GB2268428A

GB2268428A - Orbital grinding apparatus

Info

Publication number: GB2268428A
Application number: GB9214266A
Authority: GB
Inventors: Guiseppe L Cuneo
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1992-07-04
Filing date: 1992-07-04
Publication date: 1994-01-12
Anticipated expiration: 2012-07-04
Also published as: GB9214266D0; GB2268428B

Abstract

Grinding apparatus comprises a drive element (12) adapted to be rotated about a first axis (15) and a driven element (14) mounted on the drive element through a freely rotatable bearing (16) eccentrically arranged with respect to the first axis. The driven element (14) is thus rotatable about a second axis (17) spaced from, and parallel to, the first axis (17). Selectively operable locking means (21) enable the drive and driven elements to be locked together. A grinding disc (20) is mountable on the driven element for concentric rotation therewith. The grinding apparatus may be an accessory for a drill or it may be a power tool in its own right. The locking means (21) comprises a slide lever (22) sliding in drive element (12) and notch means (26) disposed on the driven element (14). Thus the apparatus is switchable between two modes of operation: circular rotary grinding or random orbit grinding. <IMAGE>

Description

GRINDING APPARATUS The present invention relates to grinding apparatus of the type comprising a grinding disc mounted on a driven element which itself is mounted through a freely rotatable bearing disposed eccentrically with respect to a drive element arranged to be rotated by a drive spindle.

Such arrangements are well known in the art and provide a particularly smooth finish on a workpiece by virtue of the "random" orbit/rotation of the grinding disc so that the appearance of scratches in the workpiece in the form of arcs or small orbits is avoided and which is an inherent problem with purely rotatory or purely orbital grinding apparatus. Nevertheless it is sometimes the case that different rates of material removal from the workpiece are desired and so it has been suggested to impose a rotational regime in grinding apparatus of the type with which this invention is concerned in order that the material removal rate can be adjusted. See for example EP-A-0230621 in which a gear ring is disposed in a housing for the sanding apparatus and two epicyclic gear rings are disposed on the grinding disc.The gear ring is moveable between three positions in which either an inner gear or an outer gear or neither gear is engageable with the gear ring so that three optional rotational regimes can be selected for the grinding disc.

When either gear on the grinding disc is engaged by the gear ring, the grinding disc is constrained to rotate about its own axis at a rate determined by factors including the dimensions of the meshing gear rings.

GB-A-1458107 discloses sanding apparatus in which a grinding pad is switchable between two modes of operation, that is to say, in one mode the pad is constrained merely to reciprocate, while in another mode it is constrained to perform an orbital motion.

It is an object of the present invention to provide grinding apparatus of the kind described above which is of simple construction and which is capable of effecting both "random" orbital/rotatory motion and purely rotatory motion In accordance with the present invention there is provided grinding apparatus comprising a drive element adapted to be rotated about a first axis, a driven element mounted on the drive element through a freely rotatable bearing disposed eccentrically with respect to said first axis such that said driven element is rotatable about a second axis spaced from, and parallel to, said first axis and means selectively to lock said drive and driven elements together, a grinding disc being mountable on said driven element for concentric rotation therewith.

The grinding apparatus defined above may conveniently be arranged as an accessory for a power tool such as a drill, in which event said drive element includes means for connection to a power tool. Such means for connection may comprise a threaded bore in the drive element for reception of a threaded stub shaft receivable in a chuck of a power drill.

On the other hand the grinding apparatus of the present invention may be a power tool in its own right, in which event it further comprises a housing mounting a motor driving an output spindle to which said drive element is connected for rotation about first said axis. Preferably said drive element includes an eccentric recess mounting said bearing and said driven element comprises a boss mounted in said bearing, and said means selectively to lock said drive and driven elements together comprises a slide lever mounted on said drive element for sliding in a direction substantially perpendicular to and joining said first and second axes between two positions thereof, in a first of which it engages notch means fixed on said driven element and in a second of which it avoids said notch means.

The invention is further described hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figures la, b and c are sections through grinding apparatus according to the present invention; Figures 2a and b are a plan view and section respectively through notch means; Figures 3a and b are a plan view and side view respectively of lock means; Figures 4a, b and c are respectively a plan view, a section along the line b-b in figure 4a, and an underneath view of a detent member; and, Figures 5a, b and c are respectively a plan view, a section along the line b-b of Figure 5a, and an underneath view of a drive element according to the present invention.

With reference to Figure la of the drawings, grinding apparatus 10 according to the present invention comprises a drive element 12 having a threaded bore 13 for connection to a rotatory drive spindle (not shown) for rotation about axis 15. The drive spindle may be that of a separate power tool such as a portable hand drill, or may be that of a dedicated grinding machine.

Whether the grinding apparatus 10 is intended as an accessory for another power tool or is part of a dedicated unit is not material to the present invention.

The drive element 12 is provided with an eccentric recess 18 in which is mounted a bearing 16. A driven element in the form of a boss 14 is journalled in the bearing 16 and is retained therein by a bolt 19 received in a threaded through-bore 23 of the boss 14. A grinding disc 20 has a central threaded stub shaft 25 received in bore 23 of the boss 14 for rotation therewith about an axis 17 which is parallel to, and spaced from, axis 15.

A detent member 24 is secured to the drive element 12 by screws 30. Lock means 21 comprises a slide lever 22 retained between the detent member 24 and drive element 12. The slide lever slides between two positions in a direction perpendicular to, and between, the axes 17 and 15.

Locking means 21 further comprises notch means 26 secured between driven element 14 and the grinding disc 20. Slide lever 22 has a depending key 32 for engagement with notch means 26 when it slides between its two positions taking key 32 into and out of engagement with notch 28 provided on the notch means 26. Figures lb and lc show the slide lever 22 in its locked and unlocked positio#ns respectively.

With reference also to Figures 3a and b, the slide lever 22 comprises a U-shaped element having arms 34 and connecter 36. Each arm 34 is provided with shoulders 36 near their free ends 38 which are enlarged and have detent apertures 40.

Figures 4a, b and c show the detent member 24, which is provided with a U-shaped groove 42 adapted to receive the slide lever 22. The groove 42 is likewise provided with shoulders 44 and a connecting rim 46. In the locked position of the locking means 21, the connector 36 of the slide lever abuts rim 46, while in the unlocked position, the shoulders 36 on each arm 34 of the slide lever 22 abut shoulders 44 of the groove 42. Thus the rim 46 and shoulders 44 of the detent member 24 limit the sliding movement of the slide lever 22.

With reference to Figures 5a, b and c, as well as Figures Ib and c, the drive element 12 is provided with two blind bores 48 which each receive a spring 50 and detent ball 52. The springs 50 serve to urge the detent balls 52 out of the blind bores 48 and into engagement the detent apertures 40 of the slide lever 22. The detent apertures 40 each have two centres (40a, b, - see Fig. 3a) corresponding to the two extreme positions of the locking means 21 so that the detent balls 52 snap into either of those two centres at the respective extreme positions.

Referring to Figure 2a and b, notch means 26 is disc-like, having a central bore 36 to allow passage of the stub shaft 25 of the grinding disc 20, and two lugs 34 for engagement with corresponding slots formed in the grinding disc 20. Lugs 34 serve to prevent any relative rotation between the grinding disc 20 and notch means 26.

Grinding disc 20 may itself be provided with an abrasive surface 21, or with means for attachment of such a surface, whichever is deemed preferable. In use, lock means 21 can be operated by the user of the grinding apparatus 10 between its two position as follows.

In its first position shown in Figure Ib, the slide lever 22, which is rotationally fixed with respect to the drive element 12, is engaged, through key 32, with the notch 28 of notch means 26. Thus the grinding disc 20 is locked with respect to the drive element 12 so that, if the drive element 12 is rotated about axis 15, then so also is the grinding disc 20. In this event, apparatus 10 serves as a normal rotary grinding apparatus and would be employed when coarse grinding is required for heavy stock removal from a workpiece.

However, by operation of the locking means 21, the user can slide the slide lever 22 to the position shown in Figure lc, where the key 32 is released from notch 28.

Thus the grinding disc 20 is free to rotate with respect to the drive element 12 through the bearing 16. In this mode of operation the grinding disc 20 performs a random orbit movement, well known in itself in the art, which is useful for fine finishing of a workpiece.

Claims

1. Grinding apparatus comprising a drive element adapted to be rotated about a first axis, a driven element mounted on the drive element through a freely rotatable bearing disposed eccentrically with respect to said first axis such that said driven element is rotatable about a second axis spaced from, and parallel to, said first axis and means selectively to lock said drive and driven elements together, a grinding disc being mountable on said driven element for concentric rotation therewith.

2. Grinding apparatus as claimed in claim 1, which is arranged as an accessory for a power tool by said drive element including means for connection to a power tool.

3. Grinding apparatus as claimed in claim 2, in which said means for connection comprises a threaded bore in the drive element for reception of a threaded stub shaft receivable in a chuck of a power tool.

4. Grinding apparatus as claimed in claim 1, further comprising a housing mounting a motor driving an output spindle to which said drive element is connected for rotation about first said axis.

5. Grinding apparatus as claimed in any preceding claim, in which said means selectively to lock said drive and driven elements together comprises a slide lever and notch means, the slide lever being mounted on said drive element for sliding between a first position in which it engages said notch means, which means are fixed on said driven element, and a second position in which it avoids said notch means.

6. Grinding apparatus as claimed in claim 5, in which said slide lever slides in a direction susbstantially perpendicular to and joining said first and second axes between said two positions.

7. Grinding apparatus as claimed in claim 6, in which said slide lever is U-shaped having a key on the base of the U for engagement with said notch means.

8. Grinding apparatus as claimed in claim 7, in which said slide member is retained between the drive member and a detent member secured thereto, detent means being provided comprising detent apertures in one or both arms of said slide lever and detent elements resiliently biassed into engagement with said detent apertures.

9. Grinding apparatus as claimed in claim 8, in which said detent elements comprise spring loaded balls received in said drive element.

10. Grinding apparatus as claimed in claim 7, 8 or 9 in which said slide element has abutment means for limiting movement thereof between said two positions.

11. Grinding apparatus as claimed in any preceding claim, in which said drive element includes an eccentric recess mounting said bearing and said driven element comprises a boss mounted in said bearing.

12. Grinding apparatus substantially as hereinbefore described with reference to the drawings.