US2248050A - Electric arc lamp - Google Patents

Description

July 8, 1941. J. ANDERSON 2,248,050

ELECTRIC ARC LAMP Filed Sept. 18, 1939 3 She ets-Sheet 1 INVENTOR. 650mg: J. ANDEQJO/V y 1941. G. J. ANDERSON 2 8,050

ELECTRIC ARC LAMP INVENTOR.

650265 J. ANDEPcSOV M PIE-L11.-

ATTORNEY.

Patented July 8, 1941 UNITED STATES Warner Bros. Pictures,Inc., New York,

PATENT OFFICE ELECTRIC ARC LAMP George J. Anderson, Hollywood, Calif., assignor to corporation of Delaware Application September 18, 1939, Serial No. 295,472

8 Claims.

This invention relates to electric arc apparatus u and has particular reference to electric arc lamps.

One object of the invention is to accurately control the feeding of the electrodes of an arc lamp toward each other to compensate for the burning away of the tips thereof.

Another object is to maintain correct relative feeding movement of a pair of electrodes toward each other and to enable such relative feeding movement to be varied as desired, with or without varying the rotation of one of the electrodes.

Another object is to provide for selective, automatic, or manual feed of an electrode for an electric arc apparatus.

Another object is to enable quick removal of N. Y., a

' ratus, as a unit, from its housing to facilitate rean electrode feeding apparatus from its housing, 5

pair or replacement of that unit. This feature is also of considerable importance in the motion picture industry where the loss of time incurred due to repair or replacement of any equipment is very costly.

The manner in which the above and other objects of the invention are accomplished will be readily apparent from the following specification, when read in conjunction with the accompanying drawings, wherein:

Fig. 1 is a longitudinal sectional view of an electric arc lamp and housing therefor, embodying the present invention.

Fig. 2 is a transverse sectional View through the electric arc apparatus and housing therefor, and

to provide an unflickering beam of light. To pro- 1 duce this unflickering illumination, one of the electrodes, generally the positive, is caused to be rotated about its axis at a steady rate, while being fed longitudinally, so as to uniformly burn,

or form a symmetrical crater, at the tip of that electrode.

The present invention contemplates a simplified drive assembly for rotating one of the electrodes, i. e., the positive, and for feeding the electrodes at desired relative longitudinal speeds,

accommodate electrodes having different burning rates, and may also be regulated to compensate for varying current supply for the electrodes while being capable of feeding the same at such a speed as to maintain a maximum of brilliancy and uniformity of illumination. This latter feature is of considerable importance in the motion picture industry, where, in the photographing of sets or scenes, large numbers of arc lamps are usually employed. Many of these lamps are turned off and on at different times, thus greatly changing the load conditions of the current supply and consequently affecting a noticeable change in .voltage. This is particularly true in cases where port-dole generating equipment of is taken along the line 22 of Fig. 1.

Fig. 3 is a sectional plan view of the rear panel and part of the arc lamp housing and is taken along the lines 33 of Fig. 1.

Fig. 4 is a sectional plan View of the intermittent driving mechanism for the negative electrode feeding head and is taken along the line 44 of Fig. 2.

Fig. 5 is a transverse sectional View through the intermittent drive and is taken along the line 55 of Fig. 4.

Fig. 6 is a transverse sectional view through the feeding mechanism for the negative electrode and is taken along the line 66 of Fig. 1.

Fig. 7 is a longitudinal sectional view through the positive electrode feeding head and is taken substantially along the line of Fig. 2.

Fig. 8 is a transverse sectional view through the positive electrode feeding head and is taken along the line 8--8 of Fig. 7.

Fig. 9 is a transverse sectional View through the feed gears and support therefor in the positive electrode feeding head, and is taken along the line 9-9 of Fig. 7,

Fig. 10 is a sectional view through the positive electrode head illustrating particularly the man ual feed drive therefor, and is taken along line l0--l0 of Fig. 8.

Fig. 11 is a transverse sectional View through the combined contact brush and heat shield unit for the positive electrode feeding head, and is taken along the line HH of Fig. '7.

Referring in particular to Fig. 1 and Fig. 2,

the electric arc lamp assembly comprises a boxshaped housing I5, open at the top thereof and having 'bafiie plates l2 and I3 extending across the top thereof to form a light seal while perinitting a draft of air to be passed therethrough. Openings as at l5, l6 and I! are formed in the lower portion of the walls of the housing It) to permit air to be passed upwardly therethrough for cooling purposes. The front wall [8 of housing it has an opening therein surrounded by a substantially cylindrical flange ii) in which is secured a lens 29 of the Fresnel type. The rear wall 2i of the housing if] has a rectangular opening 22 therein, normally closed by a rear cover member, or panel 23, which is removably secured to the wall 2| by screws 24.

The electrode feeding assembly comprises a positive electrode feeding device or head generally indicated at 25 for feeding a positive electrode or carbon A, and a negative electrode feeding device or head generally indicated at 26 for feeding a negative electrode or carbon B. Both heads 25 anad 25 are supported by a base 21, to the under surface of which is secured a drive motor 28 for the purpose of driving the electrode feeding mechanism in each head.

The base 22' has a pair of spaced ears, as at 29 and extending from opposite sides thereof. These ears, as at 29 and 39, have bearings formed therein and are movable along a pair of spaced parallel rods 3| and 32 extending from the front wall i8 to the rear wall 2| of the housin it.

One of the rods 3| is screw threaded at 33 and is journalled at the front end thereof in a bearing 34 provided in the front housing wall IS. The rear end of rod 3| is journalled in a bearing provided in the panel 23. A handle 36 is secured on the end of rod 3| extending through bearing whereby to enable manual rotation of the rod 3!. The bearing 35 and rear end of rod (ii are so formed as to prevent endwise movement of rod 3| relative to panel 23.

As will be noted in Fig. 1, ear 30 on base 21 is screw-threaded and mounted on the threaded portion 33 of rod 3|, whereby to cause movement of the entire electrode feeding assembly toward and away from lens 26 on rotation of the handle 36. That is, rotation of the handle 36 will cause movement of the arc produced across the tips of the positive electrode A and the negative electrode B into or out of the focus of the lens 20.

As shown in Fig. 3, the rod 32 is secured at 38 to the rear panel 23, and is slidably received at the front end thereof in a bearing (not shown) similar to that of 34 and mounted or formed on the front wall |8 of the housing In.

The positive electrode feeding head 25 is mounted on a sub-base 39 which is supported by posts 52 anad 52 from the main base 21. A layer 39' of insulating material, such as asbestos or the like, is interposed between the head 25 and the base 39 to electrically insulate this head.

Describing in detail the positive head 25, reference is had to Figs. '7, 8, 9, 10, and 11, inclusive. Head 25 comprises a cylindrical housing 40, having legs 4| (Figs. 1 and 2) at the bottom thereof, which are secured by bolts 42 to the subbase 39. Bolts 42 pass through suitable insulating bushings (not shown). The housing has an apertured end wall 43 at the forward end thereof, and is open at the rear thereof, there being a cylindrical shoulder 44 formed thereon and adapted to snugly receive a mating cylindrical portion of a casing 45. Casing 45 is open at the end thereof adjacent housing 40 and is removably secured to this housing by screws 46. Housing 43 and casing 45 form a substantially enclosed compartment to house the electrode feeding mechanism.

A bearing counterbore 41 is formed at the rear of the casing 45 to receive a ballbearing assemly 4%]. A cap 49, having a centrally located electrode receiving aperture 50 therein, is secured to the end of casing 45 by screws 5|, to retain he bearing assembly 48 in the counterbore 41 and prevent longitudinal movement thereof.

An electrode carrier generally indicated at 53 is rotatably supported by the bearing assembly 48. Carrier 53 comprises a tubular member 54, having a longitudinally extending bore therethrough, to loosely receive the positive electrode A. A crown gear member 55 is slidably fitted over the member 54, and abuts a shoulder 56 formed on member 54.

A lock nut 51 threaded on the rear end of the member 54 is provided to secure the gear member 55 to the tubular member 54, and also to lock the member 54 in the bearing assembly 48, to prevent longitudinal movement thereof.

Referring in particular to Figs. 7 and 9, it will be noted that the forward portion of the tubular member 54 is formed into an enlarged head 58 having a longitudinally extending slot 59 formed therein. A pair of diametrically opposed, transversely extending grooves, 60 and 6|, are cut into the head 58, to receive and guide a pair of stub shafts 52 and 63 therein, respectively. A pair of feed gears, or wheels, 64 and 65 are journalled on the stub shafts 62 and 63, respectively. Gears 64 and 65 are located in and guided against longitudinal movement by the opposed sides of the groove 58. A pair of tension springs 68 and 66 are provided between the ends of the stop shafts 62 and 63, to resiliently urge the teeth of the gears 64 and 65 into driving engagement with the surface of the positive electrode A. A spiral or scroll gear member 61 is journalled on a bearing portion formed on the tubular member 54, directly behind the head 58, and has a set of spiral gear teeth 68 formed on one face thereof which mesh with the teeth of the gripper gears 64 and 65. From the above it will be noted that relative rotation of the tubular member 54 and spiral gear member 61 will cause rotation of the gears 64 and 65 about their respective shafts, to impart a longitudinal feeding movement of the positive electrode A.

A set of spur gear teeth 69 are formed on a periphery of gear 67.

Referring in particular to Figs '7 and 8, a threelobed cam 10 is secured to the face of the crown gear member 55, intermediate gears 55 and 6! by screws. one of which is shown at 7|. A cam follower l2 rides on the surface of cam 10 and is reciprocal in a guide block 13 which extends through an opening formed in the casing 45 and is secured to this casing by screws, as at 14. That is, cam follower I2 is slidable, in a substantially vertical direction, in a bearing formed in block 73. A compression spring is interposed between the cam follower 12 and the block '73 to resiliently urge the follower 12 into engagement with the cam 70.

A portion of the cam follower 72 extends through the top of the guide block 13 and has a stop screw 15 screw threaded therethrough. The bottom end of screw 18 has a conical point formed thereon and adapted to engage any one of the teeth 69 on gear 61, when the cam follower it rides upon a flattened portion 18 of cam 18. From the above it will be noted that on rotation of the tubular member 54, the positive electrode A will be rotated and the cam follower l2 will be reciprocated three times per revolution of the member 54. As the cam follower 12 moves downwardly, the conical point of screw 16 engages a tooth on the periphery of the spiral gear member 6?, thereby arresting rotation of this member, and, due to the relative rotation between the head '58 and the gear 61, will effect rotation of the gears 64 and 65 to cause feeding movement of the electrode A. In other words, a feeding movement will be imparted to the electrode A three times per revolution of the electrode carrier 53.

In the event that it is desired to regulate the rate of feeding of the electrode A independently of the rate of rotation thereof, a lock nut 19, threaded on screw 16 and abutting the upwardly extending portion of the cam follower- 12, is loosened, allowing the screw to be raised or lowered, whereby the interval of time during which the conical point of screw 16 is engaged with one of the teeth 89 may be regulated, which of course will regulate the amount of each feeding impulse. That is, if the screw 16 is lowered, the conical point of this screw will engage a tooth til at an earlier moment on the downward travel of the cam follower l2 and will be disengaged from that tooth at a later moment, thus holding the gear t3! in a fixed position for a longer period of time. Since each feeding impulse of the electrode is of considerable duration, but causes only a very short length of travel, and, furthermore, since there are a plurality of impulses for each rotation of the electrode, it will be noted that the slight unevenness of longitudinal feeding travel will be insufficient to cause a flicker or change in the illumination of the arc.

The above mentioned positive electrode feeding head is described and claimed in my Patent No. 2,1731% granted September 19, 1939, for Electrode feeding device for electric arc apparatus. However, in that patent, a series of serrations are provided around the periphery of the gear $2, in lieu of the gear teeth 89.

teferring to Figs. 1, 8 and 10, the electrode A is adapted to be manually fed in a longitudinal direction, independently of the motor drive for the .two electrode feeding heads and 26, by a shaft which extends rearwardly from the casing iii through a hole formed in panel 23 and terminates in a handle 8|. Shaft 80 is divided into two sections which are connected together, and insulated from each other, by a coupling 82 of insulating material, such as bakelite. The inner end of shaft is journalled in a bearing 83 formed in the casing 45. A pinion 84 is secured to the inner end of the shaft 80 and is adapted to mesh with the gear teeth 69 formed on the gear member 61, but is normally out of engagement therewith. When it is desired to manually feed the electrode A; as, for example, when inserting a new electrode or when moving the electrode into a correct alignment with the negative electrode B; the handle 8| is pressed inwardly against the action of a compression spring 85, interposed between the casing and the coupling 82. This action causes the gear 84 to move into mesh with the gear teeth 69, and, on rotation of the handle 8|, the spiral gear 6'1 will be rotated relative to the head 58, to impart a feeding motion to the feed gears $4 and 65.

Due to the fact that the shaft 89 extends a considerable distance behind the panel 23, it will be noted that the handle ill will not interfere with the focusing adjustment of the electrode feeding assembly.

Included in the positive head 25 is a combination contact brush and shield assembly, generally indicated at 8?, which is situated in front of the housing ii-l to shield the electrode feeding mechanism of the positive head 25 from the intense heat of the are produced across the electrodes A and B. This assembly comprises a member 88 secured, as by screws as, to the sub-base 39 through the insulating layer 38. Note that member does not touch the housing 40, thereby permitting an insulating layer of air to extend therebetween. Member 88 has an electrode receiving aperture extending centrally therethrough, through which electrode A passes. A shield unit is secured in front of member 88 and comprises, in part, a metal plate 90, secured by screws Q! to the front face of the member 88. An asbestos plate 32 and a metal plate 93 separated from the plate 522 by the spacers 94 are secured to the plate 93 by screws S5. A horizontally extending channel 955 is provided in the front face of the member 88 and has a stationary contact shoe 9?, secured therein by a lock screw (Figs. 7 and 11). Screw 38 passes through an elongated slot as, formed in shoe 9?, whereby this shoe may be moved into different positions and then locked. The inner end of the shoe 91 is concave to fit the surface of the electrode A. Also mounted in the channel 96 is a springpressed movable contact shoe Hi9, also having its inner end concave to fit the surface of the electrode A.

Current is supplied to the movable contact shoe H19 by a flexible conductor 10! which is secured in a terminal clip I92. Clip I02 is secured to the end of contact shoe If!!! by a bolt Hi3, the head of which is engaged by a lever I84 pivoted at Hi5 to brackets I06 extending from the member I98. The opposite end of lever it is engaged by a compression spring I01 (Fig. 2).

The negative electrode feeding head 26 comprises an electrode clamp Hi9 secured to the negative electrode B and slidable along a pair of spaced guide rods H6 and HI (Fig. 6). Rods ilii and Hi are secured at their opposite ends in brackets H2 and H3 extending from a continuation of the sub-base 33. A screw threaded shaft Hd extends parallel to the electrode B, intermediate rods HQ and HI and is suitably journalled at opposite ends thereof, in bearings formed in the brackets H2 and H3. Shaft H4 is also slidable lengthwise a limited amount in its bearings.

A tooth H5, mounted on a lever H8 (Fig. 6), is carried by the clamp I09 and is normally in engagement with the threads of shaft I 14, thereby forming a travelling nut member. Lever H6 is pivoted at H? to a depending portion of the clamp Hi9 and is spring pressed in a clockwise direction to cause the tooth H5 to engage the shaft H4 by a spring H8. By depressing the lever lit, the tooth H5 will be moved out of engagement with the shaft H4, thereby enabling the clamp its to be moved along the rods Hi) and Hi, enabling the adjustment of the electrode B toward or away from the electrode A. A bevel gear IN is slidably keyed on the screw threaded shaft H4 at the upper end thereof and is maintained in continual mesh with a mating bevel gear I2I fixed to the end of a negative drive shaft I22 The above mentioned description of the details of the clamp I59, as well as the provision for allowing the screw H4 to be moved lengthwise for striking the arc, is not a subject of the present application and it is therefore not believed necessary to describe the same in further detail.

Shaft I22 is journalled in bearings I23 and I24 formed on the sub-base 39. The end of shaft I22 extends through the hole in panel 23 and terminates in a handle I25, to enable manual feeding operation of the electrode B independent of the motor drive therefor. Shaft I22 is divided into two sections which are insulated from each other by a coupling I25 of Bakelite or other insulating material.

Referring in particular to Fig. 2, the motor 28 has a gear reduction unit (not shown) provided in a housing I21 formed at one end bell of the motor. This gear reduction unit is connected to and drives a main drive shaft I29, which is journalled at the upper end thereof (Fig. '7) in a bearing I33 formed in the casing 45. A bevel pinion i3! is formed on the upper end of shaft I29 and meshes with the crown gear 55 to drive the electrode feeding mechanism of the positive head. Shaft I29 is divided into two sections which are connected together and insulated from each other by a coupling I30 of Bakelite or like material.

A worm I3I (Figs. 4 and 5) is secured to shaft 1'29 intermediate its ends and meshes with a worm gear I32 loosely journalled on a sleeve I33 which is secured to the negative drive shaft I22.

Worm gear I32 is maintained in engagement with a flange I34 on the sleeve I33 by a compression spring I 35, these members, (the flange I34 and gear I32), forming the coacting elements of a friction clutch, to enable a non-positive drive connection between the worm gear I32 and shaft I22 to be maintained. A look nut I 3'! is threaded on the end of sleeve I33 to retain the spring I35 under compression and is adjustable along the sleeve I33 to vary the friction between the gear I32 and sleeve I33.

A three-lobed cam I33 is secured, in a suitable manner, to the worm gear I32 and is engaged by a cam follower I 39 slidably mounted in a guide block I49. Block I40 is suitably secured to, and extends through, an opening formed in a protective housing I4I which surrounds the worm I3! and gear I32 and protects the same from carbon dust and the like. Housing MI is secured through the base 21, as by screws I42.

Cam follower I39 is similar to that of I2, there being a compression spring I43 interposed between this cam follower and a well, formed in the guide block 133, to resiliently press the cam follower in engagement with the cam I38. A stop screw I44 is threaded through the cam follower I39 and is adapted to be adjustably locked in different positions by a lock nut I45 threaded thereon. The inner end of screw I44 is pointed and is adapted to engage any one of a plurality of serrations provided on the periphery of a. member I Member I43 is interposed between the gear I32 and the compression spring I35 and is slidably keyed to the sleeve I33 by means of a pin I41. Thus, member I46 forms another element of the aforementioned friction clutch. From the above, it will be noted that on rotation of the worm gear I32 by the Worm I3I on the main drive shaft I29, the cam I38 will reciprocate the cam follower I39 and, consequently, the stop screw I44, which will intermittently engage the serrated member I46 to arrest the rotation of the negative drive shaft I22. Adjustment of the stop screw I44 will act to change the period during which the serrated member I46 and, consequently, the feeding of the negative electrode B is maintained in a manner similar to that described in connection with the stop screw I6.

By arranging the motor 28 to one sideof the vertical plane passing through the positive electrode A and the negative drive shaft I 22, and by inclining the main drive shaft 29, as indicated in Fig. 2, a simplified drive connection between the shaft I 29 and the negative feeding mechanism of the head 26 is obtained. This results in a minimum number of gears and other rotating parts to effect quiet operation as well as a simple and economically manufactured driving mechanism.

In order to automatically strike the arc between the electrodes A and B, an electro-magnet I49 is provided for this purpose. This electro-magnet I49 is connected in series with the circuit through the electrodes A and B, and is supported on a metallic L-shaped base I50 which is suspended by means of brackets or posts I5I from the bottom of the base 27. A metal armature I52 is pivoted at I53 to the base I50 and is held in the position illustrated in Fig. 1, when no current is being passed to the arc lamp, by a tension spring I54, extending between the armature I52 and the ear 29 of base 27. Armature I52 is pivotally connected to one end of a link I55 which, in turn, is pivotally con nected to one end of a bell crank lever I53. Lever I56 is pivoted at I5! to the lower end of the sub-base 39 and has the other end thereof extending through an aperture I 51' in sub-base I39, and formed into a yoke (not shown) which engages a groove I58 formed in the threaded shaft II 4. Shaft II 4 is reciprocal longitudinally thereof by the bell crank I53 to move the clamp I09 and electrode B from the striking position illustrated in Fig. 1 to an operating position (not shown). This type of strike mechanism, i. e., the slidable rod H4 and bell crank I55, is well known in the art and it is therefore not deemed necessary to describe same in further detail.

Bearing in mind the above description of the are striking mechanism, and assuming that the electrodes have been correctly positioned so that they will contact each other in striking position, it will be noted that when current is first passed through the lamp circuit, contact will be made across the tips of the electrodes to complete this lamp circuit. Soon after the establishment of the circuit across the electrodes the electro-magnet I49 will become effective to actuate the arrnature I52. Thus, the negative electrode B will be drawn downwardly a predetermined distance to separate the tip thereof a desired distance from the tip of the electrode A to produce the arc.

A rheostat indicated at I59 is suitably secured to the inner surface of the panel 23 and is connected in the circuit. of motor 28 to enable the speed thereof to be regulated. A control knob I60, extending on the exterior panel 23, enables adjustment of rheostat I59.

The procedure which may be followed in regulating the electrode feeding mechanism is to maintain the motor 28 at a constant speed, whereby to maintain the rotation of electrode A constant, and to adjust the stop screws 18 and M4 to regulate the feeding movements of the electrodes A and B respectively, as desired. However, regulation of the feeding movements may be obtained by merely regulating the speed of the motor 28 by the rheostat I59. Another alternative method of regulating the feeding speeds of the electrodes is to back off, or entirely remove, the stop screw I44, so as to enable the same to be ineffective to arrest the rotation of the negative drive shaft I22. In this case, the speed of the motor 28 may be regulated to obtain the cor rect feeding speed of the negative electrode B, while adjusting the stop screw 16 to obtain the correct feeding speed of the positive electrode A.

When it is desired to remove the electrode feeding assembly, including the positive head 25 and negative head 25, from the housing 19, for replacement or repair, flexible conductors I62, extending between a suitable socket on the bottom of the housing [0 and a terminal block I53 on the base 2'l,are removed. The screws 24,securing the panel 23 to the rear wall 2| of the housing ID, are then removed, enabling the panel 23 to be moved rearwardly, carrying the rods 3! and 32, as well as the entire electrode feeding unit and motor 28, out of the housing Ill. It will be seen that the entire assembly is then completely detached from housing HI. Since the forward ends of the rods 3i and 32 are merely fitted in bearings at the forward wall 18 of the housing ID, no further disconnecting of any of the supporting members of the electrode feeding assembly is required.

Although the invention has been described in connection with, and is particularly applicable to, a lens type housing, it is to be understood that with certain obvious modifications, the apparatus of the invention may be applied to a reflective type housing. For example, the opening 22 and the panel 23 covered thereby may be extended upwardly and a reflector may be secured to the panel 23.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is.

I claim:

1. Electric arc apparatus comprising the combination of a positive electrode feeding device, a negative electrode feeding device, a drive shaft for driving one of said devices, means for rotating said shaft, a shaft for driving the other of said devices, a frictional clutch operatively connecting said last mentioned shaft to said first mentioned shaft for driving said other device, and means actuated by said first shaft for intermittently rendering said clutch inoperative to drive said other shaft.

2. Electric arc apparatus according to claim 1, comprising adjustable means for controlling said last mentioned means to vary the period during which said clutch is rendered inoperative.

3. Electric arc apparatus comprising the combination of an electrode feeding device, a drive shaft for said device, a drive member rotatably mounted on said shaft, a frictional drive connection between said member and said shaft, means for rotating said member, and means actuated by said member for intermittently operating said frictional drive connection for arresting the rotation of said drive shaft.

4. Electric arc apparatus comprising the combination of an electrode feeding device, a drive shaft for said device, a member rotatably mounted on said shaft, a frictional drive connection between said member and said shaft, a cam operatively connected to said member, a cam follower movable by said cam, a stop member operable by said cam follower and adapted to arrest the rotation of said shaft on movement of said cam follower by said shaft, and means for rotating said member.

5. Electric are apparatus according to claim 4, comprising an adjustable connection between said cam follower and said stop member whereby the period during which said shaft is arrested by said stop member may be varied.

6. Electric arc apparatus comprising the combination of an electrode feeding device, a drive shaft for said device. means on said shaft forming a clutch element, a drive member rotatably carried by said shaft and forming a second clutch element adapted to engage said first mentioned clutch element to form a driving connection with said shaft, a cam operatively connected to said drive member, a serrated member slidably keyed to said shaft adjacent said drive member and on the side thereof opposite said first mentioned clutch element, means for resiliently urging said serrated member against said drive member to effect a drive connection between; said drive member and said shaft, means for rotating said drive member, and means actuated by said cam for periodically arresting the rotation of said serrated member.

7. Electric arc apparatus comprising the combination of a positive electrode feeding head, a negative electrode feeding head, a drive shaft for said positive head, means for rotating said drive shaft, a second drive shaft for said negative head, a gear operatively connected to said first mentioned shaft, a second gear rotatably mounted on said second shaft and meshing with said first mentioned gear, means forming a frictional drive connection between said second gear and said second shaft, and means comprising a cam on said second gear for periodically interrupting the rotation of said second shaft.

8. Electric arc apparatus comprising the combination of a base, negative and positive electrode feeding heads on said base, a motor on said base, a substantially horizontally extending drive shaft terminating at said negative head, the axes of said positive head and said motor extending horizontally substantially parallel to said negative drive shaft with the axis of said positive head and the axis of said negative drive shaft in substantially the same vertical plane and with the axis of said motor offset to one side of said plane, and a substantially straight shaft extending from said motor to said positive head at one side of said negative drive shaft and a worm on said substantially straight shaft and a cooperating worm wheel on said negative drive shaft.

GEORGE J. ANDERSON.

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