Japanese sen questions

james terrio

james terrio

Sharpest Knife in the Light Socket
Joined
Apr 15, 2010
Messages
22,618
I'm thinking of making a sen for getting my flats nice and flat. Not so much for major stock removal, just to get things smooth after grinding and/or draw-filing before HT.

I found a couple links with some info but still have some questions.
Don Fogg tutorial
sword forum thread
cross section pic
I'll add more links as I find them.

Anyone have more info on recommended bevel angles and so forth? I'm thinking of making it out of 1/4" CPM-3V for stiffness and edge-retention. Does that make sense? (ho ho)
 
James, I'm interested in sens as well. I've wanted to make one for a while. If I had any links other than what you've posted, I'd send them to you. I hear these things are sensational.

Should be an interesting thread.
 
71 views and one response? C'mon guys someone must have some info on these cool tools.
 
Cool, I'll check around over there. Because I don't spend nearly enough time on the web as it is! :D
 
Sam, you'll have to give drawings of the tool and it's angles and the angles to the work.
 
I use a sen all the time. I have a grizzly grinder until I can upgrade, and I don't trust myself for the finer work.

The easiest way to make a sen, and one that works like a charm, is to take a file and grind the teeth off. Then, grind about a 75 degree bevel on one of the sides.

Go back and smooth the two grind planes with about 120 or 220 grit.

That's it. If you get it too hot, you have to harden and temper it again.

It will PEEL STEEL off of a blade. Choke up on it, rock the angle up until you feel the tool bite, and just go to work. I get a little better cut if I pull it and slide it sideways just a little, so it is dragging and slicing at the same time.

If it gets dull, hit it with 120 grit again on each plane. The back plane must be absolutely flat. The cutting tooth is just a flat grind. YOu can grind it convex or concave, I have done all three. Flat works as well as anything. With a bevel this close to 90 degrees, the edge is really darn strong.

Make sure there is NO scale in the way. It takes a little time for the sen to really reach its best performance. So, you have to scrape a spot 10 or 15 times while you find the right angle and the tool shapes the metal so it can bite. After a bit, it will really amaze you.

Have fun,

kc
 
Kevin, that's awesome. How do you hold a long blade for shaping with the sen? As much draw knifing as I've done in wood, I know the clamp/support has to be sturdy.
 
I clamp a 2x4 in my bench vise, and then with a big c-clamp or a wood worker's clamp, I clamp the tang of the blade to the 2x4.

Sam is right, this thing make a ton of friction. When I am really working it, I can smell the heat. You know how hot metal gives off more vapor what whatever is on it. I keep expecting the chips to turn blue.

kc
 
Hey I know necroposting is kinda bad form, but those that complain about it also complain about the same question being asked all the time...

I found some images of a different style of sen and a work bench that should be here with these other links. Looks like a standard spoke shave or draw knife bench.

using_sen_580.jpg


sen_bench_580.jpg


-Xander
 
It does, I've never seen one with such a long "wingspan" though. I am going to attempt a shorter one for doing the Ura side on the Kamisoris I'm making. I don't have a 12" or 14" wheel to properly grind one, so I figure this might be the next best option. Although I may make the bench for fun. :D. Any woodworkers have a spoke shave/draw knife bench they care to share? I think it will make using this tool much more comfortable, even for draw filing.


-Xander
 
Please forgive me but, what does a sen do? Google has nothing worthwhile.

ETA: Never mind. I just found it.:o
 
I use a sen quite a bit. My edge is almost 90degrees and the hollow is done with a 10"wheel. I use old half-round files to make them. You can hog quite a bit off. The blade actually gets too hot to hold during the process. If I need to cool it down I use soapy water as the smoke from cutting fluid sucks.

All I can add is that you need to start off with a light touch until the sen begins to bite consistently.... then have at it!
 
Rick, you're talking about using one like a traditional sen, like a spoke shave? Do you hold yours flat against the surface, or do you angle it up slightly? Approximately what angle do you expect the cutting face to be relative to th work piece? Am I correct in assuming that lathe cutting tool geometry would be a good place to start for making one, just a larger scale?


-Xander
 
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