Mr P Mulholland AS Design and Technology St Joseph’s HS Crossmaglen Components Part 1 Mr P Mulholland AS Design and Technology St Joseph’s HS Crossmaglen

Components It is generally economically viable for manufacturers to ‘buy in’ standard components from suppliers. A Kettle Manufacturer The kettle manufacturers business is to design and manufacture kettles. While volume of output will be high the company is not in the business of making all the components to build the kettle. As a result the company will ‘buy in’ standard components.

Nuts and Bolts

Nuts and Bolts Made from low or medium carbon steel. Sometimes they are also made from high tensile steel, alloy steel or stainless steel and in some cases they are galvanised for protection against corrosion. The advantage of using nuts and bolts is that they can be easily undone. This allows components to be replaced or repaired. A nut is a collar and must fit the bolt with the same thread form and it should be of the same thread diameter. Nuts can be hexagonal or square in shape and are normally forged with a chamfer cut on one or both faces.

Screw Thread Forms Page 36 Edexcel Text Book There are several different types of screw thread each used for a specific purpose but they basically have three main uses: Converting rotary to linear motion. Obtaining a mechanical advantage. Fastenings. Screw threads have four basic forms: V- thread Square thread. Buttress thread. Acme thread

Screw Thread Forms

Thread Forms V- thread Square thread Buttress thread Acme thread General purpose Fastenings Nuts and bolts Square thread Allows large forces to be applied and is used in vices and cramps Buttress thread Used when force needs to be applied in one direction, such as woodwork vices Used with quick-release mechanisms Acme thread Used on a centre lathe where the engaging nut must clamped onto a rotating shaft This allows the tool post to move automatically along the lathe bed

Cutting Threads

Cutting Threads in Holes Internal Screw Thread Process is called tapping. To cut an internal screw thread a tap an tap wrench are needed. The tapping hole diameter is found by subtracting the depth of the thread from the outside diameter of the bolt or machine screw. Example Produce a thread in a hole for an M5 bolt. Drill hole with a 4.2mm drill bit. Depth of thread is 0.8mm.

Cutting Threads in Holes Internal Screw Thread Process Drill hole in piece of material Apply lubricant to reduce friction Place taper tap in the tap wrench to cut the screw thread Cut the thread carefully by turning the tap slowly through half a turn clockwise and then a quarter turn anticlockwise to break off the swarf. Repeat the process with the intermediate tap. Repeat the process with the plug tap. It is important to make sure that the tap is at right angles to the metal. If no the thread will not be cut straight and the screw will appear wobbly when screwed in.

Cutting Threads on a Rod External Screw Thread A thread can be cut on a rod by hand. To cut an external screw thread a die and a die stock holder are needed. Various sizes of dies are available. The die is matched to the diameter of the rod/bar. To cut a thread on a 10mm rod a 10mm die is required.

Cutting Threads on a Rod External Screw Thread Process Chamfer the end of the rod to be threaded Select die to be used, put die into die stock holder Apply lubricant to reduce friction Screw the die onto the rod Cut the thread carefully by turning the die slowly through half a turn clockwise and then a quarter turn anticlockwise to break off the swarf. Make sure the die goes onto the workpiece squarely to cut the threads properly. If this is not done a drunk thread will be produced. This means the nut will appear wobbly when screwed onto the thread.

Spacers and Washers Spacers and washers are sometimes used in machinery. Spacers are used when components need to be separated on an a shaft, e.g. on bicycle gears where it is necessary to space the gears. Spacers are available in a range of materials including HDPE, nylon and steel. Washers can be used as spacers, anti- vibration and locking devices.

Spacers and Washers Spacers Washers

Machine Screws Have parallel sides with threads cut into them Generally made from carbon steel Mass produced

Machine Screws Two main types: Countersunk Head Cheese Head Designed to fit into countersunk holes Allows head of machine screw to sit flush with the surface of the material into which it is being screwed Cheese Head A cylindrical shape Sits above the material into which it is being screwed

Wood Screws Available in three different types: Countersink Head – allow the screw to be flush with the surface Raised Head – similar to countersunk except the head is slightly domed/rounded Round Head – designed to rest on the surface of the wood