Fasteners

Mr BILLINGTON

Joining Methods - Fasteners

Materials can be joined together by fasteners which can be both permanent and non-permanent. Fixings are stock components that are not designed specifically for one product or application

Nails are the simplist form of fastener. The 'wire nail' consists of a metal straight shank with a flattened head at one end & a sharpened point on the other. They are typically only used for timber applications and are driven into a work piece by impact force using a hammer or nail gun. The head of the nail prevents them fully penetrating the material unless a nail punch is used to conceal the head flush with the material. Typically, wire nails are manufactured from steel and available with a range of coatings to resist corrosion or improve adhesion

Although simple, they are a weak joining method that only rely on friction for strength and can loosen over time. Other common types of nail are; panel pins, tacks, lost head nails, clasp nails, staples etc.

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Screws are a type of non-permanent fastener, characterised by having a helical spiral down a tapered shank, known as a thread. The threaded shank has a cutting edge which binds into the material as it is rotated. A wider head prevents the screw from going past the surface of material, as with the nail, and a screwdriver is used to drive it into the material. To allow for rotation, a female profile is cut into the head of the screw to mate with a corresponding male profile at the end of the screwdriver

Screws are suitable for timbers, polymers & metals in differing forms;

Wood Screws - often require a pilot hole, smaller than the diameter, to be drilled into the timber to locate the screw and prevent it splitting the material. As they are rotated, the thread binds into the grain of the timber and pulls itself into the surface. The head of the screw can be countersunk to be flush with the face of the material or rounded to sit on top. Typically, a slotted, cross-slot (phillips) or Pozidrive head profile is used, with latter suiting higher torque

Self-tapping Screws - have a hardened thread that is designed to cut (tap) into the material, typically hardened plastic or metal. The thread typically is cut down the whole shank and often features a gap known as a flute, which removes material as it cuts to form a threaded hole. Typically, no pilot hole is required for softer materials due to the sharp cutting tip, although Type B screws have a blunt end and do for use with metals

Machine Screws - have a straight, tightly threaded shank, that is designed to bind with a tapped female threaded hole in metal. The screws are typically smaller diameters and come in range of head profiles for different purposes such as for tamper proof/security

Bolts have a straight, threaded shank that is designed to hold unthreaded material together using a clamping force via washers & nuts. Typically, the shank of a bolt is only threaded at the end for the washer/nut assembly, & unthreaded to around the depth of the materials to be joined. The head is often hexagonal to be tightened using a spanner, although sometimes a profile is cut for an Allen key or screwdriver to be used. The washer increases the clamping force on the surface of the material by distributing the load

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Threading is a technique where a a thread can be cut into a material, typically metal, either externally (threading) or internally (tapping). The process uses a hardened steel cutting edge with the inverse of the thread helix intended to be cut;

Tap - (female) are used to cut an internal thread, typically in combination with a wrench, which clamps around the end to allow for rotation. A flute is cut along the length of the tap to allow for the removal of material, known as swarf, from the hole. In order to cut most threads, an Intermediate tap is used which has a slightly tapered shank to allow for less aggressive cutting into the material. A bottoming tap is then used for blind holes in order for the thread to be cut to the to the bottom

Die - (male) are used for external threads into cylindrical material. Cutting discs can be adjustable for wear or fixed in diameter and are typically held in a two handled holder for easy rotation. A chamfer on the cutting edge allows the die to initiate the thread and once started it naturally follows the length of the work piece. Importantly, a two turns forward and one turn back technique should be used to release swarf from the die