Recurve filet knives (why?)

[Swemek]

I think it's really annoying to sharpen many filet knives, the ones that has a recurve, like the one below. I have old wheels that I have rounded for knifes like this. But is there a reason for this shape on (some) filet knives?

My guess is that the negative curve is there for aesthetics and that the often flexible blade needs some support, which a straight blade wouldn't give?

This must be an issue for other sharpening scenarios and not only on Tormek. I have tormeks diamond wheels and want best possible sharpness on filet knives for obvious reasons.

[Swemek]

Haha I see now that the example wasn't the best. There are filet knives that are worse were the recurve starts further down the blade.

[tgbto]

In this example, I think the recurve is due to the bolster, which in turn is there for safety reasons (it prevents the index finger from sliding onto the blade), and a desire to blend it smoothly with a thin blade. The recurve has no interest in terms of how you cut, but it *will* be a PITA for sharpening.

As a general rule, knives with a bolster will be troublesome when sharpening with a Tormek : you will usually end up with a dent, usually not right at the bolster. Knives with a recurve will be troublesome when sharpening with a Tormek : you won't be able to sharpen the recurve harmoniously except freehand. Also, although recurves are always a bit tricky, a rod-base sharpening system with a narrow plate will be much, much easier to use and will allow controlled-angle sharpening. For light touch-ups, a belt system with thin, flexible belts and a bit of slack will also make the sharpener's life easier.

Japanese western-style knives are more suited to Tormek-assisted sharpening : they have no bolster and only have convex blades. Interestingly enough, the Japanese don't use this kind of flexible blades. Instead, they use massive (wa-deba) blades for filleting fish, or very thin straight blades (called "sujis" or "lasers") for thin slicing.