This is the second article in an occasional series (and the last for a while, looking at the Lathe).
Lathes are machines used for shaping various materials, usually but not limited to, metals or wood.
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.
Last time, we described the Bed and the Headstock.
This time it's the turn of the Tailstock and the Toolrest assembly.
A future article will address the tools. After that, if you're lucky, we'll look at accessories, useful machinery ... etcetera.
This, like the headstock, holds a shaft that's hollow and is machined out with a morse taper on the inboard end (over the bed). This shaft is at exactly the same height above the bed as the headstock drive shaft.
- Note that this height is the absolute maximum radius of a workpiece.
- Note also that it is not achievable in practice, as your workpiece will need to rotate before you commence cutting. Bits of trees don't come as perfectly round lumps – you couldn't mark and mount it to that degree of accuracy anyway. In practice, the stickiest-out bit of your lump of wood will be something less than this (comfortably less – trust me).
The taper is most often used to hold a point, a Centre, to support the tail end of a workpiece. Nowadays a Dead Centre (one that doesn't rotate) is rare, usually found only at flea markets, so the Live Centre is most probably the type you'll use – one with ball bearings, that rotates freely with the workpiece.
The taper can also hold, for example, a jacob's chuck when used for drilling into the centre of a workpiece – the lathe does the turning at the headstock, of course.
The tailstock can be slid to any position along the bed, is aligned with the headstock and has a handle on a screw thread to wind the centre point a little way into the end of a workpiece to support it.
When clamped in position, the shaft, the taper and the centre are perfectly aligned with the headstock drive shaft – horizontally, vertically and longitudinally.
It may be worth noting that slight misalignment is not important to between centre turning, as the workpiece is held essentially between two points (the spur drive would accommodate a slight offset) and your cuts are with reference to the spindle axis – which is still a straight line of course.
However, it would have importance when faceplate or bowl turning if, as is good practise, you support even moderate size workpieces with the tailstock during initial preparatory cuts. Because the workpiece is held firmly (to the drive shaft, via chuck or faceplate) any misalignment would try to mark a circle on it as you advance the centre – and cause vibration and extra wear on bearings if you were to actually wind it in. In the extreme, well, it'd be a case of no expense spared.
This is held in an assembly (often called the Banjo) that is moveable along the bed and clamped in a position appropriate to the current operation.
The banjo supports the rest itself, which is a rigid, rigidly clamped T-shaped bar on which to rest a tool so that its cutting edge is not dragged around by the spinning workpiece.
The banjo is different from the head and tail stocks in that it can slide not only along but across the bed, by a distance equal to a little more than that between the axis of rotation and the maximum radius of a workpiece, so that the toolrest can be adjusted to an appropriate position to suit any diameter.
Held in and clamped by the banjo, the toolrest is adjustable vertically within the banjo and can be twisted – it's the leg of the T that's clamped – to suit immediate needs. It is aligned by eye at the appropriate height and distance from the workpiece – aligned along the bed for between centre (or spindle) turning or across the bed for faceplate or bowl turning – or indeed at any appropriate angle between.
The toolrest is, generally, a straight bar between say 4" (100mm) and 12" (300mm) long, of various cross-section shapes. There aren't many rests longer than that because considerable downward force can be exerted if the tool catches – and the further from the centre support, the greater the effect of that force. Some special rests are curved in S or reverse S shapes to help with cutting bowls but all have straight, flat top surfaces, parallel with the bed.
That then, is the Lathe.
In due course it'll be the turn of the tools to get some attention.
It isn't easy to find sound, clear information for beginners, on non-commercial websites, but as good a place as any to start is: wood turning lathe
where the advice is sound.
On commercial sites illustrations there are aplenty, though not many large clear pictures – you're expected to know already. Just search Wood turning ~Lathes, ~Clubs etc. You'd be welcomed at any club.
You might also try the NZ National Association of Woodworkers website.
The gallery has some stuff to show off about.
Having now set you all searching to find out where I've gone wrong, here's something that might distract you:
Try searching for "VB36 Lathe" (without the quotes). You may find it interesting.
If you're a technical type you may want to read – or at least scan as you go – the design criteria, specifications and the realisation thereof. Fascinating stuff. (There's no ruling against drooling, so indulge yourself – I do.)
I well remember being allowed to join a queue to file past one of these things, at an exhibition – if I promised to doff my hat.
No, really folks, in fact I have stood by one and gone through the motions – but didn't get to try it for real because the demonstrator, too, was out to lunch and later I couldn't get near it.
They seem to advertise, small-wise, only in relevant magazines – there's need do no more.
Don't bother looking for a second-hand one as seemingly there's no such thing lasting more than a few minutes.
Not bad value either, for a mere, oh, £600 or so is it? ... (whisper: as a 10% deposit).
Now THAT's a lathe.Rod