The work should be held firmly on the machine table before performing any operation on it. As the drill exerts very high quantity of torque while rotating, the work should not be held by hand. If the workpiece is not held by a proper holding device, it will start rotating along with the tool causing injuries to the operator and damage to the machine.
The devices used for holding the work in a drilling machine are
Vise is one of the important devices used for holding workpices on a drilling machine table. The work is clamped in a vise between a fixed jaw and a movable jaw.
Parallel blocks are placed below the work so that the drill may completely pass through the work without damaging the table. Different types of vises are used for holding different types of work and for performing different operations.
The different types of vises are
- Plain vise
- Swivel vise
- Tilting vise
- Universal vise
‘T’ – Bolts and Clamps
The workpieces can be held directly on the machine table by means of ‘T’ – bolts and clamps. The top of the machine table has ‘T’ – slots into which ‘T’ – bolts may be fitted. The bolts of diameter 15 to 20mm are used. The clamps are made of mild steel. ‘T’ – bolts pass through a central hole on the clamp. The clamp is made to rest horizontally on the work surface by placing a suitable step block at the other end of the work.
Some of the common types of clamps are: Plain slot clamp, goose-neck clamp and finger clamp.
The step blocks are used in combination with ‘T’ – bolts and clamps for holding the work directly on the table. The step block supports the other end of the clamp. Workpieces of different heights are held by leveling the clamp on different steps of the step block.
‘V’ – Block
‘V’ – blocks are used for holding cylindrical workpieces. The work may be supported on two or three ‘V’ – blocks according to the length of the work. The work is held on the ‘V’ groove and is clamped by straps and bolts. They are made of cast iron or steel and are accurately machined.
Angle plates have two faces at right angle to each other and are made of cast iron. It resembles the English alphabet ‘L’. All the sides of a angle plate are machined accurately. Slots and holes are provided on both the faces of the angle plate. Work is clamped on one of its faces by means of bolts and nuts.
Drill jigs are used in mass production process. A jig is specially designed to hold the work securely and to guide the tool at any desired position. Holes may be drilled at the same relative positions on each of the identical workpieces.
The work is clamped and removed easily. The cost of making a drill jig is more but a low order of skill is sufficient to work with a drill jig.
Different types of drill jigs are
- Plate jig
- Box jig
- Channel jig
- Indexing jig.
- Diameter jig