FIELD OF THE INVENTION

The invention relates to implements on padsaws or oscillating or reciprocating saws, particularly pneumatically driven types and particularly to an implement for grinding and very specially for grinding in narrow saw kerfs and recesses.

BACKGROUND OF THE INVENTION AND PRIOR ART Grinders for processing surfaces are widely known.

Spread the so-called orbital sander , sander or even Sander are known for this purpose , a hand-held power tool , by which one is able , through differently structured essays ( grinding wheels ) to grind than surfaces.

Means of a motor is brought by an eccentrically positioned rotor plate spanned the sandpaper in a swinging motion. The grinding plate is rectangular and circular swings .

Orbital sanders are used for pre-and re-grinding of various materials such as Used hard and soft woods as well as in paints. The abrasive paper is attached by a snap lock or Velcro on the swing plate. By means of a dust extraction ensures an environmentally and body safe work .

Similarly, the eccentric sander , having a rotating grinding wheel , the center of which in addition performs a circular movement as the usually circular grinding plate eccentrically mounted on the drive shaft is located. Random orbit sanders are ideal for sanding of surfaces , the usual in the classical orbital sander circular grooves in the grinding material can be largely avoided by the combined rotational and oscillating movements.

However, both types of electric hand sanders have the disadvantage of being able to edit limited areas at the edges only imperfect because they grind through their schwabbelnde movement either beyond the boundary , or jolt to her , which is associated with disturbing noises and pulsing vibrations . A rand accurate work is therefore not possible.

For this, however, there are so-called delta sanders, with a small triangular sanding pad.

Here the oscillating movement is restricted to a smaller eccentric motion , thereby allowing a more accurate treatment of inner edges ..

Their removal , however, is comparatively weak in electric drive with usually 300 to 600 watts of power.

However, the application is also limited by the fact, that the abrasive papers or canvas clog rapidly with this system, since the residuals are not pushed away, but remain under the sanding pad. OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a grinding machine providing effective abrasion at oscillating front-back movement, which allows grinding close to the edges and that also removes the abraded grinding dust from the machining zone and would be able to work on crooked or inside areas in cavities, as well as on cylindrical shapes and behind undercuts.

INVENTIVE STEP

The inventive step therefore is to seek for a movement of a grinding pad, that would effectively push away the residues from the worked-on area and to keep some distance between the pad and the pad drive, so that a pad of adequate shape can be inserted into cavities and behind recesses.

SOLUTION

The intended effect of pushing away the residues is achieved by combining a grinding pad with a flexible shaft to an oscillating drive system.

This can be explained with the fact, that due to the deflection of the shaft, higher pressure is applied on the abraded residues in forward than with the backward movement. It results in a paddling motion, as revealed in slow-motion representation of Hi -speed video recordings.

Said effect results in a pushing forward of the ablated material. This allows effective grinding with the inventive device. Furthermore, the one-dimensional oscillating movement allows precise grinding of the inner edges of objects and the slender shaft allows the processing of retraced sections and undercuts, as long as the grinding pad fits into it with some tolerance for its movement.

DESIGN CONSIDERATIONS

The advance pushing of residues, based on complex oscillation phenomena therewith is empirically clearly detectable. Supported by permanent removal with blowing or sucking away the dust, premature clogging of the abrasive pad is prevented.

This was found particularly for grinding on steel or similar hard metals, but the system proved to work as well with wooden and laquered surfaces, while it is understood that parameters for other materials have to be adapted. Said parameters depend on the friction of the grinding disk, the grain size of the abrasive paper, the angle of the shaft to the surface to be machined , the number of strokes of the pneumatic actuator, the feed speed as well as the resilience and the imprint of the sanding pad, etc.

Due to the large number of interrelated parameters these might be difficult to determine. However, if approximate values for individual abrasive pad in conjunction with their application and a given angle of the shaft is determined according to the work surface, "fine tuning " manually by slightly tilting the device vertically, adjusting feed and the manual pressure on the device help to achieve the effect.

DETAILED DESCRIPTION OF THE INVENTION

The an optimum design was found with experiments on 50 x 25 mm grinding pads, where it turned out, that shafts of 18 cm length, fastened to the pad at an 10° to 15° vertical angle, resulted in an adequate movement of pushing the residues forwards due to a particular flexing movement of the shaft, as long as it had 3 mm diameter and was made of ordinary carbon tool steel. Furthermore 100 grit sanding paper or fabric has to be fixed (preferably adhesively glued) on a 2.0 mm rubber plate of shore hardness 70, which must have an overlap of approx. 2 mm to the steel base plate, which is of 1 mm thickness and 80 grams of weight.

This arrangement proved to be most effective for grinding blank rolled aluminum sheets from ALMg3 at 10,000 strokes per minute and 0.1 N / cm ² pressure.

However, it was found that these parameters cannot be achieved with an electric drive, sized like usual hand tools, due to the required high drive torque at also high oscillating speed. Therefore, the use of compressed air drive is mandatory for hand tools as it is usual for example in stitch saws for car- body works.

This drive also allows to access also difficult areas because it is located remotely over the surface and must not be guided directly over it, as for example with Delta sanders.

DESCRIPTION OF THE DRAWING

Figure 1 shows a workpiece 1 to be grinded, having a cut-out 2 and an undercut 3.

The sanding pad 4 consists of a metal grinding plate 5 with a rubber plate 7 and the abrasive cloth 8 on a shaft 6 which is clamped into the oscillating drive (not shown)

It is demonstrated, how the grinding pad has smoothened the rough surfaces 9 on areas 10 and 11 and finished the inner edge portions 12, 13 and 14.