US3715981A

US3715981A - Fluid actuator and lock for printing plate cylinders

Info

Publication number: US3715981A
Application number: US00050642A
Authority: US
Inventors: H Huffman
Original assignee: Hamilton Tool Co
Current assignee: Hamilton Tool Co
Priority date: 1970-06-29
Filing date: 1970-06-29
Publication date: 1973-02-13
Anticipated expiration: 1990-02-13

Abstract

The printing cylinder is provided with an internal inflexible clamp bar rockingly mounted, for movement selectively either to an operative plate-clamping position or to an inoperative platereleasing position, by means of a foot-controlled valve for enabling the pressman to utilize both of his hands exclusively for accurate positioning of the printing plate upon the cylinder.

Description

United States Patent [191 Huffman 1 1 Feb. 13, 1973 [54] FLUID ACTUATOR AND LOCK FOR PRINTING PLATE CYLINDERS [75] Inventor: Harold W. Huffman, Hamilton,

Ohio

[73] Assignee: The Hamilton Tool Hamilton, Ohio [22] Filed: June 29, 1970 [21] App]. No.: 50,642

Company,

[52] US. Cl. ..l0l/4l5.l, 137/6256, l37/625.66 [51] Int. Cl. ..B4lf 27/12 [58] Field of Search.l01/4l 5.1, 378, 382 R, 382 MV;

3,022,728 2/1962 Heller..... ..101/4l5.l 3,032,065 5/1962 Jolley 1 37/625.68 3 ,047,257 7/ 1962 Chester 244/85 3,149,565 9/1964v Norlin ..l01/415.l 3,158,178 11/1964 Fiala et a1. ..251/295 X 3,215,163 11/1965 Henderson.... ...137/625.68 3,329,159 7/1967 Herion ...l37/625.28 3,340,897 9/ 1967 Nevulis 137/6256 3,456,588 7/1969 Brodiem. ..101/4l5.l 3,529,629 9/1970 Cowan ..137/6256 Primary Examiner-Edgar S. Burr Assistant Examiner-R. E. Suter Attorney-J. Warren Kinney, Jr.

[ 5 7 ABSTRACT The printing cylinder is provided with an internal inflexible clamp bar rockingly mounted, for movement selectively either to an operative plate-clamping position or to an inoperative plate-releasing position, by means of a foot-controlled valve for enabling the pressman to utilize both of his hands exclusively for accurate positioning of the printing plate upon the cylinder.

15 Claims, 7 Drawing Figures PATENTEDFEB13 ms SHEET 1 [IF 3 M/VENTOR HAROLD W. HUFFMAN ATTOR PATENTEDFEB 1 3 I975 SHEET 2 OF 3 INVENTOI? HAROLD W. HUFFMAN FLUID ACTUATOR AND LOCK FOR PRINTING PLATE CYLINDERS The present invention relates to a fluid actuator and lock for the clamp bar of a printing plate cylinder.

The plate supporting cylinder of a printing press is an elongate cylinder supported at its opposite ends in bearings which permit rapid axial rotation of the cylinder. A flexible printing plate, generally rectangular in form, is wrapped once about the circumference of the cylinder, and has its opposite ends clamped securely to the cylinder in order to avoid accidental release of the plate during a printing operation.

The opposite ends of the printing plate ordinarily are gripped and held by mechanical clamps, usually screw clamps, which are tightened andloosened by means of a wrench in the hands of the pressman. In manipulating the clamp wrench, the pressman finds thatdifficulty is often encountered in the effort to simultaneously position the printing plate upon the cylinder accurately and quickly preparatory to clamping. Accuracy of plate positioning and clamping is important to the performance of high quality printing and rapid production.

A primary object of the invention is to provide fluid actuated means in conjunction with the clamp bar of a printing plate cylinder wherein said means are selectively operable for moving the clamp bar to an operative plate-clamping position or to an inoperative platereleasing position incident to manipulation of a valve under the control of the pressman. The fluid actuated means includes a pair of elongate inflatable tubular members disposed one each on opposite sides of the clamp bar whereby inflation of said members will impart a positive, uniform force to and along one face or side of the entire length of the clamp bar. Fluid actuating media at one or the other of two different pressures is introduced axially through a common conduit in an end of the printing cylinder to a pressure responsive valve on the cylinder which controls the flow of pressure media to and from said inflatable members.

A further object of this invention is to provide fluid pressure means for effecting plate lock-up upon a press cylinder with ease and despatch, and with a high degree of accuracy.

Another object of the invention is to provide an improved plate lock-up means which frees both hands of the pressman for accurately positioning the plate upon the cylinder, in the interests of saving time and labor, and producing high quality printing.

Another object of the invention is to provide an improved plate lock-up means which applies uniform clamp force automatically along the full length of a plate end margin, with improved printing results and production.

A further object is to ensure maintenance of a continuous clamping force upon the printing plate end margins during the entire course of a printing operation, to prevent loosening of the clamp means due to pull exerted thereon by a blanket cylinder rotating against the printing plate.

Another object of the invention is to provide a compact design of clamp for printing plate cylinders, which permits a reduction in the cylinder diameter.

The foregoing and other objects are attained by the means described herein and illustrated upon the accompanying drawing, in which:

FIGS. l-3 are vertical sectional views taken on line A-A of FIG. 6, showing a printing plate cylinder embodying the teachings of the present invention and illustrating three sequential positions of the clamp bar incident to locking a printing plate onto the cylinder.

FIG. 4 is a perspective view of the clamp bar.

FIG. 5 is a diagramatic view of a control circuit for actuating the clamp bar.

FIG. 6 is a schematic side view, partly in section, illustrating, in general, but not to scale, a printing cylinder assembly embodying the teachings of the present invention.

FIG. 7 is an enlarged fragmentary view of the left end of the printing cylinder disclosing the pressure responsive distributor valve.

The reference character 10 indicates a printing press cylinder, which is elongate and has opposite ends l2, 12. The cylinder has an outer curved surface 14, which is interrupted by a narrow access slot 16 coextensive with the length of the cylinder. Slot 16 leads to a wide chamber 18 formed by a deep elongate groove which is parallel to the cylinder axis, and is defined by a pair of opposed spaced

inner side walls

20, 22 disposed at an acute angleto one another.

An abutment lip 24 overhangs the inner wall 20 adjacent to slot 16, and includes an interior clamp face 26. A flexible sheet-like printing plate 30 having a hook or turned portion 28 at one end which hooks over the lip 24 and overlies the clamp face 26. The printing plate is of such length that it may be wrapped once about the periphery of cylinder 14. The plate has a second hooked or turned end margin 32 to be inserted into access slot 16 and anchored in a manner to be described.

Within chamber 18 is disposed an elongate substantially inflexible clamp bar 34 formed of steel or other rigid metal, whose length may approximate the length of slot 16. Clamp bar 34 may be substantially rectangular of form, so as to include

opposite side edges

36, 38 which are parallel to one another, and also a pair of opposite faces 40 which is substantially flat and, 42 having a depression 43 therein. Opposite ends of the clamp bar are denoted 44, 44.

Means is provided to support the clamp bar for rocking movement about its inner side edge 36. This may be accomplished by means of conventional pivots, or, in accordance with the example illustrated, the inner side edge 36 may fulcrum within a pocket 46 afforded by the baseof chamber or groove 18 where the walls thereof meet. The clamp bar side faces 40 and 42 are exposed to the chamber or

groove walls

20 and 22, respectively, and will recede from or approach said

walls

20 and 22 incident to rocking movements of the clamp bar.

The elongate outer side edge 38 of clamp bar 34 performs as an elongate swingable nose which is substantially coextensive with the length of the clamp bar, and said nose is arranged to substantially wipe or sweep against or engage the clamp face 26 of the abutment lip 24 during rocking of the clamp bar. The nose is denoted 380, and is seen to include a narrow socket or slot 48 extending lengthwise of the nose to receive the hooked end margin 32 of printing plate 30. the hook 32 has access to socket 48 through the narrow slot 16 of the groove or chamber 18. A wear plate 50 may be incorporated in socket 48 engaging the hook 34 to hold the same therein until clamped by the nose 380.

It is here noted that clamp bar 34, may be moved toward or away from either of the chamber or groove walls or 22. When moved toward wall 22, the nose and the socket 48 of the clamp bar are accessible through slot 16 for application or removal of the hooked margin 32 of plate 30 with respect to socket 48. Also, in this position of the clamp bar the nose 380 will be withdrawn from the region of lip 24 and clamp face 26, so as to free the hooked margin 28 of plate 30 for displacement from lip 24, thereby permitting bodily removal of the printing plate from cylinder 14. In the light of the foregoing, a rocking of clamp bar 34 toward wall 22 constitutes disposition of the clamp bar to an inoperative position at which the hooked ends of the printing plate are released.

When the clamp bar 34 is disposed to the inoperative position above mentioned, a printing plate may be wrapped about cylinder 14 and the opposite hooked ends thereof may be applied to lip 24 and nose socket 48 preparatory to lock-up or clamping. After the hooked ends of the plate are properly applied, the clamp bar may be shifted toward wall 20, thereby causing the clamp nose 380 to firmly press and lock the plate ends with a camming force against clamp face 26. So shifted, the clamp bar is said to assume the operative clamping or lock-up position.

Means is provided for very conveniently and efficiently shifting the clamp bar selectively or alternatively to the operative and inoperative positions aforesaid. Such means is fluid pressure operated, and may comprise a pair of flexible

elongate clamp tubes

52, 54 each of which extends substantially the full length of the clamp bar, and either of which may be inflated with a fluid under pressure so as to impose lateral force against a side face of the clamp bar, for rocking said bar about the pivot or fulcrum at 46. The flexible clamp tube 52 rests between the clamp bar face 40 and chamber wall 20, in effect, said wall 20 being preferably channeled longitudinally at 56 to accommodate tube 52. The clamp tube 54 rests between clamp bar face 42 and the face 22 of chamber or groove 18.

In operation, one flexible tube is to be inflated while the other exhausts. The tubes when inflated expand laterally against the side face of the clamp bar, To rock the bar about the pivot or fulcrum at 46, thereby to initially move and constantly maintain the clamp bar in either an operative or an inoperative position previously defined herein. The cylinder 14 may be provided with a pair of

fluid transfer ports

58 and 60 having connection with the

clamp tubes

52 and 54, respectively, preferably at corresponding ends of the clamp tubes. The ports may have connections with a fluid pressure control valve 62, to be foot operated for directing pressured fluid to one clamp tube or the other, selectively, for rocking the clamp bar to the operative and inoperative positions.

The foot operated pressure control valve 62, FIG. 6, may include a shiftable valving member 64 to be moved mechanically by means of pedal 66 and actuator 68, from the normal full-line position shown, to the lowered position indicated by the broken line. The valving member may be spring-biased constantly to the full line position indicated, but may be moved and held in the broken line position as long as a downward force is applied to pedal 66.

At 70 is indicated a high pressure fluid line, whereas 72 indicates a relatively low pressure fluid line. These fluid lines are connected to separate ports in the housing of valve 62. Fluid supply line 70 normally supplies high pressure fluid to valving member 64, which directs it into a delivery pipe 74. When pedal 66 is depressed and held down by the foot of an operator, valving member 64 is moved to the broken line position at which low pressure fluid from supply line 72 is directed into delivery pipe 74, while fluid from high pressure supply line 70 is cut off. Suitable high and low operating pressures of fluid may approximate 100 lbs. and 35 lbs., and both are constantly available at the supply lines 70 and 72, respectively.

With further reference to FIG. 6, the numeral 76 indicates a conventional rotary coupler connecting the stationary delivery pipe 74 with the rotary shaft 78 of cylinder 10. Shaft 78 carries a fixed drive gear 80, and a shaft extension 82 upon which the rotary element of the coupler is mounted.

Suitable bearings

84, 86 of the

machine frame uprights

87, 87, support the shaft in conventional manner. At 88 is indicated one wall of a gear case containing lubricant for a drive gear train including gear 80, this being conventional and of no importance to the present invention.

Fluid under pressure conveyed by pipe 74 and coupler 76, enters a concentric elongate bore 90 of shaft 78 to actuate a distributor valve generally denoted 92, said valve being a four-way, two-position pilot operative valve. Valve 92 is best illustrated by FIG. 7, and may include a longitudinally shiftable spool having three

discs

93, 94, 95 spaced apart on a common stem 97, and adapted to slide within a cylindrical valve chamber 96. Stem 97 has an extension carrying a piston 98 slidable in a cylinder 99,'the piston being normally biased to the left in FIG. 7 by a compression spring 100.

Shaft bore 90 has a pilot port 102 and a main port 104, both arranged transversely of bore 90. Main port 104 leads to valve chamber 96 at a location intermediate two

end ports

106 and 108 which are connected by means of tubes 110 and1l2 to

ports

58 and 60, respectively, (FIG. 1), of the

clamp tubes

52 and 54. Thus, as depicted by FIG. 7, fluid under pressure conveyed by pipe 74 will enter bore 90, and may flow into chamber 114 behind piston 98, and into valve chamber 96 at 104.

A low pressure fluid when conveyed by pipe 74 and bore 90, will enter chamber 114 without advancing the piston 98. Accordingly, such low pressure fluid will pass on to port 104 and into chamber 96 and port 108, whence it will enter clamp tube 52 (FIG. 2) through port 58, to shift clamp bar 34 into the inoperative or release position of FIG. 2. At the same time, clamp tube 54 will exhaust through ports 60, I12, 106 and 116.

On the other hand, a high pressure fluid conveyed by pipe 74 and bore 90, will enter chamber 114 withsufficient force to move piston 98 to the right in FIG. 7, thereby to shift the spool and

discs

93, 94, 95 to the extreme right; this resulting in a flow through

ports

104, 106, 112 and 60 causing inflation of clamp tube 54 for shifting clamp bar 34 to the operative clamping position of FIG. 3. This is the normal situation existing when the press is operating, and is depicted by FIGS. 3 and 6. As will be noted, pedal 66 is not under depression, and valving member 64 is supplying to delivery pipe 74 a constant supply of high pressure fluid from supply line 70. Accordingly, and as long as pedal valve 64 remains undisturbed, the printing plate 30 will be securely clamped as in FIG. 3, to perform its intended printing function.

Upon completion of the printing operation, the pressman may quickly release the printing plate from cylinder 10, by merely depressing the foot pedal 66 to deliver low pressure fluid through pipe 74 and into clamp tube 52, for inflating said tube 52 and rocking the clamp bar to the operative or release position of FIG. 2. Port 118, FIG. 7, serves to exhaust the clamp tube 54 while clamp tube 52 is under inflation.

At the right end of FIG. 6 is shown typical mechanism including a hand crank 120, for longitudinally shifting the cylinder shaft 78 relative to its

bearings

84, 86 for purposes of alignment in printing. This mechanism is generally used on printing equipment, and warrants no detailed explanation so far as the present invention is concerned.

The flexible

elongate clamp tubes

52, 54 are to be substantially coextensive in length with the length of the clamp bar, so that expansive force of the tubes will be equalized along the bar from end to end, thereby eliminating deflection or bending of the bar under clamping pressure. The resultant uniformity of clamping pressure acting along the full length of the printing plate end margins, ensures accurate and firm mounting and holding of the plate, which in turn assures maximum speed and quality of printing. By this means is eliminated any clamp bar deflection and variation of clamping force along the width of the printing plate, which so commonly occurs with the use of prior clamping methods involving hand clamping.

The flexible elongate clamp tubes may be formed of any suitable impervious material having the required flexibility and durability, examples of which include natural and artificial rubber, vinyl, and the various durable textiles or fabrics impregnated or coated to render them substantially impervious to air or fluid leakage. The tubes may possess also a measure of resiliency, if desired.

To facilitate information of the groove or chamber 18, and to provide for installation and servicing of the clamp bar and clamp tube assembly, the printing cylinder may be built up of a plurality of separable parts such as the displaceable insert 67 which extends from slot 16 to a parting line 69 on the face of the cylinder. The insert or part 67 may be detachably secured by means of screws or equivalent fasteners 71 upon a seat 73 formed on the main body portion of the cylinder. The length of seat 73 and insert 67 should approximate the length of cylinder 14.

The improved printing cylinder construction as herein disclosed greatly facilitates and expedites the application and removal of flexible sheet-type printing plates. By reason of the fact that lock-up or clamping of the plate may be performed pneumatically or hydraulically and without use of the pressmans hands, his hands may most effectively and advantageously be employed exclusively in accurately positioning the plate for lock-up, thereby ensuring great accuracy in plate positioning which results in high-quality high-speed printing. Quality and speed in the printing are enhanced also by the uniformity of clamping force applied to the plate end margins, made possible by the fluid pressure actuating means herein disclosed.

What is claimed is:

1. An elongate, rotatable printing cylinder having an exterior cylindrical surface, an elongate groove in one side of said printing cylinder extending parallel to the axis of said printing cylinder, said groove defining an elongate chamber having a single access slot thereto through the surface of said printing cylinder, a concave base at the bottom of said chamber, opposed, spaced apart side walls extending from said concave base and diverging from the bottom thereof at an acute angle to each other, said side walls having convergent portions at the tops thereof leading to the access slot, an elongate clamp bar pivotally mounted in said chamber for pivotal movement toward and away from the divergent side walls to locking and unlocking positions, said clamp bar having an oblong cross-sectional shape and opposite side faces and opposite edges, one of said edges comprising a convex curved base complementary in size and shape to the concave base of said chamber and being pivoted therein, the other of said edges comprising a clamping edge and having an elongate slot therein, one side face being flat and the other side face having a depression therein between the base and clamping edge, the bottom portions of the side faces being flat and parallel to one another and merging directly with said convex curved base, flexible expansible fluid operated means in said chamber on opposite sides of said clamp bar between said one flat side face and one side of said chamber and between the depression in the other side face and the other side of said chamber to pivot the bar to the locking and unlocking positions, and a flexible, sheet-like printing plate supported on the exterior surface of said printing cylinder and having opposite end margins received through said access slot, one of said end margins in overlying engagement with the convergent portion of one of the side walls of the chamber and the other end margin received in the slot in the clamping edge of said clamp bar, so that actuation of the fluid operated means on said otherside of said clamp bar causes pivotal movement of said clamp bar toward said one side of said chamber into locking position and wedges and clamps the end margins of the printing plate between the clamping edge of the clamp bar and the convergent portion of said one chamber side wall.

2. The combination as defined by claim 1, wherein said fluid pressure operated means is foot-controlled, leaving the hands of the pressman free for accurately positioning said printing plate upon the cylinder.

3. The combination as defined by claim 1, wherein said fluid pressure operated means includes a pair of fluid inflatable flexible tubes disposed within said chamber at opposite side faces of the clamp bar, said tubes being alternately inflatable to alternately apply force against the opposite side faces of the clamp bar, for imparting said pivotal movements to said clamp bar.

4. The combination as defined by claim 3, wherein said inflatable tubes are elongate of form and substantially coextensive with the length of the clamp bar, for

effecting even distribution of expansive force along the length of the clamp bar.

5. The combination as defined by claim 4, wherein said fluid pressure operated means is foot-controlled, leaving the hands of the pressman free for accurately positioning said printing plate upon the cylinder.

6. The combination as defined by claim 5, wherein is included means for supplying pressured fluid to said inflatable tubes through said foot-controlled means.

7. The combination as defined by claim 1, wherein said cylinder is formed as a plurality of separable com- 1 ponents one of which includes one of said chamber walls, said one separable component being bodily displaceable from the remainder of the cylinder to expose to view the clamp bar and the remaining chamber wall.

8. A press cylinder clamp means for the opposite hooked end margins of a flexible printing plate, comprising in combination: an elongate rotatable press cylinder having opposite ends and an outer curved surface, said curbed surface having formed therein a deep elongate chamber defined by a single elongate access slot parallel to the cylinder axis, said chamber having a concave base portion, a pair of opposed, spaced apart inner side walls extending from said concave base and diverging from their bottoms at an acute angle to one another; said inner side walls having convergent portions at the tops thereof leading to the access slot and one of said convergent portions defining an abutment lip overhanging one of said inner walls adjacent to said access slot and having a clamp face to support one hooked end margin of the printing plate; an elongate clamp bar extending lengthwise within said chamber,-

said bar having an oblong cross-sectional configuration and a pair of opposite side faces and an inner and an outer side edge extending lengthwise thereof in parallelism; the inner side edge being convex and complementary in size and shape to the concave base and pivoted in said base for supporting said bar for rocking movement about the inner side edge thereof, and toward and from said inner walls of the chamber between an operative clamping position and an inoperative release position of said bar, said opposite faces of the bar having flat, parallel bottom portions merging directly with said convex base and being exposed one to each inner wall of the chamber; the outer side edge of the clamp bar comprising an elongate pressure nose located to engage the clamp face of the abutment lip during rocking of the clamp bar to operative position; one of the side faces of the clamp bar having a depression therein between the base and pressure nose; fluid pressure operated means disposed at the opposite side faces of the clamp bar for rocking said bar selectively to said operative and inoperative positions within the cylinder chamber. the fluid pressure operated means on said one side of said clamp bar positioned between the depression and the adjacent side wall of the cylinder chamber; elongate slot means in said,

clamp bar nose and accessible through said access slot of the cylinder chamber receiving the remaining hooked end margin of the printing plate with said remaining hooked end overlying a portion of said nose,

whereby rocking of the clamp bar to the operative position wedges said hooked end margins of the printing plate between the clamp bar nose and the clamp face of said abutment li and rockingt of the clamp bar to the inoperative posi ion displaces he clamp bar nose from tively to said fluid pressure operated means during rotation of the cylinder.

11. The combination as defined by claim 8, wherein said fluid pressure operated means includes a high pressure fluid source and a relatively low pressure fluid source; and means operative alternately to rock the clamp bar to one of said positions by high pressure fluid force, and to the other of said positions by force of the lower pressure fluid.

12. The combination as defined by claim 8, wherein said fluid pressure operated means includes a high pressure fluid source and a relatively low pressure fluid source, and a single delivery pipe for conveying alternatively a high pressure fluid or a low pressure fluid to said inflatable flexible tubes, for rocking the clamp bar to said operative and inoperative positions, at least a portion of which delivery pipe is substantially concentric with said cylinder axis.

13. The combination as defined by claim 12, wherein feed of high or low pressure fluids to said delivery pipe is under the control of a foot operated valve.

14. The combination as defined by claim 13, wherein said foot operated valve is constantly yieldingly biased to feed high pressure fluid to that inflatable flexible tube which rocks the clamp bar to the operative position.

15. The combination as defined by claim 14, wherein said inflatable flexible tubes are elongate of form and substantially coextensive with the length of the clamp bar, for effecting even distribution of expansive force along the length of the clamp bar.

* a: a a

Claims

1. An elongate, rotatable printing cylinder having an exterior cylindrical surface, an elongate groove in one side of said printing cylinder extending parallel to the axis of said printing cylinder, said groove defining an elongate chamber having a single access slot thereto through the surface of said printing cylinder, a concave base at the bottom of said chamber, opposed, spaced apart side walls extending from said concave base and diverging from the bottom thereof at an acute angle to each other, said side walls having convergent portions at the tops thereof leading to the access slot, an elongate clamp bar pivotally mounted in said chamber for pivotal movement toward and away from the divergent side walls to locking and unlocking positions, said clamp bar having an oblong cross-sectional shape and opposite side faces and opposite edges, one of said edges comprising a convex curved base complementary in size and shape to the concave base of said chamber and being pivoted therein, the other of said edges comprising a clamping edge and having an elongate slot therein, one side face being flat and the other side face having a depression therein between the base and clamping edge, the bottom portions of the side faces being flat and parallel to one another and merging directly with said convex curved base, flexible expansible fluid operated means in said chamber on opposite sides of said clamp bar between said one flat side face and one side of said chamber and between the depression in the other side face and the other side of said chamber to pivot the bar to the locking and unlocking positions, and a flexible, sheet-like printing plate supported on the exterior surface of said printing cylinder And having opposite end margins received through said access slot, one of said end margins in overlying engagement with the convergent portion of one of the side walls of the chamber and the other end margin received in the slot in the clamping edge of said clamp bar, so that actuation of the fluid operated means on said other side of said clamp bar causes pivotal movement of said clamp bar toward said one side of said chamber into locking position and wedges and clamps the end margins of the printing plate between the clamping edge of the clamp bar and the convergent portion of said one chamber side wall.

4. The combination as defined by claim 3, wherein said inflatable tubes are elongate of form and substantially coextensive with the length of the clamp bar, for effecting even distribution of expansive force along the length of the clamp bar.

7. The combination as defined by claim 1, wherein said cylinder is formed as a plurality of separable components one of which includes one of said chamber walls, said one separable component being bodily displaceable from the remainder of the cylinder to expose to view the clamp bar and the remaining chamber wall.

8. A press cylinder clamp means for the opposite hooked end margins of a flexible printing plate, comprising in combination: an elongate rotatable press cylinder having opposite ends and an outer curved surface, said curbed surface having formed therein a deep elongate chamber defined by a single elongate access slot parallel to the cylinder axis, said chamber having a concave base portion, a pair of opposed, spaced apart inner side walls extending from said concave base and diverging from their bottoms at an acute angle to one another; said inner side walls having convergent portions at the tops thereof leading to the access slot and one of said convergent portions defining an abutment lip overhanging one of said inner walls adjacent to said access slot and having a clamp face to support one hooked end margin of the printing plate; an elongate clamp bar extending lengthwise within said chamber, said bar having an oblong cross-sectional configuration and a pair of opposite side faces and an inner and an outer side edge extending lengthwise thereof in parallelism; the inner side edge being convex and complementary in size and shape to the concave base and pivoted in said base for supporting said bar for rocking movement about the inner side edge thereof, and toward and from said inner walls of the chamber between an operative clamping position and an inoperative release position of said bar, said opposite faces of the bar having flat, parallel bottom portions merging directly with said convex base and being exposed one to each inner wall of the chamber; the outer side edge of the clamp bar comprising an elongate pressure nose located to engage the clamp face of the abutment lip during rocking of the clamp bar to operative position; one of the side faces of the clamp bar having a depression therein between the base and pressure nose; fluid pressure operated meAns disposed at the opposite side faces of the clamp bar for rocking said bar selectively to said operative and inoperative positions within the cylinder chamber, the fluid pressure operated means on said one side of said clamp bar positioned between the depression and the adjacent side wall of the cylinder chamber; elongate slot means in said clamp bar nose and accessible through said access slot of the cylinder chamber receiving the remaining hooked end margin of the printing plate with said remaining hooked end overlying a portion of said nose, whereby rocking of the clamp bar to the operative position wedges said hooked end margins of the printing plate between the clamp bar nose and the clamp face of said abutment lip, and rocking of the clamp bar to the inoperative position displaces the clamp bar nose from clamping relation with said abutment lip clamp face to release and free said hooked end margins of the printing plate.

9. The combination as defined by claim 8, wherein said fluid pressure operated means is foot-controlled, leaving the hands of the pressman free for accurately positioning said printing plate upon the cylinder.

10. The combination as defined by claim 9, wherein is included means for supplying pressured fluid selectively to said fluid pressure operated means during rotation of the cylinder.