad thing to take a magnified look at it, just to see that everything's in truly good shape, and ready to begin the refinement of the edge (removing the burr, at least).


David
 
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