Hammers to Use With Chisels Part 1 – Hammer Varieties

A modern-style 750gm gennou head hand-forged by Kosaburo, hung with a black persimmon handle. I purchased this high-quality head over 33 years ago. An heirloom tool and a good buddy.

Yet such is oft the course of deeds that move the wheels of the world: small hands do them because they must, while the eyes of the great are elsewhere.


This is the first article in a six-part series that condenses the advice your humble servant has given to our Beloved Customers over the years regarding the hammers they should use with our chisels. While some of this information is relevant to our warranty, all of it is relevant to how well our chisels will perform and the pleasure Beloved Customers will enjoy using them.

In this first part we will focus on the varieties of hammers we recommend. Subsequent articles in this series will focus on appropriate hammer weights and faces, how to use a chisel efficiently, the “chisel cha-cha,” the importance of rhythm, as well as a discussion about health and hammers. There may even be a song or two to hum along with. Helluvalot better than a performance of Cats, and cheaper too!

In the future we will present several different series, one with more details about hammer heads, and another explaining why and describing how to make a handle for a Japanese gennou hammer (or any hammer for that matter), with scaled reference drawings. We will of course provide the entire contents of these articles in a single wiggling bundle to our Beloved Customers that purchase one of our gennou heads. Yes, there are more perks to being a Beloved Customer than simple toe-curling joy (ツ)。It’s a cunning plan, you see.

Hammer Materials

30mm Atsunomi by Kiyotada

We sell tatakinomi chisels such as oiirenomi, mukomachinomi (mortise chisels), or atsunomi all designed to be motivated by the most efficient method available, namely a steel hammer swung by human hand and arm. I won’t debate the pros/cons of steel hammers versus wooden mallets versus plastic mallets versus brass hammers versus unobtanium-platinum alloy hammers in this post because the physics are as obvious as a lemur in a lingerie shop (they’re a bit hairy, they jump and climb all over the displays and the bra straps all slip off their shoulders, but not in a seductive manner!) beyond noting that a hardened steel hammer imparts more energy to a chisel in a more easily focused and controllable manner than any other type of beater considering the economics of both initial cost and repair/replacement cost. Some may disagree; A mind is a terrible thing to taste.

The advantages of the steel hammer are quite obvious, even without doing energy calculations, but are there any disadvantages? Mochiron (Japanese for “of course”).

Steel hammers can concentrate so much energy on a tool handle so efficiently and so quickly that they routinely destroy the handles of the sharpened screwdrivers sold as chisels nowadays in Western countries due to a faulty design detail. It’s this silly design flaw most modern Western chisels share that motivates many to use softer, fatter, energy wasting mallets made of wood, plastic or rawhide. So sad. 

An obvious solution is to use a steel hammer of a reasonable weight along with intelligent technique to effectively keep the energy imparted to the chisel within acceptable limits. But this may not be enough if the chisel design is weak.

Ooh ooh! I got’n idea. Why not design and manufacture a chisel that a steel hammer won’t destroy as a matter of course? Wow! Such an innovation would be right up there with the rumors I’ve heard of buggies that move without horses. Imagine that…

Fortunately, the tataki nomi chisels we sell are professional tools designed to be struck by steel hammers so they need not be coddled. They have a mild steel kuchigane (coned ferrule) fitted where the handle meets the blade, and a mild-steel hoop, or crown seated at the butt end of the handle. When properly fitted to a dense, straight-grained Japanese oak handle, this steel furniture does a great job of protecting the handle from splitting or breaking.

However, along with the handle, these parts do need to be setup properly to ensure they continue to protect the handle for a long time. We have provided clear instructions for how to perform this setup job here.

So, please use a hardened steel hammer with our chisels.

But there is more to hammers than just materials, so let’s continue onto the next subject.

Japanese Hammer Types

A Kosaburo head with a brand-new nuclear-flash colored Osage Orange handle

The traditional hammer used in Eastern Japan for striking chisels and general carpentry work is called a “gennou” pronounced “ghen-noh.”

Janus Coin

The gennou common to Eastern Japan is a simple symmetrical cylinder of one sort or another with a flat face on one end and a domed face on the other, often called the “ryoguchi gennou,” or the “Janus Hammer” by those with a classical education. No claws, no pointy tail. The flat face is used for striking chisels and pounding nails. The domed face is used for something called “kigoroshi” and for the last stroke when setting nails. It’s a handy tool and more stable in the swing than a claw hammer. It’s a matter of physics.

Japanese carpenters use a specialized nail bar for pulling nails effectively increasing the lifespan of their hammer handles, so claws are not necessary.

3 gennou heads. The far left head is a simple economy head. The center head is a higher-grade head slightly flared towards the ends. The far right head is an entirely hand-forged classical “swollen eye” tool by Kosaburo.

The Yamakichi style gennou head (see photo below) is another variety popular primarily in Western Japan. The tail is not pointy but rather a small square face that is useful for starting small nails and for “ tapping out” plane blades. The face typically has a slight curvature which is helpful for setting nails, but not enough to damage a chisel. The moment of inertia is less than the symmetrical gennou head so it is not as stable in the swing, but it is still a fine head.

A “Yamakichi” style head by Hiroki with a mellowed Osage Orange handle

The pictures below are of a gennou head called “Funate,” which translates to “boat hand.” I have heard it originated with ship carpenters, but am uncertain. The tail end is a small square as you can see from the photo, and is handy for setting nails. It makes a great finish hammer, but as a hammer for striking gennou it never appealed to me. But there are plenty of craftsmen that love this hammer.

a Funate gennou with a bubinga handle

Any of these hammers will do the job: it’s all personal preference.

Western Hammer Types

The purpose of this article is is not to suggest that Beloved Customers must use a Japanese gennou hammer when beating on our chisels. In fact, nearly any variety of quality steel hammer can be easily modified to do the job more-or-less satisfactorily, including claw hammers, engineer’s hammers, or even ball peen hammers, so it isn’t necessary to buy a special hammer.

Please note that the closer the hammer’s center of mass is aligned with the center of the striking face, and the greater the hammer’s moment of inertia, the better. A cylindrical head is the closest to ideal from a physics viewpoint.

We’ll talk about the relevant physics of hammers in future posts for Gentle Readers that enjoy math.

In the next post in this series we will examine the type of face a hammer used to strike our chisels should have. Please come back and bring your lingerie-loving lemur friends. A Brazilian body wax is not required.


Do you have something slinky with red lace?

If you have questions or would like to learn more about our tools, please click the see the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” We aren’t evil Google, fascist facebook, or thuggish Twitter and so won’t sell, share, or profitably “misplace” your information. If I lie may my nose grow to the size of a watermelon.

6 thoughts on “Hammers to Use With Chisels Part 1 – Hammer Varieties

  1. “…that purchase one of our gennou heads” ok, I’ll bite. Tell the peanut gallery about the gennou you sell.

    Also, what is your opinion on the daruma shape gennou?


    1. B: No, I don’t think I will make a sales pitch regarding gennou heads because the good ones are hard to get, I only have a few, and those I have are expensive. If someone is interested they can leave a message.
      Regarding daruma heads, I don’t understand the American fascination with this style. In Japan it has few uses. Wood carvers like Daruma heads because of the wide face, the fact that they don’t often need much force, and because the chisel is often held close to their body. Folks who do rough assembly work like the daruma’s huge face. I was taught to use a small one for tategu work, especially for cutting the hundreds of repeat mortises. I still use it. But for general woodworking, the daruma is not the best choice because of the lower moment of inertia (less stability during the swing and impact).
      And then there is the social stigma. If you take a daruma gennou to the jobsite, experienced carpenters will smile at you behind your back thinking you need the wide face of the daruma because you have a hard time finding the nail or chisel.


  2. No sales pitch? Is this salesman reverse psychology? Actually it’s probably for the best. I had to ask and I probably cannot afford it.

    Thanks for your opinion on the daruma head. Lots of food for thought. I still want one and I’m not even American.


  3. I assume you’ll be covering in future posts, but this novice reader would like more information about the different weights/masses of gennou as they correspond to different chisels, timbers, work, etc.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s