A vernier height gage, Fig. 4, is very useful for making drill jigs, templets, and other tools requiring very accurate measurements, and for locating working points, holes, or drill bushings. It is used for obtaining the height of projections from a plane surface, or the location of bushings in drill jigs, etc. The fixed jaw A is of sufficient thickness to allow the gage to stand upright. An extension C attached to the movable jaw B can be used for scribing lines when laying off measurements. In the absence of a height gage, the regular vernier caliper may be made to answer the same purpose by making a base which may be attached to the fixed jaw, Fig. 5.
A small angle iron, having a slot in the upright face to receive a scale for use in connection with a surface gage when laying off measurements is shown in Fig. 6. The slot should be planed perfectly square with the base of the angle iron.
A pair of accurately machined V-blocks is a necessary part of every tool-maker's kit. If made of machine or too) steel, they will not need truing so often as if made of cast iron. After roughing out the V's, every surface should be planed square. They should then be clamped, by means of finger pieces, against the rail on the planer table, the edge of the rail having been previously trued. The head of the planer should then be set to the proper angle, usually 45 degrees, and one of the angles finished; the head may now be set over the opposite way and the other angle faceplaned. The tool used should be ground to give a smooth cut, as it is not advisable to do any finishing with a file or scraper.
Fig. 4. Vernier Height Gage.
A few small gages of the most common angles will be found very convenient, as they can be used in places not accessible to the ordinary bevel protractor; the angles most commonly used are 60 degrees, 65 degrees, 70 degrees, and SO degrees. The form of gage is shown in Fig. 7. If the tool-maker should be called on to make punch press dies, one or more angle gages, as shown in Fig. 8, will be found very useful.
Many die-makers use an adjustable square having a narrow blade which passes through the aperture in the die. The amount of clearance given is determined by the judgment of the workman.
Fig. 5. Special Base Attached to Vernier Caliper.
Fig. 6. Attachment for Use with Surface Gage.
While this method does very well when practiced by an experienced man, it is rather uncertain when attempted by the novice. To get the proper clearance, the beginner should use the gage shown in Fig. 8, called, improperly, a die-maker'a square. The angle depends on the nature of the stock to be punched and on the custom in the individual shop; hut a set of three gages, one 91 degrees, one 91 1/2 degrees, and one 92 degrees, will meet the requirements, as the clearance is seldom less than 1 degree or more than 2 degrees. The angle should be stamped on the wide part of the gage, as shown in Fig. 7. To avoid springing out of shape, the stamping should be done before the gage is finish-filed at any point.
The tool-maker should always have at hand a solution of blue vitriol for coloring the surface on which he is to draw lines. To make the solution, dissolve in a two-ounce bottle of water all the blue vitriol crystals the water will take up; to this add one-half teaspoonful of sulphuric acid. This produces a copper-colored surface when put on polished steel free from grease and dirt.
Fig. 7. 60-Degree Angle Gage.
Fig. 9. Forma of Straightedge and Holder for Grinding.
A straightedge is a necessary part of a tool-maker's kit. Many tool-makers have several, varying in length from 1 inch to 12 inches, or even longer. The tool should be kept in a case in order that its edge may not become marred. For short straightedges, the form shown at A in Fig. 9 is very satisfactory; this is known as a knife-edge straightedge. For the shorter lengths, pieces of sword blade answer very well, or steel of the desired form may be procured. Often the longer lengths are made from steel rectangular in shape, one edge being planed or milled, as shown at B.
When grinding a straightedge, it is necessary to hold the piece in such a way as to prevent any spring. This may be done by centering a piece of brass or machinery steel, and then milling or planing a groove, as shown at C. The blade may be held in the groove by dropping a little soft solder at each end of the blade; if the blade is more than two inches in length, a drop should be placed at distances about one inch apart. As straightedges are usually inclined somewhat in use, it is necessary to grind not only the edge, but the portions marked e at B. The edge and the corners should be lapped by hand by placing fine emery on a flat bench lap. It will be necessary to finish by oil-stoning any high places that are not removed by lapping. To test the straightedge, try it on a master straightedge, or on a true surface plate.
Short straightedges for general use should be hardened to prevent excessive wear and also to prevent the edge from becoming bruised. To harden pieces of this character successfully, clamp pieces of iron to the sides so that from one-eighth to one-quarter inch projects. Then heat to a low red. If the edge is thin, harden in cottonseed oil, plunging the tool beneath the surface of the oil, and working it up and down and around in the oil. If the stock is too thick to harden in oil, use lukewarm water. If a little cyanide of potassium is placed on the edge just before dipping, uniform results will follow.
Master straightedges, 12 inches or more in length, are generally made from steel that is rectangular in cross-section, with the working edge left the full thickness of the stock. The edge is ground in a surface grinder, the tool being held in such a way as to do away with any liability to spring. A very satisfactory holding device is the magnetic chuck which precludes all danger of marring the piece. Long master straightedges are usually made from cast iron and are heavily ribbed to prevent springing.