Lathe Operations: Facing

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…

Advantages, Disadvantages, Precautions in Brazing

Advantages of Brazing

Following are the advantages of brazing:

(a) Brazing is used to join a large variety of dissimilar metals.

(b) Properly brazed joints are pressure tight.

(c) Pieces having great difference in cross-sectional areas can be brazed.

(d) Thin sheets, pipes and gauges that can't be joined by welding can be joined by brazing.

(e) Complex assemblies can be fabricated by this method.

(f) A brazed component has ability to preserve protective metal coating.

(g) Brazing can be done on cast and wrought materials.

(h) Corrosion resistance joints can be produced by this method.

(j) Brazing preserves metallurgical characteristics of a material better than welding.

(k) After brazing a component maintains more precision tolerances than welding.

(l) Brazing processes can be automated for bulk production.

(m) Non-metals can be joined to metals.

Disadvantages of Brazing

Following are the disadvantages of brazing:

(a) It requires tightly mating parts.

(b) It requires proper cleaning.

(c) Size of the job is limited.

(d) Joints are not successful at elevated temperatures.

(e) Colour of the filler metal may not match with that of the base metal.

Precautions in Brazing

Following points are to be adhered while brazing:

(a) Properly clean the joints so that it doesn't contain harmful elements.

(b) Use the right flux in an optimal quantity.

(c) Use proper spelter in a minimum quantity.

(d) The joint must be reasonably tight.

(e) Apply correct heat to work piece and solder.

(f) Avoid prolonged heating.

(g) Use proper atmosphere.

(h) Heat the work pieces to uniform temperature.

Difference between Brazing and Welding

(a) Surfaces to be brazed aren't raised to fusion point.(a) Surfaces to be welded are raised to fusion point.
(b) Brazed joints aren't so strong.(b) Welded joints are very strong.
(c) Brazing alloy spreads by capillary action.(c) The weld solidifies almost at the same place where it melts.
(d) Dissimilar metals can be joined.(d) Generally similar metals are joined.
(e) Brazing temperatures are low.(e) Welding temperatures are high.
(f) Components maintain more precision tolerance.(f) Components maintain less precision tolerance.


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