Lathe Operations: Facing

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Facing Operations Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end. Cutting Speeds

If you read many books on machining you will find a lot of information about the correct cutting speed for the movement of the cutting tool in relation to the workpiece. You must consider the rotational speed of the workpiece and the movement of the tool relative to the workpiece. Basically, the softer the metal the faster the cutting. D…

Brazing and Its Applications

Brazing is defined as a process of joining similar or dissimilar metals in which molten filler metal is drawn by capillary action into the space between closely adjacent surfaces of the parts to be joined.



In general, the melting point of the filler metal lies above 5000C but below the melting point of the parent metals being joined. The brazing alloy is often called spelter and can be plain brass (50% copper and 50% zinc). Increasing of the zinc content decreases the melting point of the spelter. Borax is used as a flux for brazing.



Brazing alloys containing phosphorus are referred as ‘self-fluxing brazing alloys’. These alloys contain silver, phosphorus and copper or copper and phosphorus. These alloys are very much in use for manufacturing refrigerator and electrical assemblies etc.



Applications of Brazing



There are various applications of brazing. Some of these are given below:



(a) Brazing is used for fastening of pipe fittings, tanks, carbide tips on tools, radiators, heat exchangers, electrical parts, axles, etc.



(b) It can join cast metals to wrought metals, dissimilar metals and also porous metal components.



(c) It is used to join band saws, parts of bicycle such as frame and rims.



Brazing Alloy: Composition and Melting Temperature



The brazing alloys are mainly of copper and zinc composition. The melting point of the alloy varies according to the percentage of copper and zinc. As the zinc percentage increases, melting point decreases.



Composition and Melting Temperature of Brazing Alloy
































































Percentage (%)Melting Temperature(C)
CopperZinc
10001083
9641075
86141032
7624980
7228957
7129952
68.433.6918
6337908
6040890
5050880




Brazing Equipment



Brazing Torch. A special torch is required for brazing. The usual type is supplied with main gas and air from a blower. It is fitted with adjustable taps for controlling the gas, air flow and mixture of gases.



Brazing Torch



Brazing Hearth. Brazing is best carried out in a hearth designed for the purpose. The hearth is made from steel lined with firebricks and has an electrically driven air blower mounted on it.



Brazing Hearths



Brazing Lamp. Brazing lamp is also known as blowlamp. It is used to heat up the parts to be soldered and for heating the common soldering iron. These are most often applicable to soft soldering, but are sometimes used for brazing with hard solders having a relatively low melting point (e.g. silver solders). These are available in many sizes (e.g. 1 pint, 2 pints, 5 pints etc.) as per their container capacity and are operated on kerosene. The use of inappropriate fuel deteriorates the operation of a blowlamp. The normal working pressure is 20/30 lb. per sq. in. The container should be filled upto maximum ¾th of its capacity with clean kerosene to accommodate the air pressure.

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