It is commonly know that in industry it is a concern, and a problem, to form a hole in an exact location in a workpiece. This is particularly a problem where the workpiece is cylindrical and one desires to drill on that workpiece curvature but yet have the hole formed in a dead-center position. Normally, the drill will inherently wander off the dead-center position, by virtue of the curvature of the cylindrical surface of the workpiece. It is common practice to provide a drill guide or bushing to assure that the hole will be formed on dead-center. However, the prior art does not provide for adjustment of the guide or bushing to position the hole either on dead-center or slightly off center or to position a drilled hole or the like in any other accurate position on a workpiece of any other configuration other than cylindrical.
Examples of prior art guides or jigs for drills or the like are shown in U.S. Pat. Nos. 3,138,975 and 3,685,916. These patents show drill bushings which are movable, relative to a workpiece, so that they can be positioned for guiding the drill onto the workpiece. However, they do not show any means for adjusting the bushing to have it be set in a specific adjusted position, relative to the workpiece, nor do they show a facile manner for moving the bushing out of the way when it is desired to ream, tap, or perform other operations on the drilled workpiece but to do so in the absence of the previously used bushing.
Accordingly, the present invention improves upon the prior art by providing a jig for hole formation in workpieces of various configurations, and to be able to accurately locate the hole in a precise position. This object is accomplished by virtue of having the jig include a drill guiding bushing which can be adjustably located, and its adjusted location can be re-established even though the bushing is moved off the workpiece for other operations, as mentioned.
Still further, the present invention provides for an adjustable jig which has a plurality of adjustments relative to the workpiece so that the drill or like cutting tool can be guided onto the workpiece which has been adjusted in any one or more of two or more ways, such as relative to the curvature of a cylindrical workpiece, relative to the location of a hole from the end of the workpiece, or relative to the location of a hole from a shoulder on the workpiece. All of these accurate locations are accomplished by virtue of a single jig with these several adjustment features. Further, the adjustments mentioned are readily and easily accomplished, so that repetitive drilling or the like can be carried on with the workpiece in a production type of operation and with therefore only a minimum of skill and time required. That is, the adjustment can be made at one time, and then the guide bushing can be swung into and out of position, by means of a lever or arm-type of control and locking mechanism which is readily but securely accomplished.
The aforementioned objectives are accomplished by means of a sturdy jig which is readily and easily set in the adjustment positions mentioned, and which securely holds the workpiece while it is being worked upon, and the jig is suitable for production type of accomplishment.