Outside and Inside Calipers. Instead of having straight legs with sharp points, caliper legs are bent and have blunt points. As distances are to be measured both outside and inside of solid bodies, we have outside and inside calipers. The legs of outside calipers have a large curvature so that the calipers may be passed over cylinders of their greatest capacity.

Inside calipers, Fig. 16, are much like dividers in general appearance, the ends being bent outward slightly and the points rounded. The same styles of joints used in dividers are used in calipers, and the size of calipers is also designated by the distance from the joint to the end of the leg. Spring calipers are made in sizes from 21/2 to 8 inches, while the other styles vary up to 24 inches.

Fig. 15. Steel Beam Trammels Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.

Fig. 16. Brown and Sharpe Inside Transfer Calipers.

Fig. 17. Brown and Sharpe'Outside Transfer Calipers.

Transfer Calipers

As it is sometimes necessary to make measurements behind shoulders and in chambered cavities where the ordinary calipers could not be removed after setting, it is necessary to have calipers so arranged that they may be set, changed to clear the obstruction, and then reset accurately in the first position. This is accomplished by transfer calipers, Fig. 17, in which one leg is temporarily fastened to a stub or false leg. After setting, this leg may be moved away from the stub, the calipers withdrawn, and the leg again placed in contact with the stub; the points will then be found to occupy the same position as when first set. Small curved legs may be used in place of points or trammels in calipering large objects.

Both dividers and calipers are usually set by means of a scale. In setting dividers, place one point in a graduation of the scale and move the other until it falls easily into another graduation which gives the required distance. Outside calipers are often set by placing one leg against the end of the scale and moving the other until it is opposite the middle of the graduation giving the required length. As the graduations are not mathematical lines but have an appreciable width, this last precaution is one of great importance. Inside calipers are set by placing both the scale and the caliper toe against a plane surface, as shown in Fig. 18; the other toe is then set the same as the outside caliper.

Caliper legs are comparatively slender, spring easily, and care must be taken in using them to see that the contact with the object being tested is very light. It is an easy matter to spring calipers of common sizes as much as one-sixteenth of an inch unless a gentle touch is used in handling them,

Fig. 18. Setting Inside Calipers.

Caliper Square

The caliper square is made by attaching a movable blade to the common square. In the ordinary forms it closely resembles a steel rule with two arms extending from it at right angles, one fixed near the end and the adjustable arm sliding along the scale with a clamping device for adjusting this movable arm. In order that the movable arm may be set accurately, caliper squares, Fig. 19, as at present constructed have two clamps for the movable arm. The one carrying the thumb nut is to be first clamped in approximately the right position, the clamp on the movable arm being secured after the adjustment has been made by the nut.

Fig 19. Caliper Square Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.

The sizes used vary from 3 inches up, and are limited only by the length of rule obtainable.