A technical student can make do with just a 16oz ballpein hammer, although it may be nice to have an 8oz on hand for finer finishing work. The choice of hammer design relies on the fabricator's choice.
Hammers are comprised of two parts: the Handle and Head.
Made from wood, steel or composites, a handle has two parts: the Grip and Neck.
This is the only part of the hammer that is held in the hand. It is contoured to fit the hand, increasing traction and to help prevent the hammer from escaping the grip of the user while in use. Some Grips are covered by shock-absorbing polymers to increase comfort and reduce fatigue.
The length of the Neck contributes to the force delivered to the object under the head of the hammer. A longer neck will reduce the amount of force required to achieve the same impact force as a heavier headed hammer with a regular length handle. By “choking-up” on the neck of the handle the moment arm is reduced, lessening the forces delivered. This is sometimes an advantage to those who wish to do finer or more controlled work without switching to a lighter/smaller hammer.
Hammers are typically identified by the shape of the head. The ballpein hammer head is the most common hammer design for varying kinds of metal work and the most commonly used hammer in the P&O profession.
The pein of a hammer is an alternate striking surface on a hammer’s head. In this case it is in the shape of a ball, giving this hammer its name. There are many different kinds of peins for different uses, mostly for metal working and smithing. Some alternate peins are shown in this picture: <insert picture>
The transition area on the head of the hammer between the pein or poll and the cheek is called a neck. Some necks are quite long on some hammers and others may have none. On ballpein hammers the necks are usually short and stocky but are narrow enough to sufficiently lighten the head while allowing sturdy support for the striking surfaces.
Wood and polymer (fiberglass) handled hammers are secured to the head by means of inserting the top end of the handle through a tapered hole called the “eye.” Steel handled hammers tend to be forged as a single unit.
A basic steel wedge is often used to spread the wood within the eye, securing the head on the handle. Circular wedges are becoming common and more than one wedge can also be employed. Polymer (fiberglass) and some wooden handles are also sealed with a thermoplastic resin to secure the handle within the head.
The sides of the head of a hammer, its purpose is to encapsulate the wedged end of the handle and connect the two striking surfaces. They are not intended to be used for striking as they are not positioned for balance, and is susceptible to damage or fracturing.
The body behind the main striking surface of the hammer head.
Striking surface. If the face of a hammer has a machined texture, it isn't suited to doing P&O work. The face of a ballpein hammer needs to be very slightly convex and have a smooth surface. The face has two parts:
Heel - The portion of the face closest to the user.
Toe - The portion of the face farthest from the user.
As a metal worker’s tool, both the pein and the face are designed to move metal in a user-defined direction. The magnitude of the radius used determines how aggressively it will move the metal. A small radius creates a ball shape for the pein and will move metal more aggressively than the larger radius used to dress the face. The face will also have its edges rounded to limit unwanted marking. A damaged face will damage the surface/object it strikes and could result in fractures.
Ideally, whatever is being struck should be resting securely on an anvil or riveting bar with its face at the height of the user’s metacarpophalangeal joints (MCP) with the digits flexed (in a fist).
With the striking surface at this height the face of the hammer and the work-piece will be parallel to each other and the face of the anvil. This will allow the technician more control with less fatigue while reducing the likelihood of a repetitive motion injury and developing carpal tunnel syndrome. With the surfaces being collinear the hammer is less likely to mark the work-piece where unintended.
The hammer should be held as close to the butt end as possible without the hand extending beyond it. The third and fourth fingers should be lightly gripping around the handle with minimal force to allow the handle to pivot slightly in the forehand and allow the handle to absorb the resonance of the blows.
Only light blows should be swung from the wrist alone, as it contains numerous small joints and ligaments that are more prone to injury. Moderate-force strikes should be delivered from the swing of the elbow and wrist. The elbow is a sturdier joint and delivers force with a larger set of muscles and a greater moment arm. Heavy blows should be delivered from a combination of the shoulder, elbow and wrist to include the largest number of muscles in the arm/shoulder complex and make use of the longest moment arm.
Generally, the more force delivered the less accurate the delivery. Numerous smaller/lighter strikes will provide the user the accuracy to complete finer and more precise work than a few heavy blows will.
Using a ballpein hammer is to deform metal to whatever shape is wanted. Getting a “feel” for how metal deforms takes observation and practice. Different metals require different amounts of force and will deform differently under that force and the way the force is applied.
Due to both the face and pein of the hammer being the same radius from the centre, a strike perpendicular to and centered on the work-piece will distribute the force evenly. An even force will deform the metal evenly from the centre of the strike.
To move the metal being struck in a particular uneven direction an angled or glancing blow will deform it in the direction of the angle of the blow. As with the perpendicular strike, a greater force will move more metal.