US 2471561 A
Description (OCR text may contain errors)
May 31, 1949. E. c. FIELDING GUARD FOR GRINDING MACHINES AND THE 'LIKE 2 Sheets-Sheet 1 Filed Sept. 20, 1946 /NVf/VTO @cigar Charles yielding @islanda/$32@ ATTORNEYS May 31, 1949- E. c. FIELDING f 2,471,551
GUARD FOR GRINDING MACHINES AND THE LIKE Filed sept. 2o, 194e 2 sheets-sheet 2 .A /NVf/VTO'Q dgar Char/es 97E/ding ATTO/Q/VE Y S Patented May 31, 1949 GUARD Fon GRINDING MACHINES AND THE LIKE Edgar Charles Fielding, Walsall, England Application September 20, 1946, Serial No. 698,188 In Great Britain October 25, 1945 Claims. l
This invention relates to guards for grinding wheels and the like, including circular saws and other wheel or disc-like circular abrasive or cutting members, such as cut-ofi' discs or wheels made of abrasive material or of steel.
One of the objects of the present invention is to provide an improved guard which can be readily adjusted to suit the size of the wheel or disc that it is desired to protect.
Another object is to provide an adjustable guard for a power-driven grinding wheel or the like which will eiectively safeguard operatives against accidents, such as whilst changing a wheel or disc or in the event of a wheel bursting..
A further object is to provide an adjustable guard which will enable a wheel or disc to be easily changed.
A still further object is to ensure that the grinding wheel or the like cannot be put into operation unless the guard is in its working position.
Another object is to ensure, by the adjustment of the guard, a substantially constant peripheral speed of the grinding wheel or the like .as the diameter of the wheel wears down, or when a wheel of a d iierent diameter is substituted, thereby ensuring maximum eiliciency with various wheel diameters.
According to the invention, a guard for a grinding wheel or the like comprises two overlapping half covers or hood members hingedly mounted upon a common pivot-pin and having a pin-and-slot engagement with a relatively stationary part, in combination with a screw device for moving the pivot-pin inwards or outwards whereby the pin-and-slot engagement causes the 4covers or hood members to be opened out .or
closed in as required. The pivot-pin may be carried by a slide guided in a stationary part and carrying a nut engaged by a screw. The guard members may carry pins engaging cam slots in a stationary part; or may have cam .slots engaged by pins on the kstationary part. In .either case the slots may be open at one end .so that .the pins can be disengaged therefrom, by operation of the screw device, to enable the guard members to be raised or thrown back when the wheelis .to be changed. If the wheel is operated by an electric motor, the operation of the .screw device can be arranged to cause a trip .switch to kcomeinto action to break the circuit if and when the pins are caused to leave the slots. Also, by the noperation of the screw device to vary the effective size of the guard to suit the wheel diameter, the peripheral speed of the wheel can be maintained constant by suitably controlling the driving motor. To achieve these results, the screw device may, as it is rotated, convey motion to a control shaft which may operate a trip switch and/or operate means for automatically controlling the speed of the motor.
Figure 1 of the accompanying drawings is a longitudinal section through a portion of a grinding-wheel unit provided with a guard in accordance with the present invention.
Figure 2 is a front elevation of the grinding wheel and guard.
Figure 3 is a transverse section on line III-III, Figure 1, showing the guard and wheel in rear elevation.
Figure 4 is a side elevation of the guard.
Figure 5 is a plan view. f'
Referring to the drawings, which show a convenient embodiment of the invention in connection with a guard for a grinding wheel, such as, for example, for the grinding wheel of a motordriven grinding unit described in my copending application, `Serial Number 698,187, which issued as Patent No. 2,435,622, dated February 10, 1948, the guard comprises two half covers or hood mem-- bers l, l, of substantially quadrantal or segmental contour and of channel section, so as to embrace opposite sides of the wheel 2. The two covers l overlap down the middle of the front, the vertical edge portion of one lying and being adjustable within a rebate 3 (Figures 2 and 5) in the front face of the other. They are hinged at their upper ends upon a common pivot pin 4 which can be raised. and lowered by a screw device, as hereinafter described, and the two covers together form a guard of segmental form rather less than a complete circle, so as to allow a working peripheral sector of the grinding wheel to be exposed below the bottom straight edge of the guard, as shown inFigure 2. The two guard members I are hinged upon the pivot pin 4 by means of intertting hinge knuckles .5, and the pin extends forwardly from a vertical dovetail slide 6 mounted between dovetail guides formed by two relatively stationary bracket members 7 which are carried by the end of .the tubular housing 8 of the grinding unit. The slide Bhas a rearwardly-extending arm .or lug 9 provided with a boss IU which is drilled and tapped lto form .a nut that receives a vertical adjusting screw H having a square upper -end I2 to engage a key or handle for hand operation. The lower end yof the screw H has a head or enlarged .portion t3 rotatably mounted in a suitable stationary part, such as the housing 8 of the grinding unit, and
held doWn by any convenient means, such as a flange part I4, so that the screw can rotate but cannot move axially.
The guide brackets 'I' for the slide are extended laterally, as shown in Figure 3, in the form of side plates or wings I@ of a stationary frame, being situated behind and parallel to the back of the wheel guard; and formed in these side plates I5 are two obliquely-disposed slots It having closed inner ends but open outer ends, the latter being at the edges of the plates. These slots I6 are provided one on either side of the axis of the grinding-wheel shaft Il and converge in an upward direction, being substantially or nearly in alignment with the pivot-pin 4 of the guard. Each half-cover I of the guard is provided at the back with a rearwardly-extending screw-pin or stud I8 which normally engages the slot I6 in the corresponding side plate I5 of the stationary frame. By raising the slide 6 by means of the screw II the guard `pivot-pin 4 may be elevated, as shown in Figures 2 and 3 by dotted lines, the half-covers i moving with it. The pins I8 on the backs of these half-covers are thereby lifted within their slots, and by .Y
co-operation with the oblique edges of these slots, which function as cam slots, the half-covers turn about their pivot and are closed in towards the wheel axis as the pins move up the slots, thus adapting the guard for use with a wheel of smaller diameter. On the other hand, when the screw II is turned in the reverse direction the slide 6 and pivot-pin 4 are lowered and the rear pins I8, by (zo-operation with the cam slots I6,
cause the half-covers I to open out to suit a wheel of larger diameter. Thus, as a grinding Wheel wears down, the guard can be adjusted from time to time to suit the altered size.
To enable a wheel to be easily removed the screw II can be operated to cause the pins I8 on the half-covers to leave the slots I6 through the open ends thereof, and the said half-covers can then be swung outwards clear of the wheel.
The said pins I8 on the half-covers are preferably screw-pins fitted with ixing nuts' i9 which can be tightened up when the guard has been adjusted so as to draw the half-covers against the frame, thus preventing vibration.
As the cam slots I6 are substantially in line with the pivot-pin 4, any tendency for the halfcovers to open is resisted by the pins exerting pressure on the sides of the slots in directions at right-angles to the said slots, and thus if a wheel bursts and the fragments strike the halfcovers under centrifugal force, the opening of the guard will be effectively resisted by the pins, so that the fragments will be intercepted by the guard.
In order to ensure that the guard cannot be opened, for changing a wheel or otherwise, while the wheel is rotating, provision is made for automatically breaking the circuit of the driving motor when the adjusting screw is operated to such an extent as to cause the pins I8 on the half-covers to leave the slots as a preliminary to the said half-covers being swung outwards clear of the wheel. For this purpose the lower end of the adjusting screw Il carries a bevel wheel 2G meshing with a bevel pinion 2! on a longitudinal control shaft 22 disposed parallel to the grinding-wheel shaft I'I, being mounted in bearings 23 on the housing 8 of said shaft. This control shaft 22 is formed with a screwthread on which is mounted a travelling nut 24 that is constrained against rotation by engaging 4 a flat surface on the housing 8. When the adjusting screw I I is operated to such an extent that the pins I8 on the half-covers are about to leave the cam slots I E, the said nut 24 on the control shaft is arranged to operate a trip Switch 25 whereby the circuit of the driving motor which operates shaft I'I is broken and the grinding wheel therefore stopped. The adjusting screw II can then be further rotated to cause the pins to leave the slots, when the half-covers can .be safely swung outwards by means of the handles 2S thereon so as to clear the stationary wheel. Push-button switches 21, Z'I for respectively starting and stopping the motor may be mounted on the side plates I5, as shown in Figure 3.
The said control shaft 22 can also be utilized to control the speed of the driving motor to suit the prevailing diameter of the grinding wheel and thereby automatically maintain a substantially constant peripheral speed of the wheel. This arrangement ensures that, as the grinding ywheel wears, the guard can be adjusted to suit the diameter of the wheel and, at the same time, the peripheral speed of the wheel is automatically adjusted to give maximum eiciency in grinding.
The method of speed control of the motor will depend upon the type of variable-speed motor that is employed. For example, if a self-contained A. C, motor with commutator is used, it is necessary to change the relative positions of the brushes on the commutator. In this case the control shaft 22 would be continued to a position adjacent the motor and there connected by suitable mechanical means to the brush-gear moving mechanism, in place of the usual handwheel brush control. By this arrangement, rotation of the control shaft, where the guard adjusting screw II is operated will automatically cause the relative position of the brushes on the motor commutator to be altered, thereby varying the speed of the motor. The initial setting of the brushes on the commutator would be such that the motor speed is thereafter automatically varied correctly to suit the diameter of the grinding wheel.
With a polechanging A. C. motor, however, speed change would be effected by altering the number of pairs of magnetic poles, and to effect this operation the control shaft 22 would be arranged toV operate a pole-changing switch which could be mounted on the housing 8 of the grinding-wheel driving shaft. This polechanging switch would operate a contactor panel mounted separately from, but convenient to, the grinding unit, and the stator winding of the motor would be brought out to this contactor panel, which would be designed to change the connections as required. By this arrangement, any movement of the wheel-guard adjusting screw il would automatically operate the contactor panel and change the speed of the motor. Although the possible number of speed changes of this type of motor is limited, the speed changes could be predetermined to give maximum efliciency for various grinding wheel diameters.
With a direct-current shunt motor, speed regulation would be obtained by inserting a variable resistance in the shunt circuit, and this could be done by causing the control shaft 22 or the nut 24 thereon to `operate a small contact panel to which a number of tappings have been brought from the resistance in the shunt circuit. By this means, any movement of the adjusting screw would automatically operate the contact panel, thereby altering the resistance in the shunt circuit and thus varying the speed of the motor. The value of the resistance and the speed range of the motor would be predetermined to give maximum eiciency at various grinding-wheel diameters.
In general, any type of motor could be automatically controlled, for speed variation, from the wheel-guard adjusting screw Il to suit the diameter of the grinding wheel that is in use at any time, so as to obtain maximum eiiicienoy for various wheel diameters.
The application of the invention to an adjustable guard for circular saws or to rotary cut-off tools having a wheel or disc-like cutting member made either of abrasive material or of metal, diiers in no essential respect from its application to a guard for a grinding wheel as hereinbefore described.
Instead of the guard members carrying pins engaging cam slots in a stationary part, they may have cam slots engaging pins on a stationary part.
1. A guard for a grinding wheel or the like comprising two covers extending over the wheel, a common pivot upon which the two wheel-covers are pivotally mounted, the said pivot being disposed outwards of the wheel centre, a stationary part, cam slots in the stationary part, pins on the wheel-covers engaging the slots, the slots being disposed symmetrically on opposite sides of aplane containing the axes of the wheel and of the common pivot, and means for displacing said common pivot, the slots being so disposed and shaped that movement of the pivot with respect to the wheel centre causes the two wheel-covers to turn through equal angles about the said pivot, inwards or outwards, simultaneously.
2. A guard for a rotary member comprising two covers extending over the rotary member, a common pivot upon which the two covers are pivotally .mounted the said pivot being disposed outwards of the centre of the rotary member, a stationary part, pin-and-slot connections between the latter and the two covers, the slots of the pin-and-slot connections being inclined relatively to a plane containing the axis of the rotary member and the axis of the common pivot, and means for displacing said common pivot to cause the two covers to turn angularly about the same, inwards or outwards, simultaneously, the slots being open at one end so that the pins can be disengaged therefrom to enable the covers to be thrown back away from the rotary member.
3. A guard for a grinding wheel or the like comprising two covers extending over the wheel, a common pivot upon which the two wheel-covers are pivotally mounted, the said pivot being disposed outwards of the wheel centre, a stationary part, cam slots in the stationary part, pins on the wheel-covers engaging the slots, the slots being disposed symmetrically on opposite sides of a plane containing the axes of the wheel and commonpivot, and means for displacing said common pivot, the slots being so disposed and shaped that movement of the pivot towards or away from the wheel centre causes the two wheelcovers to turn about the said pivot through equal angles, inwards or outwards, simultaneously, the said slots being open at one end so that the pins may be disengaged from the slots by moving the pivot suiciently inwards towards the wheel centre, thereby enabling the covers to be thrown back away from the Wheel.
4. A guard for a grinding wheel or the like comprising two covers extending over the wheel, a common pivot upon which the two wheel covers are pivotally mounted, the said pivot being disposed outwards of the wheel centre, a stationary part, pin-and-slot connections between said stationary part and the two wheel-covers, the slots of the pin-and-slot connections being obliquely disposed relatively to a plane containing the axis of the wheel and the axis of the common pivot, a slide carrying the pivot, a nut 'on the slide, a rotatable screw engaging the nut for moving the pivot towards or away from the wheel centre to cause the two wheel-covers to turn angularly about the pivot, inwards or outwards, simultaneously, a threaded control shaft driven by the nut-engaging screw, and a part actuated by the control shaft adapted to control a motor driving the wheel according to the positions of the wheelcovers.
5. A guard for a grinding wheel or the like comprising two overlapping half-covers extending over the wheel, a common pivot upon which the two half-covers are pivotally mounted, the said pivot being disposed outwards of the wheel centre, a stationary part, pin-and-slot connections between said stationary part and the two half-covers, the slots of the pin-an-slot connections being obliquely disposed relatively to a plane containing the axes of the wheel and common pivot, a slide carrying the pivot, a nut on the slide, a rotatable screw engaging the nut for moving the pivot towards or away from the wheel centre to cause the two half-covers to turn angularly about the pivot, inwards or outwards, simultaneously, a threaded control shaft driven by the nut-engaging screw, and a part actuated by the control shaft adapted to control a motor driving the grinding wheel according to the positions of the half-covers, the slots being each open at one end to permit of the pins being completely withdrawn from the slots by operating the screw so that the half-covers may be thrown back away from the wheel.
EDGAR CHARLES FIELDING.
REFERENCES CITED The following references are of record in the nie of this patent:
UNITED STATES PATENTS Number Name Date 588,496 Smith Aug. 17, 1897 863,643 Ransom Aug. 20, 1907 1,250,939 Anthony Dec. 25, 1917 1,351,908 Howe e Sept. 7, 1920 1,694340 Weinland Dec. 4, 1929