Machine Shop Practice

In machine shop practice we use various machine tools. The late, drilling machine, planer, shaper, milling machine, and grinding machine are the basic machines. 

The lathe turns cylindrical shapes. In turning, the workpiece rotates and the cutting tool feeds against the workpiece. The drilling machine makes holes. The planer and shaper produce flat surfaces. The milling machine cuts various shapes with rotary cutters. The grinding machine raises te precision of the workpiece and improves its surface finish.

Parts of a Lathe

The lathe is very common and useful in machine shop practice. It has five important parts; the bed, headstock, tailstock, carrige, and feed box.

The bed is the foundation member of the lathe. It is rigid in construction. The headstock, the tailstock and the carriage are all on the lathe bed. The feed box is below the headstock.

Milling Machines

In modern machine shop practice, we use milling machines instead of shapers.

There are a lot of types of milling machines. Most, however, are very similar. The column-and-knee type is the most common one.

In most knee-type milling machines, there are three possible table movements: longitudinal, crosswise, and vertical. In some there is also a rotary movement.

The three most common column-and-knee machines are the horizontal, vertical and universal. The horizontal machine consists of the following important parts: the column, knee, saddle table, overarm, spindle, etc.

Bearing and Lubrication

A machine consists of a lot of machine parts. The shaft is one of the most common and important parts.

Shafts rotate in some type of support. We call these supports bearings: Bearings keep the shafts steady.

There are various types of bearings, sleeve bearings, ball bearings, roller bearings, etc. We use different types of bearings for different purposes.

Friction gives movement resistance, and lubrication reduces friction. Proper lubrication protects the bearings and makes the movement smooth. Different types of bearings require different oils and grease. Low-speed bearings use grease and high-speed bearings require light oil. Grease gives some resistance to the movement.

Abrasive Machining

Grinding is a very important metal machining process. We have grinding machines in practically every machine shop. Not long ago, however, grinding was only a precision process. We used grinding machines only to smooth and finish a workpiece.

Now we also use grinding machines to remove metal and to shape the workpiece. People call this process abrasive machining. Abrasive machines use both grinding wheels and abrasive belts.

Abrasive machinig is a new method of grinding. It came into use only a few years ago. Abrasive machining has some advantages over other machining processes. It removes metal at high speed and the machining cost is low. The abrasive machine requires fewer fixtures and performs both rough and finish cutting.

Machine Elements

A machine consists of a number of machine elements. The most useful machine element in power transmission is the gear. The gear is virtually a wheel with a number of teeth. Gears must work in pairs. A pair of gears with different number of teeth will increase or decrease the speed of rotation.

Pulleys and belts are very common in power transmission. They can also change speeds on machine tools. Gears or pulleys rotate on shafts. The shaft must rest in bearings. Sometimes there may be couplings between shafts. We may use clutches to start or stop shaft motion.

Some machine elements may be very large. Others may be very small. However, each of them plays a part in the construction of a machine.