What is the centre lathe, what are its main parts, and what turning operations can it carry out on metal?
The centre lathe: its main parts (headstock, chuck, tailstock, carriage, cross-slide and tool post) and the operations it performs - facing, parallel turning, parting, chamfering and knurling.
How SQA National 5 Practical Metalworking covers the centre lathe: its main parts (headstock, chuck, tailstock, carriage, cross-slide, tool post) and the turning operations it carries out - facing, parallel turning, parting, chamfering and knurling - done safely and accurately.
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What this dot point is asking
The centre lathe is the main machine tool in the workshop. The SQA expects you to name its main parts, know what the turning operations are (facing, parallel turning, parting, chamfering, knurling) and describe how each is carried out safely and accurately. The skill is applied in the practical activity and sampled by the case study.
The main parts of the centre lathe
Knowing which slide moves in which direction is the key to describing operations: the carriage gives movement along the length, the cross-slide gives movement across.
The turning operations
- Facing: the tool is fed across the end of the bar with the cross-slide to leave the end flat and square to the axis. This gives a true end to measure from.
- Parallel turning: the tool is fed along the bar with the carriage at a set depth, reducing the diameter evenly along the length.
- Parting (parting off): a narrow parting tool is fed in with the cross-slide to cut the finished piece off the bar.
- Chamfering: the tool cuts a small bevel on a corner, to remove the sharp edge and help parts fit together.
- Knurling: a knurling tool rolls a diamond or straight pattern into the surface to make a textured grip (for example on a handle).
Working accurately and safely
Try this
Q1. Name the part of the lathe that grips and spins the workpiece. [1 mark]
- Cue. The chuck (driven by the headstock).
Q2. State which operation cuts the end of a bar flat and square. [1 mark]
- Cue. Facing.
Q3. Explain what knurling produces and why it is used. [2 marks]
- Cue. It rolls a textured pattern into the surface to make a grip, for example on a handle or knob.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA-style Describe4 marksA steel bar is held in the lathe chuck. Describe how you would face the end and then turn it down to a smaller, parallel diameter.Show worked answer →
Award up to 4 marks, 1 per correct stage. Hold the bar securely in the chuck so it runs true and does not stick out too far, then remove the chuck key (1). To face the end, set the cutting tool on the centre height and feed it across the end of the bar using the cross-slide, taking a small cut so the end is left flat and square to the axis (1). To turn it parallel, set the depth of cut with the cross-slide, then feed the tool along the length of the bar using the carriage (saddle), so it removes a parallel layer and reduces the diameter evenly (1). Take light cuts at the correct speed, use cutting fluid, and check the diameter with a rule or callipers (1). A strong answer links facing to the cross-slide and parallel turning to the carriage feed.
SQA-style Explain3 marksExplain the difference between facing and parallel turning on the centre lathe, and name the part that feeds the tool in each case.Show worked answer →
Award up to 3 marks. Facing cuts the end of the bar flat and square to the axis; the tool is fed across the end using the cross-slide, which moves at right angles to the bar (1). Parallel turning reduces the diameter along the length of the bar; the tool is fed along the bar using the carriage (saddle), which moves parallel to the axis (1). A third mark is given for a clear extra point, such as that facing gives a true datum end to measure from before turning, or that both leave a smaller, accurately sized workpiece (1).
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