US2737110A

US2737110A - Flat bed and cylinder printing press

Info

Publication number: US2737110A
Application number: US197218A
Authority: US
Inventors: William G Montgomery; Samuel A Huffman
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-11-24
Filing date: 1950-11-24
Publication date: 1956-03-06
Anticipated expiration: 1973-03-06

Description

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FLAT BED AND CYLINDER PRINTING PRESS March A 6, 1956 16 Sheets-Sheet 1 Filed Nov. 24, 1950 #was Mfh 5, 1956 w. G. MONTGOMERY ETAL 2,737,110

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FLAT BED AND CYLINDER PRINTING PRESS 16 Sheets-Sheet 10 Filed NOV. 24, 1950 GDGIDGEY Mardi 6, 1955 w. G. MONTGOMERY ETAL 2,737,110

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FLAT BED AND CYLINDER PRINTING PRESS 16 Sheets-Sheet 16 Filed NOV. 24, 1950 mi ,497, M

A 70m/V5 United States Patent FLAT BED AND CYLINDER PRINTING PRESS William G. Montgomery and Samuel A. Huffman, Marietta, Ohio; said Huffman assigner to said Montgomery Application November 24, 1950, Serial No. 197,218

18 Claims. (Ci. 101-191) Our invention relates to a dat bed and cylinder printing press. It relates, more specifically, to a printing press of the reciprocable bed and two revolution cylinder type. Our invention is especially applicable to multi-color presses, where a number of colors are to be printed, but most of its features are also applicable to single-color presses.

The demand by printers for greater production and higher efficiency has led to the design of presses which will operate at higher and higher speeds. There are definite limitations, however, to the maximum possible speeds obtainable with known designs.

It is well-known in the art that in a hat-bed and cylinder printing press, the sheet to be printed is carried around a revolving cylinder in such a manner that itis brought into contact under great pressure with a flat inked form which form is carried by a reciprocating type bed. There are in general use two types of flat-bed and cylinder printing presses. The first and most common is known as the two-revolution press. The second is known as the stop-cylinder press.

The existing two-revolution presses contain either one or two printing cylinders which revolve two revolutions, per cycle, at a constant or uniform speed, one revolution during the printing stroke of the type bed and the other revolution during the return stroke of thel type bed. Each printing cylinder engages the reciprocating type bed only during a portion of the printing stroke. The type bed travels at the same constant or uniform linear speed as the' printing surface of the cylinder or cylinders during the major portion of each yof its strokes. The type bed is reversed at each end of its constant speed of travel by a crank, which crank revolves a constant number'of revolutions per minute. The mechanism for reciprocating the type bed in this manner is known as a bed motion.

There are two bed motions now in general use on .tworevolution flat-bed and cylinder presses. These are known either as a two-to-one bed motion or as a three'- toione bed motion. If the crank which reverses the type bed at the end of its constant speed stroke, revolves two revolutions per' each cycle or two strokes of the type bed (one stroke forward and one stroke reverse), then the bed motion is known as a two-to-one bed motion. If the crank which reverses the type bed at the end ofvits constant speed stroke revolves three revolutions per each cycle of the type bed, then the bed motion is known as a three-to-one bed motion.

In the stop cylinder nat-bed and cylinder printing press, the printing cylinder revolves in synchronization with the type bed on the complete printing stroke of the type bed and stops completely on the opposite or reversing stroke of the type bed. The type bed travels by modied harmonic' motion during the entire printing and return stroke. The modified harmonic motion is usually a crank and connecting rod.

It has been proposed in the prior art to provide a at-bed and cylinder printingpress wherein the' bed is ICC driven with a full or modified harmonic motion and the cylinder is rotated continuously through two revolutions during each cycle of the bed motion. In this press it has been proposed to drive the cylinder with a variable crank drive by means of which it was attempted to bring the cylinder into synchronization withy the bed movement only during a portion 0f the printing stroke, the cylinder being out of synchronization with the bed throughout the remainder of the bed motion.

There are two principal reasons why operating speeds cannot be increased substantially with existing designs of two-revolution fiat-bed a-nd cylinder presses, employing either the two-to-one or the three-to-one bed motion. First, the surface speed of the printing cylinder becomes so great at the higher speeds that sheets are either damaged when taken from vthe feed board by the cylinder grippers or cannot be takenl at all. The sheets are accelerated from Zero to the full surface speed of the printing cylinder instantly. It can, therefore, be readily seen that this action is so extremely severe that taking sheets at higher speeds is thus impossible without the provision of additional costly mechanism acting to accelerate the sheet more gradually. Second, operating speeds cannot be substantially increased because of the magnitude of the forces of accelerationl and deceleration of the reciprocating type bed assemblies. These forces increase so rapidly, as speed increases, that the presses move back and forth on the oor. If the press is bolted down to the floor to prevent movement thereon, damage to its mechanism is inevitable. Counterbalancing the forces of yexisting bed motion designsis extremely dicult if not impossible.

With regard to the stop-cylinder press, one of the chief disadvantages of this type of press is the difficulty of removing, the printed sheet from the cylinder. The transfer means for removing the sheet must pull the printed sheet off the cylinder since it cannot be rolled off such cylinder when the cylinder is stopped. This difficulty is greatly increased with the larger size sheets. In connection with the feeding of the sheet in this type of press, if the sheet isfed to the top of the cylinder, a larger diameter printing cylinder is required which makes it necessary to provide a longer stroke for the bed and this, in turn, results in slower speed for a given size sheet. On the other hand, if the sheet is fed to the underside of the printing cylinder, it will be apparent that the feeder will have less capacity due to the lowering of the feed point at a distance substantially corresponding to the diameter of the cylinder causing more frequent shut downs for reloading with consequent loss of production. Furthermore, when the sheet is fed at the lower side of the cylinder, the printed side of the sheet would be down during the transfer to the next printing cylinder, if the press is a multi-color press, and during transfer to the delivery unit. Consequently, almost certain smearing and smudging of the sheets would occur.

Existing two-color flat-bed and cylinder printing presses have a transfer cylinder which has a diameter equal to one-half the diameter of the printing cylinders and which is located between the two printing cylinders for the purpose' of carrying a sheet from one cylinder to the other. This arrangement has a number of disadvantages. In the first place, during the transfer of the sheet from one cylinder to the other, the wet ink of the printed surface is towards or next to the transfer cylinder surface. Consequently, great care and precaution must be taken and means provided to prevent the printed sheet from being smeared or s'mudged. Also, thick sheets, such as cardboard, are difficult or even impossible to bend around the transfer cylinder` without cracking or other such damage to the sheets. Furthermore, the transfer cylinder is in a fixed position between the printing cylinders and cannot be moved away'from either of the cylinders at any time and, therefore, it is very difficult to make-ready each of the printing cylinders because of interference by the transfer cylinder. In addition, the iukers are necessarily located on opposite sides of each of the printing cylinders and are, therefore, not identical, being right and left hand. Many of the parts of the two inkers are different because they are right and left hand. Adjustments and settings, therefore, are diiferent and contrary to standard single color practice requiring the most experienced pressmen to make these adjustments and settings and it is also more di'icult to adjust the two type forms which must necessarily be located differently than in single-color presses. The arrangement of the transfer cylinder relative to the printing cylinders makes it impossible to design a press with such a transfer arrangement to print more than two colors. Furthermore, with this transfer arrangement, cylinders of larger diameter are required and, consequently, a longer stroke of the bed is required than for single-color presses for printing the same size sheet. All of these disadvantages of prior art two-color presses are true of the two-revolution cylinder presses and the stop-cylinder presses discussed above.

A press in which it was attempted to synchronize the cylinder with the bed movement only during a portion of the printing stroke was proposed many years ago. However, this type of press has not gone into use, apparently because of the difficulty or impossibility of accurately bringing the cylinder into synchronization for the particular period during the printing stroke. With such an arrangement, where the cylinder is not synchronized at all times, running clearances, which are necessary between the moving driving parts, apparently result in inaccuracies in the synchronization. With this type of press, a large size cylinder and a longer bed stroke is required in order to print a given size sheet than would be required if the cylinder were synchronized on the complete printing stroke as, for example, in a stop-cylinder press. Therefore, this press will operate at a somewhat slower speed depending upon this ratio. It can also be shown that the cylinder grippers will take the sheet from the feedboard at a somewhat higher speed than would be the case if the cylinder were fully synchronized.

One of the objects of our invention is to provide a tworevolution flat-bed and cylinder printing press with full harmonic bed motion and with the surface of the printing cylinder or cylinders perfectly synchronized with the movement of the type bed at all times.

Another object of our invention is to provide a press having means for reciprocating the type bed which means is so designed and constructed as to substantially counterbalance the forces created by the reciprocation of the type bed so that the press will not move on the oor even when operated at speeds substantially greater than the maximum speeds of existing flat-bed presses without bolting the press to the floor or embedding it in concrete.

Still another object of our invention is to provide a press of the type indicated which can be operated at speeds far in excess of those of conventional flat-bed presses without injury to the sheets of paper being fed into the press because the cylinder or cylinders on our press take the sheets at or near the end of the stroke of the bed when the cylinder or cylinders are stopped or 'almost stopped.

An additional object of our invention is to provide a press of the type indicated above wherein the mechanism for moving the bed and cylinder or cylinders is so designed and so located as not to interfere with reinforcement of the main frame directly under the locations wherein the printing impressions are taken, a feature which is so necessary for the required rigid impressions.

A further object of our invention is to provide a press of the type indicated with means for raising and lowering the printing cylinder or cylinders away from and towards the type bed, which means is operated directly underneath the type bed and is, therefore, much more simple and compact and has far more more rigidity than prior art arrangements which latter extend practically to the floor.

Another object of our invention is to provide a press of the type indicated with means for driving the printing cylinder or cylinders which is completely under the control of the bed-driving means on both strokes of the bed and wherein it is not necessary to lift the cylinder driving gears partly out of mesh as in existing two-revo` lution flat-bed presses and which results in excessive play or back-lash and noisy operation, the gears on our press remaining in full mesh even when the cylinder or cylinders are raised to permit passing of the form or forms on the return stroke of the bed.

Still another object of our invention is to provide a two-revolution cylinder printing press with full harmonic bed motion and having a plurality of impression cylinders cooperating with a plurality of forms on a single reciprocable type bed, so that the press is suitable for multi-color work, the cylinders being spaced apart suiciently so as not to interfere with the make-ready operation, the technique of operation thus conforming to that of single color presses with which practically all operators are familiar.

Another object of our invention is to provide a multicolor printing press of the type indicated above which is provided with transfer means including registering devices which will carry sheets from one cylinder to the next in absolute register.

A further object is to provide a multi-color press of the type indicated wherein the transfer means is such that the sheets are carried from cylinder to cylinder with nothing touching the printed side thereof so as to eliminate any danger of smearing.

Another object of our invention is to provide a multicolor press of the type indicated wherein the printed sheets will be transferred from one cylinder to the next in at condition which makes it possible to handle heavy cardboard or the like without cracking or other damage thereto.

Various other objects will be apparent from the following description and the drawings.

The preferred embodiment of our invention is illustrated in the accompanying drawings wherein similar characters of reference designate corresponding parts and wherein:

Figure 1 is a plan view, partly broken away, of a press constructed according to our invention.

Figure 2 is a view of the press, being partly in side elevation and partly in section, taken on line 2 2 of Figure l.

Figure 3 is a transverse sectional view taken on line 3 3 of Figure l.

Figure 4 is a plan view of a supporting plate for the rack reciprocated by the crank mechanism.

Figure 5 is a longitudinal sectional view taken along line 5 5 of Figure 4.

Figure 6 is a transverse sectional View through the press taken on line 6 6 of Figure l.

Figure 7 is an enlarged sectional view of the cylinder driving unit taken along line 7 7 of Figure 8.

Figure 8 is a sectional view through the cylinder driving unit taken along line 8 8 of Figure 7.

Figure 9 is a sectional view taken along line 9 9 of Figure l0 showing the cam means for actuating the clutch mechanism of the cylinder driving unit, the cam being in position to cause engagement of one clutch and disengagement of the other.

Figure 9a is a view like Figure 9 but showing the cam rotated so that both clutches are engaged.

Figure l0 is a sectional view through the cylinder driving unit taken along line 1lb-10 of Figure 6.

Figure 11 is a view, partly in vertical section and partly in side elevation, of the mechanism which produces vertical movement. of. the impression. cylinders. relative.. to .the bed.-

Figurel 12 is. a sectional vicwtaken along` line 1`212 ofFigure: 1l.

Figure 13 is a sectional view taken along line- 13--13 of Figure 1l.

Figure 14 is a sectional view taken` along line 14-14 of, Figure. 2 through the cylinder driving mechanism but showing the links and associated parts in extended relationship.

FigureV 15 is a sectionall view, taken along line 15-15 ofv Figure 18, showingv the transfer mechanism for transferring. the paper from one cylinder to the other.

Figure 15a isa side elevational View ofV one of the releasable supports provided at one end. of the transfer mechanism.

Figure 16 is a transverse vertical sectional view taken online I6-16 of Figure 15..

Figure 17' is a plan view of the transfer mechanism and the associated printing cylinders.

Figure 18" is a transverse sectional view through one end of the transfer unit' along line 18-18 of Figure l5.

Figure 19 is a detail in section showing cam means which is associated with the gripper bar of a transfer mechanism for registering the bar transversely of the cylinders.

Figure 20 is a sectional view taken along line 20-20 of'Figure 19.

' Figure 2l is avertical sectional view takenk along line 212-21 of Figure 18. l

Figure 22 is an enlarged plan view of oneend of the gripper bar of the transfer mechanism.

Figure 23 is an end view of the structure shown in Figure 22.

Figure. 24 is an enlarged plan view of the'opposite end ofthe gripper bar.

Figure 25 is an' end view of the structure shownv in Figure 24.

Figure 26 is a sectional diagrammatic View illustrating the' gripper bar and associated cylinder, the grippers on the gripper bar beingA in engagement with the sheet and the grippers on the cylinder being in position to engage the sheet.

Figure 27 is a similar view but showing both sets of grippers in engagement with the sheet.

Figure 28 is a similar view but showing the cylinder grippers in engagement with the sheet and the grippers on the gripper bar releasedy from the sheet.

Figure 29 is a diagram illustrating the relative movements. of the main crank; the clutch actuating cam; and thefhousing. of the cylinder driving unit ofthe press..

Figure 30 is a diagrammatic view illustrating` a press, constructed according to our invention, for printing. four colors.

With reference to the' drawings, we have. illustrated the general structure of our press'in. Figures 1 to 3, The press' shown includes the single bed 3d which, is mounted on the main frame 31 for reciprocation longitudinally thereof in a horizontal plane and two transversely disposed

impression cylinders

32 and 33 which are carried by the frame and are located above the path ofv movement of the bed, the cylinders having their transverse axes spaced longitudinally of the press. These two cylinders are adapted to cooperate with two printing forms F which will be suitably removably attached to the bed at proper locations spaced longitudinally of the bed'. It will be. apparent from the following description that the. bed is reciprocated with a full harmonic motion, the cylinders are rotated in the same direction at all times regardless of the direction of movement of the bed, the rotation of the cylinders is timed with the movement of the. bedso that cylinder rotation and bed' motion are in exact synchronism at all. times, and the cylinders are in contact with the forms during the movement of the bed in one direction, that is during the printing stroke, but are lifted therefrom during movement ofthe bed in theopposite direction, thatis, duringv the return stroke.

In the press illustrated, we have shown the bed horizontally disposed. However, our invention is not necessarily limited to a horizontal press but the features thereof can apply to a vertical press. The press shown in Figure 1 to .3 is for printing two colors, since it is shown with two impression cylinders, but it is to be understood that any number of cylinders may be used with the same number of forms supportedv on the bed in properly spaced relationship, the number depending upon the. number of colors desired. For example, in Figure 30, we have shown a. press with four cylinders and four beds. Transfer of the sheets from one cylinder to another is accomplished by means of a novel transfer mechanism or unit indicated generally by numeral 34. The transfer unit 34 will move vertically with vertical' movement of

cylinders

32 and 33 and will be driven in synchronism with rotation of the cylinders. It will be apparent that, if desired, we may provide our press with only one cylinder and inthat case, the transfer unit 34'will 'not.beused.

The frame 31 is illustrated best in Figures l, 2 and 3L It may assume various forms but is preferably formed in one piece and includes the

side frame members

35 and 36, the open

end frame members

37 and 38 andthe bed supporting

track members

39 and 40 which extend the full length of the frame andV which connect with the

end members

37 and 38. ItV will be noted from Figure 3 that the

side frame members

35 and 36 extend a substantial distance abovethe bed supporting

track members

39 and 40. In addition, as shown in. Figures 1, 6 and 1l., the frame` includesI the heavy transverse beam sections 41: and 42 disposed directly below the

respective cylinders

32 and 33 and with their upper surfaces just slightly below the upper edgesof the tracks 39' and 402 These

beam sections

41 and 42 are integrally joined to the side membersv 35 and 36 and the

tracks

39 and 40. As will later appear, since these heavy beam sections are located close to the upper side of the frame and directly below the cylinders' 32 andv 33, they will serve to take the thrust forces created when the'V cylinders and the forms on the bed 30 are brought into unyielding engagement. We have designed the bed motion and cylinder driving mechanisrn, to be described hereinafter, in such a manner that it is possible with this press to locate the

beam sections

41 and 42 directly beneath the bed and the cooperating cylinders where they will more effectively absorb the forces created during the unyielding impression of the cylinders on the bed which occurs during the printing operation.

As indicated above, the motion imparted to the bed will be a full harmonic motion. The mechanism for producing this motion is illustrated in Figures 1 to 5,. inclusive. This. mechanism is a crank mechanism which includes a Scotch yoke arrangement. As shown in Figure l., a flywheel 43 is. provided outside of but recessed within the side. support 35 of the frame 31.. This Hywheel is keyed on. aninwardly extending transverse shaft 44 which is supported on bearing 45 in track 39 and bearing 66. in side member. 3S. This shaft is driven continuously, when the press is operating, by means of a sprocket 47 keyed thereon within theside support 35,v as shown in Figures land 2. This sprocket is driven by a chain 48 which is driven by an electric. motor 48a supported at one end of the press within the frame 31 or by any other suitable power unit. The shaft 44 has a pinion 49 (Figure. 2)' keyed on itsinner end which engages with the large crank gear Si). rhis gear 5d' is keyed. on the inner end of a shaft 51 which is suitably mounted for rotation in a bearing 52 (Figures l and 3) in side member' 35 and in a bearing 53 in track. member 39'- Shaft 51 also carries a cam 54 (Figure 3) which is keyed thereon and which is. provided for a purpose to be explained later. Eccentrically carried by theg'ear 50 is a crank pin 55, shown matarlo 7 best in Figures 2 and 3, which carries a roller 56 that is mounted thereon by means of a roller bearing 57.

The roller 56 operates in avertical slot or groove 58 formed in an enlarged vertically disposed portion 59 of a Scotch yoke 60. This yoke 60 is illustrated best in Figures 1 to 3, and 5. It includes the vertical portion 59 (Figure 5) and the horizontal extending integral portion 61. At the end of the portion 61 and at the upper edge thereof a rack bar 62 is rigidly attached in a suitable manner, preferably removably. It will be noted best from Figure l that the portion 59 of yoke 60 is offset transversely relative to the portion 61 so that the thrust force created on the yoke 60 by crank roller 56 will be applied through the center line of portion 61 so that the thrust will be direct and will not tend to create lateral forces, it being noted that the center line of portion 61 is in the same vertical longitudinal plane as the longitudinal center line of the bed 30.

The manner in which the Scotch yoke 60 is mounted on the frame 31 for longitudinal reciprocation is illustrated best in Figures 3 to 6. The yoke is supported by a horizontal bearing plate 63 which is illustrated in Figures 4 and 5. This plate 63 extends almost the full length of the frame 31 and is attached to the lower edges of the

longitudinally extending tracks

39 and 40, as shown in Flgures 3 and 6. The plate 63, as shown in Figure 5, comprises the two

sections

64 and 65 which are at different levels, it being noted that the lower section 65 will be disposed towards the delivery end of the press. The section 64 carries on its upper face a roller bearing unit 66 which is of at elongated form. Similarly, the section 65 carries the flat bearing unit 67. The bearing

units

66 and 67 are offset transversely (Figure 4) to the same extent as the respective portions 61 and 59 of the yoke 60 with which they cooperate. Furthermore, due to the relative arrangement of the lsections 64 and 65 of the plate,

thc bearing units

66 and 67 are offset vertically to the same extent as the respective cooperating portions 61 and 59 of the yoke 60. Thus, the yoke 60 is supported on antifriction bearings for horizontal reciprocation. To prevent lateral or tilting movement of the yoke, longitudinal guides are provided at its upper and lower edges. The guide at the lower edge includes the upstanding longitudinal rib 68 (Figure 3) on plate 63 which extends upwardly into the longitudinal groove 69 formed in the lower edge of yoke 60. The upper guide includes an upstanding longitudinally extending rib or bar 70 which is rigidly secured to the upper portion of the track 40 at its inner side. This bar 70 extends downwardly into groove 71, formed on the upper edge of yoke 60, bar 70 being slidable in groove 71. F

Thus, yoke 60 is prevented from moving in any direction except lengthwise of the machine.

The rack bar 62 of yoke 60 engages a pinion 72, as shown best in Figures 1, 2, 5 and 6. This pinion 72 is keyed on a transverse hollow shaft 73 which is carried for rotation in bearings 74 and 75 (Figure 6) provided in the

respective tracks

39 and 40 intermediate their upper and lower edges, it being noted that the pinion ts snugly in the bearings. Thus, reciprocation of the yoke 60 will oscillate the pinion 72 and thereby oscillate the shaft 73. The ends of the shaft 73 have keyed thereon the large bed moving gears 76 and 77. These gears engage with the

respective racks

78 and 79 which are rigidly but removably secured to the lower side of bed 30 near the corresponding side edges of the bed.

The bed 30 is mounted for reciprocation on the longitudinally extending vertically disposed

tracks

39 and 40, as previously indicated, and as shown best in Figures 3 and 6. The bed may be of any suitable construction and is provided with a pair of bearers 80 (Figures 1 and 2) at one end for cooperating with the pair of cylinder bearers 81 on the cylinder 32 and a pair of bearers 82 at the other end for cooperating with the bearers 83 of the cylinder 33. All of the

bearers

80 and 82 are preferably removably attached to the bed and have the tapered ends' 84 (Figure 1) to facilitate moving of the cylinder bearers on and off such bed bearers, it being understood that the bearers function only during the printing stroke of the bed. The bed is further provided with the ink plates 3S and 36 (Figures 1 and 2) and suitable fastening members (not shown) for clamping the forms F thereto. With reference to Figure 3, it will be noted that the upper edges of the

respective tracks

39 and 40 are provided with the longitudinally extending channels 87 and 88 in which bed supporting rollers 89 are disposed. At the inner side of the channels 87 and 88, the

tracks

39 and 40 are provided respectively with the inwardly directed longitudinally extending lips 90 and 91.

Gibs

92 and 93 are suitably attached to the lower surface of bed 30 and are provided with outwardly extending

ledges

94 and 95 which overlap the lips 90 and 91. Thus, the bed can be moved longitudinally of the

tracks

39 and 40 with little friction since it rests on roller bearings 89 and is held downwardly in position on said bearings by cooperation of the lips 90 and 91 with the

ledges

94 and 95.

It will be noted that the bed driving pinion 72 and bed driving gears 76 and 77 will serve to drive the bed in a direction opposite to the direction of movement of the yoke 60. This is due to the fact that pinion 72 is located above yoke 60 and is an important feature since it serves to substantially counterbalance the horizontal forces created by the crank and yoke mechanism. It will also be noted from Figure 3 that the crank gear 50 extends down below the plate 63 which supports the yoke 60. This plate 63 is provided with an opening 96 through which this gear can project.

As previously indicated, the

impression cylinders

32 and 33 are rotated in one direction at all times and in exact synchronism with the bed at all times. To accomplish this, the cylinders are driven from the bed by a variable speed drive which drives the cylinders in the same direction during the movement of the bed in both directions. This special cylinder drive is illustrated best in Figures l, 2, 6, 7, 8, 9, 9a and 10.

With reference to Figure 6, it will be noted that the hollow shaft 73 has a shaft 97 extending therethrough and projecting from opposite ends. The ends of the shaft 97 are rotatably mounted in bearings 98 at the ends of hollow shaft 73. The left hand end of the shaft 97 (Figure 6) has keyed thereon a large driving sprocket 99 which is driven continuously by a chain 100 (Figure 1) that extends over a smaller sprocket 101 keyed on the constantly rotating flywheel shaft 44. The opposite end of shaft 97 has a beveled gear 102 keyed thereon. This gear 102 actuates the clutch mechanism of a cylinder driving unit indicated generally by numeral 103. This unit 103 is shown best in Figures 6 to l0.

With reference to Figures 7 and 8, it will be noted that unit 103 comprises a housing 104 made up of several sections joined together, as indicated, in an Oil tight manner so that the housing can be lled with oil. At the inner side of housing 104 is the bed driving gear 77 which, as previously indicated, is keyed on the shaft 73 and will oscillate therewith. At the opposite side of the housing 104, a cylinder driving gear 10S is fixed thereon for rotation therewith. Also, directly within the gear 105, a gear 106 is supported for rotation on housing 104 by means of a bearing 107. The gear 106 oscillates exactly the same as gear 77 but in the opposite directions. Gear 106 is driven by a pinion 108 which is keyed on the outer end of a shaft 109. The shaft 109 is supported by a bearing 110 which is formed in track 40 adjacent its upper edge and by bearing 111 formed in the side frame member 36. The shaft 109 is driven by the oscillating pinion 112 which, in turn, meshes with the bed drive rack 79 that reciprocates with the bed 30. The housing 104 (Figure 8) is rotatably supported by a roller bearing unit 113 on the extreme end of shaft 73 and -by roller