To get the thickness of a wall beyond a shoulder, as at K, Fig. 7, set the caliper so that the legs will pass over the shoulder freely, and with a scale measure the distance between the outside leg and the outside of the piece. Then remove the caliper and measure the distance between the caliper points. The difference between these two distances will be the thickness M.
Inside Calipers for Close Spaces
In Fig. 8 are shown a pair of inside calipers which are bent so as to be well adapted for calipering distances difficult of access, such as the keyway in a shaft and hub which does not extend beyond the hub, as indicated. With the ordinary inside calipers, having straight legs, and which are commonly used for inside work, it is generally impossible to get the exact size, as the end which is held in the hand comes in contact with the shaft before both points come into the same vertical plane. The engraving plainly shows how calipers for this purpose are made, and how used. Any mechanic can easily bend a common pair to about the shape shown to accommodate this class of work.[[3]]
Fig. 8. Inside Calipers for Close Spaces
Surface Gage with Two Pointers
Figs. 9 and 10 show a special surface gage, and illustrate an original idea which has been found to be a great saver of time and of milling cutters. It can also be used on the planer or shaper. By its use the operator can raise the milling machine table to the right height without testing the cut two or three times, and eliminate the danger of taking a cut that is liable to break the cutter. This tool is especially valuable on castings, as raising the table and allowing the cutter to revolve in the gritty surface while finding the lowest spot is very disastrous to the cutting edges.
Figs. 9 and 10. Surface Gage with Two Pointers
To use this surface gage, the pointer marked C in Fig. 9 is set to the lowest spot in the casting, and then the pointer B is set from it with perhaps 1/32 inch between the points for a cut sufficient to clean up the surface. Pointer C is then folded up as shown at C′ in Fig. 10, and the table is raised until the pointer B will just touch the under side of the cutter as shown at B′ in Fig. 10. In this way the table is quickly adjusted to a cut that will clean the casting or other piece being machined, and with no cutting or trying whatever.[[4]]