US2885914A - Small hole drilling machine - Google Patents

Description

y 1959 I B. E. FRANK ETAL 2,885,914

SMALL HOLE DRILLING MACHINE Filed Oct. 23, 1957 3 Sheets-Sheet 1 May 12, 1959 B. E. FRANK' ETAL SMALL HOLE DRILLING MACHINE 3 Sheets-Shet 2 Filed Oct. 25, 1957 May 12, 1959 B. E. FRANK ETAL SMALL nous DRILLING MACHINE Filed Oct. 25. 1957' 3 SheetsSheet 5 H TOCNE Y United States Patent SMALL HOLE DRILLING MACHINE Bernard E. Frank, Marlin E. Hazen, and Fay H. Stroud,

Rochester, N.Y., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application October 23, 1957, Serial No. 691,923.

2 'Claims. (Cl. 7732.4)

The invention relates to drilling machines and more particularly to machines for drilling small holes. When small holes are being drilled in a workpiece, care must be taken to prevent drill breakage. This hazard is always present due to the use of small drills which are normally operated at high speeds. These drills are usually operated at a speed only slightly below the drill breaking point. Many of the materials being drilled, particularly castings, are subject to having relatively hard spots scattered throughout the material. When a drill operating at optimum speed hits a hard spot of this type, it may be easily broken unless the hard spot is treated with care. An experienced drill operator will, with a very light touch, back oil the drill and cause it to peck slightly up and down with the drill rotating until the hard spot is broken through. He will then proceed with the drilling operation. In order to perform operations of this type, a" highly skilled operator must be used and he must be vigilant to prevent an undue amount of drill breakage and scrappingof the workpieces.

A machine embodying the invention accomplishes the same result as that accomplished by the experienced operator when encountering a hard spot. It causes. the feeding action of the drill to be interrupted and introduces a pecking action which is continued until the hard spot encountered is broken through. The machine then proceeds with the drilling operation as if the hard spot'had not been encountered. This pecking action is obtained only when hard spots are encountered and may be repeated any number of times depending'upon the number of hard spots engaged by the drill. The pecking action will not take place so long as hard spots are not encountered.

In the drawings: I

Figure 1 schematically shows a drilling machine embodying the invention with the machine in the inoperative position; 7

Figure 2 shows the controls for the machine of Figure Figure 3 shows the machine in the operative position while drilling a workpiece;

Figure 4 shows the controls for-the machine as illustrated in Figure 3;

Figure 5 shows the machine during the pecking action; and

Figure 6 showsthe controls for the machine illustrated in Figure 5. 7

Referring now to the machine and controls therefor, along bar type lever 10 is supported on a fulcrum 12", the lever being adjustably counterweighted by counterweights 14. These weights are slidable along bar 10 adjacent one end to vary the load on the drill head for different drilling operations. The drill motor 16 is suspended from the bar 10 and is furnished with a drill chuck 18 holding a drill 20. The workpiece 22 is positioned under drill 20 so that it may be drilled as desired.

The end 24 of bar 10 may be supported when in the inoperative position by a movable support such as cantiice lever spring. 26. When the bar is supported by spring 26, drill 20 is positioned above workpiece 22 and is prevented from engaging the workpiece. An electric motor 28 drives eccentric cam 30 through appropriate gear reduction. Cam 30 is positioned. underneath bar 10 at a point intermediate drill motor 16 and the bar end 24. When cam 30 is rotated in a counterclockwise direction, it engages bar 10 and moves the bar up and down to obtain the desired drill pecking action.

A feed cam. 32 may be driven by motor 34 through appropriate gear reduction. This. camdetermines the maximum feed rate of the drill 20 through the workpiece. This feed rate is preferably coordinated with the drill speed. so that a maximum amount of material may be removed within a given time while giving due consideration to the life of the drill. A spring loaded cam follower plunger 36. is secured to bar 10 at point 38 intermediate drill motor 16 and the bar end 24. It may be located adjacent but spaced. from cam 30. Plunger 36 is biased against cam 32 by spring 40 so that. the plunger is n01"- mally engaged with the. cam and the spring is normally; compressed: to a predetermined position. Plunger 36 is. connected with tandem switch 42 and actuates the switch as" will be explained below. Tandem switch 42 is pref.- erably a micro switch. Only slight movement of plunger 36'. is required to actuate it.

A. manually controlled switch 44 is provided adjacent a source of electricity 46 to control the entire operation of the mechanism. While the source of electricity is illustrated diagrammatically as a battery, it may of course be any source including power supply lines normally available in a shop. Manual switch 44 will start the entire drilling cycle when it is closed.

Three circuits are connected to switch 44. Circuit 48 controls motor 34 andv includes contacts 50 of a threecontact switch 52 and contacts 54 of tandem switch 42. Circuit 56 includes contacts 58 of switch 52 and contacts 60 of switch 42 and controls motor 28. Circuit 62 includes contacts 64 of switch 52 and controls the drill motor 16. Switch 52 has its contacts 50, 58 and 64 closed when bar 10 is moved off spring support 26 and lowered until drill 20 is immediately adjacent the workpiece 22.

In. the inoperative position shown in Figures 1 and 2, drill 22 is positioned above workpiece 22, cam 30 is in the horizontal position illustrated with its high point 66 in a plane substantially parallel to the axis of rotation of the cam. Bar. 10 has its end 24 resting on spring 26. Plunger 36 is engageable with the eccentric cam 32 at its high point 68. All of the contacts of switch 52' are opened and micro switch 42 has contact 54 closed and contact 60 opened. Thus none of the motors are energized and the machine is at rest. The workpiece may be removed and replaced with the machine in this position.

In order to operate the machine, manual switch 44 is closed and bar 10 is removed from spring support 26. The bar is permitted to pivot about fulcrum 12 until all of the contacts of switch 52 are closed. Bar 10 is normally permitted to pivot in this direction by proper adjustment of counterweights 14 so that the counterweights do not entirely balance the machinery supported by the portion of the bar opposite the counterweights. When contact 50 of switch 52 is closed, circuits 48 and 62 are energized, thus energizing drill motor 16 and cam motor 34. Cam motor 34 is energized since contacts 54 of switch 42 are normally closed. Cam 32 begins to rotate in a clockwise direction as is illustrated in Figure 3. The machine and the controls are now in the position shown in Figures 3 and 4. Bar 10 and the dependent structure including drill motor 16 are supported on cam 32 by spring loaded plunger 36. They are gradually lowered by the action of the cam obtained by its profile and rotation. As cam 32 rotates clockwise, the end of plunger I 36 approaches the rotating axis of the cam, thus permitting the drill motor to turn the drill through the workpiece at its maximum permissible rate.

If and when a hard spot is encountered in the workpiece being drilled, the additional support offered the mechanism by the hard spot will cause the spring biased plunger 36 to be relieved of a portion of its supporting load. The plunger will thus be moved slightly to actuate micro switch 42. When this switch is actuated, contacts 54 are opened and contacts 60 are closed. Circuit 48 to cam motor 34 is thus interrupted, causing the rotation of cam 32 to be held in abeyance at the point at which the hard spot was encountered. Since contacts 60 were closed, circuit 56 is then energized and cam motor 28 is started. Cam 30 will be rotated counterclockwise and its high point 66 will engage bar 10, moving the bar slightly up and down repeatedly until the drill breaks through the hard spot. This cyclic action of the drill caused by cam 30 is equivalent to the pecking action normally obtained by an experienced drill operator. Cam 30 will stop in the position illustrated in Figure 1 during each rotating cycle and will immediately commence another rotation cycle as it receives a signal that the hard spot is not broken through. This signal is provided by the continued energization of circuit 56 and deenergization of circuit 48.

When the hard spot is broken through, bar will again be lowered and plunger 36 will again engage feed rate cam 32 so that it is held in the normal drilling position. Feed rate cam 32 has, during the entire pecking action, remained stationary at the point where the normal drilling operation was cut off. When plunger 36' again bears the full supporting load of bar 10, switch 42 is actuated to open contact 60 and close contact 54. Cam motor 28 is thus deenergized and cam motor 34 is energized to continue the interrupted rotation of feed rate cam 32. The drilling process then continues as if the hard spot had never been encountered. Switch 42 may be so constructed that its contacts may not be reversed unless pecking cam 30 is in the position shown in Figure 1. Thus the pecking cam is kept clear of bar 10 during the normal drilling operation.

The pecking action of the machine may be repeated any number of times during the drilling of the workpiece until the hole being drilled is completed. Upon completion of the operation, the operator manually lifts lever 10 and supports it on spring 26. Thus switch 52 is opened and the workpiece may be changed. The operator may also he required to open the hand operating switch 44 as an added safety precaution.

A drilling machine and controls therefor have thus been provided which will drill through a workpiece having occasional hard spots and will overcome the hard spots in the manner of an experienced drill operator. The unit provides automatic controls which require a pecking action to overcome hard spots, these controls being initiated only when hard spots in the workpiece are encountered. Should no hard spots be encountered in any workpiece, feed rate cam 32 will cause the drill to be passed into the workpiece and removed therefrom in a continuous operation without interruption.

What is claimed is:

1. Control. mechanism for a rotary drill, said mechanism comprising a motor for rotating said drill, a feed rate cam for controlling the linear feed rate of said drill, a motor for driving said feed rate cam, a first circuit for controlling said rate cam motor, a cyclic cam for intermittently reversing the linear feed direction of said drill, a motor for driving said cyclic cam, a second circuit for controlling said cyclic cam motor, and means controlling said circuits for energizing said first circuit and de-energizing said second circuit under normal drill operation, said circuit controlling means deenergizing said first circuit and energizing said second circuit when the feed rate determined by said feed rate cam exceeds the actual feed rate of said drill.

2. Drilling mechanism for drilling holes at a predetermined feed rate in a workpiece and including means for overcoming hard spots in said workpiece, said mechanism comprising a support lever, a fulcrum for said lever, counterweights on one end of said lever for substantially counterbalancing said mechanism, a drill motor depending from said lever on the opposite side of said fulcrum from said counterweight, a drill rotatably driven by said motor, a feed rate cam for said mechanism, a feed rate cam follower operatively attached to said lever adjacent the end thereof opposite said counterweights and engageable with said feed rate earn, a switch operatively connected to be actuated by movement of said cam follower relative to said lever, said switch having a set of normally closed contacts and a set of normally open contacts, a cyclic cam operatively positioned beneath said lever for intermittent engagement therewith when said cam is rotated, a cam motor for rotating said feed rate cam, a cam motor for rotating said cyclic cam, a switch actuated by pivotal movement of said lever in a direction to lower said drill motor, said last named switch having three sets of normally open contacts which are closed by said lever pivotal movement, a first circuit including one set of contacts of said three-contact switch and the normally closed contacts of said other switch and said feed rate cam motor,

a second circuit including a second set of contacts of said three-contact switch and said normally open contacts of said other switch and said cyclic cam motor and a third circuit including the third set of contacts of said threecontact switch and said drill motor, said first circuit energizing said feed rate cam motor and said third circuit energizing said drill motor when said lever is pivoted about said fulcrum to lower said drill motor, said lever being pivoted about said fulcrum at a predetermined rate determined by said feed rate cam and said cam follower to control the feed rate of said drill, said cam follower supporting substantially the entire unbalanced weight of said lever and said drill motor, said drill carrying an increased proportion of said unbalanced weight when a hard area in the workpiece being drilled is encountered, said cam follower thereby actuating said cam follower switch to reverse said normally closed and said normally open contacts, thereby deenergizing said first circuit and energizing said second circuit, said feed rate cam motor being thereby deenergized and said cyclic cam motor being energized to rotate said cyclic cam to impart an intermittent up-and-down motion to said drill through said lever and said drill motor until said hard spot is drilled through, said cam follower then again supporting substantially the entire unbalanced weight of said lever and said drill motor and reversing said cam follower switch whereby said second circuit is deenergized and said first circuit is energized to continue the drilling operation under control of said feed rate cam.

References Cited in the file of this patent UNITED STATES PATENTS 1,911,138 Clute et al May 23, 1933

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