CHAPTER XIX. 
WORKING-DRAWINGS. 
le fii'st points to be determined before commencing a working-drawing ara 
one . 及 6 aU( ^ ^ le s i ze of tlie paper. The least scale wliicli it is convenient to use is 
coed lnC 1 *^° ^ 16 f 00 t， an d the greatest scale for a whole drawing should seldom ex- 
d ffi aU 一 】 1 aii d a half to the foot. Jf a smaller scale than one inch be used, 
y will be experienced in writing the rivet spacing between the rivet holes, 
five ^ l ° l) a P er 8 l 10U kl be from three and a half to four and a half, or even 
山 ， ,. GG . * aut ^> for the length, it is better to use roll- paper, and not to cut it until 
^ , 1 s the drawing be determined ; for it is a great convenience to be able to 
^ he working- drawings for a bridge upon a single sheet, 
me" こ ， foUoWug ミ 8 a cli'augbtsman'a equipment for making working- drawings in a 
to 1Ca l 加は ex P e( litious mnniier : a table from four to five feet wide, from six 
ris 0 ^ eG t l on g， about three feet higli ; a pair of steps each four or five inches 
co a- ル 1 ’ 00 feet long ; a bevelled steel straight- edge, at least three feet long ; a beam 
吻 广 ' ^ au o eu ^ screw afctacliinoufc ; a couple of small triauglos ( rubber ones 
duod 把 . 的 り ； Somo and six-H pencils ; a little tracing-paper ; a finely divided 
a 〇 00 ぶ' 出ぬ hoxwood scale (tlie subdivisions being quarters, eighths, and sixteenths); 
a ふ tlic) 0X ば ^ US ^ rnmeu ^ s, including a protractor and a pair of hairspring dividers ; 
offices «^ SUa l of rubbers, tiles, pens, etc., that one finds in draughtsmen’s 
姐 akh o ■ s< l Uares ， large triangles, and parallel rulers should never be used in 
i m g a ^i-king.drawing. The first can never be depended upon, because of tlie 
^ulev 1 1 ^ 0 f l lav i n g botli board and T- square always perfectly true ; no wooden 
)0 reil Gd on uofc to warp ； and parallel rulers are a delusion. 
l oag 二 a few iuc hes it is permissible to turn right angles with triangles, but for 
ac curate] aU0GS ^ eam com l〕 a8S should be used ； and parallel lines can be most 
]ayi Ufr e J diawu by erectiug a perpendicular near each end of tlie original line, and 
ti.ian^l e8 仙 ^ lem e< l ua ^ distances. When distances are a littlo too great for tlie 
Used • bf ’t aiK \t 00 small for the beam compass, tlie large ordinary compasses can be 
to b: U / Ml わ 6 found that they are seldom required. The four-H pencils are 
draught C 几 、 Vl 出 11 容 dimensions, etc., and the six-H ones for drawing lines. The 
fo r ru |. Smau 8 h ou W always have at least one of the latter sharpened to a chisel edge 
hi a ac i^^’ ilUd anofch cr to a point for sketching. He will find it to be greatly to 
a ge to keep his pencils always well sharpened, for an error of tlie width 
