Home >> Cyclopedia-of-architecture-carpentry-and-building-a-general-reference-v-09 >> Ab Cd to Skylight Work >> Principles Employed for Obtaining_P1

Page: 1 2

PRINCIPLES EMPLOYED FOR OBTAINING APPROXI MATE BLANKS FOR CURVED MOULDINGS HAMMERED BY HAND The governing principles underlying all such operations are the same as every sheet-metal worker uses in the laying out of the simple patterns in Haring ware. In other words, one who understands how to lay out the pattern for a frustum of a cone understands the principles of developing the blanks for curved mouldings. The principles will be described in detail in what follows.

Our first problem is that of obtaining a blank for a plain flare, shown in Fig. 340. First draw the center line A B, and construct the half-elevation of the mould, as C D E F. Extend D E until it inter sects the center line A B at G. At right angles to A B from any point, as H, draw H 1 equal to C D, as shown. .Using II as center, and with H 1 as radius, describe the quarter-circle 1 7, which is a section on C D. Divide 17 into equal spaces, as shown. Now using G as center, with radii equal to G E and G D, describe the arcs D 7' and E E°. From any point, as 1', draw the radial line 1' G, intersecting the inner arc at Ex. Take a stretchout of the quarter-section; place it as shown from 1' to 7'; and draw a line fmm7' to G, intersecting the inner arc at E°. Then will Ex 1' 7' E° be the quarter-pattern for the flare D E in elevation. If the pattern is required in two halves, join two pieces; if required in one piece, join four pieces.

In Fig. 341 is shown a curved mould whose profile contains a cove. To work this profile, the blank must be stretched with the stretching hammer. We mention this here so that the student will pay attention to the rule for obtaining patterns for stretched moulds. First draw the center line A B; also the half-elevation of the moulding, as C D E F. Divide the cove E D into an equal number of spaces, as shown from a to e. Through the center of the cove c draw a line parallel to e a, extending it until it meets the center line A B at G, which is the center point from which to strike the pattern. Take the stretchout of the cove c e and c a, and place it as shown by c e' and c a'. When ing the flare a' e', c remains stationary, e' and a' being hammered wards e and a respectively. Therefore, from c erect a vertical line

intersecting H 1, drawn at right angles to A B, at 1. Using H as center and H 1 as radius, describe the arc 1 7, which divide into equal spaces as shown. With G as center, and radii equal to G a', Gc, and G e', describe the arcs e" 1' 7', and a" a". Draw a line from e" to G, inter secting the center and lower arcs at 1' and a". Starting from 1', lay off the stretchout of the quarter-section as shown from 1' to 7'. Through 7' draw a line towards G, intersecting the in ner arc at a"; and, extending the line upward, intersect the outer arc at e". Then will a" e" e" a" be the quarter pattern for the cove E D in elevation.

If the quarter-round N 0 were re quired in place of the cove E D, then, as this quarter-round would require to be raised, the rule given in the former Instruction P a p e r on Sheet Metal Work would be applied to all cases of raised mouldings.

In Fig. 342 is shown a curved mould whose profile is an ogee. In this case as in the preceding, draw the center line and half-elevation, and divide the ogee into a number of equal parts, as shown from a to h. Through the flaring portion of the ogee, as c e, draw a line, extending it upward and downward until it intersects the center line A B at G. Take the stretchouts from a to c and from e to h and place them re spectively from c to a' and from e to.h' on the line h' G. Then, in work ing the ogee, that portion of the flare from c to e remains stationary; the part from e to h' will be stretched to form e h; while that part shown from c to a' will be raised to form c a. From any point in the station ary flare, as d, erect a line meeting the line H 1, drawn at right angles to A B, at 1. Using H as center and H 1 as radius, describe the quarter-section, and divide same into equal spaces, as shown. With G as center and with radii equal to G a', G d, and G h', describe the arcs a" a", 1' 7', and h" h". From h" draw a line to G. Starting at 1', lay off the stretchout of the section as shown from 1' to 7'. Through 7' draw a line to G, as before de scribed. Then will h" a" a" h" be the quarter-pat tern for the ogee E D.

Page: 1 2