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Topics - Gilles

Knife Sharpening / Polishing angle calc
May 15, 2020, 06:21:50 PM
Hello everyone,
It makes several months, I am reading with very much interest, the different posts and I have learned a lot about sharpening.
This is my first post on this forum and I would like fist to thank all the contributors for sharing their knowledge.
My first Tormek was a T3, and I didn't like it because the USB support was not strong enough to keep the blade of a planer perfectly perpendicular.
Later on, I found a very cheap Tormek 4000, all in stainless steel. I try it in a dark area and I didn't realize that the stone was not a Tormek stone and that the shaft was twisted! After a while, I found someone to make me a new shaft and I bought a second hand Japanese wheel SJ250. This purchase was finely a very good one.
So now I have a SG200 wheel to sharpen knifes and I have a wider wheel to polish them (before the leather wheel).

I have tried to use the TormekCalc² to keep the same angle with the 2 stones but I realize that it was not possible. The second wheel was always grinding the edge heel instead of the edge tip.

I wanted to find the lowest possible knife angle that would polish the tip.
I have spent some time to understand all the formula of the TormekCalc² of JVH.
What is nice with the Tormek problem is that everything can be analyzed through triangle geometry. It is no more mathematic, it is only geometry, nice geometry, and I have solved my problem of polishing angle.
I share with you this spreadsheet that does the same calculation as the TormekCalc² and some more calculation; however this is done with a totally different objective. TormekCalc² is a very user friendly tool (Thank you JVH) and I don't want to compete with it. My aim is to do a very simple spreadsheet so that everyone could understand every formula and modify them as they need.
I took the liberty of using as much as possible the same letter and the same name as in TormekCalc² so that people could understand the drawing and the formula more easily.

I have also study the impact of the knife thickness and the tapered knife on the real grinding angle.
It gives me the idea to realize a Jig centering bushing before I realize that JVH has already realized it.
I have added a sheet dedicated to that.

I hope that my calculations are good. The first trial I have done was OK with a flat piece of steel of 3mm with a single bevel grinding. With the same angle as the grinding wheel, I could see the polishing of the hell and with the correction of the angle, I could see the polishing of the tip. I am happy. It works for that!

I do not have a very tapered knife so I was not able to validate my calculation for that. 

Now that I understand how to use the Tormek, I need to go to practice and play with it.

Kind regards