Sharpening Question

I do my sharpening with a Lansky system and I generally get good results. I do have a problem that perplexes me. When I get to the tip of the blade it takes longer to raise a burr on the edge, thus the grind line gets wider than that of the straight portion of the blade. This makes for an unflattering grind line. Is this a symptom of using a clamp type sharpening device or am I doing something wrong. And don't even suggest that I use a bench stone as I would really butcher my knives with one. Also, does a Spyderco 204 give nice even grind lines?

 

[Paracelsus]

I'm not sure that this is a problem caused by your sharpening system so much as a reflection of thicker steel or a wider angle edge at the tip of your knives. What knife are you talking about?

I have seen this 'problem' occur on several production folders with poor primary grinds. It will not effect the performance of the newly sharpened edge however. It just looks a little funny.

 

[Chang]

I believe the problem is that your tip area has more distance from the angle guide hole selector extension on the clamp than the rest of the edge. The farther the edge portion is from the clamp section with the holes, the lower the angle will be. Use trigonometry to figure out why. The height of the hole remains fixed. At the 25-degree mark, the elevation of the bottom of the hole from the knife edge (this is only vertically) is approximately 1.5", plus 50% of the blade thickness, if your knife is ground on both sides. The distance from the back of the clamp to the edge immediately in front of the clamp is about 4.084" if the edge protrudes 0.5" out. In my diagram, the base of the edge would be ground at degree approximately arctan(1.5 / 4.0835) on the 25-degree selector, which is about 20.17-degrees. On the tip section, which has about 12-percent more distance from the guide holes than the base of the edge (immediately in front of the clamp), the angle would be different.

It would be arctan(1.5 / 4.574) because the distance is further. This is about 18.15-degrees. The lower angle makes it take longer to grind through when sharpening.

The solution if this bothers you is to clamp the blade crooked and have the tip section be about the same distance from the guide holes as the rest of the edge. This system doesn't get everything perfect, but if you think about it a good deal, you can figure out the best way to clamp it. I am really sleepy right now, so if the math doesn't quite work out, sorry. And if my measurements were wrong, sorry. But I sold my Lansky a long time ago and so these measurements are what are on my calculator program I made to get the real angles (the angle slots aren't really correct). If there are any questions, e-mail me. General rule is that the farther edge from the clamp back, the more low the angle. The closer, the more high the angle.

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Chang the Asian Janitorial Apparatus

 

[Chang]

Just thought I might include this for extra reference. The 17-degree hole is actually about 13-degrees (if the knife edge protrudes 1/2" from the clamp end). Also, the 20-degree slot is actually about 17-degrees. The 25-degree hole is actually about 21-degrees. The 30-degree hole is about 25-degrees. These are rough figures and depend on how your clamp pieces are aligned etc, but they are a lot closer than the Lansky's guide hole labelings. I really wish the guys at Lansky did the math before labeling the clamp. They made me grind off way more metal than I had to with their wrong labelings.

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Chang the Asian Janitorial Apparatus

 

Some of the knives I've sharpened with the system and have had problems with: Benchmade 940, several CTKT knives. Part of the problem is that a lot of folders don't leave much flat stable area on the blade on which to place the clamp. I think this ties in with Chang's geometric analysis of the problem. It sounds like i'm talking myself into getting a Spyderco 204.

 

[Gary W. Graley]

Dan, the Sharpmaker is, to me, a SharpKeeper, in that it maintains the edge. If you need to create the initial bevel the 204 will take you a long long long time, probably too long and some people give up too soon and are frustrated thinking they are doing it wrong, but they just didn't do it long enough to get to the REAL edge.

The Lansky, an ok system, I don't prefer it for several reasons, it can mark the back of your blade, the blade can work it's self free and fall into your lap, most disconcerting!, and as you have already found out, you need to move the clamp along the back to keep the bevel width even all along the edge.

To set the main bevel, on severely dull knives, I use my Norton Tri-hone set and that does take some time to learn to control the knife. But once it's set I do use the 204 as a SharpKeeper and a leather strop. Also use the Spyderco flat ceramics after the Norton when sharpening as well.

Recently I sharpened a knife for a friend, that had a convex chisel edge, that posed a problem as it had a zero secondary edge, to maintain that I had to do something totally different from the above listing;
I took a piece of Deer skin, very soft material, laid it on the table and laid 4" wide strip of sandpaper on it and pulled the knife in a stropping motion across it, rolling as I go to keep with the convex edge.
80 grit
220 grit
320 grit
600 grit
and then out to my buffing wheel and finally onto my leather strop, the edge? WOW it cuts standing hair easily, worked great, a lot of work but worth it.

Good luck, getting the edge can be a fun thing, stay with it!

G2

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