How to use a Japanese hammer (gennoh)

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How to use a Japanese hammer (gennoh)

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Last Update:2008/4/1

Part names on a Japanese Hammer

Types of Japanese hammers

When choosing a hammer, determine the dimensional configuration and weight you require.

Make sure that there are no distortions on the hammer
Make sure that the handle is straight
Make sure that the wood grain on the handle is clearly seen, and staright
The head of the hammer should not feel loose when gripping the handle

With a properly quenched hammer, the hammer should never chip, shatter or peel away.

Names and sizes

Gennoh (玄能) (double-head, square-head, octaganal-head, straight-head)	g	75	115	150	185	225	300	375	450	570	670	750
	monme (匁) (1 monme = 3.75g)	20	30	40	50	60	80	100	120	150	180	200
Kakuhakoya Hammer (角箱屋金槌)	gauge mm			18	21	24	27	30
Sakikiri Hammer (先切金槌)	gauge mm	12	15	18	21	24	27

How to use

Generally when a nail is to be hammered, a simple hammer or gennoh is utilized. But when a small wedge or chisel is to be struck, many in Japan tend to use a gennoh instead. Most carpenters carry numerous sizes of hammers and gennohs. The gennoh typically has two different faces. One is slightly rounded (convexed), while the other end is flat. When a nail is initialled hammered, the flat side is used, and for the final touch the rounded side is used so there is minimal damager to the surface of the wood. As a rule, when hammering the center of the nail-head should align with the center of the face of the hammer head.

Light blows

Hold the end of the handle, use the elbow as the fulcrum, and allow the wrist to assist the momentum of the swing.

Heavy blows

Use the base of the arm as the fulcrum and moving the arm in a semi-circle motion will increase your striking power.

Using both arms

When holding a large hammer with both arms, use your waist as the fulcrum, and allow your upper body to assist the striking momentum.

Maintenance

When finished using your hammer or gennoh, wipe with an oil soaked cloth/rag and then dry with a cloth and store.

When the hammer becomes loose

With hand-made hammers, the middle of the head inlet is made to be slightly narrow so the handle does not easily dislodge on its own. If by chance the the handle (or the hammer head, which ever way you look at it) becomes loose, simply tap the handle wedge further into the hammer head to tighten the grip.

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