Thread: Sen Zen

Durante's recent thread piqued my interest about the Japanese sen. I recommended the tool as a possible way for a beginner to make a razor without the need for a specialized grinder.

My research into the sen was pretty minimal. I know that it was traditionally used as a sort of drawknife/scraper in lieu of filing. I saw a post (possibly written by Jim Rion) of a razor-maker's sen designed for cutting hollows. It was basically a bar of hard steel with a curved edge at the end.

With that basic information, I went about making my own sen. I started with an old file because it was free and the steel is relatively hard. I dulled the teeth a bit and ground a robust edge into the end. I tested it on a 52100 kamisori blank I had started working on earlier.

To summarize the results: it works! There is definitely some skill involved: you want to shave the steel off, not gouge the blade. I experimented a with edge angle, blade angle, and pressure. I found I was dulling my sen quickly at first, but that improved as I figured the technique out. It took me about an hour to rough out the ura.

I don't want to give too much advice, as I'm still inexperienced and I want others to experiment. I found myself having to go back and re-sharpen often, especially at first. If I didn't have a grinder that could do the job quickly, I would want to make several sen so I wouldn't have to sharpen as often. Also, light pressure seems to work better. The best advice I can give is "Try It!". I'm sure you all have some old files laying around. It's a free tool and fun too. I definitely prefer the sen to draw filing or sanding: it takes some skill that eases the tedium of hand work.

I'll post some photos as soon as possible.

Phillip

Here are the pics. I think that with a little practice, this technique could work very well.

Shigefusa used a variety to make his knives.
Those are very useful to fix Kamisori when the Omote gets too flat.

Phillip, I did post about that--I was given a sen by one blacksmith who's recently started making razors. It's definitely an act of patience, working with it. But I have the feeling you're a patient man...

That is a good tool you have made. It has worked well for you!
I have scraped machine ways and learned to use various scrapers. A dead flat edge made perpendicular to the tool flats and shaped to the required curve as looked at about 20º from flat on the table removes a surprising amount of metal in a fairly short time. A scraper similar to a draw shave with the 90ºedge square/ perpendicular to the flat will work well also. Hone the tool to a polish and you will have surprisingly little to finish with grinding or abrasive paper.
You have done well!
Respectfully
~Richard

Just a stupid question. This tool looks a little like a chisel yet you're 2nd pic implies you are using the reverse or ura. Do you use one or both sides ?