Turning materials is one of the earliest machine tool activities. The process involves rotating material against a moving single point cutting tool to create parallel, cylindrical and tapered forms.
The main machine tool for turning is a lathe. Lathes for production work are generally automated or CNC controlled and have materials bar fed to the chuck rather than being loaded manually. When turning, material (wood, metal, plastic, or ceramic materials) is rotated and a cutting tool is moved along 2 axes of motion.
The main turning processes are:
Parallel turning – where the tool path is parallel to the work on the outside produce precise diameters and depths and forms. Alternatively inside the of the bar or work piece can be turned called boring to produce tubular components.
Taper turning – Taper turning is when the tool is moved in two axes at an angle to the centre line of the workpiece and the machine to create a conical taper or point. It requires a special toolpost (compound slide), offsetting the tailstock that supports a longer workpiece and turning it between centres or taper turning attachment to achieve this.
Facing off and parting off grooving – this is when the tool is moved at right angles to the material: Either across the face or end of the bar to achieve a flat smooth face or with a thinner parting tool to cut right through and create a ‘finished’ component. A similar grooving tool is used to create grooves on a turned component that can locate washers, seals or circlips.
Form tools can be pre-ground to create suitable shapes eg: spheres and ball ends. Alternatively
a) using hydraulic copy attachment
b) C.N.C. (computer numerically controlled)
Each group of materials to be turned has an optimum set of tool or cutting angles.
The work piece to be machined will usually be either raw material in rolled, drawn or extruded stock form. Or will be a forging, casting or part machined component from another process.
i.e. the machining of internal cylindrical forms (generating) a) by mounting workpiece to the spindle via a chuck or faceplate b) by mounting workpiece onto the cross slide and placing cutting tool into the chuck. This work is suitable for castings that are to awkward to mount in the face plate. On long bed lathes large workpiece can be bolted to a fixture on the bed and a shaft passed between two lugs on the workpiece and these lugs can be bored out to size.
Is used to remove material from the inside of a workpiece to create a hole through or part through. This process utilizes standard drill bits held stationary in the tail stock or tool turret of the lathe.
This is the process of pressing and cutting of a serrated pattern onto the surface of a part to use as a hand grip using a special purpose knurling tool.
Reaming and Broaching
Creating smooth accurate bores with a drill is not normally possible as the helix and cutting edge/lands and tip create spiral witness marks down the bore. Using reamers after drilling ensures bore dimensions and tolerances are kept and a smooth or oil bearing wall is created. This is done at a slower speed than drilling.
Screw threads can be turned on a lathe using a cutting tool. Usually having a 60, or 55° nose angle, these often are for single-point threading. This is done using hand taps and tailstock centre, or, alternatively using a tapping device. These often have a slipping clutch to reduce risk of breakage of the tap. Tapping can also performed on a drill press.
External and internal thread forms can be cut as well as taper threads, double start threads, multi start threads and worms.