Mandrel is used for holding and rotating a hollow piece of work that has been previously drilled. The work is revolves with the mandrel, which is mounted between two center.
The mandrel should be true with accurate center holes for machining outer surface of the work piece concentric with its bore. To avoid the distortion and wear it is made of high carbon steel.
The end of mandrel is slightly smaller in diameter and flattened to provide effective gripping surface of the lathe dog set screw. The lathe dog and the catch plate rotate the mandrel and it is it drives the work by friction.
To secure the mandrel in the work and it is driven by a copper or lead or pressed by a special mandrel press.
The different types of mandrels are employed according to specific requirements.
- Plain mandrel
- Collar mandrel
- Step mandrel
- Screwed mandrel
- Gang mandrel
- Cone mandrel
- Expansion mandrel
The plain mandrel is most commonly used in shops and finds wide applications where large numbers of identical pieces having standard size holes are required to be mounted on it.
The body of the mandrel is slightly tapered and the difference in diameter being 1 to 2 mm per 100 mm length. The length varies from 55 to 430 mm the taper is provided for proper gripping of the work piece. Plane mandrel is suitable for only one size of bore.
For different sizes of holes in work pieces and different mandrels are used.
Collar mandrels having solid collars are used for turning work pieces having holes of larger diameter, usually above 100 mm. The construction reduces weight and fits better than a solid mandrel of equal size.
Step mandrel is having steps of different diameter may be employed to drive different work pieces are having different sizes of holes without replacing the mandrel each time. This type of mandrel is suitable for turning collars, washers and odd sized jobs used in repairing workshops.