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Edge Reading Disparities
Just received an email from a customer with a question. He just finished sharpening a blade and  then garnered these three measurements at three different points on the edge: 90, 180, 220. He was wondering if his test methodology might be flawed.

First of all - even if one were intentionally trying to screw up the measurements, it's doubtful that one could produce this disparity in readings on a well ground and thoroughly deburred edge.  Now, please don't take this as a challenge Exchange members! As a rule though, the statement is accurate.

90 - 180 - 220 do bear the mark of a wire (or false) edge however. In the first case (90), the edge had just enough structural stability to sever the test media cleanly. In the latter two measurements (180, 220) it didn't and either dented or folded the wire edge over before severing the test media. There could be other edge problems that could manifest in this manner  but I advised the customer to look for a wire edge first.

Wire edges do make me think though. Usually, once a  wire edge is removed, there is no significant reduction in sharpness. In the case of our customer, and once the wire edge is removed, he should end up with an edge that measures around 90. This leads me to believe that the  width of the wire edge is about the same at the top as it is at the base where it will be separated from the newly created and structurally improved edge apex. So the problem with wire edges is that they are just "too tall" for their own good. So how's that for pure conjecture on my part? My mind is a terrible burden. I visualize microscopic things in dinner plate size and then draw conclusions. Those visualizations are sometimes later proven correct and sometimes not. I never reveal my batting average - too embarrassing.
I suppose it could also be the edge was not ground well or consistently.  Considering the large variance, I too would suspect remaining burr and/or wire edge.  Who knows how long the customer ground away at the edge and the type of burr (LOW) that was formed.  Depending on the steel and other factors some burrs are a pain to remove.

From my experience, big variances in sharpness along the edge are almost always indicative of inconsistent deburring.  Grinding is quick and easy compared to (expletive deleted) deburring.  I’ve had some knives that were extremely frustrating and time consuming to deburr.  I’ve always guessed difficult to remove super malleable burrs depend on steel hardness, but that’s just a guess.

Then again, I like and try to preserve a toothy edge while deburring which makes deburring much more pesky than deburring a polished edge.

A microscope or at least a really good loupe would be very useful for determining what is up with the customer’s edge.
Edge leading/ edge trailing style of sharpening has also important impact on burr formation and consequently on deburring.

Generally, burr formed by edge leading sharpening is smaller and easier to deburr than a burr formed by edge trailing sharpening.

I have now a good opportunity to compare both approaches. On Tormek I sharpen in the edge leading regime while on a belt grinder I sharpen in the edge trailing regime. The diameter of the grinding/contact wheel is the same in both cases.


This burr business is head scratching  stuff Jan. I agree that edge trailing produces more prodigious burrs than edge leading. How the various elements of the  burr form  and what happens in what order mystifies me. Not to mention the physical characteristics of the steel that makes up the burr and the edge apex that it was attached to.
Mike, I fully agree with you, for me it is a head scratching stuff also. Especially the edge leading burr.



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