In jigs and fixtures the workpiece or blank has to be strongly and rigidly clamped against the supporting surfaces and also the locating features so that the blank does not get displaced at all under the cutting forces during machining

While designing for clamping the following factors essentially need to be considered:

• clamping need to be strong and rigid enough to hold the blank firmly during machining clamping should be easy, quick and consistently adequate
• clamping should be such that it is not affected by vibration, chatter or heavy pressure the way of clamping and unclamping should not hinder loading and unloading the blank in the jig or fixture
• the clamp and clamping force must not damage or deform the workpiece
• clamping operation should be very simple and quick acting when the jig or fixture is to be used more frequently and for large volume of work
• clamps, which move by slide or slip or tend to do so during applying clamping forces, should be avoided
• clamping system should comprise of less number of parts for ease of design, operation and maintenance
• the wearing parts should be hard or hardened and also be easily replaceable
• clamping force should act on heavy part(s) and against supporting and locating surfaces
• clamping force should be away from the machining thrust forces
• clamping method should be fool proof and safe
• clamping must be reliable but also inexpensive

Various methods of clamping

Clamping method and system are basically of two categories:

(a) General type without much consideration on speed of clamping operations

(b) Quick acting types

(a) General clamping methods of common use:

• Screw operated strap clamps as typically shown in Fig.
• The clamping end of the strap is pressed against a spring which enables quick unclamping

Common strap type clamping.

• Clamping from side for unobstructed through machining (like milling, plaining and broaching) of the top surface. Some commonly used such clamping are shown in Fig

Clamping from side for free machining of the top surface

Clamping by swing plates

Such clamping, typically shown in Fig, are simple and relatively quick in operation but is suitable for jobs of relatively smaller size, simpler shape and requiring lesser clamping forces.

Other conventional clamping methods include:

• Vices like drilling and milling vices.
• Magnetic chucks

• Chucks and collets for lathe work

  Quick clamping methods and systems

  Use of quick acting nut :– a typical of such nut and its application is visualised schematically in Fig

Quick acting nut for rapid clamping.

Cam clamping

• Quick clamping by cam is very effective and very simple in operation.
• Some popular methods and systems of clamping by cam are shown in Fig
• The cam and screw type clamping system is used for clamping through some interior parts where other simple system will not have access.

Quick clamping by cams

• Quick multiple clamping by pivoted clamps in series and parallel. This method shown in Fig. is capable to simultaneously clamp number of rods even with slight diameter variation
• Quick clamping by hydraulic and pneumatic force for strong and light clamping respectively
• Light but quick clamping by bayonet type clamp as indicated in Fig.