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Full text of "Modern Mechanical Engineering Vol-I"

102                                PATTERN-MAKING
The Lathes.—These take the first place in all shops, since all the
turning is done by the pattern-maker, who alone is competent to estimate
matters relating to taper, jointing, loose pieces, and moulder's requirements
generally. Lathes of from 6 in. to 8 in. centres are for common use. It is
desirable to have one with a set-over headstock for taper-turning. The lathe
has the ordinary tee-rest. The heads and rest are usually mounted on a
wooden bed, but iron beds are common. Lathes of higher centres, say iz
in., and having long beds are necessary in shops where pipe and column work
is done, and these frequently have a sliding rest. Large face work, as that
of fly-wheels, gear wheels, &c., is done on one of the long bed lathes, fitted
with a headstock spindle extended at the rear to carry a large face plate, and
having a floor rest there. It is better to have a face lathe with a deep head-
stock bolted to a floor plate, which may also carry a loose poppet, and having
a sliding rest on a stand mounted on a floor plate at the front. The chucks
used are simple and few, comprising the fork, the bell, and the face plates
of various diameters. The sheet anchor of the pattern-turner is the large
assortment of wooden chucks, made and used for a variety of patterns,
attached directly or through the medium of blocks, screwed on and recessed
to receive patterns for rechucking instead of cutting into the solid plates.
The Saws.—The circular and the band saws should form part of the
equipment of every shop. Suitable sizes of circular saws are from 14 in. to
18 in. diameter when new. The table must have a fence for cutting strips
to uniform widths, and a canting movement to the table is desirable for
sawing lags to a bevel without waste of material. A rising and falling table
is of value for rebating and shouldering. The band-sawing machine is
indispensable for cutting curves, and a tilting table permits of cutting bevelled
edges.
The Planing Machines.—Though a number of small shops do not
include these in their equipment, they are great time-savers. There are
three chief designs, the first machines one surface only, the second machines
parallel surfaces, and the third, by adjustments of the lower table, imparts
taper. So much of this kind of work has to be done in the pattern-shop that
the fully equipped machine soon recoups its outlay. The procedure is to
plane one face of the stuff over the top table, taking care not to exercise too
much pressure on the board, especially when it is thin and liable to spring
and produce a winding surface. The trued face is then placed on the lower
table, and carried along by the feed rollers, while the upper face is planed
with the revolving cutters. A fence is fitted to the top table for use when
the edges of boards are being planed.
The Wood Trimmer or Mitre Cutter.—This machine is hand-operated
through a lever, and saves a good deal of time otherwise spent in planing ends
of shorter pieces, held in the vice or laid on the shooting board. The
fences, two in number, for right- and left-hand cutting can be set to anj*
angle. Some of these go on a bench, others on floor-stands. The knives
in machines of different dimensions will take a good range of work, from.
7 in. long by 4 in. thick in the smallest, to about 18 in. by 5 in. in the largest.