It’s interesting how things come full circle with tools, terms, and old cars. In recent years planishing hammers have been a buzz term (or tool) in the automotive fabrication world. It seems almost every professional car building has one or two in their shop and more and more DIY enthusiasts are putting one in their shop. But what does a planishing hammer do and why would you need one? We decided to give you a crash course in what a planishing hammer does.
First to understand the tool you need to understand the tool name. The term planishing basically mean to smooth or flatten metal and can be done with a power assisted tool or even by hand with a body hammer or slapping spoon. A planishing hammer is simply a power assisted way to quickly smooth or flatten metal.
Planishing hammers are not a new tool and have been around since the 1930-1940’s and were heavily used in the aviation fields during WW2. Eventually they were transitioned into the automotive industry and body shops and fabrication shops around the country were using these to quickly repair damaged panels. A planishing hammer typically consists of an air operated “hammer” that moves very quickly up and down and almost vibrates the metal and a lower anvil that is similar to the dolly you would use when doing work by hand. These parts are connected by a C-shaped hoop that could be made of cast iron or just thick walled square or round tubing. This frame gives you the room to rotate a part inside of the frame during the smoothing process. The depth of the throat is very important as you may need to rotate the part often to get every square inch of the damage smoothed out.
Smoothing, flattening and stretching are the most common uses of a planishing hammer. If your hammer is powerful enough you can actually stretch metal. This is performed by turning the air pressure up substantially and run the part back and forth over the same area. With the hammer striking so fast and hard on the metal it will eventually stretch the metal and you will notice the metal begin to develop a bulged area where the metal is stretched. This is good if you need to raise the metal in a certain area but is actually counter-productive if you’re simple trying to smooth out a weld or body damage. We suggest running your planishing hammer on a low pressure (under 50psi) for smoothing and over 50 psi for stretching and shaping of sheet metal.