How big are Japanese water wheels?

[Chef Niloc]

I got asked a question the other day that I could not answer, and I can't find the answer anywhere? What size are the wheels used to grind out the hollow back of traditional kitchen knives?

[DSChief]

Using this as a typical wheel, my guess would be in the area of about 3 foot Dia.

[Mucho Bocho]

Here's a good one too

http://www.youtube.com/watch?v=KQI3jXk7sY8

[Crothcipt]

A couple of knives I have bought seem to have 2 different sizes of shallowness. Meaning 2 different sizes of wheels.

[kartman35]

I thought the hollow back was created during the forging process...like with a hammer.

6:55

[Lefty]

I do not regret watching the second video one bit. That was actually pretty freakin' amazing to watch. I like the serious face turned big goofy grin, at the end.

[Lefty]

Ok, I just watched the Carter one and it was awesome too.

[Korin_Mari]

We're getting a new wheel from Japan soon and I was told that it was over 500 kgs.