Speaker notes The elements of the lathe are described below Headstock – This contains the gears or pulleys that allow the operator to change the speed of the spindle. Spindle – This is the rotating shaft that runs through the headstock and is often hollow to allow bar to be feed through the headstock. The workholding devices are held on to the spindle. Lathe bed and slideway – This is the backbone of the machine that the saddle runs on, it is parallel to the spindle axis. It can engage with the lead screw to cut threads and often has a power feed as well. Saddle – Supports the crosslide and allows the cutting tool to move along the spindle axis. Cross slide – This is mounted on the saddle and moves 90 to the spindle axis, it is used for facing off or for changing the depth of cut. This often has a power feed. Compound slide – Fitted to the top slide and supports the tool post. It can also be swivelled to different angles to cut tapers and chamfers. Toolpost – Holds the cutting tool at the correct height firmly to allow machining to take place. Tailstock – This runs on the lathe bed slideway and is inline with the spindle axis, it has a barrel that can be moved in and out by the handwheel. It can be used to hold drills, drill chucks, dead centres and live centres. These are held in a tapered hole bored down the centre of the barrel called a Morse taper. Leadscrew – This is an accurate screw thread that is geared to the spindle and allows threads to be cut with a single point tool.
Speaker notes Before setting up work isolate the lathe from the power supply. The last method is the most accurate.
Speaker notes Information about the cutting tools that can be used on lathes can be found on page 195 of the Candidate Handbook.
Speaker notes Ask learners to investigate the different cutting speeds for different materials and tool types.
Speaker notes Remind learners that every time a workpiece is removed from the workholding device, accuracy is lost, even if you painstakingly clock the workpiece up again using a dial test indicator. A skilled operator should be able to machine to an accuracy of 0.02 mm.
Speaker notes Remind learners that as drills are harder to keep cool than external cutting tools, the cutting speeds are slightly slower.
Speaker notes For efficient boring: Use slow feed rates (0.03 mm/rev). Use only light cuts (0.3 mm to 0.5 mm at a time). Remember to turn the cross slide handle anti-clockwise to remove metal. If the tools does chatter, try sticking a small weight on the tool near the tip. Use a Vernier height gauge or scribing block to transfer the height from the centre to the tool tip.
Speaker notes Learners should make sure that they never use hand reamers under power.
Speaker notes Remind learners that the tool has hardly any lateral strength and cuts along the axis of the machine should not be attempted.
Speaker notes Remind learners form tools are not easy tools to use, as there is often a wide cutting edge in contact with the workpiece that can cause the tool to be overloaded. Low lathe speeds should be selected when using form tools to prevent heat build up and the tool snatching.
Speaker notes Remind learners to make sure the knurling tool is dead square and on centre height and the workpiece securely held.
Speaker notes Remind learners about checking work and carrying out quality checks – information about the tools that can be used for this can be found in the Chapter 4 Powerpoint.