TURNING. 
screw. Ill each of these heads is a centre- 
pin terminating in a point at one end, and 
in a central hole at the other, like the cen- 
tre-pin, in the poppet-head of any other 
lathe.; the use of which is to atFord point- 
centres when the points are turned towards 
each other, or hole centres when the con- 
trary is the case'; and- lastly, there is a 
small rest with its support, slidable and 
adjustable along the bar, as in another 
lathe. These instruments, which cost five 
or six shillings at the watch tool shops, will 
therefore support any piece of four or five 
inches long, and three inches diameter be- 
tween the centres, and the method of pro- 
ducing the rotation is by passing the cat- 
gut strftig of a bow once or twice round the 
work, and drawing the bow backwards and 
forwards with one hand, while the other is 
employed in applying the tool. The turn- 
bench itself is held steady in a vice fixed to 
a bench or stand. 
Such pieces as have a hole through the 
centre, are drawn tightly upon an arbor or 
mandrel, having a pulley or ferril fixed upon 
it, to carry the gut or bow-string, and the 
mandrel itself is turned between the centres 
upon its own pointed extremities. There 
are mandrels fitted up in different ways for 
holding the work firmly, and jf flat, at right 
angles to the motion ; but we cannot con- 
sistently with brevity enter upon a descrip- 
tion of them, which will immediately be 
understood by inspection in a wor kshop. 
The common lathe of the turners in 
wood, called the pole-lathe, is the same 
thing as the watchmakers turn-bench, but 
upon a large scale, and a little varied. In- 
stead of the horizontal bar it has two long 
stout bars of wood, called sheers, forming 
what is called the bed of the lathe, and its 
two poppet-heads are upright blocks of 
wood, mortised in between the sheers, 
above which they rise and carry the centre 
screws, and betvveen which they are move- 
able, and may be wedged firmly at any 
required distance from each other. The 
work itself is either put between the cen- 
tres, or upon a wooden mandril, and it is 
made to revolve by a string or band, pro- 
ceeding from a long springing pole at the 
ceiling or roof of the shop, round the work, 
and thence to a treadle or foot board, 
which acts by alternate pressure from the 
foot, while the workman applies the cutting 
tool with his hands. 
In these, and all similar lathes, the rota- 
tion is made backwards and forwards; and 
there are some kinds of work in which such 
a motion is advantageous; but in general 
it is much preferable that the work should 
constantly revolve the same way, as shown 
in the lathe described under that article, 
usually known by the name of the foot- 
lathe. In the regular foot-lathe, work is 
very seldom turned between tlie opposite 
centres, though this method certainly affords 
great truth and precision. The mandrel 
is here an essential part of the apparatus, 
which is always used. It has been .shown 
that it is supported by a centre on the 
left hand, called the back centre, and by a 
steel collar in the middle poppet-head ; and 
that the right hand extremity, or nose of 
the mandrel, terminates in a screw, either 
convex or concave, the latter of which is 
preferred in the best latlies. The various 
description of pieces screwed upon the 
nose of the mandrel, for holding or carrying 
work, are called chucks, probably because 
the work is mostly fastened by being dri- 
ven, jammed, or choked into them. 
When work is to be turned between cen- 
tres by the foot-lathe, a centre-chuck, or 
steel-piece, carrying a projecting point, is 
screwed on the nose of the mandrel ; and as 
this piece is not harder than blue, and may 
not always screw home to exactly the same 
bearing, accurate workmen are in the habit 
of turning or shaving the point in its place, 
so that it shall be truly centered. The op- 
posite centre is afforded by the moveable 
poppet-head, and ought to be truly in the 
axis; and the mandrel is made to carry the 
work round by an arm and pin, or by any 
other ready method of connection. 
Work, which is not to be turned between 
centres, is usually fastened to, or fixed in, a 
block or wooden chuck screwed on the 
mandrel. As it would be almost impossible 
to screw a wooden chuck upon the convex 
nose of a mandrel, and take it off as occa- 
sion required during the process, without 
altering the position, it is found much best 
that the screw of the mandrel should be 
hollow, and a brass chuck screwed therein, 
having its projecting screw to receive the 
wooden chuck ; because, by this means, the 
work may be taken off repeatedly, if need- 
ful, without ever separating the brass and 
the wood ; and the brass and the steel will 
take the same position when screwed toge- 
ther again. 
Metallic or other work may be fastened 
to a wooden chuck by cement, or by glue, 
or by turning a cell in the wood, and driv- 
ing the work gently and carefully into it 
till fixed. 
