[Illustration: Screw-Cutting Lathes]
An English lathe, now in use at the Rogers Locomotive Works, Paterson,
N.J., contains several novel features. The ways are flat on the faces,
instead of having raised Vs; and this is a feature of all English
lathes, and of those known in this country as the Freeland lathes. A
great deal of discussion has at various times taken place as to the
relative qualification or merits of these two forms of lathe bed. The
advocates of the flat way, with Vs at the edges of the way, claim
superiority on the score of steadiness, increased wearing surface, and
strength; while, on behalf of the raised Vs, it is urged that, the Vs
being true, the saddle is bound to travel true, because there can be
no lost motion on the slides; whereas any lost motion, from want of
adjustment of the slides in flat ways, is liable to be reproduced
twofold in the work, for the reason that 1/100 of an inch lateral
movement of the slide carriage becomes 1/50 of an inch in the diameter
of the work. Then, again, the most of the wear upon a lathe bed takes
place at the part at and near the running center of the lathe, because
the saddle is, on account of short jobs, more used in that part than
on any other. As a result, when wear has taken place, the saddle, if
adjusted to suit the worn part, becomes too tight to travel over the
unworn part of the bed; and hence, after the wear has taken place, a
proper adjustment of the lathe saddle becomes impossible if the job is
a long one. In the case of raised Vs, however, the wear simply causes
the saddle to fall vertically, so that an amount of wear equal to
1/100 of an inch would have the same effect as lowering the tool 1/100
inch, its effect upon the work being almost imperceptible by ordinary
measurement. On the other hand, however, V lathes are usually made
with either a weight or a spring to keep the saddle down; and as a
result, when the cutting tool stands far out from the tool post, the
saddle is apt to tip, especially in the case of boring with a lathe
tool. In some cases, the raised Vs are accompanied with gibs to secure
the saddle; but in many instances the gibs are given too little
wearing surface. In the lathe above referred to, there are three ways
in one casting, with the slide angles on the outer edges. There are
also three separate and independent tail stocks fitting into the two
openings between the ways. The running head has one cone pulley
connected by suitable gearing to three face plates. The three centers
at the running head are stationary. The slide rest saddle spans the
three ways, having a V slide which contains three separate slide
rests, all connected by a nut to the feed screw, so that all three are
operated by the one screw. In addition to this, the two back slide
rests have the nuts so attached that they can be moved by means of a
separate screw, the object being to facilitate setting the cuts, since
it would be a tedious matter to set all three tools to an equal cut,
or to their desired respective cuts, without means of operating two of
them independently. To set the cut during screw-cutting operations,
the ingenious device shown in our engraving is provided. A represents
the cross-feed or slide rest screw, which operates the three slide
rests. It is fast to the notched wheel, B, and is operated by it in
the usual way. C is a short screw which provides journal bearing for
the screw, A, by a plain hole. It is screwed on the outside, and the
plate in which it fits acts as its nut. It is fast to the handle, D,
and is in fact operated by it. The handle or lever is provided with a
catch, E, pivoted in the enclosed box, F, which also contains a means
of detaining the catch in the notches of the wheel, or of holding it
free from the same when it is placed clear. If, then, the lever, D, be
moved back and forth the feed screw, A, and hence the three slide
rests, will be operated; while, if the catch be placed in one of the
notches on the wheel, B, both the screws, A and C, will act to operate
the rests. When, therefore, the operator is cutting screws, he sets
the catch, E, into one of the notches so soon as the tools are
properly adjusted to the work; and then lifting the catch, E, he turns
the wheel, B, so that the catch falls into the next notch, and this
puts the cut on. When the tool has taken that cut, and while the
latter saddle is traveling back, the catch is placed in the next
notch, and so on, the cut for the forward travel always being put on
as above while the saddle is traveling back. Thus is insured an
exactly equable amount of cut on the whole three rests. When the
lever, D, is not in use, the catch is removed from the wheel, B, and
is allowed to rest against the pins, G or A, provided for that
purpose. For piston rods, or for work such as cutting jack screws,
this lathe is very useful. It is obviously, however, a special tool.
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