Fig. 443 illustrates a gage for showing the proper location of the hole from the edges A and B, Fig. 444. It consists of a base having four pins for the edges A and B to rest against. These pins are flatted on the contact edges to prevent wearing. The piece of work to be gaged is placed in position and clamped to the gage with machinist's clamps, Fig. 445, and the gage is fastened to the faceplate of the lathe in such a manner that the work can be removed without disturbing the location of the gage.
A short plug, fitting very accurately, is then inserted in the hole in the model. By means of a lathe indicator, the gage can be located so that the plug runs perfectly true. When this has been accomplished, the model may be removed and the bushing hole drilled and bored to size, after which the bushing may be made, hardened, ground to size, and forced to place. The location of the drilled hole may be tested by placing the piece of work on the gage against the pins, and entering the gage pin in the hole in the work and bushing, Fig. 446. If the pin is a close fit in the holes, a very slight error in location may be detected. When a slight error is allowable, and it is not considered advisable to hold the location too close, the pin may be made a trifle small, thus transforming the gage into a limit gage.
If it is necessary to make a locating gage, for testing the center distance of two holes, one pin may be made removable, while the other is rigidly fixed, as shown at C, Fig. 447. If the gage is made with both pins fixed, and the pins are a good fit in the holes, it is a difficult operation to remove the piece of work. Withdrawing one pin allows the piece of work to be readily taken from the fixed pin.
Fig. 445. Piece Clamped in Gage.
Fig. 446. Gaging Hole.
When making a gage of the form shown in Fig. 447, the fixed pin C may be located by approximate measurements; but the hole should be drilled by some method that insures the pin standing perfectly square with the base of the gage. If a small limit of variation is permissible in the center to center measurement A, the model may be placed on the gage with the large hole on the fixed pin C, and the location of the hole for the movable pin may be transferred from the model by drilling and reaming. If extreme accuracy is essential, it will be advisable to clamp the model to the gage as described, then to fasten the gage to the faceplate of the lathe, place an accurately fitting pin in the small hole in the model, and by means of a lathe indicator locate the gage so that the pin runs perfectly true. The model may then be removed and the hole drilled and bored to size.
Fig. 447. Simple Form of Locating Gage Showing Method of Use.
Fig. 448. Gage for Measuring Locations and Directions of Holes.
Locating gages are made to measure the location of one or more holes from another hole or shoulder, or both. Fig. 448 is a gage to measure the locations of holes a and b from the hole c and shoulder d. The hole c is set on a stud solid with the base, and a and b are gaged by means of the hardened and ground pins shown.
Micrometer locating gages are very commonly used in many shops. They are especially valuable for measuring such pieces as require very close watching, or where a certain variation is permissible, for by means of micrometer readings the amount of variation in thousandths of an inch is easily determined. Fig. 449 shows a micrometer gage used in measuring the angle surface a in connection with base b and shoulder c.
Fig. 449. Micrometer Gage.