Power hammers (Yoder and Pettengil are two common makes) are also electric reciprocating machines, but they operate in a manner quite different from a Pullmax. Again, the lower die is stationery, and the upper die is arranged so its speed and stroke are variable, allowing it to hit with an enormous range of power-from very light taps to extremely heavy hits! The top die, and the parts that move with it, can weight up to 30 pounds, and this entire weight is thrown down against the bottom die with a force that can be enormous. With low-crown dies, the size of the contact patch from a single hit can be the size of a quarter! These machines are unmatched for quickly developing shapes in sheetmetal panels, and they can be used with both stretching dies and the thumbnail style of shrinking die. These machines are very heavy, noisy, and expensive, so they are pretty much limited to high-end metalshaping businesses-they are generally out of the league for home craftsmen.
Planishing hammers are usually air operated, and they have a variable-stroke top die that hammers against a stationery lower die. (The term "planish" means to smooth by hammering.) These machines hit very rapidly, and each hit is relatively light. While it is possible to do some shaping of metal with planishing hammers, they are better suited for smoothing panels shaped in some other way, or for concentrating a hammering force into small areas (like a headlight bucket, for example), or for flattening welds. There is a very broad range of these machines available, from entry-level machines made offshore that retail for around $100, to beautiful copies of the now out-of-production Chicago Pneumatic machines that sell for more than $8,000. As in most things, you get what you pay for, and the higher-end machines are more powerful, versatile, and user-friendly than the less-expensive machines, but they are all useful to some degree.
Fay Butler has more experience with the Pullmax than anyone I know, and he was one of the leading innovators who discovered how the machine can be used for a much broader range of work than the original manufacturer ever imagined! Fay has published an excellent book about setting up and operating the machine, as well as designing, building, and tuning shop-made tooling for it. For more information, contact Fay Butler at (413) 477-6449, e-mail him at fay@faybutler.com, or visit www.faybutler.com.
Now you can e-mail your questions to Professor Hammer at covell@cruzio.com or send mail to Professor Hammer c/o STREET RODDER, 774 S. Placentia Ave., Placentia, CA 92870. We'll print your name and city unless you request otherwise. Ron Covell has made several metalworking videos, and offers an ongoing series of workshops across the nation covering all aspects of metalworking. Check them out online at www.covell.biz, or call (800) 747-4631 or (831) 768-0705 for a current schedule of workshops or for a free catalog of videos, books, and fine-quality metalworking tools. You can also send a request by mail to Covell Creative Metalworking, 106 Airport Blvd., #105, Freedom, CA 95019.