GB2066149A

GB2066149A - A vibrating saw

Info

Publication number: GB2066149A
Application number: GB8039263A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-12-21
Filing date: 1980-12-08
Publication date: 1981-07-08
Also published as: DE8032483U1; CH631907A5

Abstract

A vibrating saw comprises a vibrating plate (27) which is secured in a resilient manner and driven by the alternating magnetic field of an electro- magnet. A blade (31) is fixed between this vibrating plate and a spring (4) to form a mechanical oscillating system, the natural frequency of which is at least approximately equal to the frequency of the supply current to the electro-magnet (12). The frequency can be tuned by modifying the tension of the blade (31) or the latter's point of attachment to the spring (4). <IMAGE>

Description

SPECIFICATION A vibrating saw The present invention relates to a vibrating saw.

Conventional vibrating saws comprise a horizontal vibrating plate which is secured in a resilient manner by its ends and driven by the alternating magnetic field of an electro-magnet supplied with an alternating current. Means are provided for restraining the lower end of a saw blade and the upper end of the blade is attached to the end of a resilient arm connected to a rigid bent arm. The natural frequency of the mechanical oscillating system is at least approximately equal to the frequency of the supply current.

A saw of this type is described in German Patents 833 667 and 666 552.

The object of the present invention is to improve the efficiency of a saw of this type and to make it easier to use.

According to the present invention there is provided a vibrating saw comprising a horizontal vibrating plate which is secured in a resilient manner at its ends and driven by the alternating magnetic field of an electro-magnet supplied with an alternating current, means for securing the lower end of a saw blade of the saw, the upper end of the blade being fastened to the end of a resilient arm attached to a bent rigid arm, the natural frequency of the mechanical oscillating system being at least approximately equal to the frequency of the alternating supply current, and means for tuning the natural frequency of the mechanical oscillating system.

Means are preferably provided for regulating the tension of the blade and the natural frequency of the oscillating system. In order to increase the efficiency of the saw, one must work at a frequency close to resonance, consequently the natural frequency of the mechanical oscillating system must be close to the excitation frequency. A connection of adjustable length between the upper attachment of the blade and the resilient arm makes it possible to regulate the tension of the blade and the natural frequency of the system.

The upper mechanical oscillating system comprising the resilient arm and the upper attachment of the blade, must have a natural frequency slightly higher than the excitation frequency in order to prevent deformation and fracture of the blade. Additionally if the natural frequency of the upper system is lower than the frequency of the vibrating plate, the blade will be deformed each time the blade carries out an ascending movement.

Means are preferably provided for tuning the natural frequency of the upper mechanical oscillating system and comprise a counter weight slidable along the resilient arm to be fixed at any point of said arm.

Alternative means for tuning the natural frequency of the upper mechanical oscillating system comprise a spring strip fixed below the resilient arm and movable along said resilient arm.

In known saws, the blade is under considerable bending and torsional stress at its attachment points. This stress may cause premature fracture of the blade. In order to obviate these drawbacks, the means provided for the attachment of the lower end of the blade having a vibrating plate preferably comprise a clamp pivoted about a pivot at right angles to the cutting plane and means provided for attachment of the upper end of the blade preferably comprise a clamp pivoted about a pivot perpendicu lartothe plane of oscillation. The blade may thus flex freely towards the rear when it is in use, whereas that part which is clamped in the upper clamp remains aligned with the rest of the blade whilst the pivot point of the clamp carries out an oscillating movement in the form of an arc of a circle.

The accompanying drawings illustrate one embodiment of the invention by way of example.

Figure 1 is an elevational side view of a saw according to the invention; Figure 2 is a partial exploded perspective view of the saw; Figure 3 shows the connection of an upper attachment of the saw blade to an oscillating arm of the saw; and Figures 4to 7 are side and plan views of the two embodiments of means facilitating tuning of the natural frequency of a mechanical oscillating system of the saw.

The saw comprises a frame 1 provided with four feet comprising suction discs 2 and supporting a rigid bent arm 3 at the end of which are fixed two superimposed resilient steel strips 4 and 5 fixed so that they can be adjusted longitudinally by means of two screws 6 and 7. The strip 4 is longer than the strip 5 and fixed at its end is a clevis 8 in which a clamp 9 is pivoted about a pivot 10 perpendicular to the plane of the drawing. The clamp 9 may be tightened by means of a wing-nut 11. Fixed at the centre of the frame is an electro-magnetic 12 with a vertical core 13 on which a pole-piece 14 is screwed (Figure 2).The electro-magnet 12 is completely surrounded by a vertical wall 15, whereof two opposite sides 16 and 17 constitute slides for two supports 18 and 19 of bent metal sheet, provided with a notch 20 in which screws 21 engage, thus making it possible to fix the supports at the desired height.

The upper part of the supports 18 and 19 form rounded housings 22 and 23 extending over slightly more than 180 . Mounted in these housings are two cylindrical rubber members 24 and 25 comprising a radial slot along one generatrix. These members 24 and 25 are retained axially by lugs 26 obtained by cutting and bending metal sheets 18 and 19. The ends of a steel plate 27 are engaged in the slots in the members 24 and 25. This plate 27 is thus secured in a resilient manner, in all directions, by its ends.

Attached at the centre of the plate 27 is a clevis 28 in which a clamp 29 is pivoted about a pivot 30 located in the plane of the drawing in Figure 1, i.e. perpendicular to the plane of the saw blade 31 held by its ends in the clamps 9 and 29.

Furthermore, the wall 15 comprises a thicker portion 32 in which a vertical cylindrical housing is provided, in which a post 39 engages freely, at the end of which post a table 33 is fixed by a clevis 34 and a horizontal pivot 35 provided with a locking nut making it possible to lock the table 33 in a horizontal position or in an inclined position. A nut 36 makes it possible to fix the post 39, i.e the table 33 at the desired height. The table 33 is provided with a slot 37 for the passage of the blade 31.The mass of the plate 27, of the clamps 9 and 29 and of their devises, the mass of the spring 4 as well as the constants of the resilient parts are calculated, respectively measured, so that when a standard blade 31 is fitted in the clamps 9 and 29, the natural frequency of the mechanical oscillating arrangement is at least approximately equal to the supply frequency of the electro-magnet 12, i.e. Hz. It is possible to adjust this natural frequency by fixing the blade 31 so that it is more or less taut.

Adjusting the tension of the blade 31, i.e. adjusting the tuning of the frequency, may be carried out simply by fixing the clevis 8 to the spring strip 4 by means of a screw 38 making it possible to modify the distance between the clevis 8 and the strip 4.

The slots 20 in the plates 18 and 19 and the screws 21 make it possible to fix the plate 27 at a greater or lesser distance from the pole-pieces 14 of the electro-magnet, i.e. to modify the oscillation amplitude of the plate 27. however, any adjustment by the user constitutes a delicate operation. The plate is thus regulated for the desired maximum amplitude and regulating the amplitude is effected by altering the power of the magnetic field. To this end, intermediate leads are provided on the winding of the electro-magnet, leads which are connected to a switch which is not shown. Thus, when a rapid feed is desired, for example for straight lines or materials which are easy to saw, maximum power is selected, whereas for delicate work, curves and materials which are difficult to saw, one works at lower amplitudes.

The vibrating plate 27 flexes as it vibrates, so that its ends also tend to move towards the centre. The attachment by means of rubber blocks 24 and 25 allows this movement.

The pivotal connections of the clamps 9 and 29 protect the blade 31 from dangerous stress.

The possibility of fixing the table 33 at any level, between a lower level and an upper level, makes it possible to use the blade 31 rationally over its entire cutting length.

Naturally the invention is not limited to the embodiment described, but it may have numerous variations. In particular, the supports 18 and 19 could be of completely different shape. They do not necessarily have to be adjustable. These supports could be fixed directly to the electro-magnet.

In order to tune the frequency of the upper mechanical oscillating system, the strip 5 could be provided with two oblong holes and be fixed by two screws 40 and 41 (Figures 4,5). By releasing the two screws 40,41, the spring strip 5 is able to move along the strip 4 and be fixed in the desired position by retightening the screws 40,41.

Another method for tuning the natural frequency of the mechanical oscillating system is to provide the resilient arm 4 with a counter weight 42 sliding along this arm and able to be fixed at any point of this arm, for example by means of a screw 43.

Instead of being fixed by means of a rivet, as shown in the drawing, the clevis 8 of the upper clamp 9 could be fixed to the spring 4 by means of a screw. By providing a longitutinal slot in the strip 4, it would be possible to modify the frequency by moving the point of attachment of the clevis 8 to the spring 4. In place of a spring strip, it is possible to use any otherform of spring or system of springs, for example a spiral spring. In this case, the arm 3 must naturally be adopted in order that the spiral spring is fixed as an extension of the blade 31.

Claims

1. A vibrating saw comprising a horizontal vibtrating plate which is secured in a resilient manner at its end and driven by the alternating magnetic field of an electro-magnet supplied with an alternating current, means for securing the lower end of a saw blade of the saw, the upper end of the blade being fastened to the end of a resilient arm attached to a bent rigid arm, the natural frequency of the mechanical oscillating system being at least approximately equal to the frequency of the alternating supply current, and means for tuning the natural frequency of the mechanical oscillating system.

2. A saw as claimed in claim 1, in which the means for tuning the natural frequency of the oscillating system comprises a connection of adjustable length located between the upper attachment of the blade and the resilient arm.

3. A saw as claimed in claim 2, in which said connection of adjustable length is a screw.

4. A saw as claimed in any one of claims 1 to 3, in which an upper mechanical oscillating system of a saw comprising the resilient arm and the means for securing the upper part of the blade has a natural frequency higher than the excitation frequency.

5. A saw as claimed in claim 4, in which the said upper mechanical oscillating system includes means for tuning its natural frequency.

6. A saw as claimed in claim 5, in which the means for tuning the natural frequency of the said upper mechanical oscillating system comprise a counter weight slidable along the resilient arm such that it can be fixed at any point of said resilient arm.

7. A saw as claimed in claim 5, in which the means for tuning the natural frequency of the said upper mechanical oscillating system comprise a spring strip fixed belowthe resilient arm and able to move along said resilient arm.

8. A saw as claimed in any of claims 1 to 7, in which the means for securing the lower end of the blade to the vibrating plate comprise a clamp pivoted about a pivot perpendicular to the cutting plane.

9. A saw as claimed in claim 8, in which the means for securing the upper end of the blade comprise a clamp pivoted about a pivot perpendicularto the plane of oscillation.

10. A vibrating saw substantially as hereinbefore described with reference to the accompanying drawings.