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…

Hard Soldering an Alternative to Brazing

Hard soldering (silver soldering) is an alternative to brazing. It specially implies the use of the filler materials containing silver, which have lower melting point than brazing spelter and therefore associated with greater ductility and often greater strength. Hard soldering is general term used to cover brazing and silver soldering. However, hard soldering can be defined as an intermediate stage between low temperature soft soldering and high temperature brazing.



The operation of brazing and hard soldering are almost identical and the two terms are used synonymously. Hard soldering normally means silver soldering, which has a lower melting temperature than brazing. Silver soldering is used principally for fine work and in case where joint is required to be stronger than soft soldering, but where, at the same time it is not desirable to raise the work to the brazing temperature.



Groups of Hard Solders



Hard solders can be divided into following two groups:



(a) Low Temperature Silver Brazing Alloys.  These contain copper, zinc and cadmium with up to 50% silver and have a melting point ranging from 6000C - 8000C. These alloys are used for most general engineering applications where strength is required.



(b) Silver Solders. Silver solders contain silver from 50 to 80%, copper up to 30% and zinc up to 20%. These have a melting point ranging from 700°C to 780°C. These are known as hard, medium or easy grade solders. Hard grade consists of 80% silver and 20% copper. Medium grade consists of 75% silver, 20% copper and 5% zinc. Easy grade consists of 50% silver, 30% Copper and 20% Zinc. Since all silver solders look alike, it is usual to scratch the whole length of solder bar as per markings.



Composition and Melting Temperature of Silver Solder



The various compositions and their respective melting points are given in the table below:



Composition and Melting Temperature of Silver Solder

































CompositionMelting Range (in 0C) 

Uses
ElementPercentage
Silver

Copper

Zinc

Cadmium
49 - 51

14 - 16

15 - 17

18 - 20
620-640Very fluid and easy to use (Grade C)
Silver

Copper

Zinc
60 - 62

27.5 - 29.5

9-11
690-735Particularly suitable for electric work (Grade A)
Silver

Copper

Zinc
42-44

33-38

18.5-20.5
700-775Used for general engineering work




Silver Soldering Procedure



The procedure to carry out silver soldering is as follows:



(a) The joint gaps for silver soldering should be between 0.05 mm and 0.15 mm.



(b) The parts must be clean and fit properly.



(c) Flux and secure the parts. Borax is the suitable flux.



(d) Heat the parts slowly.



(e) Apply the solder.



(f) Allow the parts to cool down.



(g) Cut and remove binding wire.



(h) Pickle the parts in caustic soda solution.

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