By: Gundobad von Dettelmach
Wise Ogre Armory
Planishing is the process of smoothing out curves on dished or raised metal. I use two different methods, and will describe both here. Whether to use one or the other is a judgement call that I will leave to the reader.
The heavy mallet method requires less skill, but more force. It also will not take out hammer or metal dish marks, so If your piece is marked up from the rough forming, this is not for you, unless you want to also use the flat-hammer method for fine finishing. You will need a ball-stake and a heavy soft-face mallet. My mallet is ironwood, 2.5 inches diameter, 5 inches head length, with a 14 inch handle. A rawhide mallet will also work, but not a leatherworkers mallet. I am referring to the heavy metal-encased mallets with rawhide face. I have two ball-stakes that I use. One is approximately 3 inches in diameter, the other 4.5, both are welded to 1 inch bar stock. The small one used to be a bearing, the large one was a shot-put. I have a socket in a stump to hold the stakes.
The way it is done is to place your work on the ball-stake, and strike it so that it forms somewhat to the curve of the ball. See figure one. Strike as if to hit the ball, and use a goodly amount of force. The soft face of the mallet will give, conforming at least slightly to the curve of the piece and the ball. It will also force the piece to form to the ball. You will need a ball smaller than the piece, of course, but the closer the ball matches the curve you want, the easier it is to planish well. Planishing a breastplate on a 3 inch ball won't work well with this method, but can be done with the flat-hammer method.
For flat-hammer dishing you will need a light hammer with a smooth flat face. A body-workers planishing hammer is best, and many different varieties are available. See figure two for drawings of such hammers, as well as mallets.
This method requires more skill, or at least more hand-eye coordination, than the mallet method. Again, you place your work on the ball. When you strike, use a light amount of force, just a tap. You will have to do a lot of tapping. Strike so as to hit the piece exactly where it rests on the ball-stake, so as to "pinch" the metal between the ball and the hammer face. You will also want the hammer face be as close as possible to a tangential plane to the sphere of the ball stake. See figure three for an illustration without the geometry jargon. The sound produced by a correct strike is distinctly different from an incorrect strike. Strike just the ball. Then strike the piece, just held in your hand, not on the ball. The ball should make a sharp "ping", the loose piece a flatter "tock" sort of noise. A correct planishing tap will sound very much like the strike of the ball. You can planish out hammer and dish marks by repeatedly going over the marked area. The metal will gradually move into the low spots, out of the high spots. If you are dedicated enough, you can work your pieces to the point that they won't need much if any polishing.
If the surface of your piece takes on a "dimpled" appearance, you are striking too hard for a perfect finish, but some people like that dimpled look. You can also go over a roughly planished piece with a ball-peen hammer to get a more extreme version of this finish. I would recommend against this, except on stainless, as those deeper, smaller dimples are rather rust-prone, and hard to polish clean.