Gage Making and Lapping. Various
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Fig. 7. Receiving Gage
Fig. 6 shows a very simple style of snap gage. This type is easily duplicated. In this gage spacers E are used which are made to the required size for the piece to be gaged. The plates F are parallel pieces of hardened steel which have been ground and lapped. When the gage becomes worn, all that is necessary in order to duplicate the original size is to remove the plates, lap the surfaces true, and lap off the required amount on the spacer. A limit gage can be made by adding another plate and using spacers of proper length as shown at G.
Method of Making a Receiving Gage
The receiving gage, Fig. 7, is a very difficult gage to make, and on account of its cost, it is rarely used except where it is absolutely necessary to do so. The gage is made to fit accurately the entire profile of the piece to be gaged, and is made of a series of small pieces fitted together, the object being to overcome as far as possible the distortion of the steel when passing through the hardening process. The base H is of machine steel, case-hardened, and its upper surface lapped perfectly level. The pieces J are ground and lapped on the bottom, and the formed edges are lapped by hand to fit the model. To obtain the best results, fit the pieces J to the model while the pieces are soft, and fasten them to the base H by screws. The dowel holes are now drilled and tapped with a fine pitch tap, say 5/16 inch diameter, 32 threads per inch. After the pieces J and the base are hardened, soft steel screws are turned securely into these holes and dressed off flush with the top and bottom of the pieces J and the base. After the pieces are lapped to fit the model, they are tightened in their places, and the soft screw bushing drilled and reamed through for the dowels. It is impracticable to attempt to lap dowel holes true, especially when they are tapered and do not line up. This soft screw bushing will be found useful on many other tools where dowel holes are apt to change during hardening.
Fig. 8. Universal Snap Gage for Large Work
Making a Universal Snap Gage
Fig. 8 shows a universal snap gage that is designed especially for large work. All that is necessary to make one gage cover a wide field is to set the gage to the required diameter (from standard length rods, so that the pointer stands at zero), then as the gage hangs on the piece to be gaged, it is swung so that anvil L passes over the highest point, and the pointer will record 200 times greater than the actual error. Any one who has used a large micrometer for measuring such work as is found in arsenals knows the difficulties under which one is obliged to obtain measurements. One man will hold the micrometer on the breech of a large gun and another man will do the measuring. With this form of gage one man can measure very handily, as all that is necessary to do is to note the number of graduations traversed by the pointer when the gage passes over the work.
* MACHINERY, June, 1905.
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