The Japanese Gennou (Hammer)

[Warren Mickley]

The Japanese persimmon, Diospyros kaki, is in the same genus as our American persimmons. We have Diospyros virginiania, (NJ and PA south and west) and D. texana (CO to TX). Common ebonies are also in this genus, Makasser, Gaboon, and others.

[Stanley Covington]

Exactly....insane maybe....but I would never do anything that crazy, hehe.

How do you feel about mokume gennou? I like them, they seem like one of the few tools where that sort of thing would be acceptable. Baba makes them, but his patterns are not for me.

I find the mokume finish attractive, but I have no experience with it in anything but knives. Since it is an acid etch over differing layers of metal, it seems like it might not improve with time and wear, but I don't really know.

Stan

[Tony Wilkins]

Thanks for posting this Stan. Very informative.

[Frederick Skelly]

Thanks Stan! I always enjoy your tutorials!
Fred

[Stanley Covington]

Thanks Stan! I always enjoy your tutorials!
Fred

Fred:

It is my pleasure!

Stan

[Mike Holbrook]

Wait, I have more questions!

Brian was kind enough to answer a couple questions via PM. It seems the more I learn the more there is to learn.

I am wondering why there are square, octagonal, round and shorter round shapes for these tools? I ordered a couple with the short wide round shape simply because "I have heard" how painful it is to smack a finger/hand with a hammer. I am hoping the wider head will reduce the chance of my having to repeat errr experience that sensation. I thought the wider head might spread the shock/damage setting nails or driving chisels?

I also wonder what weights people like. Apparently Derek's favorite is a 375g model. I think Brian has a 675g gennou for mortising, woow! Stanley hints at what sizes he likes but does not exactly own up. I started with lighter models than Brian, at least until I earn my robe and slippers. My current Japanese chisel collection has more light and medium weight chisels. I believe my heavy Swedish gouges are designed to be hit with wood mallets.

[Stanley Covington]

Wait, I have more questions!

Brian was kind enough to answer a couple questions via PM. It seems the more I learn the more there is to learn.

I am wondering why there are square, octagonal, round and shorter round shapes for these tools? I ordered a couple with the short wide round shape simply because "I have heard" how painful it is to smack a finger/hand with a hammer. I am hoping the wider head will reduce the chance of my having to repeat errr experience that sensation. I thought the wider head might spread the shock/damage setting nails or driving chisels?

I also wonder what weights people like. Apparently Derek's favorite is a 375g model. I think Brian has a 675g gennou for mortising, woow! Stanley hints at what sizes he likes but does not exactly own up. I started with lighter models than Brian, at least until I earn my robe and slippers. My current Japanese chisel collection has more light and medium weight chisels. I believe my heavy Swedish gouges are designed to be hit with wood mallets.

Mike:

Good question. Idunno why the many shapes, perhaps for the same reason there are so many shoe styles.

I can confirm what you heard about smacking fingers.

The daruma style (named after the buddhist priest of legend who meditated for so long he lost his ams and legs) has a wider face and so is preferred by carvers who need a wider face because they switch chisels every few strokes and tend to choke up on the handle instead of changing hammers so they lose the sense of the precise location of the gennou's face. But I have never heard of selecting a wider face so it hurts less....

I like round faces for nailing, but the square face with rounded corners for everything else. Actually, for nailing, the Yamakichi style works better than the standard symmetrical gennou IMO. I am not overly fond of the 8 sided heads, although I have several. They tend to dig into the wood's surface too much when doing kigoroshi, ruining the fibers.

I just got hold of 5 new gennou heads. From the left:

1. 100 monme (375gm, 13.23oz); Kosaburo (Hasegawa Kosaburo, RIP)
2. 100 monme (375gm, 13.23oz); Hiroki (Aida Hiroki)
3. 90 monme (337.5gm, 11.9oz) Hiroki
4. 80 monme (300gm, 10.6oz) Hiroki
5. 60 monme (225gm, 8oz) Hiroki

As for weights, the 100 monme is the standard carpenter's gennou in Japan. Most people can do most anything they need to with it.

I have a couple of these of course, but what I use varies with the job. The gennou must be matched with the chisel, the chisel with the wood and the depth and dimensions of the cut and the required speed and precision. I tend to prefer lighter chisels for most chisel work such as cutting joints for joinery, furniture and casework. A 60 monme (8oz) by Kosaburo is the weight of the hammer I use the most nowadays. Good control, nice period, good rhythm.

For rougher work, a 100 is a good weight. That is the weight of the smaller gennou in my previous post.

For structural joint cutting, a 250 monme (938gm, 33oz) is a good authoritative weight for hogging wood using a stout tataki chisel by Kiyotada or Usui with a durable edge. But a gennou this size will overwhelm a smaller oire nomi. That is the weight of the big gennou in my previous post.

I am still searching for a suitable planing robe and slippers.

2d

PS: The Kosaburo at the far left is an older style, and harder to make. Notice the swell in the middle. You don't see many like that around anymore. It is new, but old stock, and the storage conditions were not optimal as witnessed by the rust. The advantage to a simple, undecorated head IMO is that it ages well and develops character, growing in wabi sabi, instead of just looking worn out and dirty. I got it at a good price from a store that knows how much I like Kosaburo's products, and that I don't mind a spot or two of rust.

Hiroki was one of Hasegawa san's apprentices, and is said to be as good as his master in most respects. Very precise eye. Properly aligned. No twisting. Clean lines. A great gennou. I talked with Aida san last last Thursday, and he said he is backlogged 2 to 3 years out. Business is good.

[Brian Holcombe]

That's a great find Stanley! That shape is particularly difficult to find and quite beautiful. Amazing how a chunk of iron and steel can have such appeal.

[Mike Holbrook]

Stanley, thanks for the additional information and especially for the pictures. Still I think we need to come up with much better reasons for needing all the different shapes, less the wives start getting suspicious! My wife does not have the buy clothes for style habit so I may have trouble with the "same reason as there are so many shoe styles" argument.

I have a 225g Tenryu Daruma I am working on a handle for. I have some decent splits but my shaving horse is in pieces at the moment and I am stuck doing other things for a few days grr. I ordered a 300g, shaped more like the ones in Stanley's picture, to try too because somehow it sounded right for me and my work and I wanted to try the more conventional shape head. We will see if I get the 300g, as I added a request for a handle to a Japan-Tool Online Shopping order and I left the shipping at the low/slow level.

Brian is generous in answering most questions, but for some reason he remains tight lipped on the sources for proper slippers and robe subject.

[Brian Holcombe]

Awesome, did you pick up the 300g Hiroki?

Just remember, if you can't find a proper robe, you can always default to a reliable country tweed sportcoat and chukkas.

[Stanley Covington]

Awesome, did you pick up the 300g Hiroki?

Just remember, if you can't find a proper robe, you can always default to a reliable country tweed sportcoat and chukkas.

Brian:

Glad you like the Kosaburo. They had one last one in stock, but the rust was considerably worse. I suspect that someday I will regret not buying it when I could.

Yes, I bought the 300gm Hiroki too.

I will remember your sartorial advice. Will Harris Tweed work?

I picked up some dark blue steel-toed jikatabi that might do the job instead of slippers, but the planing robe.... that is going to be more difficult I fear.

Stan

[Brian Holcombe]

I would like to enlist your help in finding some jikatabi if you wouldn't mind lending your assistance in terms of comparing sizing.

Harris tweed is a good start

[Mike Holbrook]

Yes, I ordered the 300g Hiroki too. If Stanley and I both ordered from Japan Tool then I think his order went in first and he will get the only one they had. They list the 300g as out of stock now but it was still listed when I ordered. Maybe Stanley ordered from a different source? Does Brian know Japanese Gennou stock that well?

How about a nice McKenzie plaid tartan kilt or is that just not done? Air out ones differences and such.

[Brian Holcombe]

I think the plaid kilt will do well, seems like it would be right at home while riving lumber.

Stanley is in Japan so I believe he bought from a local hardware store. So only stocks one or a few of each item, so that makes sense that it went out of stock right after you ordered. 300g is good a majority of cabinet work. I like the big gennou for chopping mortises or using with a heavy chisel, but thats about it. The light one makes the rounds for dovetail work. Then I have a file finished funate shape Hiroki that I use whenever the mood strikes me.

[Mike Holbrook]

Thanks for the clarification Brian. I got a confirming email from So, and they have the money, so I think they had one when I placed the order. I just hope I did not toss a monkey wrench in the works by requesting a handle with the head. I thought I might learn what a proper handle looks like before I shave mine all the way down, although I do have Derek's design and pictures & descriptions from other members to work from.

Maybe after my kilt comes in I will toss a few cabers around, required if you are wearing a clan kilt, maybe rive a little lumber, as that does sound appropriate too....then maybe, just maybe I will be able to handle one of those 675g Gennous.