Active between at least 1929 and 1966, the Pneumatic Drop Hammer Co. of Boston made drop hammers which were especially popular among aircraft manufacturers. Their double-hammer design (matching hammers swinging simultaneously above and below the work) created less vibration and need not be installed on the ground floor on a thick concrete pad.

Information Sources

• A 1929 edition of Machinery and Production Engineering. "A precision pneumatic drop hammer—The pneumatic drop hammers of the type shown in Fig. 1, which are manufactured in a range of sizes by the Pneumatic Drop Hammer Co., 261 Franklin Street, Boston, Mass., U.S.A., are noteworthy for their ease of operation and the extreme delicacy of control which is possible. These hammers..."
• A 1942 issue of Aero Digest has the following (later included in the 1943 book, Metal Forming by Flexible Tools, by Chris J. Frey and Stanley S. Kogut.)

  DROP-HAMMER DESIGN
  Since there was no hammer equipment on the market readily convertible to aircraft use, each aircraft manufacturer was compelled to design and build his own and, since the rope-hammer type was the easiest and simplest to produce, this unit became almost standard equipment. However, as soon as drop-hammer production methods proved their value, several machine companies began manufacturing equipment for aircraft production. Chambersburg Engineering was first, with the Ceco Stamp, a pneumatic hammer, which is now widely used throughout the industry. Lake Erie Engineering manufactured a pneumatic hammer of similar design, as well as a hydraulic drop hammer. Then, the Pneumatic Drop Hammer Co. developed a drop hammer which eliminates the need for a high ratio of anvil to ram. This hammer is unique in its design since it is a double action type, in which the bottom platen, moving upward to meet the falling head, demonstrates a practical application of Kent's law; 'If two inelastic bodies of equal momenta impinge directly one upon the other from opposite directions, they will be brought to rest.' By proper arrangement and control the opposing heads of a double-action hammer meet each other with the same force at impact, causing them to stop without shock or vibration to their supporting members. Since the force of each head is equal, and their ratio to each other is equal, all the energy excited at impact is consumed in performing the work on the object placed in the dies. The dropping head is met by the anvil lifted by air. The motions of the two heads are reversed at impact and returned to operating position, resulting in a powerful, shockless, vibrationless light weight machine which eliminates the heavy anvil and massive foundation required in other types of hammers. The loss of energy inevitable in the old type of drop hammer, due to absorption by the anvil, its foundation and surroundings, is reduced to zero in this machine because all the developed energy is absorbed in the work. Since it requires no heavy foundation, it may be readily moved from one place to another.

• 1966 MacRae's Blue Book lists Pneumatic Drop Hammer Co., 200 Adams St.. Braintree, Mass., as a maker of drop hammers.