Lathes are machines used for shaping various materials, usually, but not limited to, metals or wood.

This is the first of two articles looking at Woodturning Lathes and how they work to enable you (well, me anyway) to shape pieces of wood into highly desirable objects that people want to buy or which can be given away to family, friends, neighbours or indeed anyone at all prepared to take them off your (my) hands.

The idea of the lathe is, of course, to cause the workpiece to rotate in a controlled manner in order to allow you to cut away the wood that you don't want and leave the bits that you do. So how does a lathe do that?

It needs a motor and a means of controlling the speed of rotation, a means of coupling the workpiece to the motor, a toolrest to prevent the cutting tools from being rotated with the wood – and of course, the cutting tools themselves.

The component parts of a lathe are the Bed, the Headstock, the Tailstock and the Toolrest - and all are engineered to a high standard.

In this article we're looking at the Bed and the Headstock.

This is fixed to a rigid metal sub-frame, which should itself be securely fixed to a stand or a sturdy bench.

The bed itself is sometimes a substantial, polished steel cylinder some 3" (75mm) or so in diameter or it may be two parallel cylinders of a smaller diameter.

More usually it is a pair of parallel steel tubes, rectangular in section, with the appropriate surfaces finely ground for accuracy and ease of sliding the tailstock and toolrest to their required positions.

This is firmly fixed to the left-hand end of the bed (as you stand in the working position). As the motor turns, the top of the workpiece is moving towards you, and the surface nearest you is moving down (onto the tool).

It consists of a framework (substantial, of course) with two bearings at an appropriate distance apart, say 6" to 10" (150 - 250mm), for rigidity. The drive shaft is fixed through, to and between them, perfectly aligned with the longitudinal centre of the bed.

The motor is at the outboard end of the headstock, leaving the inboard end (over the bed) clear for working.

The motor is usually offset from the line of the drive shaft, turning the protruding end of it via a system of gearing pulleys, thus allowing the workpiece to be rotated at various speeds (the motor speed will be far, far too fast if directly fixed (despite that comment, there are a few lathes that do have so-called direct drive, – their motors are controlled by some heavy duty electronics).

More modern lathes may have electronic speed control but even there, two speed ranges, pulley-driven, are common as it's not easy to apply full power at low speeds.

The protruding inboard end (over the work area of the bed) of the drive shaft carries both a male screw thread and, inside it, a concentric female tapered round socket that mates with a suitable spindle.

The screw thread can be used with a faceplate, which is a flat plate with a boss at its centre machined with a mating female thread. Holes are drilled in various positions around the plate for screwing through and fixing a workpiece to it.

The screw thread is also used, separately, with a chuck – for chuck, think electric drill – the mechanism on the business end that holds a drill or screwdriver bit.

The tapered round socket and the mating tapered spindle are machined and ground precisely to a particular shape called a Morse Taper. They come in various sizes, from (smallest) 1 up to 7, of which the first three are used on woodlathes and the most common for our use is the second - called MT2 or 2MT.

The reason for a taper? For bowl turning, we want a way of driving a workpiece, in order to shape it in such a way as to prepare it for mounting in the chuck. A straight shaft, no matter how finely fitted to its mating socket will slide and turn without transmitting any power.

The taper allows tight fitting with virtually no slide. It fits quickly and can be removed with a tap or two from a removal bar inserted from behind, through the hollow drive shaft. That bar slides easily, is quite heavy and is commonly called a Drift (to 'drift' it out rather than hammer it out).

The morse taper has two main uses:

• To enable the workpiece to be driven when turning spindles (longer than they are wide) in which case a Spur Drive is used. This is a conical point surrounded by four radial sharp edges that bite into the end of a workpiece, the other end of it being supported at the Tailstock.
• It can also be used to carry a Jacob's Chuck (usually rather larger than the variety found on an electric drill).

The distance between drive shaft and bed will, of course, determine the absolute maximum diameter of the workpiece. This is usually around, say, 12 to 18" / 300 - 500mm.

Some more robustly made lathes allow the headstock to swivel, turning the drive sideways towards you and allowing a greater diameter of workpiece – using an extra means of holding the toolrest.

Here endeth the first article. Next time we'll look at the Tailstock and the Toolrest.

Articles by Rod

20.09.10 Front Page

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