What You Need to Know to Start Turning – More:
Mark Baker takes a look at holding work on the lathe securely.
Holding work securely is very important. Get this wrong and work can come loose and heaven forbid, come off the lathe when working. Not something one wishes to encounter I can assure you.
It’s best not to ask me how I know that. Anyway, chucks, drives and centres are the names of the items that are used to hold work securely on the lathe and there is a bewildering array one can buy. The easiest way of determining what’s needed is to break this down into the two styles of turning mentioned previously: faceplate turning and spindle turning.
Spindles are usually held initially between centres. There are two types of centres: headstock and tailstock centres. Headstock centres comprise drive centres, drive spurs or prong drives – of those, there are many
which fit in the headstock directly in the Morse-taper hole, in the threaded headstock spindle. The most often Morse-taper (MT) used on woodturning lathes to house the revolving centres and drives are either 1MT, a thin small taper and the most commonly used. 2MT is a thicker version of the 1MT. Some drive spurs are designed to be held in chuck jaws. All types are used to lock/bite into the timber to drive it round. They come in a variety of shapes and forms and usually with sharpened blades, teeth or rings to bite into the wood. The number of spurs/prongs is relevant as to how they might be labelled so you might have two or four prongs – a four prong-drive is the most common of this type. The bigger the work being used, the bigger the drive needs to be to drive it properly; 19–32mm are the most commonly used drive sizes and will suit most turner’s needs for the majority of things turned on a midi-sized lathe mentioned previously.
The other type of centres fit into Morse-taper holes drilled into the tailstock quill. These are used to support the wood at the other end while it is being turned. The most common type are called revolving centres, meaning as the wood turns round, the centre in the tailstock revolves with the wood. There is an older and almost never used version now called a dead centre, which does not revolve when the wood is turning round.
Revolving centres come in various shapes and sizes. The most common type has a point on the end to press into the wood a little way and support it. But the end shape can be a sharpened ring, a ring of teeth a cone or a dome. The revolving centres with points, rings or rings of teeth are the most often used types. Some of the more expensive ones have interchangeable heads.
It is worth noting that tailstock revolving centres can be used to support work help in a chuck or on a screwchuck or faceplate. I would recommend as an ideal starting set of centres: a four-prong drive with 25mm diameter head and a pointed-conical end revolving centre. These often come as standard with a new lathe. Chair legs, stair spindles, balustres can all be turned between centres alone, but there are some projects like: boxes, goblets, vases spinning tops and others that might require your turning the tailstock end of the work to cut the shape properly. This means that you will need to use a chuck to hold the work.
Bowls, platter blanks and other work where the grains runs across the lathe bed – 90° to the axis of the lathe bed is typically undertaken in part or wholly using the following methods.
Faceplates are typically a machined piece of metal with a threaded female section at the back that fits onto the spindle of your lathe. The top section is a flange, available in various widths, with countersunk holes where screws are inserted into the work to firmly secure it. This method is best used on wood with a flat face to prevent any rocking of the chuck. The bigger the work, the wider the faceplate you will need to secure it and provide maximum stability. While the faceplate is usually affixed centrally to the work, there are occasions when it can be fixed off-centre so you can turn items to a different shape. This is called off-centre or multi-axis turning. There is a version that can fit directly onto chuck jaws and these re-called faceplate rings.
The faceplate is usually fixed on what will be the top section of the bowl. The screws should be long enough to provide a secure hold, but not so long that when the bowl is reversed (it is usually fitted to a scroll or geared chuck for this process) you will not be able to turn away all the screw marks when hollowing out the inside. A faceplate or faceplate ring of 100–150mm in size is ideal.
There are two types of screw chuck that you are likely to encounter. The first is similar to a faceplate, but has a screw in the centre of it. The flange of this type may also have screw holes in it and the second type is designed to fit the jaws of a scroll chuck. The screw fits in the centre of the chuck and when a workpiece
is tightened onto the screw, the top rim of the jaws acts in the same way as the faceplate section and supports the work.
In each case, a hole of the correct size is drilled into the wood – on what will be the top face of the work –
and the wood is screwed down onto the screw. This type of chucking is only to be used if the face of the
wood is flat. If it is not, the wood will wobble and you will not get a secure hold. The larger the work, the wider or bigger the faceplate section needed to provide proper support. As with the faceplate, the screw chuck is usually fixed centrally to the work, but it can be used for off-centre turning too. Screw chucks are usually used to hold the work initially while rough shaping before holding it in a chuck to refine it further.
Chucks come in various shapes and sizes to suit different projects and types of lathe, but fundamentally, they screw onto the headstock spindle and have jaws that can be contracted or expanded to hold work and accessories. The most commonly used types are scroll or geared chucks, which can be opened and closed by using a type of key.
Chucks are screwed onto the threaded headstock spindle – different lathes have varying thread sizes so chucks can come direct machined in the body to fit the relevant lathe or, more commonly, have interchangeable inserts that suit lathes. The latter are better options for most people because new inserts can be bought if one buys or gets another lathe that has a different thread size so you don’t have to buy a complete new chuck.
The jaws can be contracted to clamp down onto a round tenon also known as a spigot. This is called compression mode. This holding method can be used for both faceplate and spindle work. It is important to ensure that the tenon is of a size that allows the jaws of your chuck to secure the work and gives as much jaw contact with the wood as possible. It is also vital that the tenon and recess are cut to the correct shape to suit the jaws. If you get the shape wrong, the hold is compromised. The tenon profile will typically be either parallel or dovetail in section to suit the jaws being used. The larger the work, the larger the diameter of the jaws you will need to provide proper support. This type of hold can be used on faceplate and spindle work.
You can also expand the jaws of the chuck to hold in a recess. This is called expansion mode. This method is commonly used for large, wide faceplate work such as platters and large bowls. Using recesses on spindle work is rarely used due to the risk of splitting the grain.
A little tip: it is worth making a note or drawing up a chart of the internal and external movement ranges of
your sets of jaws. This means you won’t have to keep cross-checking during the turning time, and
you can set your measuring devices to a suitable size. You will often encounter a number of manufacturers offering chuck packages, which typically include a chuck with a set of jaws, a screw chuck insert and a faceplate ring or threaded one. These can often represent excellent value for money and are worth considering. Aim for a chuck about 100mm in diameter with jaws that will grip onto about 50–60mm spigots and grip into approx. 75–80mm external recesses. As this can cope with a lot of work before you buy more accessories and jaws to fit it.