TURNING. 201 
to be placed at any distance from the centre, according to 
the size of the work, and to place them at those parts where 
it will be most convenient to apply them. 
The form of these clamps is shewn more particularly in 
fig. 7 : /are sliders of metal, which are fitted to the grooves 
in the chuck; and the grooves are dove-tailed, so that these 
sliders can be put into the grooves at the back of the chuck, 
but will not draw through the grooves into the front. 
Screws are tapped into the sliders, and draw the clamps, 
fi, against the face of the chuck, and hold fast the work, 
which is placed beneath their claws. The clamps, h, have 
shanks projecting from them at right angles, which pass 
through the grooves, and keep the clamps from turning round 
to one side. 
Figs. 8. and 9. represent the callipers used by turners to 
take the measure of their work; they are made of two 
curved pieces of steel-plate, united together by a joint. 
When they are opened, as in fig. 9, the dimensions of a 
round piece of work may be conveniently taken between 
their points, as shewn by the dotted circle; but if the points 
are closed together, as in fig. 8, so that they pass each 
other, then the callipers are adapted for measuring the dia¬ 
meter of internal cavities, by the distances of their points 
from each other. 
Fig. 10. is a gauge for measuring the depth of hollow 
work. 
When a piece of metal work is to be turned between 
centres, a small chuck, b, (figs. 10. and 12.) is screwed 
to the mandrel; in the end of this chuck, at b, is a hole, 
which is made square withinside, and the work has a square 
filed at one end to fit the hole. The other end of the work 
is supported by the back centre, a small hole being made 
in the end to receive its point; or if the end of the work 
is sharp-pointed, the back centre pin is drawn out of its 
socket, and turned end for end : the end of the pin opposite 
to the point has a small centre hole for the reception of such 
pointed work. Iron and steel work may be turned very 
conveniently by means of a square, but not very accurately; 
and after the work has been taken out of the lathe, and the 
square cut off, if it be required to turn the work again 
in the lathe, it is very difficult to find the true centre. 
Drivers 13. and 14. are contrivances for retaining the 
work firmly in its situation. 
The turning of elliptical or oval work, such as picture- 
frames and snuff-boxes, is performed in the same lathe, and 
with the same tools, as the circular work; but the lathe is 
provided with a chuck, which causes the work to traverse 
in a very curious manner, by a motion given to it m a direc¬ 
tion to and from the centre of the mandrel as it revolves; so 
that a tool held up against the work will cut an eliptical 
figure instead of a circle. The mode of action of this inge¬ 
nious apparatus is described best by reference to the trammel 
or elliptic compasses; see fig. 22. An octagonal or square 
board A A, B B, has two grooves cut in its surface, which 
intersect each other at right angles; this board is held down 
upon the surface where the ellipse is to be described, 
with the centre lines of the cross grooves coincident with the 
two diameters of the intended ellipse, and of course their 
intersection will be its centre. The curve D D is traced be¬ 
yond the circumference of the board, by means of a pen or 
pencil, which is fixed at F, to a radical bar or beam FGH; 
this bar carries two other points or pins, G and H, which 
are attached to sliders, inserted into the cross grooves of the 
board, as shewn in the figure: the sliders are fitted in truly, 
so that each of them will have a motion in its respective 
grooves: thus the slider of the pin H will move along A A; 
and the slider of G, along the groove B B. By turning 
about the beam FGH, the sliders go backwards and for¬ 
wards in their cross grooves with a simultaneous motion ; 
so that when the beam has gone one-fourth way about, one 
of the sliders will have moved from the circumference of the 
board A B, to the common centre of the cross grooves: and 
when the beam has gone half round, the same slider will 
have proceeded the whole length of the cross, and arrived 
at the opposite side of the circumference. The same applies 
Von. XXIV. No. 1637. 
to the other slider, and when one slider is at the centre, the 
other will always be at the circumference. 
The pins F and G H can be fixed at any part of the 
beam at pleasure (though this is not so represented in the 
drawing), for the purpose of setting the trammel to draw any 
particular ellipsis ; thus, place the beam in the direction of the 
line A A, then the pin G will be in the centre of the cross 
grooves; now fix F at such a distance from the centre, as 
is equal to half the small diameter of the ellipse, and set H so 
far distant from G, as the difference of the two diameters; 
consequently, from F to H will be equal to half the longest 
diameter. Now in turning the beam round from the direc¬ 
tion A A, till it comes to the direction B B, the point G will 
depart from the centre along B B, and H will approach it 
along A A, till it gets to the centre. Then will the pencil 
F be so much farther from the centre, as G is distant from 
H, and the pin has in its circuit traced one-fourth of an 
ellipse. The beam being turned quite round, will complete 
the whole curve. 
This apparatus may be applied to turning by some modifi¬ 
cation. Suppose the two cross grooves made in a round 
board, as large again as that represented in the figure ; then, 
if the whole apparatus be inverted, and the beam F G held 
fast in a vice, or otherwise, the board with the cross may be 
traversed round upon the fixed sliders, in the same manner as 
the beam could be traversed round upon the fixed board; 
Suppose a tracing point is held to the back of the board, 
exactly opposite to the place where the tracing point F is 
fixed to the beam, and held fast; it is evident that its point 
will trace the same ellipse on the back of the board, that was 
described on the surface which the board lay upon in the 
former instance: or a chissel being held fast in the same spot, 
will cut the board elliptical when it is turned round; and 
the chissel being successively applied at different points along 
the line of the beam, a series of concentric ellipses may be 
turned in the board, to make mouldings for picture-frames or 
other ornaments. If the distance of the two fixed pins G and 
H, and the chissel F, is altered, it will vary the proportion 
between the two diameters of the ellipsis, in the same manner 
as before described of the trammel. 
TU'RNINGNESS, s. Quality of turning; tergiversa¬ 
tion; subterfuge.—So nature formed him, to all turningness 
of sleights; that though no man had less goodness, no man 
could better find the places whence arguments might grow of 
goodness. Sidney. 
TU'RNIP, s. [neepe, Sax.; napus, Lat. Those who write 
our word turnep are therefore warranted.] An esculent root. 
See Brassica. 
The goddess rose amid the inmost round. 
With wither’d turnip -tops her temples crown’d. Gay. 
TURNISSA, a small town in the south-west of Hungary; 
18 miles north-by-west of Csakathurn. 
TU'RNPIKE, s. [turn and pike, or pique.'] A cross of 
two bars armed with pikes at the end, and turning on a pin, 
fixed to hinder horses from entering.—I move upon my axle, 
like a turnpike. B. Jonson .—Any gate by which the way 
is obstructed.—The gates are shut, and the turnpikes locked. 
Arbuthnot. 
TU'RNSICK, adj. Vertiginous; giddy.—If a man see 
another turn swiftly and long; or if he look upon wheels 
that turn, himself waxeth turnsick. Bacon. 
TU'RNSOL, s. [keliotropium, Lat.] A plant. Miller. 
—Her chaplet of heliotropium or turnsole. B. Jonson. 
TU'RNSPIT, s. He that anciently turned a spit, instead 
of which jacks are now generally used. It is now used of a 
dog that turns the spit. 
I give you joy of the report 
That he’s to have a place at court; 
Yes, and a place he will grow rich in, 
A turnspit in the royal kitchen. Swift. 
TU'RNSTILE, s. Cross bars turning ona pin in a foot¬ 
path, to admit foot passengers and to exclude large animals. 
Twirling turnstiles interrupt the way, 
The thwarting passenger shall force them round. Gay. 
3 F TURNUL, 
