Smiley!!

[Peter Eaton]

Hopefully someone can answer this. Not sure why but I got what I call a 'smiley' on a couple of blades yesterday.
By that I mean the grind was OK until the last section where the belly started to curve, then it widened and narrowed towards the tip. My fail as was tired and should have called it a day but we live and learn I guess.

So my thoughts are that I might have 'swept' the blades too much on the last portion on the grind possibly as opposed to keeping the edge square to the wheel , well if that make sense?

Thanks in advance

[tgbto]

Peter,

The issue you mention is part of what makes sharpening, even on a Tormek with jigs, some kind of an art. The way the edge width varies along the length of the knife, and in particular in the tip area, depends on the combination of the curvature at the tip, the geometry of the blade itself (scandi vs flat grind for instance), and the way the blade thickness varies lengthwise when you get closer to the tip.

The method I use to avoid said smiley is the following, and assumes for now you are reproducing the current edge:
Begin by putting sharpie on the edge all the way to the tip.
Grind a complete stroke the entire length of the blade, and just lift the handle when you get to the tip, trying to maintain a consistent flow of water (no pivoting or sweeping at all to get a good reference).
Check your grind wrt the sharpie. If your grind is widening on the tip section you'll need to pivot the knife so it rides *up* on the wheel. *Down* if your grind is too narrow.
Rinse, repeat.

Now a couple things to keep in mind :
- The position of the jig on the knife has an importance. A general rule of thumb is to put the jig somewhere around the center of the curvature of the tip (See this advanced sharpening instructional video that contains a lot of info that might help you). If you put the jig too close to the knife handle you might see an early widening of the edge when you start having to lift the handle (it might be what caused the first variation in the issue you're having). Too far and the edge will get too narrow too fast. You can compensate for those by pivoting as mentioned earlier, but that is avoidable.
- If you're changing the edge angle on a knife, the sharpie method will not work. Yet as you will most likely be using a coarse grit, you should be able to tell from the grind marks whether your grind is getting wider or narrower towards the tip.
- Sometimes you have to pivot backwards (ie tip towards you) a LOT to avoid getting wider at the tip.
- If you prefer function over looks, it might be OK to see a wider bevel at the tip, as that happens when you want to maintain edge angle as the blade angle gets more acute. I do that on the short gyuto that my wife uses a lot. So it slices consistently well all the way to the tip, and edge retention in the tip area is better while it sees heavier use than on longer knives.

Hope this helps,

Nick.

[RickKrung]

I have not watched the advanced sharpening video tgbto mentions, or if I have. it's been long enough that I do not recall how it covers the matter of lifting the blade to deal with the tip, but there is a seminal discussion of lifting versus pivoting on this forum, started by Wootz.  tgbto mentions both lifting and pivoting, but they are different and it is important to understand the difference.  After Wootz's post and the ensuing discussion, there was a rush towards pivoting, from which development of the Pin Pivot Collar (PPC) arose. This is actually where I figured out that the lifting may need to be fairly dramatic in order to keep the bevel angle and width consistent, but I also went heavily toward pivoting - for a while.  I now hardly do any pivoting and hardly ever use my PPCs.  I've seen it said that the new KJ knife jigs provide for some pivoting with the use of the inner stop. 

Rick

[tgbto]

Reading Rick's post I realized I may have not been very precise : pivoting can be done with the older or newer Tormek jigs, around the handle itself, tweaking the amplitude according to the lever arm, how the handle contacts the USB, etc. I was not talking PPC specifically. Although they do help when you have to pivot much, I find that it is often doable with the basic jig. To be honest I mostly use my PPC when I need to sharpen a small knife with a bunch of big ones with just one projection distance.

The newer (KJ) might limit how much you can pivot using the standard stop though.

The pivoting is mentioned by Wolfgang around 35:50 in the video (pivoting so the blade rides up) or 43:30 (down).

The position of the jig relative to the tip of the blade will also impact how dramatically you can lift. The whole discussion of clamping in the advanced sharpening video is well worth watching.

[Peter Eaton]

Thanks for the detailed reply Nick, its appreciated.

I will look at the video.

Many thanks

Pete