Patent GB-418020-A (GB)
Title: Improvements in and relating to electrically-driven drills
IPC: B25D11/10
Filed: 1933-06-12
Abstract: 418,020. Drilling-machines. HURD, F. W., 70, Cunningham Park, Harrow, Middlesex. June 12, 1933, Nos. 16784 and 33740. [Class 83 (iii).] In a portable electrically-driven rotary and percussive drilling-machine the rotor and its shaft are reciprocated axially by a cam and spring to impart hammer blows to the drill during its rotation. The force of the blows may be varied from zero to a maximum, so that the drill may rotate without percussive action, or the device may be incorporated in a machine having percussive action only. The rotor 1, Fig. 1, is secured against a collar 2a on the hollow shaft 2 by means of a spring ring 2b, the shaft being mounted in roller bearings 3, 4 which have a slight amount of axial play and are secured to the shaft by screwed collars 11, 12. Projections 13 on the collar 11 are pressed into contact with cams 14 on a fixed collar 15 by means of a spring 18 located between a flange on the collar 12 and a thrust bearing 20 held by a hollow plug 17 screwed into a boss 10 of the motor casing. The drill 22 is driven by a plug 23 splined within the shaft 2 by means of a pin and slot 24, the hammer blows being imparted to the plug 23 by means of a sleeve 26 attached to the collar 12. The rearmost position which the plug 23 can assume is determined by a plunger 27 adjustably secured to the stationary plug 17 at 28, thus determining the gap at 30 between the sleeve 26 and the plug 23 to vary the force of the blows or to maintain the plug out of reach of the sleeve. In a modification, wherein the drill is rotated through reduction gearing, the rotor 1, Fig. 4, and bearings 3, 4 are secured on the hollow shaft 2 by collars 31-33 and a spring ring 34, the collar 31 having a flange 36 on which are provided the projections 13 co-operating with the cams 14 on a stationary ring 14a. The spring 18 acts between the collar 31 and a thrust bearing 20 on the end cover 21 of the motor casing, this cover also carrying the adjusting plunger 27. A pinion 39 on the shaft 2 engages a gear 40 supported by a flange 42 on the casing and meshing with an internally toothed gear 38 whose sleeve 37 carries the driving pin 24. The gears 38, 40 are interchangeable to vary the drilling speed, the flange 42 having a number of pins 41 for supporting gears 40 of different size. In a further modification the adjusting plunger 27 is attached to the end cover 21 which screws in the boss 43 to effect the adjustment, a flange being provided on the casing 8 to prevent ingress of dirt &c. when the cover recedes from the casing. The radial thrust bearing 20 is replaced by a journal thrust bearing whereof the outer race is secured in the cover 21 so that in the outer position of the cover, the teeth 13 are held out of contact with the cams 14 and the drill then partakes of rotary motion only. When used for percussive action only, the driving lugs 23<a> are dispensed with and the drill is splined in the body of the machine by means of a collar. The weight of the rotor 1 and the strength of the spring 18 may be varied to adjust the force of the percussive blows imparted to the drill.