Angle Determination and Tip Work

Szilard

Szilard

Joined
Mar 5, 2012
Messages
363
My question is twofold. I have gotten a lot better at sharpening after a bit of practice. I use a Sharpmaker and I generally throw it up at 40 degrees which I assume means that I am sharpening my knives at a 20 degree angle. I can now get pretty much any knife that I put some work into to take the hair off my arm. It doesn't hurt that I don't let my knives get too dull to begin with, and I only use very fine stones with light pressure. It generally doesn't take that long to touch up, but even if it does - I prefer that than risking ruining blades with my still novice tinkering skills.

First question : How can I figure out the angle that the knives, new or old, are sharpened at? Is there any way to figure out if I am basically re profiling them? Is this simply a visual/experience related process?

Second question : I know enough to know that I don't want to pull the tip off the sharpmaker. I prefer to use the triangle edge, but I sometimes use the flats as well. How can I invest a little extra time to really get a razor sharp tip? I don't have a problem sharpening all the way up to the tip, and I don't have a problem destroying my tips, I just want to get those tips really pointy.

Thanks BF. As ever you are wonderful.
 
For the angle i've seen a superb tool from CATRA it's a laser goniometer http://www.catra.org/pages/products/kniveslevel1/lkep.htm
I think it's also possible to develop something less precise built homemade...
For the pointy question it's all geometry you could change a little the tip geometry in order to ensure a correct action of the stone.
Use the flat side not the triangle to ensure good contact.
 
There are several good videos on sharpening the tip. Still learning myself, hopefully the post I did below is helpful:
www.bladeforums.com/forums/showthre...y-and-knives-Fan-post?p=10691453#post10691453

It was meant for freehand on stones, but the concept should be applicable for sharpmaker as well. When reaching the belly towards the tip, keep the edge always perpendicular against the vertical imaginary line, so the edge that meets the sharpmaker flat always 'cut' downward.
 
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If you have some calipers, you can use trigonometry to determine the edge angle (assuming its a V edge). Basically you measure the thickness of the "edge root" (where the primary grind meets the secondary bevel), then measure the vertical distance from the apex of the edge to the edge root (or, alternatively, the width of the secondary bevel). You can then define a triangle where the secondary bevel is the hypotenuse, one side is half the edge root thickness, and the other side is the centerline of the blade from the edge to the edge root. Then solve for the small angle at the edge, which will be half of the total inclusive angle.

A more intuitive way to accomplish what you want is to simply mark the edge bevel with a sharpie. Make a few passes on the sharpmaker and see where the sharpie was removed. If it is removed evenly across the width of the bevel, then your edge matches the sharpmaker angle exactly. If it only removes sharpie on the edge side of the bevel, your knife's angle is more acute than the sharpmaker. If only on the blade side of the bevel, then your angle is more obtuse than the sharpmaker.

As for the tip. I do not own a sharpmaker, but I would not use the triangle side of the stones for the tip. I try to stop my sharpening stroke just as the tip makes contact with the stone as the blade is swept along the belly curve. If you go farther the tip tends to get rounded, if you stop short it doesn't get worked. It would be almost impossible to do that on a triangle stone.

The method of sharpening is hard to describe, but again I think a sharpie would be useful. Observing where the sharpie gets removed will allow you to see what you need to correct. In my case, the tendency is to under-angle near the tip (sharpie removed only on blade side), so I have to raise the handle just a bit more towards the end of the stroke in order to correct it. But that is on benchstones, I don't think you'd have that problem with a sharpmaker. But you may not actually be getting all the way to the tip on your strokes, and the sharpie will tell you if that's the case. Just take it a stroke or two at a time and observe carefully. You should be able to figure out what you need to do.
 
If it is a flat edge you like to know the angle of, use a normal scissor. Put the edge in the scissor until its fits on the edges both sides. Lock the scissor in that position. Lay down the scissor on a paper, draw lines with a pen with support from the scissors edges – and measure the angle with a protractor.

It is not a perfect way to measure – but you come close. You cannot see if the angle is similar on both sides of the edge – but you will get the total angle of the edge +/- some tens of 1 degree.

Thomas
 
Definitely heed Robs92XJ's words. I use a sharpmaker and it took me a while to 'get it'. The way I really learned was the sharpie trick, made it so much easier. Try that before buying tools or reprofiling them. Slow, steady, and just the wait of the knife is enough to get a really good edge.
 
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