Three reasons why *you* need a Japanese swordsmith’s hammer for forging knives.
- Size – the small face is better suited for working on a narrow target, keeping the hammer from hitting the anvil as the bevel gets thinner
- Weight – though the face is small, the long body carries the weight of a much larger hammer behind it, focusing the energy to better move the steel
- Balance – with practice, the balance of the weight forward design causes it to walk neatly along the blade while the hammer does most of the work for you
…and besides that, they just look cool. So if you are a bladesmith, find one or make one.
Two hand hammers are all that is required for most bladesmithing, a larger one for rough work and a smaller one for finishing. Individual preferences will vary, but a recommended weight range for the large one is 1.5kg-2kg (~3.5lbs-4.5lbs) and the smaller one 1.2kg-1.4kg (~2.5lbs-3lbs). Large mukozuchi for a striker are found in a few sizes between 3貫/kan (11.25kg / 24.8lb) and 1貫/kan (3.75kg / 8.26lb).
Though more of a dog’s head style, the one below was entirely hand forged from a length of scrap axle (~4140?) rod about 1.5″ in diameter and 6″ long (about 3lbs. according to Practical Blacksmithing p.267 – which is not in all editions). A fellow metal worker and aspiring smith, Anthony Rabideau, was over from the mainland a few weeks ago and assisted as the striker for the initial forming and punching work. The rod was upset on one end until shortened by about half an inch, widening the face end enough to form the octagon shape and still be left with a 1.5″ diameter. Anthony made a version of his custom combination slitter and punch from an old chisel to create the eye, and we forged a drift to open it up.
Yesterday I finished shaping and filing the face, then reheated the piece for some clean up forging of the sides and around the eye, hardened and tempered it, cut off the excess half inch above the eye, and then cleaned it all up with a sen and finished by draw filing. The face is a somewhat rounded 1 3/8″ square with diagonally rounded corners and the edges parabolic-ally rounded off to prevent marks. The head tapers down to 1″ by 1 5/16″ above the eye and the length of the head is 5 7/8″. The handle was hand shaped from an old axe handle and is currently 12″ long but may be shortened and tuned as I get used to the hammer. Sealed with a coat of pure tung oil.
Points to note are that the length of the head and the angle relative to the handle mainly depend on the height of your anvil, generally a slight backwards tilt and length of not more than 4-5″ will work with a standard western anvil setup. Too much angle/length and your hand will be lower than it should when striking (like a file maker’s hammer), too little and your shoulder will be raised which is not good either. To be more true to form, I would recommend making the weight a little less forward by keeping the diameter consistent or starting with a slightly larger but shorter billet and tapering down near the face.
Material: Scrap steel axle, reclaimed axe handle