Long Knife Jig asymmetry problem

[Jan]

When I watched the video in question, I was horrified. 

Positioning the knife so obliquely to the grindstone cannot lead to sharpening a consistent knife edge. Also the method of using sharpening steel was not correct. The beginning of the video reminds me of prestidigitator's performance with grinder and knife. 

Jan

[Elden]

    I told you in the past that your English is probably better than mine, Jan. You made me use the dictionary with that post. 

[Jan]

Sorry Elden, it was not my intention! 

When I realized how great is the change in the bevel angle when the knife meets the stone at an oblique angle, I began to think about how to use it for sharpening scissors which don't have the same bevel angle along their entire length. 

Jan

[Ken S]

It is easy to think of a consistent bevel obtained by careful use of a jig as for appearance. The other factor, perhaps more important, is that careful use of a jig with the same settings over time will result in less metal being removed.

Ken

[grepper]

If you examine a freehand sharpened knife under a microscope, there is a lot of micro beveling back from the edge.  Well, at least when I do it. 

So all of the passes that I took back from the edge were just wasted time and like Ken said wasted metal.  Obviously, if you don't hit the edge the knife is not getting any sharper.

Consider what happens if you hit the edge on part of the blade, but miss on others because the blade was tilted away from the edge.  Obviously, eventually a perfectly useable edge can be created, but it's easy to imaging what's going on down there and easy to see under a scope.

[Ken S]

grepper,

On a bandsaw blade, that pattern might be called"skip tooth".

Ken

[carvingcat]

After a bit of advice from Tormek Support I've managed to get my jig sorted! It turns out it was bent when I received it and so the results were not as expected, but I have managed to gently knock it back straight and now it performs perfectly. I straightened it by eye, and to check it was going to be correctly set up I marked the stone with a pencil to see where the blade would touch on either side. The images show very minor deviation now and I imagine any difference in bevel angle will be insignificant. Thanks to Stig for the advice!




Before



After









The lines show negligible difference for each side of the blade

[Jan]

Thank you Carvingcat for posting information concerning your bent knife jig and congrats to your successful straightening it. 

The measurement you have done is not sufficient, but necessary condition for its symmetrical functioning.

Jan

[Ken S]

A verypractical suggestion. One for the memory bank!

Ken

[Herman Trivilino]

After a bit of advice from Tormek Support I've managed to get my jig sorted!

Did they tell you straighten it out? So you were no longer afraid you might break it?

[Ken S]

I purchased a used (abused?) roughing gouge. I think the previous owner had a major catch with it. It was bent where it entered the handle. After much thought and concern, I finally put it in my woodworking vise and slowly leaned on it. To my pleasant surprise, straightening it took much less time than debating the issue. The solution was gradually applying the pressure.

Worst case scenario, T C was that you might have to replace the part or look for another jig. In the process you learned a new skill. I would call that a win. I do see Herman's point. Metal is often more brittle than we realize.

Ken

[Jan]

A very practical suggestion. One for the memory bank!

Ken

''But let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil.'' 

Jan

[Ken S]

Great quote, Jan. Source?

Ken

[Jan]

King James Bible, Matthew 5:37.
http://biblehub.com/matthew/5-37.htm

Jan

[Ken S]

Interesting.

Ken