Say the word “Estwing” on a construction site and every person within earshot will know you are referring to a single-piece steel hammer based on a nearly century-old design. Invented by Earnest Estwing, this type of hammer has been produced since 1923 by the company he founded. The grips on early models made from stacked leather disks—and you can still get them with that feature—but most Estwings now have nylon rubber grips.
The idea behind single-piece construction was to eliminate wood handles (which can break) and the connection between head and handle (which can come loose). The downside to this design is that it seems to transmit more vibration to the arm of the user than hammers with handles made from wood, composites, or advanced materials such as titanium.
About 10 years ago the company introduced the Weight Forward Hammer, a steel headed model with a square face and a curved fiberglass handle. A stunningly beautiful tool, it went out of production several years back—in my view because the unconventional shape of the head and handle, and the square Euro-style striking face were off-putting to traditionalists.
Estwing’s newest offering, the AL-Pro, is a multi-piece model with a steel claw and striking face permanently attached to a single-piece aluminum head and handle. The head is hollow and contains shot to provide added weight while dampening vibration and provide a dead blow. The hammer has a magnetic nail starter and like most other Estwings, a thick nylon-rubber grip to eliminate shock. The look is unconventional, as is the 14-ounce weight, which is light for a framing hammer.
Traditionally framers used 22- to 28-ounce hammers to produce the requisite driving power, and paid the price with repetitive motion injuries to their arms and shoulders. The current thinking is that lighter is more ergonomic, which is where E=1/2MV² comes in. In classic mechanics, kinetic energy (which for hammers equates to driving force) for non-rotating objects is equal to ½ mass (the weight of the head) times velocity (speed of the swing) squared. Simply put, swing faster and you can generate the same nail driving force with a lighter hammer.
The practice of using lighter hammers for framing is not completely new; I once worked with a carpenter who put an extra-long wooden handle on a 20-ounce head and claimed it drove as well as a much heavier hammer. He spoke of it in terms of leverage but I think it worked because with the same speed of swing the extra-long handle meant the head moved faster through space. Years later, Stiletto popularized the idea of lighter is better by introducing titanium hammers. Lighter than steel and more resistant to the transfer of vibration, titanium is too soft to drive nails so Stiletto’s hammers are equipped with hardened steel striking faces. In designing the AL-Pro, Estwing went with aluminum because it’s lighter and easier to work with than titanium and not subject to the patents held by Stiletto.
http://www.core77.com/posts/58187/Estwing-AL-Pro-Hammer