CNC Machining of hardware and certificated engine replacement parts.

"Hardware" is the term used - to describe the various types of fasteners and small items used to assemble and repair aircraft structures and components. Only hardware with traceability to an approved manufacturing process or source should be used. This traceability will ensure that the hardware is at least equal to the original or in properly altered condition.

Hardware that is not traceable or is improperly altered, may be substandard or counterfeit, since their physical properties cannot be substantiated. Selection and use of fasteners are as varied as the types of aircraft. Therefore, care should be taken to ensure fasteners are approved by the Federal Aviation Administration (FAA) for the intended installation, repair, or replacement. Threaded fasteners (bolts/screws) and rivets are the most commonly used aircraft fasteners because they are designed to carry shear and/or tensile loads.

CNC machining of aerospace bolts. 

Most bolts used in aircraft structures are either general-purpose, internal wrenching, or close-tolerance AN, NAS, or MS bolts. In certain cases, fastener manufacturers with approved CNC machining facilities produce bolts of different dimensions or greater  strength than the standard types. Such bolts are made for a particular application, and it is of extreme importance to use like for like bolts in replacement. Design specifications are available as military specifications and industry design standards such as NAS, the Society of Automotive Engineers (SAE), and Aerospace Material Standards (AMS). 

Aircraft bolts can be identified by code markings on the bolt. These markings generally denote the material of which the bolt is made, whether the bolt is a standard AN-type or a special-purpose bolt, and sometimes include the manufacturer.

AN standard steel bolts are marked with either a raised dash or asterisk, corrosion resistant steel is marked by a single dash, and AN aluminum-alloy bolts are marked with two raised dashes.

Special-purpose bolts include high-strength, low-strength, and close-tolerance types. These bolts are normally inspected by magnetic particle inspection methods.

Typical markings include "SPEC" (usually heat-treated for strength and durability), and an aircraft manufacturer's part number stamped on the head. Bolts with no markings are low strength. Close-tolerance NAS bolts are marked with either a raised or recessed triangle. The material markings for NAS bolts are the same as for AN bolts, except they may be either raised or recessed. Bolts requiring non-destructive inspection (NDI) by magnetic particle inspection are identified by means of colored lacquer, or head markings of a distinctive type.

In general, bolt grip lengths of a fastener is the thickness of the material the fastener is designed to hold when two or more parts are being assembled. Bolts of slightly greater grip length may be used, provided washers are placed under the nut or bolthead. The maximum combined height of washers that should be used is 1/8 inch. This limits the use of washers necessary to compensate for grip, up to the next standard grip size.

Over the years, some fasteners' specifications have been changed. For this reason, it is recommended when making repairs to an aircraft, whose original hardware is being replaced, that you must first measure the bolt before ordering. rather than relying on the parts manual for identification. In the case of plate nuts, if proper bolt grip length is not available, add shims under the plate. All bolt installations which involve self-locking or plain nuts should have at least one thread of the bolt protruding through the nut.

Torque control equipment.

The importance of correct torque application cannot be overemphasised. Undertorque can result in unnecessary wear of nuts and bolts, as well as the parts they secure. Overtorque can cause failure from overstressing the threaded area. Uneven or additional loads that are applied to the assembly may result in wear or premature failure. Be sure that the torque applied is for the size of the bolt shank not the wrench size.

Add the friction drag torque to the desired torque. This is referred to as "final torque," which should register on the indicator or setting for snap-over type torque wrenches. Many applications of bolts in aircraft/engines require stretch checks prior to reuse. This requirement is due primarily to bolt stretching caused by overtorquing.

Replacement parts in aero engines and gearboxes.

CNC machining of engine replacement parts must be part 21 approved. Serviceable parts originate from the engine manufacturer, authorised service facilities, or facilities with FAA parts manufacture approval PMA or technical standards order TSO. The alternative is airworthy certified used parts.