GB2163688A - Hole finishing method - Google Patents

Abstract

A drill 4 having a cutting edge 4a on an outer peripheral surface is axially inserted into a hole 10 of a circular cross section formed in a material softer than the drill and having at least a portion of a diameter smaller than that of the drill, while keeping the drill from being rotated. Thereafter, the drill is withdrawn leaving a hole of parallel finished bore. <IMAGE>

Description

SPECIFICATION Hole finishing method BACKGROUND OF THE INVENTION 1. Field of the invention: The present invention relates to a method of finishing holes formed in a workpiece.

2. 2. Description of the Prior Art: It is general practice to form holes in syn thetic resin or rubber products by defining such holes at the time the products are injec tion-molded or cast-molded. For forming holes in products of a soft metal such as aluminum, it is general to define such holes when the products are die-cast.

Projections on dies or molds for forming holes in workpieces are progressively tapered to facilitate die or mold removal. Accordingly, the holes formed in the workpieces by the projections are also tapered with their inside diameters uneven in the longitudinal direction thereof.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hole finishing method capable of easily finishing the inner peripheral surface of a hole so that it will have a uniform inside diameter throughout its longitudinal direction.

To achieve the above object, a hole finish ing method of the invention comprises the steps of inserting a drill having a cutting edge on an outer peripheral surface into a hole of a circular cross section formed in a material softer than the drill and having at least a por tion of a diameter smaller than that of the drill, while keeping the drill from being posi tively rotated, and thereafter withdrawing the I drill from the hole.

The above and other objects, features and advantages of the present invention will be come more apparent from the following de scription when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front elevational view of drills used in effecting a hole finishing method of the invention, the view showing in cross sec tion a member of synthetic resin having holes to be finished; and Figures 2 and 3 are front elevational views illustrating progressive steps of the hole finish ing method.

DESCRIPTION OF THE PREFERRED EMBODI I MENTS A method of the present invention for fin ishing holes in a synthetic resin product or workpiece will be described.

An attachment 1 for a drilling machine or a tapping machine has a pair of spindles 2 mounted on a lower surface of the attachment 1. A pair of drills 4 is attached by collet chucks 3 to the spindles 2, respectively, the drills 4 being nonrotatable and positionally adjustable. Each of the drills 4 has a helical cutting edge 4a on an outer peripheral surface thereof. A presser bar 5 is retractably mounted on the lower surface of the attachment 1 between the drills 4 and has a semispherical presser 6 on a distal end thereof. A coil spring 7 is disposed arpund the presser bar 5 between the presser 6 and the lower surface of the attachment 1 for normally biasing the presser bar 5 to move downwardly.

A synthetic resin member or workpiece 8 is placed on a table 9 below the drills 4, and has a pair of holes 10 defined in opposite sides thereof and each having a diameter progressively greater toward its upper end. The table 9 has a pair of fixture members 11 for fixing the synthetic resin member 8 on the table 9, and a pair of drill holes 12 disposed respectively below the holes 10 in alignment therewith.

The synthetic resin member 8 is formed by injection molding or case molding.

The holes 10 in the synthetic resin member 8 will be finished as follows: The synthetic resin member 8 is placed on the table 9 and fixedly positioned by the fixture members 11 therebetween. Thereafter, the drills 4 mounted on the spindles 2 are positionally adjusted into alignment with the holes 10 in the synthetic resin member 8. The drills 4 have a diameter equal to the maximum diameter of the holes 10. When the drills 4 have been positioned, the attachment 1 is lowered without positively rotating the drills 4 until the presser 6 of the presser bar 5 is held against the surface of the synthetic resin member 8. Continued downward movement of the attachement 1 causes an upper portion of the presser bar 5 to be withdrawn into the attachment 1, as shown in Fig. 2, and also causes the drills 4 to enter the holes 10.

Since the drills 4 are not rotated, the helical cutting edges 4 of the drills 4 cut obliquely into the inner peripheral surfaces of the holes 10. Therefore, the diameter of the holes 10 is equalized to the diameter of the drills 4 throughout the length of the holes 10.

If the holes 10 were finished with the rotating drills 4, the inner peripheral surfaces of the holes 10 in the soft synthetic resin member 8 would be cut off by the drills 4 and would be roughened. The drills 4 as they are held nonrotatable according to the present invention can smoothly finish the inner peripheral surfaces of the holes 10.

After the attachment 1 has been lowered a predetermined distance to insert the drills 4 through the holes 10, the attachment 1 is lifted. As the attachment 1 is raised, as shown in Fig. 3, the presser bar 5 urged by the spring 7 downwardly is caused to emerge progressively from the lower surface of the attachment 1 for thereby enabling the presser 6 to press the synthetic resin member 8 against the table 9 at all times. Therefore, the synthetic resin member 8 is prevented from moving up with the drills 4. When the attachment 1 has been raised a certain distance (greater than the length of the holes 10 or the thickness of portions of the synthetic resin member 8 where the holes are formed), the drills 4 are drawn out of the holes 10. The finishing operation is now completed.

The present invention is not limited to the illustrated embodiment. The workpiece with holes to be finished may comprise a hard rubber product or a metal product softer than the drills 4. The method of the invenion can be used for finishing holes of incomplete configurations formed by a process other than molding or casting. Furthermore, as many drills as desired may be employed.

Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims (6)

1. A method of finishing a hole in a workpiece comprising the steps of: (a) inserting at least one drill having a cutting edge on an outer peripheral surface thereof into a hole of a circular cross section formed in a workpiece of a material softer than the drill and having at least a portion of a diameter smaller than that of the drill, while keeping the drill from being positively rotated; and (b) thereafter withdrawing the drill from the hole.

2 A method according to claim 1, wherein a pair of drills is mounted on and projects from a lower surface of an attachment of a machine tool, there being a presser bar upwardly retractably mounted on the lower surface of said attachment between said drills and normally biased by a spring disposed therearound for pressing engagement with the workpiece.

3. A method according to claim 1, wherein said drill is single in number and mounted on an attachment of a machine tool.

4. A method according to claim 1, wherein said workpiece comprises a synthetic resin member formed by injection molding or cast molding.

5. A method according to claim 1, wherein said hole is progressively greater in diameter toward one end thereof across said workpiece.

6. A method of finishing a hole in a workpiece substantially as described herein and with reference to the accompanying drawings.