In Fig. 5 are shown a pair of calipers which are very handy in measuring work from shoulder to shoulder or from a shoulder to the end of the piece of work. For this purpose they are much handier, and more accurate, than the ordinary "hermaphrodites." The legs are bent at AA so as to lie flat and thus bring the point of the long leg directly behind the short one which "nests" into it, as at B, so that the calipers may be used for short measurements as well as for long ones.
Double-jointed Calipers to Fold in Tool Box
In Fig. 6 are illustrated a pair of large calipers that can be folded up and put in a machinist's ordinary size tool chest. The usual large caliper supplied by the average machine shop is so cumbersome and heavy that this one was designed to fill its place. It can be carried in the chest when the usual style of large caliper cannot. It is a very light and compact tool. It is a 26-inch caliper, and will caliper up to 34 inches diameter. The top sections are made in four pieces, and the point ends fit between the top half like the blade of a knife, as shown in the engraving. Each side of the upper or top section is made of saw steel 1/16 inch thick, and the lower part or point of steel ⅛ inch thick. The double section makes the tool very stiff and light.
The point section has a tongue A, extending between the double section, which is engaged by a sliding stud and thumb nut. The stud is a nice sliding fit in the slot, and the thumb nut clamps it firmly in place when in use. B, in the figure, shows the construction of the thumb nut. C is a sheet copper liner put between the washers at A. The dotted lines in the engraving show the points folded back to close up. The large joint washers are 1¾ inch diameter, and a ⅝-inch pin with a ⅜-inch hexagon head screw tightens it up. The forward joints are the same style, but smaller. The main joint has two 1¾-inch brass distance pieces or washers between the two main washers. The top section is 12½ inches between centers, and the point sections 15 inches from center to point. Closed up, the calipers measure 16 inches over-all.
Fig. 6. Large Double-jointed Calipers
Kinks in Inside Calipering
Close measurements may be made by filing two notches in each leg of an inside caliper so as to leave a rounded projection between, as shown at E, Fig. 7. Then, with an outside caliper, D, the setting of the inside caliper, B, is taken from the rounded points. The inside caliper can be reset very accurately after removal by this method. A still better way is to have two short pins, CC′ set in the sides of the inside caliper legs, but this is not readily done as a makeshift. To measure the inside diameter of a bore having a shoulder like the piece H, the inside caliper F may also be set as usual and then a line marked with a sharp scriber on one leg, by drawing it along the side G. Then the legs are closed to remove the caliper, and are reset to the scribed line. Of course, this method is not as accurate as the previous one, and can be used only for approximate measurements.
Fig. 7. Methods of Inside Calipering