February 13, 1930. The Model Engineer and Practical Electrician. 163
set, which isn’t desirable, but loose off one side
from the buffer-beam.
Now replace one cylinder, set it so that the piston-rod lines up by
eye with the centre of the driving axle, and put
the clamp on to hold it in position. Pull out the
piston-rod as far as it will go; hold a piece of
string or cotton back up against the cylinder
cover, and stretch out tightly so that it lies
directly above and parallel with the centre of the
piston-rod. If the cotton also crosses the centre
of the driving axle, the position of the cylinder
is correct ; if not, shift it till you get that result.
Tighten up the toolmaker’s clamp so that the
cylinder will not accidentally shift, and then,
with a No. 30 drill in a small handbrace, make
four countersinks in the frame, using the holes
in the cylinder bolting-face as jig. If by any
chance you have managed to get the holes set
so that the drill will not enter straight, use a
bent scriber and carefully mark off the position
of the holes with that, carefully centre-popping
heavily after the cylinder is removed
from
frame.
Repeat the process with the other
cylinder; then take the steam-chest out of the
frame, and drill the whole lot of holes with
No. 30 drill ;a block of wood jammed between
frames will prevent any distortion.
Clean off
tingly for the wide-spaced double bars and allgator crosshead in small work. "They are easiest to make, stand up fine to stress and wear (and accidents!) and look ‘the real goods.’ Crossheads when made single-sided with a large-headed pin, the head of which is sunk in. а pin-drilled recess in the back of the block, are quite
gauge.
satisfactory
If, however,
for engines
up
to ,33-in.
anybody wants a correct
double crosshead with bearings back and front, the deep recess for the little end can (in|the absence of a proper milling- machine) be’ cut with a slot-drill running at good speed in the three-jaw or drill chuck, the slot being formed in the end of a piece of steel bar of suitable cross-section, clamped to the tool block of the lathe апа traversed across the cutter. The small piece of steel containing the ‘slot is cut off afterwards and machined up to form the crosshead. Alternatively, the centre part, can be made in the shape of a plain fork, |formed by filing or milling; the top and bottom shoes are filed up from scraps of steel, tied on with a bit of iron binding wire, and finally brazed in position, using ordinary soft brass wire as a jointing medium instead of spelter. Leave the
Exhaust boss
Roil
Level How
to Line
Up Averill
the burrs with a file, or a much larger drill used as a countersink will do the necessary. Replace the steam-chest, and line up the tapped holes in it with the drilled holes in the frame. The cylinders can then be placed in correct position, and the screws put in. The latter do not have to withstand the back thrust of the piston as with the usual type of cylinder. ‘Their only job is to keep the assembly together and prevent it turning. Back thrust is taken up by the spigot of port face which enters the steam-chest, and the stress is transferred direct to frames by steam-chest spigots. The cylinders can Бе removed at any time without disturbing pipe connections, etc., by simply taking out the four screws and disconnecting the main driving rod by pulling out the crosshead or gudgeon-pin. Guide-bars, Crossheads
and Brackets or Yokes--
Suitable for these cylinders can, be made according to the sizes given on the “ Fayette” blue-prints ; and if thus, will be suitable for our little shunting engine. Guide-bars can be cut from 3/16th-in. square silver-steel rod (drill rod) and filed up to: shape, or may be just plain bars of 3/16th in. by $ in., bevelled off at the ends to clear.connecting or main rods. Although many :full-sizéd railroads now use the Laird type ef guides and crosshéad, and others use a Бох crosshead: with. single’ bar, I plump unhesita-
Cylinders.
turning until after brazing 1s through ; and then, if the job comes out O.K. and no apple-pie er almond-rock about it, set it up in our old friend the independent four-jaw chuck and turn the bosses for the piston-rods. I have already given bags of instructions how to fit crossheads so they really do support the piston-rod (іп 95 per cent. of the commercial engines I have repaired the opposite was the case—crosshead ‘* fitted where it touched," and not always then— makers please note) so need not repeat, save to emphasise that a correct-fitting sharp drill be used tó push through the gland and stuffingbox ‘when making the correct location of the ‘hole in the piston-rod boss. Guide yokes can be filed from steel plate,. to Fayette " drawings, or' any other shape desired; all you need, is a file, hacksaw, and patience. Next, valve gears.
A New Italian Ship Model Testing Tank. A magnificently equipped tank for the trial of models of ship hulls was completed іп Коте
in 1929 by. the Italian Government.
Тһе tank
is goo ft; long, 41 ft. wide and 20 ft. deep, and the main carriage is designed. for a maximum speed. of. nearly: до, ft. per second. The, model
shaping. machine, in. the workshop.. „attached, to the: tank: will take а. model 26 ft..in length. ..
