Concentricity Gage

This invention relates to a concentricity gage and, more particularly, to a gage for determining the concentricity between two axially spaced bores in a workpiece.

Many types of workpieces are formed with two axially spaced bores which must be concentric with one another to a high degree of accuracy. One or both of these bores may be a cylindrical surface, an axially splined surface or a thread. Gages for determining whether such bores, especially those having a pitch diameter, are concentric within the desired degree of accuracy are normally of complicated and costly construction. Furthermore, conventional gages of this type are so designed as to require an entirely separate gage for each differently sized bore.

The primary object of this invention is to provide a concentricity gage that is of simple and relatively economical construction and which requires the substitution of only two components for gaging differently sized bores.

Other objects features and advantages of the present invention will become apparent from the following description and accompanying drawing, in which:

FIG. 1 is a generally vertical sectional view of a concentricity gage according to the present invention; and

FIG. 2 is an exploded perspective view of the gage.

The particular gage shown in the drawing is designed for checking the concentricity of bores in a workpiece 10, such as a splined bore 12 and a threaded bore 14 spaced axially from bore 12. However, it will be apparent from the description that follows that the gage of this invention can be designed for checking the concentricity of two axially spaced bores of various types regardless of whether they are plain cylindrical bores, splined bores or threaded bores.

The gage itself which is designated 16, comprises a mandrel 18 having an accurately ground, cylindrical shaft 20 extending axially from and concentric with a conical collet expander 22. A generally conventional expandable collet 24 is arranged on collet 22 and is adapted to be expanded by means of a screw 26 threaded into the smaller end of expander 22 and having a washer 28 thereon adapted to abut against the end of collet 24. The external surface of collet 24 is formed for close fitting relation with the bore 12 of the workpiece. In the particular embodiment illustrated in collet 24 is formed with a plurality of axially extending splines 30 for close interfitting engagement with the splines in bore 12. The tight fitting relationship between collet 24 and bore 12 is obtained by tightening screw 26 so as to expand collet 24 firmly into bore 12. Expander 22 and collet 24 are ground so as to be concentric to a high degree of accuracy to the central longitudinal axis of mandrel 18. Thus, when collet 24 is expanded into engagement with bore 12, the longitudinal axis of mandrel 18 is concentric to a high degree of accuracy with the pitch circle of bore 12.

Gage 10 includes a plug 32 which is shaped and sized to be snugly received within the bore 14 of the workpiece. Thus, if the bore 14 is threaded as shown, plug 32 would be formed with a thread 34 having a close fit with the threaded bore 14 in the workpiece. Plug 32 has an enlarged knob 36 machined with an annular recess 37 to receive a rocker ring 38. Ring 38 is loosely retained within knob 36 by a snap ring 40. One end face of ring 38 is fashioned with a pair of diametrically opposite, rounded protuberances 42. The opposite end face, that is, the end face within knob 36, is likewise formed with a pair of diametrically opposed, axially projecting, rounded protuberances 44. Protuberances 44 are displaced circumferentially 90.degree. from the protuberances 42. When plug 32 is threaded fully into bore 14 protuberances 42 engage end face 46 of workpiece 10 and protuberances 44 abut against the internal face 48 of plug 32. These two sets of protuberances prevent the plug 32 from becoming cocked or skewed to the axis of bore 14 in the event that the face 46 on the workpiece is not accurately perpendicular to the axis of bore 14. Plug 32 is also formed with an accurately dimensioned bore 50 which is accurately concentric to the pitch diameter of thread 34. Bore 50 extends at least to the end portion of plug 32 on which the thread 34 is ground.

When the plug 32 and the collet 24 are interengaged with their respective bores 12 and 24 on the workpiece, the cylindrical shank 20 of mandrel 18 extends axially through bore 50 and beyond the outer end face of plug 32. A "go" bushing 52 has a central axial bore 54 which has an accurate sliding fit on the shank 20 of mandrel 18. At one end thereof bushing 52 is formed with a radial enlargement 56. The radially outermost surface of enlargement 56 is spaced radially from the central axis of bore 54 a distance relative to bore 50 which represents the maximum concentricity tolerance adapted to be checked by the gage. For example, if the gage is designed to check the concentricity of bores 12 and 14 within 0.005", then the radius to the outer surface of enlargement 56 is ground substantially 0.005" less than the radius of bore 50. To facilitate the introduction of the leading end of bushing 52 into bore 50, bushing 52 is formed with a radially inwardly tapered leading end 57 and plug 32 is formed with an enlarged bore 58 adjacent its outer end which is connected with bore 50 by a conical portion 60.

In using the gage of this invention collet 24 is inserted in the splined bore 12 of the workpiece. Thereafter mandrel 18 is directed through the threaded bore 14 in the workpiece so as to seat collet expander 22 within collet 24. Screw 26 is then tightened so that collet 24 is expanded into firm engagement with bore 12 in the workpiece. The mandrel is prevented from rotatin when screw 26 is tightened by gripping the non-circular end 62 with a wrench. After the mandrel is so engaged with the workpiece, concentricity plug 32 is threaded into bore 14 to a position wherein rocker ring 38 is coamped firmly between the end face 46 of the workpiece and the face 48 of recess 37. Bushing 52 is then rotated and advanced on the shank 20 of mandrel 18 so that the enlargement 56 is disposed within bore 50. If bore 14 is concentric to bore 12 within the specified tolerance, for example 0.005", then bushing 52 will rotate freely on shaft 20. However, if bores 14 and 12 are skewed relative to one another or offset radially relative to one another a distance greater than the specified tolerance, then the enlargement 56 will not rotate freely around 360.degree. within bore 50. If bushing 52 binds within bore 50 this is an indication that the two bores 12 and 14 are not concentric within the required tolerance.

If it is desired to check the concentricity of two bore of different sizes than bores 12 and 14 within the same tolerance limits, it is only necessary to substitute a properly dimensioned collet 24 and a properly dimensioned plug 32. The same mandrel 18 may be used and the same "go" bushing 52 may be employed with the mandrel 18. It is only necessary that collet 24 and plug 32 be dimensioned and have a configuration corresponding to the two bores in the workpiece to be checked. Thus, either of the bores can be threaded, splined or simply plain cylindrical surfaces. In any event, a collet such as shown at 24 should be employed so that the mandrel can be clamped to the workpiece so that its axis is accurately concentric with one of the bores in the workpiece. While the gage of this invention can be used for checking the concentricity of two cylindrical bores, its primary usefulness resides in checking the concentricity of two bores at least one of which has a pitch diameter as is the case with threaded and splined bores.