US2723497A

US2723497A - Two-wheel grinding machine

Info

Publication number: US2723497A
Application number: US247427A
Authority: US
Inventors: Paul A Grobey
Original assignee: Bryant Grinder Corp
Current assignee: Bryant Grinder Corp; Bryant Chucking Grinder Co
Priority date: 1951-09-20
Filing date: 1951-09-20
Publication date: 1955-11-15
Anticipated expiration: 1972-11-15

Description

Nov. 15, 1955 Filed Sept. 20, 1951 07 I I W W M 0 /4/ W L [7 P. A. GROBEY TWO-WHEEL GRINDING MACHINE 4 Sheets-Sheet l 1955 P. A. GROBEY TWO-WHEEL GRINDING MACHINE 4 Sheets-Sheet 2 Filed Sept. 20, 1951 NOV. 15, 1955 GROBEY 2,723,497

TWO-WHEEL GRINDING MACHINE Filed Sept. 20, 1951 4 Sheets-Sheet 3 1955 P. A. GROBEY TWO-WHEEL GRINDING MACHINE 4 Sheets-Sheet 4 Filed Sept. 20. 1951 United States Patent Ofifice 2,723,497 Patented Nov. 15, 1955 1 2,723,497 TWO-WHEEL GRINDING MACHINE Paul A. Grobey, Springfield, Vt., assignor to Bryant Chucking Grinder Company, Springfield, Vt., a corporation of Vermont Application September 20, 1951, Serial No. 247,427 15 Claims. (Cl. l-5) This invention relates to grinding machines each provided with two grinding wheels to each of which the work is presented at difierent times.

One object of the present invention is to provide improved means for rapidly shifting the work from one to the other of the grinding wheels.

More specifically a further object of the invention is to provide means which gives an initial push to the work holder to change from one to the other of its positions, the momentum imparted by the initial push being sufficient to carry the work holder through to the other position Without further expenditure of moving force.

A further object is to provide in a grinding machine provided with a face grinding wheel improved means for truing the grinding face of such a Wheel and for feeding the wheel relative to the work piece to compensate for wheel wear and truing.

Further objects and advantages will appear from a description of the machine shown in the accompanying drawings in which Figure l is a top plan view of a grinding machine embodying the invention.

Figure 2 is a detail sectional view on line 2-2 of Figure 1.

Figure 3 is a detail sectional View on line 3-4 of Figure 2.

Figures 4 and 5 are views similar to portions of Figure 1, but showing the parts in different positions.

Figures 6, 7 and 8 are detail sectional views on lines 66, 7-7, and 8-8 respectively, of Figure 1.

Figure 9 is a fragmentary front elevation showing the face grinding wheel slide approaching its retracted position preparatory to the dressing of the face grinding wheel.

Figure 10 is a detail sectional view on line 10-10 of Figure 7.

Figure 11 is a fragmentary top plan view of the facing wheel holder partly broken away and in section on line 11-11 of Figure 9.

Referring to the drawings, and more particularly to Figure l, the machine comprises a bed 1 on which is mounted a work head 2 for linear motion, the direction of this motion being up and down as viewed in this figure. It may be mounted on suitable Ways shown as bars 3 and 4 which may be connected to the head 2 by expansible and contractible dust-excluding covers 5. Also mounted for linear motion and at right angles to the work head 2 is a tool head 6. This may be similarly mounted on bars, one of which is shown at 7, likewise being protected by dust guards such as 8. The work head 2 has journaled therein a work spindle having at one end a suitable work holder 10. This work holder and spindle may be rotated as by a motor 11 mounted on the work head and connected as by a belt 12 to a suitable pulley on the work spindle in a manner well known in the art.

The tool head 6, as shown best in Figures 1 and 11, has journaled therein a pair of grinding wheel spindles 15' and 16. The spindle 15 has thereon an axial abrasive grinding. wheel 17, which as shown, may be an internal grinding wheel arranged to grind an internal bore in a work piece 18 carried by the work holder 10. The spindle 16, as shown best in Figure 11, carries a face grinding abrasive wheel 20 having an annular end face 21 arranged to grind off the end face of the work piece 18. The grinding wheels 20 and 17 can be moved into and out of grinding relation to the work head by the linear motion of the tool head 6.

The face grinding wheel 20 with its spindle 16' is mounted not only for linear motion with the head 6, but also for motion in the same direction as the head 6 and relative thereto for a purpose which will later appear. To this end, and as shown in Figure 11, the spindle 16 is journaled on the bearings 25 and 26' in a casing 27 which is slidably mounted as within the longitudinal ball bearings 28' in a portion 29 of the wheel head. This portion of the wheel head is provided with a cap 30' which bridges across the rear end of the casing 27 and is secured to the portion 29 as by bolts 30a; This cap 30 is provided axially with a closure plug 31 internally threaded at 32 for cooperation with an abutment screw 33' threaded therethrcugh and having its inner end 34' arranged to bear" on a bearing cap 35, closing off a recess 36in the casing head 37 which houses the bearings 26. The casing 27- is pressed rearwardly to hold it against the inner end of the abutment screw 33 as by one or more springs 40 each seated in a socket 41 in the head portion 29 and bearing against a pin 42 slidab'le within the recess and bearing against a laterally extended portion of the casing head 37.

As shown, the spindle 16 carries the rotor 44 of a motor, the stator 45 of which is fixed to or integral with the casing 27. Thus the face grinding wheel 20 is adjustable axially as by turning, of the abutment screw 33 but is normally held back against this screw. The rear end of the screw 33 has secured thereto a hand wheel by which it may be manually turned, and secured to this hand wheel is a ratchet wheel 51. Cooperating with the teeth of this ratchet Wh68l 51 is a ratchet dog 52 (see Figures 8 and 9) pivoted to an arm 53 which is pivoted on a boss 54 on the head portion 29, a retaining ring 55 serving to hold the arm 53 on the boss 54. On the lower end of the arm- 53" there is journaled a cam follower roll 56 with which cooperates at certain times a cam element 57 carried by the bed 1. The arm 53 is normally held as by a spring 58 (see Figure 8) in contact with an adjustable stop screw 59 carried by a lug 59a extending from the cap 30, and as shown in Figure 8, the angular position in which this arm 53 is normally held is such that when the wheel head is moved to the right as viewed in Figure 1 sufficiently for the follower roll 56 to engage on the cam 57, this cam has the effect of swinging the arm 53 to the left as viewed in Figure 8, causing the ratchet dog 52 engaging in the teeth of the ratchet wheel 51 to turn this wheel, and consequently the abutment screw 33, in a direction to advance the face grinding wheel relative to the Wheel head by a predetermined amount. This is for the purpose of advancing the face of the grinding wheel preparatory to a face truing operation in order that the face truing operation will leave the wheel face at a predetermined distance with respect to the wheel head relative to the work so that when the wheel head is again advanced to a predetermined point the face of the Work will be ground off to a predetermined point relative to the work holder.

The means for so truing olf the face of the wheel is shown best in Figures 7 and 10. A shaft 69 (see Figures 1 and 8) is journaled longitudinally in a casing member 61 secured to the top of the wheel head 6. The forward end of this shaft 60, as best seen in Figure 10, extends through and is secured in a block a. This block 60a has secured to opposite faces thereof a pair of flat springs 62, 63 the opposite ends of which are secured to an arm 64 which carries at its outer end a truing device 65. As shown in Figure 10, this truing device may be adjusted toward the face of the grinding wheel 20 asby turning an adjusting screw 66 and it may be fixed. in

adjusted position as by tightening a set screw 67. The

springs 62 and 63 allow the dressing tool 65 to be adjusted independently of the screw 66 toward and from the face of the grinding wheel 20, and this adjustment, as shown, may be produced by the turning of a screw 70 having a knurled head 71 provided with indexing markings 72 for cooperation with a pointer 73 carried by the block a. This screw is threaded through the block and its inner end bears against one arm of a bell crank lever 74 journaled at 75 in an extension bracket 76 of the arm 64. The opposite end of the bell crank lever 74 is rounded as at 76a and bears in a recess 77 in the block 60a. It will be evident that by turning the screw 70, the bell crank lever 74 may be rocked, moving the fulcrum 75 and with it the arm 64 substantially axially with respect to the grinding wheel 20. The truing device 65 may be arranged to extend through an arcuate slot 80 in a guard plate 81 partially covering the outer face of the face grinding wheel 20, this guard plate having a cut away portion at 82 within which the work piece may be extended when the wheel head is moved axially into grinding relation between the face grinding wheel and the work. 7

The shaft 60 is rocked to bring the truing device across the annular end face of the face grinding wheel 20 at suitable times. It may be actuated by hand whenever desired by grasping and moving a handle 85 (see Figure 7) extending laterally from the arm 64, but it may also be actuated automatically by the retraction of the wheel head to a point beyond that required to effect the compensating feed of the wheel 20. For this purpose the rear end of the shaft 60 has secured thereto one end of an arm 86 (see Figures 1 and 8) to the outer end of which is pivoted a link 87. The lower end of the link 87 is pivoted at 88 (see Figure 9) to an arm 89 fulcrumed at 90 on a bracket 91 projecting from the wheel head 6, and having at its rear end portion a cam roller 92 journaled thereon. In idle position of the truing device, a stop lug 93 on the arm 89 contacts an adjustable abutment screw 94 as shown in Figure 9, but when the wheel head is retracted sufficiently, the roller 92 rides up an inclined face 95 of a cam block 96, which is pro- 4 vided with a foot 97 by which it may be attached as by bolts 98 to the top face of the bed 1. Thus as the wheel head is retracted sufiiciently, the arm 89 is lifted, which lifts the rod 87 and rocks the shaft 60, causing the dressing diamond 65 to be swung across the grinding face of the grinding wheel 20, thus causing this face to be trued. On forward motion of the wheel head thereafter, the truing device is returned to its starting position shown in Figure 7 as by a spring 99 (see Figure 8). It will be noted that the cam 57 which actuates the feed by acting Y on the cam follower roll 56 has completed its action when the cam roll 92 has been moved sufiiciently to start the dressing of the wheel by the cam 95, the roll 56 still being held on the fiat portion of cam 57 as viewed in Figure 8 while the dressing action is taking place.

The advance and retraction of the wheel head is produced by rotation of a cam shaft 100 (see Figures 1, 2 and 6), having a cam actuating a follower 101 on a lever 102, the upper end 103 of which is connected to a rod 104 secured to the Wheel head 6. The wheel head may be normally pressed toward retracted position as by suitable springs including, for example, a spring 105 shown attached at one end to the lever 102 and at its opposite end to the bed 1.

The work piece carried by the work head may be presented alternately into cooperative relation to the grinding wheels 17 and 20 and such presentation may be produced automatically by the rotation of the cam shaft 100. It will be understood that this cam shaft 100 is rotated once for each cycle of the machine, this rotation being effected by power from any suitable source (not shown).

For the purpose of moving the work head from one to the other of its operative relations to the two wheels on the wheel head, the work head is provided with a a pair of

bearings

140, 141.

rearwardly extending arm portion 110, shown best in Figures 1 and 4. At the rear end of this arm there is journaled therein a shaft 111 carrying a crank arm 112 (see also Figure 3). The outer end of this crank arm has journaled therein a crank pin 115 upon which is pivoted one end of a link 116. The other end of this link 116 is provided with a ball portion 117 mounted in a socket block 118 having externally threaded thereon an internally threaded sleeve 119. The sleeve 119 is suitably journaled in fixed axial relation in the bed 1 and is provided with a spiral gear 120 with which meshes a spiral gear 121 carried by a shaft 122 having a hand feed wheel 123 secured to its outer end. This feed wheel 123 may be turned by hand as desired, or it may be arranged to be moved automatically by any suitable means as through the rocking of an arm 124 journaled thereon and having a ratchet feed mechanism engaging in a ratchet wheel 125 secured to the shaft 122. Such arrangements of feed mechanism are old and well known, however, and form no part of the present invention. It is sufiicient to say that by turning of the crank member 112 from the position shown in Figure 5 where it is extended in line with the rod 116 to a position 180 therefrom where the crank arm 112 overlaps the rearward end of the rod 116, the work head is moved from its position where it may be acted upon the face grinding wheel to the rearward position where it is in operative relation to the grinding wheel 17. When it is in operative relation to the grinding wheel 17, operation of the feed mechanism which turns the shaft 122 acts to produce the cross feed motion of the work with reference to the grinding wheel 17.

Means are provided by which the work head may be moved automatically from one to the other of its operating positions and as shown this movement is accomplished by a cam carried by the cam shaft 100. Referring to Figures 2, 4 and 5, it will be seen that the cam shaft 100 carries a cam provided with two outwardly extending lobes 131 and 132. This cam 130 is adapted to coact with a follower 133 on a lever 134 fulcrumed at 135 on a bracket 136 carried by the bed 1. The upper end of the lever 134 has pivoted thereto as at 138 a rod 139 which is mounted for axial sliding motion in At its inner end this rod 139 carries a grooved track member 142 in which is mounted a follower 143 carried by the crank pin 115. Whenever in the rotation of the cam shaft 100 one of the lobes 131 and 132 presses the lower end of the lever 134 inwardly, the upper end of this lever is pulled in the opposite direction and the track member 142 is pulled to the left as shown in Figure 4. This acts to turn the crank arm 112 from either of its positions shown in Figures 1 and 5 toward the position shown in Figure 4, this giving the work head an impulse tending to move it out of whichever position it happens to be in toward the other position. Figure 3 shows one of these positions in full lines and the other position in dotted lines, these positions being spaced by substantially double the effective length of the crank arm. As the lobes 131 and 132 are quite narrow, this impulse, which is effective only during the first portion of the first half of each full stroke of the work head, tends to start the motion of the work head and through its momentum its motion is continued through the dead center position with relation to the rod 139, and until the work head has completed its full stroke. A spring connected at one end to the lever 134 and at its other end to a fixed anchorage 151 on the bed tends to aid in returning the guide block 142 to its right hand position and completing the motion of the work head from one to the other of its positions. As shown best in Figure 5, the connection from the upper end of the lever 134 to the rod 139 is through a block 155 threaded onto the outer end of the rod 139 and having sockets for the reception of the inner ends of clevis pins 138 carried by the forked extremity 156 of the lever 134. The cam shaft 100 may be provided with other cams for controlling other functions and operations in the machine cycle including, for example, side truing of the grinding Wheel 17, but as these do not constitute portions of the present invention they are not shown nor described herein.

From the foregoing description of certain embodiments of this invention, it should be evident to those skilled in the art that various changes and modifications may be made therein without departing from its spirit or scope.

I claim:

1. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a pair of grinding wheels mounted on said bed and spaced in the direction of motion or" said work head, a feed member, a shaft journaled in said head, a crank arm on said shaft of a length substantially one half of said space, a link connecting said crank arm to said feed member, and means for rotating said crank arm by steps each of substantially one half a revolution with said crank arm overlapping said link or in substantial alinement therewith and thereby present work on said work holder in operative relation to one or the other of said wheels.

2. In combination, a bed, a work holding head, means supporting said work head for motion on said bed in one linear direction, a pair of grinding wheels mounted on said bed and spaced in the direction of motion of said work head, a feed member, a shaft journaled in said head, a crank arm on said shaft of a length substantially one half of said space, a link connecting said crank arm to said feed member, means for rotating said crank arm by steps each of substantially one half a revolution with said crank arm overlapping said link or in substantial alinement therewith and thereby present work on said work holder in operative relation to one or the other of said wheels, and means for moving said feed member in the direction of motion of said work holder.

3. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a shaft journaled in said head, a crank arm fixed to said shaft, a link having one end pivoted to the outer end of said crank arm and extending in the general direction of motion of said head, the opposite end of said link having a pivotal mounting on said bed, said crank arm when in either of two angular positions lying substantially in line with the direction of motion of said head defining a position of said head, said positions being spaced apart by substantially twice the length of said crank arm, an element movable transverse to the direction of motion of said head and operatively connected to the pivot that is between said link and crank arm, and means actuable to move said element to move said pivot out of substantial alinement between said arm and link to start motion of said head from one to the other of said positions and then to release said element for return to initial position, to thus permit the momentum of the parts to carry said pivot through dead center position with respect. to said element and to continue motion of said head to the other of said positions.

4. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a shaft journaled in said head, a crank arm fixed to said shaft, a link having one end pivoted to the outer end of said crank arm and extending in the general direction of motion of said head, the opposite end of said link having a pivotal mounting on said bed, said crank arm when in either of two angular positions lying substantially in line with the direction of motion of said head defining a position of said head, said positions being spaced apart by substantially twice the length of said crank arm, an element movable transverse to the direction of motion of said head and operatively connected to the pivot that is between said link and crank arm, means actuable to move said element to move said pivot out of substantial alinement between said arm and link to start motion of said head from one to the other of said positions and then to release said element for return to initial position, to thus permit the momentum of the parts to carry said pivot through dead center position with respect to said element and to continue motion of said head to the other of said positions, and spring means operatively connected to said head to insure completion of its motion to such other position.

5. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a pair of grinding wheels mounted on said bed and spaced in the direction of motion of said work head, means actuable to start the motion of said work head from one to the other of two positions in one of which one of said wheels may operate on work carried by said work head and in the other of which the other of said wheels may operate on such work, the momentum of said work head completing its motion to said other position, one of said grinding wheels being a face grinding wheel, means for truing the face of said face grinding wheel, and means for adjusting said face grinding wheel axially relative to the other of said wheels to compensate for wheel wear and truing.

6. In combination, a bed, a work head, means supporting said work head for rectilinear motion on said bed, a wheel head, means supporting said wheel head for rectilinear motion on said bed in a direction transverse to the direction of motion of said work head, a pair of grinding wheels carried by said wheel head spaced apart in the direction of motion of said work head, one of said wheels being a face grinding Wheel, and the other of said wheels being an axial grinding wheel, means supporting said face grinding wheel for axial motion relative to said wheel head, means for moving said wheel head to bring saidaxial grinding wheel to and from grinding relation to work carried by said work head when said work head is in one portion of its path of motion, and said face grinding wheel to and from grinding relation to said work when said work head is in another portion of its path of motion, means operatively connected to said work head for moving said work head from one to the other of said path positions when said wheel head is retracted, a face truing device carried by said wheel head, means operatively connected to said face grinding wheel and said bed for advancing said face grinding wheel relative to said Wheel head on retraction of said wheel head to a predetermined position to compensate for wear and wheel truing of said face grinding wheel, and means operatively connected to said truing device and bed for actuating said truing device to true said face grinding wheel on further retraction of said wheel head on said bed.

7. In combination, a bed, a wheel head mounted on said bed for motion thereon in one linear direction, a casing on said wheel head, a wheel spindle journaled in said casing, means supporting said casing on said wheel head for linear motion, an abutment carried by said head and positioned to be engaged by said casing and defining the limit of backward position of said casing relative to said head, a wheel truing device carried by said head and mounted for motion across the face of said Wheel, a cam on said bed, means operatively connected to said head for moving said head relative to said bed, means for advancing said abutment and thus advancing said wheel, means carried by said bed and positioned to be contacted by said cam and be actuated thereby to actuate said advancing means to advance said abutment, casing and wheel relative to said head on retraction of said head to a predetermined position on said bed, a second cam fixed to said bed, and truing actuating means carried by said head and contacted and actuated by said second cam to true said wheel on retraction. of said head further than for actuation of said abutment.

8. In combination, a bed, a work head, means supporting said work head on said bed for motion in one linear direction, a shaft journaled in said head, a crank arm fixed to said shaft, a link having one end pivoted to the outer end of said crank arm and extending in the general direction of motion of said head the opposite end of said link having a pivotal mounting on said bed, said crank arm when in either of two angular positions each lying substantially in line with the direction of motion of said head defining a position of said head, said positions being spaced apart by substantially twice the length of said crank arm, an element movably mounted on said bed transverse to the direction of motion of said head and operatively connected to the pivot that is between said link and crank arm, and means actuable to move said element to move said pivot out of substantial alinement between said arm and link to start motion of said head from one to the other of said positions and then to release said element for return to initial position to thereby permit the momentum of the parts to carry said pivot through said dead center position with respect to said element and to continue motion of said head toward the other of said positions.

9. In combination, a bed, a work head, means supporting said work head on said bed for motion in one linear direction, a shaft journaled in said head, a crank arm fixed to said shaft, a link having one end pivoted to the outer end of said crank arm and extending in the general direction of motion of said head the opposite end of said link having a pivotal mounting on said bed, said crank arm when in either of two angular positions each lying substantially in line with the direction of motion of said head defining a position of said head, said positions being spaced apart by substantially twice the length of said crank arm, an element movably mounted on said bed transverse to the direction of motion of said head and operatively connected to the pivot that is between said link and crank arm, means actuable to move said element to move said pivot out of substantial alinement between said arm and link to start motion of said head from one to the other of said positions and then to release said element for return to initial position to thereby permit the momentum of the parts to carry said pivot through said dead center position with respect to said element and to continue motion of said head toward the other of said positions, and spring means operatively connected to said head to insure completion of its motion to such other position.

10. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a pair of grinding wheels mounted on said bed and spaced in the direction of motion of said work head, a

feed member, a shaft journaled in said head, a crank arm on said shaft of a length substantially one half of said space, a link connecting said crank arm to said feed member, means for rotating said crank arm by steps each of substantially one half a revolution with said crank arm overlapping said link or in substantial alinement therewith and thereby present work on said work holder in operative relation to one or the other of said wheels, said rotating means being movable transverse to said direction, and connections from said rotating means to said crank including interengaging elements relatively movable in said direction.

11. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a pair of grinding wheels movable on said bed and spaced in the direction of motion of said work head, means for moving said work head from one to another of a pair of positions in one of which one of said wheels may operate on the work and in the other of which the other of said wheels may operate on said work, one of said grinding wheels being a face grinding wheel, means for truing the face of said face grinding wheel, and means for adjusting said face grinding wheel axially relative to the other of said wheels to compensate for wheel wear and truing.

12. In combination, a pair of members comprising a bed and a work head, means for supporting said work head for motion on said bed in one linear direction, a link operatively connected at one end to one of said members, a shaft journaled in the other of said members, a crank carried by said shaft and connected to the other end of said link, said crank and link substantially overlapping in one position of said head and being in substantial alinement in another position of said head, and means in operative engagement with the juncture of said crank arm and link mounted for motion laterally of said linear direction and actuable to move said head from either of its positions toward the other position.

13. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a pair of grinding wheels mounted on said bed and spaced in the direction of motion of said work head, a shaft journaled in said head, a crank arm on said shaft of a length half that of said space, a link operatively connecting said crank arm to said bed, said crank arm overlapping said link when work on said work head is in operative relation to one of said wheels and in substantial alinement therewith when work on said work head is in operative relation to the other of said grinding wheels, and means engageable with the connection between said crank arm and link and movable transverse to the direction of motion of said work head actuable to start the motion of said work head from one to the other of its positions, momentum of the parts completing such motion.

14. In combination, a pair of members comprising a bed and a work head, means for supporting said work head for motion on said bed in one linear direction, a feed element on one of said members, a shaft journaled in the other of said members, a crank carried by said shaft, a link connecting said crank to said feed element, said crank and link substantially overlapping in one position of said head and being in substantial alinement in another position of said head, means in operative engagement with the juncture of said crank arm and link mounted for motion laterally of said linear direction and actuable to move said head from either of its positions toward the other position, and means for actuating said feed member to adjust said work head on said bed in either position of said crank arm.

15. In combination, a bed, a work head, means supporting said work head for motion on said bed in one linear direction, a pair of grinding wheels mounted on said bed and spaced in the direction of motion of said work head, a feed member carried by said bed, a shaft journaled in said head, a crank arm on said shaft of a length half that of said space, a link connecting said crank arm to said feed members, said crank arm overlapping said link when work on said work head is in operative relation to one of said wheels and in substantial alinement therewith when work on said work head is in operative relation to the other of said grinding wheels, means engageable with the connection between said crank arm and link and movable transverse to the direction of motion of said work head actuable to start the motion of said work head from one to the other of its positions, momentum of the parts completing such motion, and means for actuating said feed member to adjust said work head on said bed in either position of said crank arm.

References Cited in the file of this patent UNITED STATES PATENTS 444,016 luetz Ian. 6, 1891 1,549,600 Mueller Aug. 11, 1925 1,559,206 Van Norman Oct. 27, 1925 1,598,583 Cook Aug. 31, 1926 1,739,753 Flanders Dec. 17, 1929 2,310,338 Arms Feb. 9, 1943 2,420,081 Johnson May 6, 1947 2,544,604 Mader Mar. 6, 1951