US3263573A

US3263573A - Feeding device working in stepwise manner

Info

Publication number: US3263573A
Application number: US358996A
Authority: US
Inventors: Gosta E Fogelstrom; Carlsson Osten Erik
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1963-04-16
Filing date: 1964-04-13
Publication date: 1966-08-02
Anticipated expiration: 1983-08-02
Also published as: GB1011279A

Description

g- 1966 a. E. FOGELFQTRGM ETAL 3,253,573

FEEDING DEVICE WORKING IN STEPWISE MANNER Filed April 13, 1964 3 Sheets-Sheet 1 g- 1966 c5. E. FOGELSTR5M ETAL 3,253,573

FEEDING DEVICE WORKING IN STEPWISE MANNER Filed April 15, 1964 5 Sheets-Sheet 2 INVENTOR Qsn E, Faun 5mm BY 5%? -eck 60mm Q42 2 424 Am: uEY

g-' 1966 G. E. FOGELSTROM ETAL. 3,263,573

FEEDING DEVICE WORKING IN STEPWISE MANNER Filed April 15, 1964 3 Sheets-Sheet 5 3 MW ff MmJ T c n AC V W; 3 E mm 4 as 6 0 United States Patent 3,263,573 FEEDING DEVICE WORKING EN STEPWHSE MANNER Giista E. Fogelstriim and Osten Erilr Carlsson, Naclra, Sweden, assignors to Atlas Copco Airtieholag, Nacka, Sweden, a corporation of Sweden Filed Apr. 13, 1964, Ser. No. 358,996 Claims priority, application Sweden, Apr. 16, 1963, 4,113/63 10 Claims. '(Cl. 91-217) This invention relates to feeding devices for rock drills and more particularly to feeding devices of the type working in stepwise manner by the aid of a reciprocating motor and a number of stepping or locking members thereon providing uni-directional locking action against the feed bar or shell on which the rock drill is movable, such locking action being reversible by means of reversing elements associated with the locking members.

In feeding devices of this type the reversing elements hitherto have been operable independently of each other and have been shifted wholly manually, which has demanded the operator to be present at the forward end of the feed bar each time when it comes to the point of returning the feeding device to the starting position. This renders simultaneous handling of multiple drills diflicult and it is an important object of the invention to make possible automated return or rearward feed of the feeding device. Another object of the invention is to provide a certain dependency in operation between the reversing elements in that shifting of one of the reversing elements from forward to rearward feed brings about shifting of the other reversing element to the rearward feed posi-.

tion, whereas shifting of the other reversing element from forward to rearward feed position will still be independent of the first mentioned reversing element, leaving the latter in the forward feed position. A still further object of the invention is to provide a simple and effective reversing mechanism for the locking members whereby the mem bers for purposes of making automated shifting more easy can be shifted by a relatively small angular movement of the reversing elements.

'The foregoing and further objects and advantages of the present invention will become apparent hereinafter as this description proceeds, reference being made to the accompanying drawings in which an embodiment of the invention is illustrated by way of example and by which the invention is not to be considered limited as it may be carried out in many dilferent ways within the scope of the claims. In the drawings FIG. 1 is a top view of a feed bar and a rock drill provided with the feeding device according to the invention, FIG. 2 is a side view of the arrangement in FIG. 1. FIG. 3 shows the feeding device in FIG. 2 in a forward position on the feed bar and shifted for return. FIG. 4 shows the feeding device in FIG. 2 in starting position on the feed bar. FIG. 5 shows on a larger scale a longitudinal sectional view through the feeding device with the cylinder and piston means in extended position. FIG. 6 shows the feeding device in FIG. 5 in contracted position. FIG. 7 is a top view of the feeding device in FIG. 5. FIG. 8 is a fragmentary side View of the rear locking member in FIG. 5. FIG. 9 shows a section on the line 9-9 in FIG. 5. FIG. 10 shows the locking member in FIG. 8 after it has received an opposite inclination by the reversing element. FIG. 11, finally, shows the locking member in FIG. 9 with the reversing element in a second position of adjustment.

In the figures the feeding device is generally designated by the numeral 2a and consists of a cylinder 21 in which a slidable piston 22 is tightly guided. The cylinder 21 carries a front cover 23 and a rear cover 24 which to- Patented August 2, 1966 ice gether with a back piece 26 are connected to the cylinder 21 by means of through tensioning bolts 25. A piston rod 27 is connected to the piston 22. and projects to the rear through a guide sleeve 28 in the back piece 26. A sealing ring 29 in the back piece tightens against the piston rod 27.

A tubular distributing slide 34 is slidably guided in suitable bores in the rear cover 24 and piece 26 between the end positions depicted in FIGS. 5 and 6. The distributing slide 30 surrounds the piston rod 27 with a considerable clearance and is provided with an inner flange 31. A ring 32 aflixed to the piston rod 27 adjacent the piston 22 engages the flange 31 just prior to the piston 22 reaching the end position depicted in FIG. 5, at which instant the distributing slide 30 is shifted to the position shown in FIG. 5. Furthermore the piston rod 27 has a shoulder .33 which in its turn engages the inner flange 31 just prior to the piston 22 reaching the end position depicted in FIG. 6, at which instant the dis tributing slide 34} is shifted to the position shown in FIG. 6.

Pressure fluid is supplied via a conduit 35 to a nipple 36 on the underside of the rear cover 24 and is conducted from the nipple through a bore 37 to the outer surface of the distributing slide 30. In the position shown in FIG. 5 pressure fluid then passes the through holes 39 and acts thanks to the clearance between the distributing slide 3t} and the piston rod 27 under full pressure on the rear face of the piston 22, at which instant the piston rod is moved into the: cylinder 21 and the feeding device 20 is contracted. Pressure fluid disposed in front of the piston 22 is expelled through a pas sage 4S and a wide peripheral groove 40 in the distributing slide to an outlet 38. After shifting of the distributing valve 3% as shown in FIG. 6, pressure fluid is conducted from the bore 37 via the Wide groove 40 to the passage 48 leading to the front face of the piston 22. The piston rod 27 is then moved outwardly from the cylinder 21 and the feeding device 2a is extended thereby. Simultaneously herewith the chamber behind the piston 22 is emptied through the interior of the distributing slide 34B and the outlet 33 which has been opened by the rear edge, of the distributing slide 3d. As long as pressure fluid is supplied to the conduit 35 and the bore 37, the feeding device 20 evidently will perform extensions and contractions following in automatic succession one upon the other, since shifting of the distributing slide 30 will take place by means of the ring 32 and the shoulder 33 each time the piston 22 reaches proximity of the respective end positions.

A rod 41 disposed coaxially with respect to the piston rod 27 projects from the front cover 23 in forward direction. A boss 42 is carried by each of the

rods

27 and 41, which bosses carry through parallel axles 43. About each axle 43 there is pivotally affixed a locking member or plate 44. The two locking plates 44 support themselves against a feed bar 45 for a rock drill and form locking members displaceable along the feed bar. These locking plates are provided for carrying the feeding device 20 and have a unidirectional reversible locking action, to be described hereinafter, in the longitudinal direction of the bar. The feed bar 45 has two coplanar parallel guide flanges 46 and each locking plate is provided with slots 47 turned in opposite directions, into which slots the flanges 46 project. The width of the slots 47 is chosen somewhat greater than the thickness of the flanges 46, by reason of which the locking plate can tilt between two outer positions, shown in FIG. 8 and FIG. 10, respectively, which-are inclined in opposite directions with respect to the feed bar. In these outer positions the slots 47 evidently will clamp the flanges 46 providing a frictional engagement between the locking plate 44- and the flanges 46 if the inclination of the locking plate is increased by force actuation on the axle 43 in one axial direction of the feed bar. If on the other hand the axle will be actuated by a force tending to decrease the inclination of the locking plate, the locking plate 44 will be able to slide freely along the flanges 46. In the outer position shown in FIG. 8 a force actuation on the axle 43 to the right evidently will lock the locking plate 44 to the feed bar 45, which is indicated by dot and dash lines, whereas a force actuation to the left will cause the locking plate 44 to slide freely to the left. Thus one receives a uni-directional locking action to the right and free movability of the locking plate to the left. In the outer position depicted in FIG. one receives in analogy herewith uni-directional locking action and free movability in opposite directions.

A pair of reversing elements are arranged for positioning the locking plates 44 to the alternative outer positions. Each of the reversing elements consists of a housing 50 turnably arranged at one side of the respective locking plates 44 on the piston rod 27 and the rod 41, respectively. The housing 50 is turnable between two positions of adjustment defined by a transverse pin 52, which projects radially from the

respective rods

41 and 27 and by coaction with a groove 53 in the housing 50 limits the turning motion of the latter. A pair of diametrically opposed elastic biasing or spring means directed axially towards the appurtenant locking plate 44 and consisting of spring pressed

plungers

54, 55 are provided in the housing 50. The

plungers

54, 55 are biased by compression springs 56 axially in outward direction from the housing 50 engaging the locking plate 44 at the upper as well as at the lower side of the axle 43. A shoulder 57 on each

plunger

54, 55 restricts the axial projection thereof by engaging the inner wall of the housing 50. In order that the diametrically

opposed plungers

54, 55 shall be able to move the locking plate 44 into inclined outer position, either of the plungers must be thrown out of operation. This is accomplished by two dimples 58, 59 disposed at an angular distance from one another somewhat smaller than 180 degrees, which dimples are provided on the side of the locking plate 44 facing the plungers. The dimples 58, 59 are disposed in such manner than the plunger 55 of the reversing element 50 falls into the dimple 59 in the forward feed position of the reversing element 50 shown in FIG. 9. This throws the plunger 55 out of operation while the opposed plunger 54 continues to push against the upper part of the locking plate 44 thereby moving the plate into the inclined position for forward feed shown in FIG. 8. When the reversing element is turned to its rearward feed position shown in FIG. 11, the plunger 55 leaves the dimple 59 and pushes the lower part of the locking plate 44 while the opposed plunger 54 falls into the upper dimple 58 and is thrown out of operation thereby. The inclination of the locking plate 44 will then be according to FIG. 10.

The reversing elements 50 are provided with operating handles 60 projecting in lateral direction. Chamfered portions 61 are provided at one side of each of the dimples 58, 59 for making the passage of the

respective plungers

54, 55 to and from the dimples more easy. As soon as the plunger 54 with its spring 56 under certain compression during shifting from forward to rearward feed reaches the chamfered portion 61 of the dimple 58, the spring force acting on the plunger 54 therefore will assist in turning the reversing elements 50 the remaining angle to their fully shifted position, which final turning is performed under compression of the spring acting on the other plunger 55. Thanks to the closeness of the empty dimple to the adjacent active plunger the full turning angle during shifting will be small. The two reversing elements 50 on the respective rods 51 and 27 are mounted with the plungers turned away from each other. Since the handles 60 as well as the locking plates 44 in the two positions of adjustment preferably should be parallel the plungers on the reversing element which is sitting on the rod 41 are mounted upside down with respect to the reversing element 50 and its plungers on the piston rod 27. For making possible exchangeability between the locking plates 44 and correct cooperation with the respective reversing elements, the locking plates 44 are provided with opposed slots 47 in paired symmetrical disposition as depicted in FIGS. 9 and 11.

To one of the handles 60, for example to the forward handle, there is aflixed a coupling rod 62 which extends to and under the other handle 60. When the forward handle is swung upwards the coupling rod 62 simultaneously therewith will move the rear handle to the other position of adjustment upwards whereby both reversing elements 50 are moved from forward to rearward feed position.

On the flanges 46 in front of the feeding device 20 there is slidably guided a slide 65. On a transverse pivot 67 carried by an upstanding bracket 66 on the slide 65 there is in conventional manner affixed a drill 68 carrying a drill steel 69. A conventional drill steel guide 70 may be provided forwardly on the feed bar 45 for guiding the drill steel 69.

To the rear end of the slide 65 is fixed an upstanding plate 71, FIGS. 5 and 7, having a central hole 72 therethrough. The rod 41 of the feeding device 20 projects into the hole 72 and at opposite sides of the plate 71 there are arranged annular rubber buffers 73 around the rod 41. Thrust plates 74, which are axially afiixed to the rod 41, are arranged outside the rubber buffers 73 alternately pushing each against one of them when the feeding device moves in forward or rearward direction along the feed bar 45. The hole 72 surrounds the rod 41 with a considerable clearance, due to which fact the feeding device 20 will be supported substantially solely by the two locking plates 44.

From a suitable pressure source, not shown, pressure fluid is supplied via a conduit 78 to a two way valve 79 fixed to the rear end of the feed bar 45. In the open position of the valve 79 shown in FIG. 2, a pressure fluid is conducted to a hose 80 and thence to the open main valve 81 of the rock drill 68, the main valve being indicated diagrammatically only in the figures. Pressure fluid from the main valve drives the hammer motor (not shown) of the rock drill. Via a passage 82 a portion of the pressure fluid is branched to passages passing through the transverse pivot 67 and thence onto the bracket 66 and the conduit 35, whereby the feeding device receives pressure fluid and starts operation.

At a suitable location on the forward end of the feed bar 45 there is affixed a cam plate 83 which by means of a bolt 84 can be fixed in a selective position to holes 85 on the feed bar 45. The cam 83 is arranged to cooperate with the coupling rod 62 or the forward handle 60 on the feeding device 20.

In the position shown in FIG. 2 the feeding device 20 thus receives pressure fluid and its piston 22 is brought into reciprocation while the hammer motor of the rock drill 68 is operating. With the reversing elements 50 and the locking plates 44 in the position shown in FIG. 2 and FIGS. 59, the successive extensions and contractions of the feeding device 20 will produce a successive stepwise displacement of the feeding device 20 in forward direction along the feed bar 45. The rear thrust plate 74 of the feeding device 20 transmits the feeding force, which is defined by the pressure in the cylinder 21 in front of the piston 22, to the plate 71 of the slide 65 via the rear rubber buffer 73. The pressure in front of the piston 22 displaces the cylinder 21 and the rod 41 in forward direction while the forward locking plate 44 slides along the flanges 45. As soon as the drill 69 has penetrated into the rock a distance corresponding to a full throw of the piston, the distributing slide 30, FIG. 5 will be shifted, whereby the piston 22, the piston rod 27 and the rear locking plate rapidly will be brought forward to the position shown in FIG. 6. During such movement the forward locking plate 44 forms a support for the feeding force by locking against the feed bar 45. As the drilling work progresses the rock drill 68 is thus fed in forward direction. When the desired drilling depth has been reached the feeding device 20 will approach the cam plate 83, which will turn the forward handle 60 from the forward feed position corresponding to FIG. 9 to the rearward feed position corresponding to FIG. 11. Simultaneously herewith the coupling rod 62 will turn the rear handle 60 to the same position of adjustment, whereby the inclination of both locking plates 44 is shifted in the manner hereinbefore described. Such shifting will be performed easily thanks to the small turning angle necessary for shifting and to the assistance provided by the springs 56 of the plungers 54. In the new position of the reversing elements 50 and locking plates 44 shown in FIGS. 3, 4 10 and 11, the successive extensions and contractions of the feeding device will produce a stepwise return of the feeding device back to the starting position on the feed bar 45 under the action of a pulling force on the slide 65 defined by the pressure behind the piston 22. Return is finished in FIG. 4 and at this instant the coupling rod 62 encounters the valve 79 and moves it to cut-off position. The pressure fluid supply to the drill 68 as well as to the feeding device 20 is interrupted hereby and operation of these parts ceases.

When a new working cycle is to be started, the operator depresses the rear handle 60, FIG. 4, whereby the coupling rod 6-2 and the forward handle 60 simultaneously are pushed down to a position corresponding to forward feed. The locking plates 44 will now again take up the inclination shown in FIG. 2. Simultaneously herewith the two-way valve can be opened without hindrance, FIG. 2, which alternatively may be performed manulally or by spring action, at which instant the new working cycle is started.

What we claim is:

1. A feeding device for rock drills comprising an elongated feed bar for slidably supporting a rock drill therealong, a pair of locking members movably mounted on said feed bar, adjustable means on said locking members providing in a first position of adjustment uni-directional locking against said feed bar to allow forward and to prevent rearward movement of said members along said feed bar and in a second position of adjustment unidirectional locking against said feed bar to allow rearward and to prevent forward movement of said members, a pressure fluid operated extensible and contractable feed motor connected to said drill and movable therewith, said motor including cooperating cylinder and piston elements coupled one to each of said locking mem bers for moving said members and thereby said rock drill step by step along said fee-d bar by successive extensions and contractions of said motor in the direction defined by the position of adjustment of said adjustable means, means for automatically controlling the delivery of pressure fluid to said motor for continuously extending and contracting said cylinder and piston elements, first and second reversing elements movably mounted on said motor each adjacent one of said locking members for movement between a forward and a rearward feed position and having means thereon for moving said adjustable means from their first to their second position of adjustment as a result of said reversing elements being moved from said forward to said rearward feed position, said first reversing element being journalled for movement from said forward to said rearward feed position independently of said second reversing element for purposes of rendering said feed motor inactive by causing opposite locking action of said members, and coupling means connected to said second reversing element and engageable with said first reversing element for moving the latter from said forward to said rearward feed position in unison with said second reversing element.

2. A feeding device according to claim 1 in which there are provided cam means on said feed bar cooperating with said reversing elements and said coupling means for mechanically shifting said reversing elements in unison from said forward to said rearward feed position upon said feeding device having moved a predetermined feed length, and means for adjusting the longitudinal position of said cam means on said feed bar.

3. A feeding device according to claim 2 in which a pressure fluid supply line is connected to said drill and there is provided a cut off valve in said line rearwardly on said feed bar actuatable to cut off the fluid supply to said rock drill, and an abutment on said feed motor cooperating with said out off valve for causing actuation thereof upon said feeding device having moved back said feed length.

4. A feeding device according to claim 1 in which each locking member consists of a locking plate pivotally mounted about an axle disposed on said feed motor transversely with respect to said feed bar, said locking plate being pivotable about said axle between two outer positions inclined in opposite directions with respect to said feed bar, clamping surfaces on each locking plate frictionally cooperating with said feed bar in said outer positions thereby to provide said uni-directional locking in forward and rearward direction, respectively, a pair of biasing means on each said reversing element disposed adjacent each locking plate at opposite sides of said axle and pushing against said locking plate for pivoting it about said axle, and means for throwing respectively one or the other of said opposite biasing means out of operation for providing forward or rearward feed, respectively, depending on the feed position of said reversing elements.

5. A feeding device according to claim 4 in which there are provided angularly spaced dimples on said locking plates at opposite sides of said axle for alternately receiving said biasing means, whereby respectively one or the other of said biasing means is thrown out of operation.

6. A feeding device according to claim 1 in which said reversing elements are journalled for turning movement about an axis disposed longitudinally of said feed bar, an operating handle on each reversing element, and a longitudinal coupling rod connected to one of said handles and engageable with said other handle for shifting said handles and thereby said reversing elements in unison from said forward to said rearward feed position.

7. A feeding device for rock drills comprising an elongated feed bar for slidably sup-porting a rock drill therealong, a pair of locking members movably mounted on said feed bar and supporting themselves thereon, adjustable means on said locking members providing in a first position of adjustment uni-directional locking against said feed bar to allow forward and to prevent rearward movement of said members along said feed bar and in a second position of adjustment unidirectional locking against said feed bar to allow rearward and to prevent forward movement of said members, a pressure fluid operated extensible and contractable feed motor disposed longitudinally of said feed bar, said motor including cooperating cylinder and piston elements coupled one to each of said locking members for being carried thereby on said feed bar and for moving said members step by step along said feed bar by successive extensions and contractions of said motor in the direction defined by the position of adjustment of said locking members, means for automatically controlling the delivery of pressure fluid to said motor for continuously extending and contracting said cylinder and piston elements, a connection between said feed motor and said rock drill for transmitting the step by step movement of said feed motor to said rock drill, said connection having means providing relative movability between said drill and said feed motor transversely to the longitudinal direction of said feed bar to permit said feed motor to rest solely on said locking members, first and second reversing elements movably mounted on said motor each adjacent one of said locking members for movement between a forward and a rearward feed position and having means thereon for moving said adjustable means from their first to their second position of adjustment as a result of said reversing elements being moved from said forward to said rearward feed position, and means for synchronizing the movement of said reversing elements from said forward to said rearward feed position.

8. A feeding device according to claim '7 in which there are provided cam means on said feed bar cooperating with said reversing elements and said synchronizing means for mechanically shifting said reversing elements in unison from said forward to said rearward feed position upon said feeding device having moved a predetermined feed length, and means for adjusting the longitudinal position of said cam means on said feed bar.

9. A mechanism movable by fluid power step by step in either direction along an elongated support comprising a pair of locking members movably mounted on said support and supporting themselves thereon, adjustable means on said lock-ing members providing in a first position of adjustment uni-directional locking against said support to allow forward and to prevent rearward movement of said members along said support and in a second position of adjustment uni-directional locking against said support to allow rearward and to prevent forward movement of said members, a pressure fluid operated extensible and contractable motor disposed longitudinally of said support and carried solely by said locking members thereon, said motor including cooperating cylinder and piston elements coupled one to each of said locking members at the opposite ends of said motor for being carried by said members on said support and for moving said members step by step along said support by successive extensions and contractions of said motor in the direction defined by the position of adjustment of said adjustable means, means for automatically controlling the delivery of pressure fluid to said motor for continuously extending and contracting said cylinder and piston elements, first and second reversing elements movably mounted on said motor each adjacent one of said locking members for movement between a forward and a rearward position and having means thereon for moving said adjustable means from their first to their second position of adjustment as a result of said reversing elements being moved from said forward to said rearward position, and means for synchronizing the movement of said elements from said forward to said rearward feed position.

10. A mechanism according to claim 9 in which each locking member consists of a locking plate pivotally mounted about a horizontal axle disposed on said motor transversely with respect to the longitudinal direction of said support, said locking plate being pivotable about said axle between two outer positions inclined in opposite directions with respect to said support, clamping surfaces on each locking plate frictionally cooperating with said feed bar in said outer positions thereby to provide said uni-directional locking in forward and rearward direction, respectively, a pair of biasing means on each said reversing element disposed adjacent each locking plate at opposite sides of said axle and pushing against said locking plate for pivoting it about said axle, and means for throwing respectively one or the other of said opposite biasing means out of opera-tion for providing forward or rearward movement of said motor, respectively, depending on the position of said reversing elements.

References Cited by the Examiner UNITED STATES PATENTS 1,297,925 3/1919 Stage 92-15 1,740,683 12/1929 Gartin 9215 1,909,179 5/1933 Huffman 92161 3,160,074 12/1964 Leander et al. 91-217 SAMUEL LEVINE, Primary Examiner.

P. E. MASLOUSKY, Assistant Examiner.

Claims

1. A FEEDING DEVICE FOR ROCK DRILLS COMPRISING AN ELONGGATED FEED BAR FOR SLIDABLY SUPPORTING A ROCK DRILL THEREALONG, A PAIR OF LOCKING MEMBERS MOVABLY MOUNTED ON SAID FEED BAR, ADJUSTABLE MEANS ON SAID LOCKING MEMBERS PROVIDING IN A FIRST POSITION OF ADJUSTMENT UNI-DIRECTIONAL LOCKING AGAINST SAID FEED BAR TO ALLOW FORWARD AND TO PREVENT REARWARD MOVEMENT OF SAID MEMBERS ALONG SAID FEED BAR AND IN A SECOND POSITION OF ADJUSTMENT UNIDIRECTIONAL LOCKING AGAINST SAID FEED BAR TO ALLOW REARWARD AND TO PREVENT FORWARD MOVEMENT OF SAID MEMBERS, A PRESSURE FLUID OPERATED EXTENSIBLE AND CONTACTABLE FEED MOTOR CONNECTED TO SAID DRILL AND MOVABLE THEREWITH, SAID MOTOR INCLUDING COOPERATING CYLINDER AND PISTON ELEMENTS COUPLED ONE TO EACH OF SAID LOCKING MEMBERS FOR MOVING SAID MEMBERS AND THEREBY SAID ROCK DRILL STEP BY STEP ALONG SAID FEED BAR BY SUCCESSIVE EXTENSIONS AND CONTACTIONS OF SAID MOTOR IN THE DIRECTION DEFINED BY THE POSITION OF ADJUSTMENT OF SAID ADJUSTABLE MEANS, MEANS FOR AUTOMATICALLY CONTROLLING THE DELIVERY OF PRESSURE FLUID TO SAID MOTOR FOR CONTINUOUSLY EXTENDING AND CONTRACTING SAID CYLINDER AND PISTON ELEMENTS, FIRST AND SECOND REVERSING ELEMENTS MOVABLY MOUNTED ON SAID MOTOR EACH ADJACENT ONE OF SAID LOCKING MEMBERS FOR MOVEMENT BETWEEN A FORWARD AND A REARWARD FEED POSITION AND HAVING MEANS THEREON FOR MOVING SAID ADJUSTABLE MEANS FROM THEIR FIRST TO THEIR SECOND POSITION OF ADJUSTMENT AS A RESULT OF SAID REVERSING ELEMENTS BEING MOVED FROM SAID FORWARD TO SAID REARWARD FEED POSITION, SAID FIRST REVERSING ELEMENT BEING JOURNALLED FOR MOVEMENT FROM SAID FORWARD TO SAID REARWARD FEED POSITION INDEPENDENTLY OF SAID SECOND REVERSING ELEMENT FOR PURPOSES OF RENDERING SAID FEED MOTOR INACTIVE BY CAUSING OPPOSITE LOCKING ACTION OF SAID MEMBERS, AND COUPLING MEANS CONNECTED TO SAID SECOND REVERSING ELEMENT AND ENGAGEABLE WITH SAID FIRST REVERSING ELEMENT FOR MOVING THE LATTER FROM SAID FORWARD TO SAID REARWARD FEED POSITION IN UNISON WITH SAID SECOND REVERSING ELEMENT.