Abstract: A gauge for indicating the correct alignment for a thumb hole of a bowling ball having a ring with a circular abutment section having a central axis, the ring having an aperture through the opening inside the abutment section, the ring also having a circular track concentric and coaxial with the central axis and angular indicia on the ring. A fin is attached to the ring extending in a plane which includes the central axis. A thumb plate having a periphery which fits and rotates in the track, the thumb plate having a centrally located thumb aperture with a boundary having a generally flattened portion against which the top of the thumb will bear and an opposite generally rounded portion against which the bottom of the thumb will bear, the thumb plate also having an index mark to align with the angular indicia on the ring to indicate the correct angular orientation of the thumb hole to be drilled in the bowling ball.

Abstract: A vacuum dish (10) is rigidly bolted (60) to the support table (12) of a milling machine (14). A bowling ball (74) is set down onto the upwardly directed hard rim (72) of the vacuum dish (10). An elastomeric seal (86) is moved upwardly along the sidewall (66) of the vacuum dish (10), onto an upwardly converging conical surface (70) which borders the rim (72). This puts the elastomeric seal (86) into contact with both the conical surface (70) and an adjacent surface portion of the bowling ball (74). Precision lead screw mechanisms (42, 48, 44, 50) are operated to shift the support table (12) and the vacuum dish supported bowling ball (74) along X and Y axes, to position the bowling ball (74) relative to the vertical axis (Z) of a hole boring bit (30). The hole boring (30) is both rotated and moved vertically downwardly to form a finger or thumb hole in the bowling ball (74).

Abstract: A span gauge for measuring the distance between a thumb hole and a finger hole on a bowling ball comprised of a plate having a curved edge fitting the contour of the bowling ball and an angle positioning post pivotally attached to the edge of the plate. The radius of curvature on the curved edge is equal to the radius of curvature of the surface of the bowling ball and the pivoting post is attached to one end of the curved edge. A calibrated scale on the curved edge permits measurement by inserting the pivoted post in a pre-drilled thumb hole to determine the point at which the finger hole is to be drilled. The pivoted post allows the span gauge to compensate for the pitch angle of pre-drilled thumb holes which may vary from ball to ball.

Abstract: A gauge to measure and to indicate the divergence of the axis of a bore in a bowling ball from a radius of the bowling ball. This enables the orientation of grip holes in one bowling ball to be measured so they can faithfully be reproduced in another bowling ball. The gauge includes a reference plate which is to be pressed against the outside of the ball, a plug pivoted to the reference plate which enters a bore and expands so as to bear against its inside wall to align the plug, and a pointer mounted to the plug which, with a scale on the reference plate, indicates the relationship between the bore and the radius of the bowling ball. This in formation enables one to set up a drilling machine to reproduce this hole in another ball.