Operations to flatten surfaces, make holes, and cut threads Figure Machining tools include drill presses, bandsaws, lathes, and milling machines.
Each tool is based on the principle of removing unwanted material from a workpiece using the cutting action of sharpened blades.
(i) Drill press:
The drill press shown in the Figure is used to bore round holes into a workpiece. A drill bit is held in the rotating chuck, and, as a machinist turns the pilot wheel, the bit is lowered into the workpiece’s surface.
As should be the case whenever metal is machined, the point where the bit cuts into the workpiece are lubricated.
The oil reduces friction and helps remove heat from the cutting region.
For safety reasons, visas and clamps are used to hold the workpiece securely and to prevent material from shifting unexpectedly.
It is recommended to use a smaller pilot hole before drilling the final one if the hole is large. This increases the accuracy of the hole and allows the bits to last longer.
When drilling through the hole, make sure the bit will not drill into the table after drilling through the work.
(ii) Band saw:
A machinist uses a band saw to make rough cuts through metal figures The blade is a long, continuous loop with sharp teeth on one edge, and it rides on the drive and idler wheels.
A variable-speed motor enables the operator to adjust the blade’s speed depending on the type and thickness of the material being cut.
The workpiece is supported on a table that is capable of being tilted for cuts that are to be made at an angle.
The machinist feeds the workpiece into the blade and guides it by hand to make straight or slightly curved cuts.
When the blade becomes dull and needs to be replaced or if it breaks, the bandsaw’s internal blade grinder and welder are used to clean up the blade’s ends, connect them, and reform a loop.
(iii) Milling machine:
A milling machine (or mill) is used for machining the rough surfaces of a workpiece flat and smooth and for cutting slots, grooves, and holes Figure The milling machine is a versatile machine tool in which the workpiece is moved slowly relative to a rotating cutting tool.
The workpiece is held by a vies on an adjustable table so that the part can be accurately moved in three directions (along the plane of the table and perpendicular to it) to locate the workpiece precisely beneath the cutting bit.
A piece of the metal plate might be cut first to an approximate shape with a bandsaw, and then the milling machine could be used to form the surfaces smooth and the edges square to their final dimensions.
In this type of operation, the workpiece is used to feed against the cutting tool which makes the high rotational speed at a fixed centre.
In this type of machining operation, there are different types of cutters used in milling operations, and in the cutting tools of the milling machine, the number of teeth on it depends on the circumference of the cutting tool.