Twist drill bits are available in a wide choice of tooling materials and lengths with the variations targeting specific projects. Structural fasteners, used to join sheet metal structures securely, come in thousands of shapes and sizes with many of them specialized and specific to certain aircraft. Stresses in Structural Members An aircraft structure must be designed so that it accepts all of the stresses imposed upon it by the flight and ground loads without any permanent deformation. Press Brake Since most cornice brakes and box and pan brakes are limited to a maximum forming capacity of approximately 0. Select a drill about 0.
Generally, sheet metal made of aluminum alloys is used in airframe sections that serve as both the structure and outer aircraft covering, with the metal parts joined with rivets or other types of fasteners. Do not attempt to withdraw a reamer by turning it in the reverse direction because chips can be forced into the surface, scarring the hole. The bars must be kept clean, smooth, and well polished. Hand Cutting Tools Many types of hand cutting tools are available to cut light gauge sheet metal. On some material, the forming operation must be performed by passing the material through the rolls several times with progressive settings on the forming roll. The diameter of the punch is stamped on the front of each die holder.
Since some structural fasteners are common to all aircraft, this section focuses on the more frequently used fasteners. This type of crimping block is designed to be held in a bench vise. This tool is used by holding it against the shank end of a rivet while the shop head is being formed. Larger ones spread the driving force over a larger area and are used for the riveting of thin skins. Solid punches vary in both size and point design, while hollow punches vary in size. The radius of the nose on the clamping fingers is usually rather small and frequently requires nose radius shims to be custom made for the total length of the bend. To make the fold, adjust the machine correctly and then insert the metal.
Angle adapters have an extended shank fastened to the chuck of the drill. Use universal head rivets in all other surface areas. A cracked abrasive wheel is likely to fly apart when turning at high speeds. A cut can be started anywhere on a sheet of metal. Files are graded according to the tooth spacing; a coarse file has a small number of large teeth, and a smooth file has a large number of fine teeth.
Drill motors are available in many different sizes and models. The second number is the numerator of a fraction in sixteenths of an inch and identifies the length of the rivet. Then, roll the remainder of the sheet through the machine. Remove the head by breaking it off. When the handle is returned to its original position, the jaw and blade return to their original positions and release the metal.
Although any type of hardwood is suitable, maple and ash are recommended for best results when working with aluminum alloys. To drill, proceed as follows: 1. When correctly adjusted, the microshaver leaves a small round dot about the size of a pinhead on the microshaved rivet. A bent drill bit makes an oversized hole and may whip, making it difficult to control. Failure to do so causes the rivet shank to bend with the first blows of the rivet gun and causes the material to become marred with the final blows. Repeat this procedure until the desired curvature is obtained, then release the upper roll and remove the metal. The step drill bit consists of a smaller pilot drill point that drills the initial small hole.
The working face of a header should be properly designed and smoothly polished. Pneumatic guns operate on air pressure of 90 to 100 pounds per square inch and are used in conjunction with interchangeable rivet sets. The drill bit is attached to the drill rod by shrink fitting, brazing, or silver soldering. However, some types of large radii contoured parts can be formed by a combination of hand forming and pressing operations. Actual cutting is done on the end of the reamer.
A good practice is to calculate the minimum rivet diameter and then use the next larger size rivet. When the height of the part is less than the distance between the drill and the table, the table is raised. The bending capacity of the brake is determined by the bending edge thickness of the various bending leaf bars. Figure 4-78 illustrates acceptable ways of laying out a rivet pattern for a repair. The gauges can be made by cutting a piece of material to the required finished radius and comparing it to the radius being formed by the rolling operation.