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especially for the work by Chesterman, of London, England, and before being
used were tested and checked with a master tape at McGill University. Frequent
rechecks were made during the progress of the work.
The importance of uniform temperature in the shop during long, continuous
operations, such as the planing of these chord sections, was indifferently appre-
ciated at first or until the results of ununiform temperature were made very
evident. In one case, where the operations were to be continued for 24 hours or
more, the temperature was allowed to drop during the night, when practically no
other work was being done in the shop. On checking the member over on
completion it was found to be nearly 3“; in. longer at one side than on the
other, with the result that this member had to be refaced. On another occasion
when difficulty was being encountered in getting the several webs to check up
correctly, the trouble was traced to the fact that an oil rivet forge was in operation
a short distance away on one side while a door leading outwards was being con<
tinually opened and closed on the other side. After the erection of a screen
between the member and the door and the removal of the rivet forge no further
trouble was encountered. To avoid similar trouble thereafter a graphic
thermometer was installed on such members, and work was stopped if the tempera-
ture varied more than a certain specified amount.
One of the most laborious planing operations on this work was the facing
of the enormous steel castings which formed the first story of the main shoe. These
castings were 20510" x 6’-8”:and 4ft. high and weighed approximately 40 tons each.
There were four of these castings under each shoe, their webs, Hanges, and interior
diaphragms being from 2V2 in. to 3 in. thick. The castings were planed on a large
machine designed especially for this work, the cutting tool of which had a travel
of 10 ft. transversely and 30 ft. longitudinally. The castings were faced top and
bottom and two sides. There were two cutting tools fitted on the horizontal
cross head by which the operator was able to start one tool from the centre of the
casting and the other one at the edge, reducing the time of the total operation by
one-half. The finishing cut, however, was done with one tool across the entire
face of the casting, about 20 hours being required for this tool to make one entire
cutting. There was also a cutting head on each side attached to the vertical
head of the machine by which the sides of the casting could be faced without
turning the casting on its edge. Under fair conditions it required about two
weeks to completely plane one of these castings. As there were sixteen required,
this part of the work, therefore, required from eight tonine months‘ continuous
work in itself.
On the first one or two castings that were finished it was found on checking
them up that, while at the ends they were exactly to gauge, there seemed to be a
slight concavity near the centre, in one case amounting to nearly ‘()2 in,
Exhaustive tests were made on the machine to determine how this could have
occurred, but no explanation could be arrived at unless it was due to releasing of
internal stresses in the casting when the outer crust had been removed by the
cutting tool, thus causing a slight warp during the machining. To guard against
such a future contingency, it was decided to rough finish one face on both sides,
leaving about 1'1‘. in. for the final cut, then turn the casting over and completely
100
finish the opposite face. The casting was then again llll"l1(‘(l and the final cut
made on the original face. It was found that much more satisfactory results
were obtained by following this programme.
The boring of the pin holes and half pin holes in the gusset plates of the
chords and in the shoes was performed on a large boring mill which has already
been described. When the member was once placed in its correct position on
the bed of the machine, it was not necessary to move it until all the holes were
bored. In such an operation as boring the shoe. where there were live distinct
pin holes, these holes could be bored without disturbing the member, thus
assuring that all holes would be absolutely parallel and at right angles to the
vertical and longitudinal axes of the member.
10we;r:lfOlrE1d:s’:5r:dI>3:e1:325: ()3): itn. iln diainctcr) were at the connections of the
Compression members and :1]: out ie main shoe. The pin holes in the smaller
Smaller twin boring machine tnleinbt-rs excclit CYCl)ars were bored on the
end in members up to 90 knit“ 1 tan d ‘$‘tn1tIltZlI1COUSl)' bore the holes in each
was necessary to make a second adiig’tL him members exC(Tde['l this length‘ It
used to check the diameter of thi Ti mem 0 the m'Cml)er. Spend] gaugcs-were
I ’ oles, and transit and level were invariably
required to obtain the proper adjustment,
. The boring of pin holes in eyebars wa
which bored the hole at both ends of the e
“'35 bored “'3 l“> 137$?!’ than the nomii
allowed for wear of tool,
of the tool, only one eycbzi
s done on an eyebar boring machine
yebar simultaneously. The pin hole
I I . 1.:il.diametcr of the pin plus IIIHI in.
11 on er to minimize the chance of error from wearing
r was bored at a time,
The method of checking the unifor
by the specification, was to pile the fut]
on top of one another and to require t
in length of the finished bars, as proposed
Tlllmlxer of bars required for any one panel
difficulty through the holes at each elulu Ifius pass sinlulmnmusly and whhom
x n( o the assembled bars. This was not
found to work satisfactor' v '
and the pins allowed Suff;E(;‘z11t5I:::y(l:$liCl':;:lf:)C1Wl!Cl1 the diameter of the holes
other methods were med’ but it was f(f)’und1I1 an a1>precialile error to creep in.
accurate method was by direct mmsur 7).) 9'Xpt'rience that the only really
bar. ement with K‘ steel tape on each individual
Particular care was also neg
of temlmmmrel when Dyeb-“sessar)' in this work to
Inla 'in out the '
centre was taken for the pin centre ,
through the centre of the pin how; 3
amounted to more than fig in.
rejected.
Ellrlhlle bod)’ Of the bar was spotted along
when t;]E(3‘.':“EI.l'tr'C line between the ends and
nd the aCtu;ll'ltltl(7n between the line passing
V the bar W1. iccntre of the bar at any point
(5 required to be straightened or was
ASSlCMl3LI.VG. The 5
be assembled in the shot
the heavy chord sections,
ltecification re
) and re quimd that Mk
amed in place.
(‘om x -
pression diagonals,
l splices in main members
Ill“ 0DCration of assembling
3'" Post and shoe was a very
m