GB2146925A - Drill point grinding machine - Google Patents

Abstract

A grinding machine for grinding drill points comprises grinding means, which in the example shown includes a grinding wheel (26) with two coaxial annular grinding surfaces (28, 28A) of different grinding capabilities, the grinding means being rotatable on a single spindle (25) about the axis thereof and a chuck (30) for receiving drills (32) to be ground and mounted on a carriage (35) for linear sliding movement along rails (36) such that a drill point can be passed in a straight line transverse to the axis of the spindle (25) across an axial end surface of the grinding means, the chuck (30) being rotatable in 90 DEG steps about its axis and the chuck (30) and the grinding means being relatively angularly movable (by means of pivotal mountings) such that the angle between the plane of the axial end surface of the grinding means and the axis of the chuck (30) is variable for grinding primary and secondary facets on a drill (32) to be ground. The grinding wheel axis can also be angularly adjusted in order to vary the grinding surface (28, or 28A) presented to the drill point. <IMAGE>

Description

SPECIFICATION Drill point grinding machine This invention relates to a drill point grinding mci'ine, particularly for small diameter drills up to about 8mm.

Especially in the field of printed circuit board production, there is a need for extremely sharp and accurate drills. The regular replacement and maintenance of drills is a routine factor in this field and is a constant problem in production and quality control.

If drills are allowed to become blunt, then expensive circuit boards, which are drilled as one of the final stages of production, can be ruined.

The invention aims therefore to provide a grinding machine for drill points which is cheaper to produce and easierto operate than known machines, which usually are operated only by skilled operators as part of a re-grinding service offered by specialists outside the factories producing the boards.

Most machines for this purpose employ two separate grinding wheels set at very specific angles to one another, and a moving table which permits the drill held in a collect chuck to be swung about a vertical axis so that the four facets required can be ground. Movable optical systems are required for examining the drill point before and after grinding.

The invention thus proposes a grinding machine for drill points comprising grinding means on a single spindle rotating about an axis, a chuck for receiving drills to be ground mounted on a carriage for linear sliding movement whereby a drill point can be passed in a straight line transverse to said axis across the axial end surface of the grinding means, the chuck being rotatable by 900 steps and the angle measured around said line between the plane of said surface and the axis of the drill being variable by a relative pivotting movement between the grinding means and the carriage so as to produce the primary and secondary facets.

Preferably, it is the carriage which can be swung between defined stops in an arc about said line, the sliding movement occurring on linear bearings coincident with said line.

According to another aspect, the invention proposes a grinding machine for drill points comprising a grinding wheel on a single spindle having two coaxial annular grinding surfaces of different grinding capabilities, said axis being angularly movable to adjust the positions of said surfaces relative to a grinding plane.

Such a machine permits coarse grinding of a badly damaged or worn drill point, followed by fine finishing. Preferably, the two surfaces are radially displaced on the circular face of the grinding wheel and the axis is moved by swinging the entire mounting of the grinding wheel about a fixed pivot point offset from the axis.

In order that the invention shall be clearly understood, an exemplary embodiment thereof will now be described with reference to the accompanying drawings, in which: Figures 1 and 2 show enlarged details of a typical drill point; Figure 3 shows a top perspective view of a grinding machine according to the invention; Figure 4 shows a front perspective view of the machine, with an eyepiece fitted; and Figure 5 shows a scrap sectional view on V-V of Figure 3.

In Figure 1,the end view of a typical drill point shows the two flutes 10, the flat primary and secondary facets 11 and 12 and the point 13, exactly on the axis of the drill. Figure 2 shows a point angle of 1300, with the primary facet 11 at a relief angle of 15" to the tangent 14 at the cutting edge 15 on the conical end envelope. The secondary facet 12 is inclined at a further 15 , i.e. 300 relief angle to the tangent 14. The grinding machine is required to produce or reproduce these four facets with extreme accuracy, although for other drills the angles may be different, and provision is made for such variation.

The machine has a solid cast metal base 20 with two bearing pillars 21,22. A bearing surface 23 receive a bearing housing 24 for the spindle 25 of a grinding wheel 26. The spindle is belt driven at its rear end 27 from a motor (not shown). The surface 23 tilts backwards at an angle of about 15 , so that there is a similartilt at the surface of the grinding wheel 26. The latter has two annular grinding surfaces 28, 28A of different coarseness. The wheel is adjusted forwards and backwards by a threaded adjuster 29.

A chuck 30 mounted on a work spindle 31 is slidable longitudinally in a chuck head 34 and lockable by lever 34A. The chuck receives a drill 32, the point of which fits into and just projects from a support head 33, as is conventional. The head 34 can be mounted in a number of positions, by means of different sets of holes, on a slide plate 35. These positions determine the transverse angle ou of the axis of the drill. This angle is half the point angle of the drill to be sharpened.

The rotary position of the drill 32, after it has been set initially in the chuck 30, can be indexed by rotation of indexing means 31A. This has four positions which allow a quarter rotation between each. The function will be explained later.

The slide plate 35 can be adjusted along two guide rails 36 which are rigidly mounted in L-shaped arms 37. The arms are themselves supported on outwardly projecting stub axles 38 which are mounted for both rotation and longitudinal sliding i.e. across the width of the machine, in linear bearings 40,41 in the bearing pillars 21,22. By this means, the whole solid chuck unit consisting of chuck 30, head 34, plte 35, rails 36, arms 37 and axles 38 can be moved by a lever 42 against the bias of a spring 43. in so doing, the drill point projecting from the support head 33 vcan be traversed across the two grinding surfaces 28, 28A of the grinding wheel 26.

In addition to this sliding movement, the chuck unit as described above can also be swung through a limited angle, in the present case 15 , about the axis 44 of the stub axles 38. In order not to move the drill point is arranged to lie exactly in the axis 44 and can be adjusted to this position by sliding of the work spindle 31. Thus, the swinging movement only alters the angle of the point relative tothe grinding wheel, although it does not alter the angle a. . By this means, provision is made for grinding the primary and secondary facets 11 and 12 of the point.

The two positions of the arms 37 are illustrated in Figure 5. They are determined by a rigid pin 45 which engages a bush 46 in the base of pillar 21. This bush has an elongate hole 47 so that the pin has an accurately defined lateral swing which determines the 150 movement of the unit and of the drill point.

The unit is spring counterbalanced (not shown) so that its normal position is lowered (with the drill point at 300 to the grinding wheel), but it is easily manually lifted to its upper position (15 to the grinding wheel). Alternatively, the movement may for convenience be effected by a foot pedal.

A microscope and eyepiece 50 are mounted on the arm 37 (Figure 4) and are used for accurately setting the position of the drill point. The graticule in the eyepiece can be used to set the angular starting position of the drill in the chuck, and also to set the amount of stock which projects beyond the axis 44 and which will therefore be removed in a pass across the grinding wheel.

In use, from the starting position, the chuck is rotated 900 (one index position), and the unit, in its lowered position, is then traversed by operation of the lever 42 from right to left, to cut the secondary facet of one lip of the drill point. The unit is then raised and traversed left to rightto cut the primary facet. The chuck and drill are rotated exactly 1800 (two index positions) in the chuck head 34 and the procedure repeated to cut the secondary and primary facets of the second lip.

Referring now to Figure 3, the invention also envisages another useful innovation. Since frequently a coarse grinding is required first to deal with badly worn or damaged drills, the grinding wheel has two grinding surfaces 28 (coarse) and 28A (fine).

Since these surfaces are subject to wear at different rates, means must be provided to allow accurate mutual adjustment of the surfaces. For example, if the coarse surface 28A is worn, it must be brought forward into the line of movement 44 of the drill point. This is achieved by a slight pivotting movement of the whole grinding wheel unit consisting of housing 24, spindle 25 and wheel 26. The housing 24 is located by a pin 51 projecting upwards from the base 20 and about which it can pivot. Its angular position is determined by two pegs projecting inwards from the sides of the base and adjustable by knurled heads 52, 53. Other alternative methods are possible.

It will be seen that by pivotting anticlockwise about this eccentric pin 51, the surface 28A can be brought forward and surface 28 moved back.

This arrangement allows two methods of proceeding. The first follows the steps given above, using a single traverse and return for the first lip (two facets) and a second for the second lip. the mutual positions of the outer coarse (28) and inner fine (28A) grinding surfaces are such that in this case the secondary facet of each lip receives a coarse grinding followed by a fine finish, while the primary facet receives only a fine grinding on the return travers. The course surface 28 which it reaches second is set back slightly so the primary facet does not reach it.

The second alternative can be used for larger diameter drills and cases when a drill is very worn or damagaed and a larger cut of material must be removed. In this case,four separate traverse to and fro are made, one for each facet of both lips. The unit is lowered for the first and third traverse and raised for the second and fourth. Then, each facet is ground on both the coarse and fine surfaces on the right to left movement, but not at all on the return.

Claims (9)

1. A grinding machine for grinding drill points comprising grinding means rotatable on a single spindle about the axis thereof and a chuck for receiving drills to be ground and mounted on a carriage for linear sliding movement such that a drill point can be passed in a straight line transverse to the said axis across an axial end surface of the grinding means, the chuck being rotatable in 900 steps about its axis and the chuck and the grinding means being relatively angularly movable such that the angle between the plane of the axial end surface of the grinding means and the axis of the chuck is variable for grinding primary and secondary facets on a drill to be ground.

2. A machine as claimed in claim 1, wherein the carriage on which the chuck is mounted is movable in an arc, about the intended position of the drill point, between defined stops, the linear sliding movement of the carriage occurring in linear bearings coincident with the line along which the drill point is intended to pass.

3. A machine as claimed in claim 1 or 2 wherein the grinding means comprise a grinding wheel having two coaxial annular grinding surfaces of different grinding capabilities.

4. A machine as claimed in claim 3, wherein the grinding wheel and spindle together with a mounting therefore are pivotable about a fixed pivot offset from the axis of the spindle.

5. A machine as claimed in claim 2 or any claim appendant thereto, wherein the carriage is mounted on a pair of stub axles which are mounted for sliding and limited pivotal movement in the linear bearings.

6. A grinding machine for grinding drill points comprising a grinding wheel on a single spindle having two coaxial annular grinding surfaces of different grinding capabilities, the axis of the spindle being angularly movable to adjust the position of the surfaces relative to a grinding plane.

7. A machine as claimed in claim 6, wherein the grinding surfaces are radially displaced on the circular face of the grinding wheel.

8. A machine as claimed in claim 6 or 7, wherein the grinding wheel and spindle together with a mounting therefore are pivotable about a fixed pivot point offset from the axis of the spindle.

9. A grinding machine for grinding drill points substantially as described herein with reference to the drawings.