. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . x to %,but in turning the shears at points d and e, the metal islikely to be torn and the pattern ruined. The circularshears, as shown in Figure 104, can be used to advantagein cutting the small curves in patterns E and F. The small circle in the center of pattern G, Figure 139,is cut out by using a hollow punch, as shown in Figure114. The metal is placed upon a lead or wooden block. A 160 SHEET ME
. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . x to %,but in turning the shears at points d and e, the metal islikely to be torn and the pattern ruined. The circularshears, as shown in Figure 104, can be used to advantagein cutting the small curves in patterns E and F. The small circle in the center of pattern G, Figure 139,is cut out by using a hollow punch, as shown in Figure114. The metal is placed upon a lead or wooden block. A 160 SHEET METAL WORKERS MANUAL punch ofm the required size is placed upon the circle andstruck with a heavy mallet or hammer. If the piece ofmetal remains in the punch, it can be removed by strikingthe punch lightly with the hammer. Hollow punches aremade in various sizes. When an opening is to be cut in a piece of light metalas at a in pattern I, Figure 139, place the metal upon ablock of lead; then by using a hollow punch or small thinchisel, cut a hole in the metal large enough to insert thepoint of the lower blade of the circular shears in theopening; then cut along the line in the direction of the. m WL Figure 143.—Notched Patterns, the Shaded Portions Being the Notches. arrow. The outer circle is cut in the usual manner,which completes the pattern. Gutting Elbow Patterns.—When cutting elbow pat-terns or similar forms, as shown in H, Figure 139, thestraight cuts b to c, c to d, d to e, are made with thestraight snips, or upon the square shears. The uppercurve of the pattern is cut by using the straight shears,starting at e and making one continuous cut ending at 6. In using the hand shears, a mistake is often made by SHEET METAL WORK AND PATTERN DRAFTING 161 the student in cutting beyond the stopping point shownon the pattern. This can be avoided by always complet-ing the cut with the point of the shears. When cuttingfrom a to b, Figure 141, the end of the shears should bedirectly
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