In many situations, including the manufacture of aircraft, the angle of a fastener hole relative to the surface through which it extends is required to be within very close tolerances. For example, such holes in aircraft are generally required to be within two degrees of normal to the surface. Thus, during the manufacturing process it is necessary to check each hole to ensure that it is within the allowed tolerance.
There are a number of known methods and devices for measuring the angularity of such fastener holes. One method is to insert a pin into the hole and to use a protractor to measure the angle. This method has the disadvantage of requiring the pin to be precisely dimensioned to the hole so that it will fit tightly in the hole. If the pin is too small, the fit will not be tight and the measurement will be inaccurate; if the pin is too large, it will not fit into the hole. The method also has the disadvantages of being fairly awkward to carry out and of requiring two separate tools: the pin and the protractor.
Another method is to insert a fastener into the hole and then to use shims or feelers under the head of the fastener to evaluate the fit. This method also has the disadvantages of requiring a tight fit between the hole and the fastener, of being awkward to carry out, and of requiring more than one tool. In addition, this second method requires experience in evaluating the degree of angularity that exists.
The known gauges for measuring hole angularity are numerous and include gauges for a variety of special purposes. Some of the known gauges include a plug that is precisely dimensioned to the hole for tightly engaging the hole. This type of gauge does not function well if the hole varies in size sufficiently to make the fit between the plug and the hole loose or to prevent insertion of the plug into the hole. Other known gauges include a member that makes linear contact with a sidewall portion of the hole. Such gauges do not provide accurate readings if there is any significant variation in the angularity of the sidewall of the hole around the circumference of the hole. This drawback can be partially compensated for by taking a number of readings at different points around the circumference. However, such a procedure makes the measuring of the angularity an unreasonably long process. Another type of known gauge is one in which there are two or more point contacts between a member that is inserted into the hole and the sidewall of the hole. This type of gauge also has the disadvantage of being subject to inaccurate readings because of variations in the angularity around the circumference of the hole.
Hole angularity gauges are disclosed in U.S. Pat. Nos.: 1,852,760, granted Apr. 5, 1932, to J. G. Sisson; 1,890,607, granted Dec. 13, 1932, to S. V. Hite; 1,965,131, granted July 3, 1934, to R. J. O. Simpson; 2,134,262, granted Oct. 25, 1938, to H. J. Phillips; 2,527,758, granted Oct. 31, 1950, to J. E. Oslund; 2,714,256, granted Aug. 2, 1955, to L. J. Watson; 2,706,338, granted Apr. 19, 1955, to C. Ackerman et al; 3,114,978, granted Dec. 24, 1963, to E. Porter; and 3,162,953, granted Dec. 29, 1964, to E. Porter. The gauges disclosed by Sisson, Simpson, and Oslund are of the type that make linear contact with the hole sidewall. The gauges disclosed by Hite, Phillips, Watson, and Ackerman et al make contact with the hole sidewall at two or more points. The gauges disclosed in the two Porter patents include a precisely dimensioned plug for fitting into the hole. The diameter of the plug is adjustable in some of the embodiments disclosed by Porter. The gauges in each of the above-cited patents, except Hite and Phillips, include a member that fits into the hole and that is pivotably attached to another member that engages a surface around the hole. In the gauges disclosed by Sisson, Simpson, Phillips, Watson, and Ackerman et al, the pivoting of the sidewall engaging member is spring biased to bring the member into contact with the sidewall. The Porter gauges include spaced apart legs, rather than a flat surface, for engaging an object around a hole therein to accommodate a flat or a curved surface.
U.S. Pat. No. 2,546,532, granted Mar. 27, 1951, to J. B. Wade discloses a protractor-type gauge for measuring the tangential angle of the outer portions of the impeller vanes of a centrifugal impeller pump. U.S. Pat. No. 2,787,865, granted Apr. 9, 1957, to M. J. Gross discloses a device for honing a bore and for indicating when the desired diameter of the bore has been reached. When the diameter of the hole is large enough, a downwardly biased sleeve that is carried by the honing mechanism enters the bore and triggers a switch to indicate that the honing operation is complete. The sleeve pivots to automatically adjust to the angle of the bore. U.S. Pat. No. 4,200,987, granted May 6, 1980, to M. G. Schmitt discloses a gauge that apparently measures the diameter only of a hole and that fits fairly closely in the hole but makes contact at two points only.
The above patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative the prior art.