TYPES OF CHUCK AVAILABLE - Limited only by human ingenuity over the ages
Faceplate
By my own definition, a faceplate is a type of chuck. A faceplate is a flat
metal disc which screws onto the the spindle and grips the wood by means of
woodscrews passing through fixing holes in the plate.
Screwchuck
A faceplate which has a single screw, fixed in position and projecting from
the exact centre of the face, is known as a "screwchuck". These are useful because
the wood can be fitted quickly by hand. They can be purchased separately or,
frequently, they are supplied as a freebie with a multi chuck. They can be made
out of wood on your lathe!
Cupchucks and "jam-chucks"
Cupchucks appear in all the old books as they have been used for hundreds of
years. For ages, there was nothing else and the name chuck was synonymous with
"cupchuck". The commercial ones were cast iron with a hole, tapered or parallel,
to take the wood, and threaded to fit the lathe spindle. The principle of operation
was that the wood was roughly turned or pared down with knife or axe, and hammered
into the hole in the "chuck" to grip the work. If the cupchuck is made from
scrap wood and hollowed out to fit the workpiece it is called a "jam chuck".
Multi Purpose Chucks
Most turners nowadays think of a chuck as one of the modern "multi chucks" which
are supposed to grip just about anything. These complex and expensive devices
are very desirable - although not strictly essential. There is a bewildering
variety of multi purpose chucks available. Most of them can be classified as
either "collet chucks" or "scroll chucks". Collet chucks have only a limited
movement in the jaws, normally about 6mm change in diameter. This means that
the wood has to be accurately cut to fit into the chuck jaws. The chuck jaws
or "collets" are specially shaped with a hook or dovetail section to get a positive
grip on the wood. The special jaws are made to either expand into a prepared
recess in the wood or they contract over a "spigot" which again has to be prepared
on the end of the workpiece. Scroll chucks have the advantage of a much larger
jaw movement. This makes it much easier to prepare the wood to fit, because
less accuracy is needed. Scroll chucks are much more expensive to manufacture
than collet chucks and a good scroll chuck with a selection of dovetail jaws
can cost more than a lathe. Scroll chucks use the same mechanism as metal turning
chucks and have a powerful grip. A four jaw scroll chuck can grip some wood
blanks, particularly square section blanks without any preparation. The security
of grip is only good enough for small projects because of the small contact
area but the saving in preparation time is sufficient to justify the extra cost
of this type of chuck to a professional turner.
Scroll Chucks v. Collet Chucks
If you are only turning for a hobby then the time and inconvenience of having
to accurately prepare the wood to fit the chuck is of little consequence. A
good multi purpose collet chuck is all you require and will give an equally
strong grip to a scroll chuck.
Choosing a COLLET CHUCK
It is important to be able to grip in both directions - internally and externally.
Some of the older chuck designs can only grip in one direction - or the chuck
has to be dismantled and reassembled in a different form to change over from
internal grip to external or vice versa.
The Masterchuck is not a collet chuck
It is actually a four jaw self centering scroll chuck. The scroll is conical.
It is an example of a chuck which grips in either expansion or compression and
it also offers a valuable alternative to the need to prepare the wood to fit
the chuck - the chuck can be fitted with wooden jaws which are shaped to fit
the job! You often need to rechuck a workpiece to finish turn the part previously
held (and thus rendered inaccessible) by the chuck jaws. Home built wood jaw
sets are ideal for "second op. work" as they say in engineering. Quadrants of
scrap wood or plywood are screwed on to the face of the existing metal jaws.
The assembly is mounted on the lathe and the wood jaws turned to shape. They
can just as easily be re-shaped later for another job. The wood jaws can be
as simple or elaborate as the job demands and they can grip internally or externally.
If they are shaped while on the chuck they are bound to run true.
Dovetail jaws v engineering style stepped jaws
You might imagine that all that is necessary with any chuck is to push the piece
of wood into the chuck jaws and tighten up. After all, metal turning chucks
work that way. Alas, life is not so simple for the woodturner. Wood is a weak,
soft material compared to metal and, to grip it securely, the chuck jaws must
clamp over a large surface area. Engineering chucks have small jaws which touch
a small area on the workpiece. This is fine for gripping metal but does not
work on wood because the the jaws would crush into the material long before
they generate enough friction to grip securely. Turning at the end of a cylinder
held this way would wrench the wood out of the jaws. To grip properly the jaws
must be shaped to fit all round the circunference. Also, for maximum grip, the
chuck jaws should hook over a "dovetail" shape on the wood. This locks the wood
firmly into the chuck. Woodturning chucks are therefore designed with these
special "dovetail" jaws as standard. They are shaped to touch all round the
workpiece.
The Masterchuck has dual purpose jaws which have dovetails shaped on both the inside and the outside gripping areas. This allows either contracting grip or expanding grip, using the same jaws. The wood must be the correct diameter to fit the curvature of the jaws and shaped with the correct angle of "dovetail".
Glue Fix Chucks
A workpiece can be glued to a chuck made from scrap wood screwed to the faceplate.
When the work is finished the scrap piece can be turned away using a parting
tool. There are chucks available which use hot-melt glue to fix onto the workpiece.
When the work is finished the workpiece is removed by heating the chuck to re-melt
the glue.
Sticky Chucks
This is a development of the above by Jack Cox. A metal disc is heated before
the glue is applied. This gives a very strong joint. When the project is finished
the metal disc is heated to release it leaving a flat surface with no recess.
More info on sticky chucks.
Ring Chucks
A relic from the past described by Frank Pain in his excellent book "The
Practical Woodturner" 1957. He called it his "eggcup chuck".
This looks like a faceplate with a thread turned on the periphery. It has a
ring which screws onto the rim of the faceplate. The ring has a restricted opening
to trap the wood inside it. The idea is that you turn down the wood between
centres with a flange at one end. The ring is big enough to pass over the wood
but the flange is trapped firmly inside the ring giving an unsurpassable rigid
grip. If you have one of these you will find it really useful for small cylindrical
projects like peppermills, goblets and of course eggcups. The coil
grip chuck is based on a giant "eggcup chuck" and perorms well
in ring chuck mode for projects up to 3" diameter.