Lathe fixtures are the special type of workholding devices that are used to mount the job which cannot be easily mounted on the standard work holding devices like chucks, collets, mandrels, faceplates, etc.
It also consists of an arrangement for locating and fastening the fixture rigidly and accurately within a metal lathe.
In a metal lathe, the fixtures are mounted either in a chuck or a face plate.
The lathe fixture mounted in a chuck is shown in the below image.
Similarly, the image shown below is of a lathe fixture for boring that is mounted by using a faceplate.
In the above image, you can see that the workpiece is mounted on the faceplate and two holes are required to be bored.
For accurate mounting of the fixture on the faceplate, the slots are provided on the faceplate.
The counter weight is also provided on the faceplate that balances the weight of the workpiece during the machining process of the workpiece.
The counter weight provided on the faceplate has the mass equal to the mass of the workpiece that is off-center.
Why are lathe fixtures needed?
Generally, it is very easy to mount the regular shaped workpiece in the standard workholding devices like lathe chuck, collets, centers, mandrels, faceplates, etc.
There is no need for lathe fixtures if the job can easily be mounted with the above workholding devices.
But there are various jobs that have different shapes (which are generally manufactured by casting or forging). So for such types of jobs, the mounting becomes difficult in the above-mentioned workholding devices.
Hence the lathe fixtures are needed to easily hold the workpiece having unusual shapes.
How to design lathe fixtures (or turning fixtures)?
For designing a lathe fixture, the following major points should be considered.
- The lathe fixtures should be lighter in weight as it rotates during the machining process.
- The size of the fixtures should be small, otherwise it will touch the lathe bed.
- The counter balance weight should be provided with the fixture which helps in reducing the vibrations during the rotation of the fixture.
- The constitution of a turning fixture should be such that the effect of centrifugal forces is minimised.
- While designing the turning fixtures, the design should be such that the overhanging part is less, so that its bending can be avoided.