Laying Out a Horizontal Sundial Plate
To make a sundial accurately it is necessary to lay out the lines for the particular locality where it is to be used, as a dial will vary slightly according to the latitude. The parts may be made of wood, metal, or stone. A good method is to have a bronze casting made from a wooden pattern. The lines may be cut with a lathe and planer in a machine shop, or engraved by hand.
Fig. 1
Lay Out the Dial Plate Symmetrically, Allowing Space for the Style
The illustrations show how the dial is made. The lines, as indicated in [Fig. 1], should be laid out very carefully, first on a pattern. Draw a horizontal line near the top which represents the six-o’clock line, A-VI, in [Fig. 2]. Then lay out another line AH, at right angles to A-VI. Take a point C at any convenient place and construct the right-angled triangle ABD. The angle CAB should be equal to the degree of latitude of the place. The angle CBD equals CAB. Take a compass and set it to a radius equal to the side BD, and draw the quadrant DF from E. From D draw the line DG out for same distance and parallel with A-VI. Now divide the quadrant DF into six equal parts. Draw the lines E1, E2, E3, etc., and where they intersect the line DG, draw the lines from A, as A-I, A-II, A-III, etc. These are the hour lines. Divide each of the six divisions of the quadrant into four parts, and draw the lines, as shown between the 3 and 4 divisions. These are the 15-minute parts. Each of these parts may be divided in turn, and this is best done by eye, unless the dial is quite large.
The Dial is Mounted Horizontally with the High End of the Style toward the North
Fig. 2
Fig. 3
Diagram for Marking the Dial and Making the Style
This will complete one-half of the dial. The other half is done in the same manner, leaving a space between the line AH and its corresponding line for the other side of the dial. This space should be equal to the thickness of the upright shadow-casting piece, or style. The style has its base equal in length to the line AH, and its angle, S, equal to the latitude, or the angle CAB. It is mounted in the space with the high end at 12 o’clock. It may be fastened to the dial with screws passing through the base. Mount the dial horizontally on a suitable pedestal. The style should be exactly north and south, with 12 o’clock toward the north. The dial will be fast or slow over clock time. This is corrected by consulting an almanac and setting the clock accordingly from the dial. A correction plate may thus be made and mounted on the pedestal.—F. B. Walters, Baltimore, Md.