CA1313309C

CA1313309C - Hand sander

Info

Publication number: CA1313309C
Application number: CA000574962A
Authority: CA
Inventors: Miksa Marton
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-08-18
Filing date: 1988-08-17
Publication date: 1993-02-02
Anticipated expiration: 2010-02-02
Also published as: JPH01135460A; DE3727487C2; NO883661L; RU1834788C; DK459888D0; ATE63710T1; EP0303955B1; DK459888A; DE3727487A1; BR8804195A; AU2112088A; NO883661D0; DD282194A5; ES2022553B3; GR3002603T3; AU596026B2; EP0303955A1; DE3862909D1

Abstract

ABSTRACT OF THE DISCLOSURE

Hand sanders with a backup pad moved in a circular path (orbital sanding machines) are inclined to strong vibrations as a result of poor mass compensation of the eccentrically moved backup pad. Using the invention, two equal adjustable bodies are to be fitted on the shaft of the hand sander whose centres of gravity are symmetrical to the symmetrical axis connecting the shaft axis and the axis of rotation. In particular, these may be eccentric adjustment rings. These bodies form part of a counterweight whose effect may be adjusted by altering the position of these bodies precisely to the imbalance to be compensated.

Description

~and sander This invention is a hand sander with a motor-driven shaft, a backup pad connected to this shaft, whose axis of rotation is eccentric to t~e axis of the shaft, and an adjustable counterweight connected to the shaft, which compensa~es the imbalance caused by the eccentricity of the backup pad.

The DE-OS 27 45 129 is a hand sander of this type, for example.
On this hand sander the backup pad does not rotate but is guided on a circular path caused by the eccentric connection between the driven shaft and the backup pad. Such machines are primarily used for finish sanding because the translatory movement of the backup pad on a circular path does not cause any sanding marks.

It can be seen without going into further detail that the eccentric fitting of the backup pad on the driven shaft causes an imbalance which must be compensated by a counterweight. On the conventional hand sander this counterweight is formed by a body which is secured nonpermanently on the face side of the backup pad end of the driven shaft by bolts. Instead of this the counterweight could also be fitted so that it can be pushed to and fro. The backup pad itself is fitted in an eccentric recess at the end of the sha~t. It is a matter of course that the radial forces running through the shaft axis, to which the counterweight and the eccentric recess are fitted symmetrically, are in oppocite direc~ions to each other relative to the shaft axl s .

.~

1 31 330q On another hand sander, the US-PS 27 51 725, a semi-circular counterweight is basically fixed rigidly at the backup pad end of the driven shaft. The backup pad itself is fitted on an eccentric relative to the shaft.

Hand sanders of the type described are operated with replaceable sanding papers which are fitted to the outside of the disc.
Although the mass of the sanding paper to be fitted on the backup pad can be taken into account when determining the size of the counterweight there is the possibility of using different sanding papers suitable for the different types OL work for which the backup pad may be employed, which may also have different masses so that certain imbalances may occur as a result of the type of sanding paper used which are very unpleasant at the very high speeds at which such sanders are normally operated and can have a strong negative effect on the worker operating the sander. Although it is possible to have a different counterweight for each different backup pad for the sander described above, and to change this together with the backup pad, the replacement of the counterweight is not only extra work so that it is often the case that it is not done, but also the counterweight assigned to a specific backup pad may easily be lost so that in practice it is not available for use anyway.

In view o this the task of the invention is to ensure by simple means which cannot be lost that the backup pad with the sanding paper can always be balanced perfectly and without the trouble which may lead to the balancing work not being carried out.
There should also be the possibility of using not only sanding papers of different designs but also backup pads of different constructions and~or different sizes without this leading to damaging vibrations of the machine by imbalance.

This task is solved by the invention having the counterweight made up of two equal adjustable pieces whose centres of gravity are symmetrical to the symmetrical axis connecting the shaft axis and the axis of rotation.

On hand sanders built as per the invention the centres of gravity of the two counterweights produce a resulting radial force along the symmetrical axis during rotation of the shaft whose size depends not only on the mass of the bodies themselves but also on their angled position relative to the symmetrical axis. By chan~ing the angled position of the two adjustable bodies the required counter force which also produces a radial force relative to the symmetrical axis to compensate the imbalance can be set very precisely. Thus, the invention offers the opportunity of producing compensation even for small imbalances of the bac~up pad with its sanding paper by changing the angled position of the adjustable bodies. This adjustment of the bodies can be carried out without any great effort so that the operators of such hand sanders will be pleased to complete the task, and the counterweights cannot be lost since they generally remain connected to the machine at all times and seParate counterweights are not required for each different backup pad.

A particular advantage of the design of the hand sander as per the invention is that the adjustable bodies do not have to form the counterweight alone, but may be used together with a fixed body on the shaft whose position and size is such that it compensates the i~alance of a backup pad of a predetermined average size. The radial force produced by this body fixed to the shaft cannot only be incre~ed by the tWQ adjustable bodies but also reduced if the two adjustable bodies are on the opposite side of the axis of rotation of the shaft relative to the fixed body.

4 1 31 330q In the simplest case the adjustable bodies may be screwed into the shaft from the outside and on the perimeter of the shaft a number of threaded holes be arranged to allow the bodies to be screwed in at various positions from which the one producing the best compensation may be selected. It would also be possible to arrange several parallel rows of such threaded holes into which adjustable bodies of various sizes might be screwed, the larger of which allow rough compensation to allow the use of backup pads of various sizes, whilst the smaller screw-in bodies allow fine compensation to balance differences between backup pads of the same type and~or to adapt for various sanding papers.

The use of bodies screwed into the shaft to alter the effective mass of the counterweight only allows an imbalance to be compensated in stages. Although any imbalance may be reduced to the point where it no longer ~auses irritation by means of suitably selecting the size of the screw-in bodies and the distances between the holes, the complete compensation of imbal ances is only possible if the adjustable bodies on hand sanders designed as per the invention are constantly adjusta~le.
Constantly adjustable bodies can be presented in many different constellations. Thus, for example, straight guides may be provided on two opposite sides of the shaft in which sliding bodies may be t~ghtened in any position. In the same way this type of guides ancl sliding bodies may be provided on the perimeter of the shaft. A particularly simple design which allows constant adjustment of the bodies consists of one cylindrical section of the shaft on which two adjustment rings are fitted axially behind ea~h other ~ith their centres of gravity eccentric t~ the shaft axis. Then by simply turning and fixing the adjustment rings the eccentric centres of gravity can be distributed infinitely on both sides of the symmetrical axis mentioned above so that the imbalance caused by the backup pad and sanding paper may be compensated in full.

The adiustment rings used in this constellation of the invention may have very different designs. In the simplest case these adjustment rings may be made up of clamping belts whose clamping devices form a concentrated mass which may be adjusted along the perimeter of the shaft. Instead of this, solid adjustment rings with a shoulder on their outside to form the adjustable eccentric mass may also be used. This shoulder may also serve at the same time to mount a radial setting screw. In a preferred constellation of the invention, however, adjustment rings with a circular contour and an eccentric drill hole are used. These adjustment rings are extremely simple to manufacture and have good stability. The setting screw may be used to fix the adjustment ring at the point where the rings have the greatest thickness.

To facilitate good symmetrical positioning of the adjustment rings they may be provided with a scale which functions in conjunction with a reference mark on the jacket surface of the shaft, or vice versa. This scale may also show the positions which the rings theoretically must have for use with various backup pads and/or sanding papers. Here again it is possible to use sets of rings with various eccentric masses to compensate the imbalance of various backup pads on the one hand and of sanding papers on the other. A combination of adjustment rings and screw-in bodies is also possible, of course. The drill holes for the screw-in bodies may also be marked to show in which position these bodies are to be fitted when using certain yrin ding discs and/or sanding papers. Thus, in general, a preferred constellation of the invention provides for the adjùstable bodies and/or the shaft to have markings assigned to selected positions of the bodies.

1 31 330q In a preferred constellation of a hand sander as per the invention the shaft has a central threaded drill hole at one end for mounting on the threaded journal of a motor shaft and at the other end an eccentric recess in which the bearing for the backup pad is fitted. In addition the backup pad end of the shaft has an eccentric section of enlarged diameter which is opposite to the eccentric bearing of the backup pad relative to the axis of the shaft. The adjustable bodies are fitted on the section of the shaft bordering on this eccentric section.

The invention is described and explained in more detail in the following using the design examples shown in the drawings. The features in the description and drawings may be used individually or together in any combination for other constellations of the invention. The drawings show the following:
ig. 1 a longitudinal section through the parts of a hand sander essential to the invention as per the invention, ig. 2 a plan view of the part of the hand sander shown in Fig. 1 in the direction of arrow II, ig. 3 a side view of the part of the hand sander shown in Fig. 1 in the direction of arrow III, ig. 4 a diagram showing the effect of the adjustable bodies of t~e counterweights on the hand sander shown in Fig. 1, ig; 5 a diagram showing the radial force produced by the counterweight dependent on the setting of the adjustable bodies and ig. 6 another constellation of a hand sander as per the invention, shown in a side view similar to Fig. 3, but turned through 90 degrees compared to Fig. 3.

The hand sander shown in Figs. 1 to 3 has a shaft 1, which at one end is provided with a concentric threaded drill hole 2, which allows the shaft 1 to be secured on the hand sander's motor shaft 3 shown only as a dotted line in Fig. 1. At the other end of the shaft there is a cylindrical recess 4 which is mounted eccentric to the threaded drill hole 2. The offset between the axis 5 of the shaft 1 and the axis 6 of the eccentric recess 4 is marked in Fig. 1 by e. In the eccentric recess 4 there is a bearing mountiny for a backuP pad 7 which comprises a journal 10 fitted in the recess 4 by means of ball bearings 8 and 9, which has a central threaded hole 11 for mounting a threaded journal supporting the backup pad 7. When operating the hand sander the backup pad 7 is moved by the shaft 1 rotatin~ around its axis S on a circulax path with radius e without itself turning around its axis 6 because the rotating mounting of the backup pad 7 in the recess 4 of the shaft 1 prevents a torque being transferred to the backup pad 7 which would be sufficient to overcome the forces opposing a rotation of the backup pad 7 which occ-lr during sanding.

The mounting of the backup pad 7 in the shaft 1 means that radial forces are applied to this shaft which become apparent in the form of strong vi~rations of the hand sander. The size of these radial forces or imbalance depends on the mass of the eccentric backup pad 7 and its mounting, the path radius e and the speed of the shaft 1. Since the speed of hand sanders is very high, for example in the range of 20,000 rpm, the imbalance can be most significant and make the use of the machine impossible.

TQ compensate this imbalance on the design example shown the backup pad 7 end of the shaft 1 has a section 21 with a larger diameter which is mounted eccentric to the axis 5 of the shaft 1 in such a way that it produces a radial force to counteract any imbalance caused by the backup pad 7. The axis 22 of the section 21 is thus on the opposite side of the axis 5 of the shaft 1 to axis 6 of the backup pad 7, on the same plane which runs through axis 5 of the shaft 1, which forms a symmetrical axis 23 in the design. In addition the shaft 1 has a section 24 of smaller diameter at the other end to the backup pad which is also slightly eccentric to the axis 5 of the shaft 1, but in the same way as the backup pad 7. During the manufacture of the shaft 1 this smaller section allows fine balancing of the imbalance caused by the eccentric sections 21 and 24 to a preset value.

On conventional hand sanders the imbalance of the shaft 1 is designed so that it compensates the imbalance of a backup pad 7 fitted with a sanding paper 1~ of a certain size and construction as well as possible. However, there is a need to use backup pads of various constructions for different sanding work, for example, of different size and/or different hardness, and thus of different mass. It is also possible to use sanding papers with various bearing material and various grain sizes whose masses may be vastly different from one another.

Therefore the radial forces produced by these bac~up pads or sanding papers are different from those to which the imbalance of the shaft 1 is set, so that this once again can produce considerable vibrations which make working with the hand sander difficult if not even impossible.

In the desi~n example shown in Figs. 1 to 3 there is the possibility of setting the effect of the counterweight connected to the shaft 1 to backup pads and sanding papers of various masses so that vibrationless operation of-the hand sander is ensured in any event.

To this end the counterweight connected to the shaft 1 not only consists of section 21 of enlarged diameter, but also comprises two adjustable bodies in the form of adjustment rings 31 and 32 which have a circular con tour and an eccentric drill hole. These adjustment rings 31 and 32 are mounted axially behind each other on the central cylindrical section of the shaft 1. As a result of their eccentric drill hole they each have an eccentric centre of gravity relative to the axis 5 of the shaft 1, whose position may be moved by turning the adjustment rings 31 and 32 around a circular path concentric to the shaft axis 5. The two adjustment rings 31 and 32 may be adjusted by means of their radially penetrating setting screws 33 and 3~ in any angled position to the shaft 1 and thus also to the symmetrical axis 23 which connects the shaf~ axis 5, the axis 6 of the backup pad 7 and the axis 22 of the eccentric shoulder 21. So that the position of the two adjustment rings 31 and 32 can be determined they have degree scales 35 and 36 on their perimeters which are opposite a line marking 37 on the perimeter of the shaft 1 and a line marking 38 on the top of the eccentric section 21. These markings 37 and 38 lie on the plane defined by the symmetrical axis 23 and the shaft axis 5.

As mentioned above the radial force produced by an eccentric mass depends on the mass m of the eccentric body, the distance r of the centre of gravity of the mass from the axis of rotation and the rotational speed. If the rotational speed is expressed 131330q as usual by the angular speed L~ , then the radial force is ~ = mr ~. Since the angular speed c~ is the same for all parts driven by the shaft 1 when the hand sander is in operation, it can be ignored. Thus, the radial force produced by one of the adjustment rings 31 or 32 ~assuming that the design of the adjustment rings is the same) is proportional to the product of mr. If both adjustment rings are set so that their centres of gravity are symmetrical to the symmetrical axis 23 and each forms an angle 'a' to the symmetrical axis, the resulting radial force is proportional to the product of the factor ~ = 2mr.cos~
(see Fig. 4). It is of interest that when the angle '~' is less than 90~, the radial force which is proportional to ~ is added to the radial force which results from the mass mO and the distance rO from the shaft axis 5 of the centre of gravity of the mass of the eccentric section 21. However, if the ad~ustment rings 31 and 32 are brought into a position at which ll is greater than 90, the resultant ~ of the two components mr acts opposite to the radial force produced by the eccentric section 21 so that this latter radial force is reduced. Thus, both arrangements whose imbalance is greater than that compensated solely by the eccentric section 21 and also imbalances which are smaller than this value, can be compensated by simply turning the adjustment rings 31 and 32. This produces a large range of variations extending from mOrO - 2mr up to mOrO + 2mr, as shown in Fig. 5. A particular advantage of this is that using the continously turnable adjustment rings it is possible to attain very precise compensation of any imbalance within the given range in a very simple manner. The scales 35 and 36 on the perimeters of the adjustment rings 31 and 32 contain details of the positions assigned to certain backup pads and/or sanding sheets. In addition the scales facilitate a precisely s~mmetrical setting o~ the adjustment rings relative to the symmetry axis 23.

1 3 1 ~;~0~

In the embodiment of the invention shown in Fig. 6, instead of said turnable, eccentric adjustment rings mounted on the shaft, as adjustable bodies 41 and 42 bodies are used which are fixed on the perimeter of the shaft 51 and which on their ends directed towards the shaft 51 have threaded pins (not shown) with which they are screwed into appropriate threaded drill holes 43 and 44, which are distributed over the perimeter of the , shaft 51. The bodies 41 and 42 have such diverse masses that moving the smaller body 42 over the entire variation range of almost 180~ corresponds to moving the larger body 41 from one position to the next which in turn means that through the selection of the position of both bodies it is possible to attain a very fine adjustment although these bodies may only be moved a discreet distance. The arrangement may also be made that the threaded drill holes 43 are each assigned to the larger bodies 41 for various backup pads, with the smaller bodies 42, on the other hand, being able to serve to compensate for the imbalances caused by various sanding sheets. The threaded drill holes 43 and 44 are marked with markings 45 and g6 in the form of numerals, letters and other symbols which allow the assignment of each position of the screwed-in bodies 41 and 42 to certain backup pads and/or sanding sheets.

Fig. 6 shows the shaft 51 and the backup pad 52 in a view vertical to the symmetry a~is 23 as shown in Fig. 4, similar to the cut o~ Fig. 1, so that only the bodies 41 and 42 fitted on one side of the symmetry axis in the drawing plane are visible. It is therefore obvious that there is the same arrangement of bodies 41 and 42 on the reverse side of the shaft 51 which is not visible in Fig. ~ and it must be ensured that the bodies 41 or 4~ are arranged symmetrically in pairs to the said symmetry axis.

The invention is not limited to the portrayed design examples, but deviations are possible from these without leaqing the framework of the invention. It can be seen immediately that there are a large number of possibilities for fitting bodies which may be adjusted against a shaft so that their angled position can be changed relative to the axis of a shaft. Thus, for example, it would be possible to arrange bodies which may be pushed in a straight line on a plane vertical to the shaft axis on both sides of the shaft axis so that if these bodies are adjusted the alteration in the angled position goes hand in hand with an alteration in the distance r from the shaft axis. In this way an adjustment characteristic deviating from that in Fig. 5 would be attained. On the other hand it would also be possible to secure adjustable bodies to the perimeter of the shaft using clamping strips, or simply to use clamping strips in the form of hose collars directly as adjustable bodies. With all implementations of the invention it should be ensured that the adjustment of the bodies can be carried out by the user with ease when necessary.

Claims

1. Hand sander with a motor-driven shaft, a rotating backup pad connected to this shaft, whose axis of rotation is eccentric to the axis of the shaft, and an adjustable counterweight connected to the shaft, which compensates the imbalance caused by the eccentric mounting of the backup pad, characterised by the fact that the counterweight comprises two equal adjustable bodies whose centres of gravity are symmetrical to the symmetrical axis connecting the shaft axis and the eccentric axis of rotation.

2. Hand sander as per claim 1, characterised by the fact that the counterweight comprises a body permanently secured to the shaft whose position and size are such that it compensates the imbalance of a backup pad of a predetermined average size.

3. Hand sander as per claim 1, characterised by the fact that the adjustable bodies are screwed into the shafts from the outside and that there are a number of threaded drill holes for screwing in the bodies in selected positions on the perimeter of the shaft.

4. Hand sander as per claim 1, characterised by the fact that the adjustable bodies are formed by means of two adjustment rings fitted behind each other on a cylindrical section of the shaft with centres of gravity eccentric to the shaft axis.

5. Hand sander as per claim 4, characterised by the fact that the adjustment rings have a circular contour and an eccentric drill hole.

6. Hand sander as per claim 1, characterised by the fact that at least one of the components surrounding the adjustable bodies and the shaft is provided with markings assigned to selected positions of the bodies.

7. Hand sander as per claim 1, characterised by the fact that the shaft at one end has a central threaded drill hole for mounting the threaded journal of a motor shaft and at the other end has an eccentric recess, in which there is a bearing arrangement for the backup pad, as well as an eccentric section of enlarged diameter at the backup pad end, which is opposite to the eccentric bearing for the backup pad relative to the axis of the shaft, and that the adjustable bodies are arranged on the section of the shaft bordering the eccentric section.

8. A motor driven sander having a body with means at one end for detachably mounting said body to a motor driven shaft and, at the other end, a cylindrical recess, the longitudinal axis of which is eccentrically located with respect to the longitudinal axis of said motor driven shaft;
bearing means in said recess for receiving a spindle of a backup pad;
first counterweight means comprising a portion on said body being of enlarged diameter with respect to said body and being eccentrically positioned with respect to said motor driven shaft but opposite to the eccentrically located cylindrical recess and being located at the end of the body remote from said motor driven shaft;
and second, adjustable counterweight means comprising two rings of circular configuration with eccentrically formed openings therein and mounted on said body for detachable securement to any location on the periphery of said body; the centers of gravity of said counterweight means being symmetrical to a symmetrical axis connecting the axis of the motor driven shaft and the eccentric axis of rotation;
said two adjustable counterweight means being located on adjacent the other.

9. Apparatus according to claim 8, wherein at least at one of said adjustable counterweight members and said body portion is provided with markings assigned to selected positions of the bodies.

10. Apparatus according to claim 8, wherein said adjustable counterweight means are located on the body and in axial alignment with the first counterweight means of enlarged diameter.

11. Apparatus according to claim 8, wherein the first counterweight means is integrally formed with said body.

12. Apparatus according to claim 8, wherein said two adjustable rings are positioned on said body against the upper surface of said first counterweight means.