Caliper

“ Soon after the first graduating machine was put into use, the vernier caliper, reading to thousandths of an inch, was brought out by Mr. Brown; the first was made as early as 1851. In the following year he applied the vernier to protractors. A writer, in speaking of the invention of the vernier caliper, says, “It was the first practical tool for exact measurements which could be sold in any country at a price within the reach of the ordinary machinist, and its importance in the attainment of accuracy for fine work can hardly be overestimated.” ”

“ All measurements are from the center line upon which the bushing No. 1 is placed. Taking this as a starting point we find the caliper to read 1 inch. Bushing No. 2, which is undergoing the test, should be 5⁄8 inch from this center line. It has a 1⁄4-inch hole, and we therefore insert a plug of this diameter. Now adjust the tongue of the caliper to the bottom of this plug (as shown in the engraving) and the vernier should read 1.625 minus one-half the diameter of the plug, or 1.500, and any variation from this will show the error of the jig. ”

“ The combination caliper and divider shown in Fig. 15 is one that is not manufactured by any of the various tool companies. It is, however, one of the handiest tools that can be in a machinist's kit, as it lends itself to so many varied uses, and often is capable of being used where only a special tool can be employed. The illustration suggests its usefulness. The tool can be used as an outside caliper, as an inside caliper, and as a divider. ”

“ The capacity of the screw machine is, therefore, many times greater than that of a lathe, while the diameters and lengths of the various parts of the work will be more uniform than can be done by caliper measurements, being in this case varied by the wear of the cutting edges of the tools only, which eliminates the errors liable to independent caliper measurement. ”

“ In order to increase the usefulness of these tools, the attachments shown in Fig. 16 may be made. In the upper left-hand part of the engraving the details of a useful addition to the caliper are shown. A is made of machine steel, while the tongue B is of tool steel, hardened and ground and lapped to a thickness of 0.150 inch, the top and bottom being absolutely parallel. This tongue is secured to A by the two rivets CC. The thumb-screw D is used for fastening the attachment to the sliding jaw of the vernier or slide caliper. ”

“ In scribing a circle with a pair of dividers mark the center with your center punch first as this will prevent your dividers from slipping.
(10) Inside calipers are used for measuring the inside diameters of cylinders and the like, and, conversely (11) , outside calipers are used for measuring the outside of anything that is round. In either case you measure the distance between the points of your caliper with your rule to find the diameter of the thing. (12) A center punch is always useful to make [62] a starting point in metal with, for it can’t be rubbed off or lost sight of. ”

“ Schœner and Richter are in 1813 mentioned as inventors of the first “universal forest measure” or caliper. The improvement of calipers to their modern efficiency has been carried on since 1840 by Carl and Gustav Heyer and by many others until now self-recording calipers by (Reuss, Wimmenauer, etc.) have become practical instruments. For measuring the heights of trees, Hossfeld had already a satisfactory instrument in 1800 ”

“ A Vise Used as a Caliper Gauge
Not infrequently it is desired to know the distance from one side to another of some part that cannot be directly measured with a rule, and when no calipers are at hand. But with a vise handy, the measurement can be made with ease and with sufficient accuracy for all practical purposes if the vise is not too worn. This trick is particularly adapted for calipering threaded parts, as threads cannot be measured readily with ordinary calipers. How this may be done is shown in the sketch, which illustrates the method as applied to a screw. ”

“ The sizing of the outer diameter of the bushing, which was 1.158 inch, must be done so accurately that it was not thought wise to trust to the ordinary micrometer caliper. An indexing device was therefore made having a calipering lever with a long end, in the ratio of 10 to 1, which actuated the plunger of a dial test indicator of the well-known type made by the Waltham Watch Tool Co. The thousandth graduations on the dial of this indicator would then read in ten-thousandths, permitting readings to be taken to one-half or one-quarter of this amount. ”

“ For small lathe work of odd size as when it is required to turn work to fit holes reamed by a worn reamer that is below the standard size, a gauge such as in Fig. 1403, is sometimes used, the mouth a serving as a caliper and the hole b as a collar gauge for the same diameter of work. It is obvious that such a gauge may be applied to the work while it is running in the lathe, and that when the size at a wears too large the jaw may be closed to correct it ”

“ A small spiral spring, marked I, gives the rod a constant downward pressure, so that, when taking a measurement, the base of the tool is placed on the piece of work, and the rod always finds the bottom of the hole; then, by tightening the knurled screw F the rod is clamped in position and the tool may be picked up and its measurement read from the dial. The graduations on this instrument are similar to those of the vernier caliper, only they are much plainer, as a half-inch movement of the rod turns the dial one complete revolution. ”

“ If it were attempted to drill the holes through the beam at exactly one inch apart, having only one hole in the clamping head and using it as a jig for the purpose, it would be found very difficult, if not impossible, to get the holes all of one size and exactly one inch apart. The design of the micrometer beam caliper shown in Fig. 17, which has been patented by Mr. Frank Spalding, Providence, Rhode Island, is such, however, that it is not necessary to drill more than one hole through the clamping slide. ”

“ Calipers possess one great advantage over more rigid and solid gauges, in that the calipers may be forced over the work when the degree of force necessary to pass them on indicates how much the work is too large, and therefore how much it requires reducing. ”

“ These are turned to diameters, and are the most readily secured by the use of the micrometer calipers to be had of any large watchmakers' tool and supply house. In addition to the diameters named, we must get the proper height for the balance, which is represented by the dotted line b. The measurement for this can usually be obtained from the old cylinder by simply comparing it with the new one as it rests in the cement chuck. The true tool for such measurements is a height gage. ”

“ But the workman of the general machine shop who has no experience in measuring by thousandths has no idea of the accuracy with which he sets two calipers in his ordinary practice. The great difference that the one-thousandth of an inch makes in the fit of two pieces may be shown as in Fig. 1419, which represents a collar gauge of 5⁄8 inch in diameter, and a plug 1⁄1000 inch less in diameter, and it was found that with the plug inserted 1⁄8 inch in the collar it could be moved from a to b, a distance of about 5⁄16 inch, which an ordinary workman would at once recognise as a very loose fit. ”

“ In this case the top surface of B was used and no allowance had to be made for its thickness. In case the bottom surface is used, 0.150 must be deducted from the reading of the caliper.
Fig. 16. Attachment for Vernier Calipers
It is very easy to make a mistake in setting a bushing, and such a mistake is equally hard to detect unless some such means of measuring as this is at hand. It often happens that jigs and fixtures are put into use containing such errors, and the trouble is not discovered until many dollars' worth of work has been finished and found worthless. ”

“ Free from the defects named in the following rules for the use of the inspecting instruments:
FOR SHOT.
70. Inspecting Instruments.—One large, small, and one medium ring gauge, and one cylinder-gauge for each calibre. The cylinder-gauge shall have the same diameter as the large gauge, made of cast iron, and three calibres in length. One hammer weighing two pounds, and having a flat face and a conical point; one searcher, of steel wire, with a handle; one pair of calipers and standard scale; one cold chisel; steel punches. ”

“ Experts always true springs after they have been staked to the balance and a light weight calipers tapered on one end to a smaller diameter than the collet is used for spinning the balance, making observations, and corrections. ”

“ A short space is first turned by hand feeding, as at D, Fig. 7, and when the calipers show that the diameter is slightly greater than the finished size (to allow for a light finishing [11] cut, either in the lathe or grinding machine) the power feed for the carriage is engaged; the tool then moves along the work, reducing it as at E. Evidently, if the movement is along a line b—b, parallel with the axis a—a, the diameter d will be the same at all points, and a true cylindrical piece will be turned. ”

“ CALIPERS, DIVIDERS, AND SURFACE GAGES
In the present chapter we shall deal with the simpler forms of tools used for measuring, such as ordinary calipers, and their use; surface gages; special attachments for scales and squares, facilitating accurate measuring; and vernier and beam calipers. ”

“ For measuring the distance of a slot or keyway from a surface, the form of calipers shown in Fig. 1424 is employed; the straight leg has its surface a true plane, and is held flat against the surface b of the slot or keyway, and the outside or curved leg is set to meet the distance of the work surface measuring the distance c. These are termed keyway calipers.
There are in general machine work four kinds of fit, as follow: The working or sliding fit; the driving fit; the hydraulic press fit; and the shrinkage fit. ”

“ But you who, when beginning to cut out back or belly, having no sort of experience whatever, must use every care possible, and keep calipers No. 3 (double) going constantly, as, with their aid, you will at once see by the outside half the thickness registered at the inner; then you can pare away with gouges, small and large, and with spoke shaves, Nos. 48 and 53, until you get a fairly sloping and somewhat level surface from bare three-sixteenths of an inch in centre to full three-thirty-seconds of an inch all round by the edges, as shown by calipers. ”

“ When the surfaces of work are to be parallel, they can be measured with calipers. Surfaces to be at a right angle can be tested with a square; those to be in line can be tried with a straight-edge, and in each case the truth or alignment of the surfaces is tested by contact of the testing tool. ”

“ We can readily see that as we increase the height of the heel of the impulse face of our tooth we must also increase the angle of impulse imparted to the cylinder. With the advantages of accurate micrometer calipers now possessed by the horological student it is an easy matter to get at the angular extent of the real lift of any cylinder. The advantage of such measuring instruments is also made manifest in determining when the proper proportion of the cylinder is cut away for the half shell. ”

“ The micrometer is so set that when a gage, G, of exact size, is placed between the measuring points, the long arm of the indicator stands at the 0 mark. If the pieces being calipered vary in the least from the standard size it will be readily noted by the movement of the pointer. Hard rubber shapes turned from rough casting often vary from 0.003 to 0.005 inch after having passed the inspector's test with an ordinary micrometer. With this attachment the inspector's helper can detect very minute variations from the limit size. ”

“ Considerable progress can be made by some watchmakers in removing the spring from the balance and placing it on a colleting tool or tapered broach and then truing the flat and round as good as possible, after which it should be perfected in the calipers. When the balance is spinning in the calipers and the spring is true in the flat there will be no jumping or quivering of the coils as observation is made across the top of the inner four or five coils. ”

“ The former of these is employed in measuring the dimensions of outside work, and the latter, for that on the inside. This kind is called the in-and-out calipers; and it is especially useful in turning a cylinder, or pin, which shall exactly fit an internal cylinder already made, and vice versâ.
8. There is but little difference in the management of turning different substances. The principal thing to be attended to is to adapt the velocity of the motion to the nature of the material; thus wood will work best with the greatest velocity that can be given to it. ”

“ Before we proceed with our work it will be necessary for us to make some accurate measurements, as we cannot afford to do any guess work by measuring by means of the old staff. I have used a number of different kinds of calipers and measuring instruments for determining the various measurements for a balance staff, but have met with more success with a very simple little tool which I made myself from drawings and description published some years ago in The American Jeweler. This simple little tool is shown in Fig. ”

“ VI. Calibration Correction.—The calibration of the resistance box and the bridge-wire corresponds to the calibration of the stem of the mercury thermometer, but the process is much simpler for several reasons. It is more easy to obtain a uniform wire than a uniform tube. The scale of the wire is much more open, it corresponds to a very small part of the whole scale, and the process of calibration is easier. One box when calibrated will serve for any number of thermometers of different ranges and scales, and covers the whole range of temperature (see Calibration) . ”