US3782044A

US3782044A - Wide abrasive belt type lumber planing machine

Info

Publication number: US3782044A
Application number: US00249175A
Authority: US
Inventors: P Olin
Original assignee: Timesavers Inc
Current assignee: Timesavers Inc
Priority date: 1972-05-01
Filing date: 1972-05-01
Publication date: 1974-01-01
Anticipated expiration: 1991-01-01
Also published as: AU4659272A; CA953918A; JPS5226635B2; JPS4930997A

Abstract

A wide abrasive belt lumber planing machine in which the planing action is performed by a contact drum-supported abrasive belt as the workpiece is moved through the machine, with its top surface in contact with the belt. An in-feed pressure shoe and an outfeed pressure shoe press down on the workpiece just as it enters and leaves the abrasion zone, and to preclude the generation of abnormally high friction loads due to variations in thickness of the workpiece, the force with which the in-feed shoe is pressed down is produced by a pressure-regulated air cylinder.

Description

United States Patent 91 Olin WIDE ABRASIVE BELT TYPE LUMBER PLANING MACHINE [75] Inventor: Paul H. Olin, Minneapolis, Minn. [73] Assignee: Timesavers, Inc., Minneapolis,

Minn.

[22] Filed: May 1, 1972 [2]] Appl. No.: 249,175

[52] US. Cl. Sl/l38 [51] Int. Cl B24b 21/00 [58] Field of Search 51/135 R, 137-139, 51/76 [56] References Cited UNITED STATES PATENTS 554,758 2/1896 Wigell et a1 51/139 X 3,208,187 9/1965 Ernst 51/76 R 3,271,909 9/1966 Rutt et al.... 51/138 X 2,791,070 S/l957 Schaller ..5l/l38 Jan. 1,1974

FOREIGN PATENTS OR APPLICATIONS 1,921,566 12/1970 Germany 5l/l38 Primary Examiner-Othell M. Simpson Attorney-lra Milton Jones [57] ABSTRACT A wide abrasive belt lumber planing machine in which the planing action is performed by a contact drumsupported abrasive belt as the workpiece is moved through the machine, with its top surface in contact with the belt. An in-feed pressure shoe and an outfeed pressure shoe press down on the workpiece just as it enters and leaves the abrasion zone, and to preclude the generation of abnormally high friction'loads due to variations in thickness of the workpiece, the force with which the in-feed shoe is pressed down is produced by a pressure-regulated air cylinder.

6 Claims, 5 Drawing Figures A112 PRESSURE 'PATENTED JAN 1 I974 SHEET 2 0F 3 Flea WIDE ABRASIVE BELT TYPE LUMBER PLANING MACHINE This invention relates to wide abrasive belt lumber planing machines, wherein an endless conveyor belt carries workpieces horizontally through the machine beneath the contact drum of an abrading headfor engagement by an abrasive belt trained around the contact drum; and the invention has more particular reference to improvements in such machines whereby the power required for driving its conveyor belt can be significently reduced from what was heretofore required. This makes it possible to use a less expensive drive motor and drive transmission without in anywise impairing the operation and performance of the machine.

The abrasive head of machines of this type comprises an endless coarse grit abrasive belt trained around two vertically spaced apart rollers that have their axes parallel and horizontal. The lower one of these rollersis the contact drum, the axis of which is fixed with respect to the frame of the machine during operation of the machine. The contact drum is driven by a motor mounted on the machine frame to thus impart orbital motion to the abrasive belt normally in the direction opposite to the movement of the workpiece through the machine. The upper roller is an idlermounted for bodily up and down motion and biased upwardly when the machine is in operation to maintain tension on the abrasive belt.

Workpieces are carried under the abrading head by the top stretch of a horizontally oriented endless conveyor belt that is driven by a motor separate from the one that drives the contact drum. The top'stretch of the endless belt is solidly supported by frame-carried structure which includes freely rotating rollers and a flat, horizontal platen by which the top working stretch of the conveyor belt is firmly supported directly beneath the contact drum.

As a workpiece is carried through the machine by the conveyor belt, and just before it comes in contact with the abrading head, and again just after passing out from under the head, the workpiece should be firmly pressed down against the conveyor belt, so that its upper surface travels as nearly as possible in a horizontal plane spaced above the lowermost surface of the contact drum-supported abrasive belt a distance determined by the amount of stock to be planed off. Without such firm downward pressure on the workpiece directly upstream and downstream of its contact with the drumsupported abrasive belt, there would be no assurance of achieving accurate planing of the workpiece. It is, therefore, essential to the success of the operation to hold the workpieces firmly down on the conveyor belt.

The means for thus pressing the workpiece down against the conveyor belt comprises a pair of pressure shoes which extend transversely across the conveyor belt and project inwardly towards and under opposite sides of the contact drum to slidingly engage the workpiece in zones closely adjacent to, but at opposite sides of, the zone of abrasion. Farther from the contact drum, at each side of it, there are freely rotatable rollers that engage the upper surface of the workpeice in its passage to and from the abrasion zone. Both the pressure shoes and the freely rotatable rollers have a degree of bodily up and down motion and are biased downwardly so that they exert a yielding downward force on the workpiece. Heretofore, the biasing force upon both the in-feed pressure shoe as well as the outfeed pressure shoe and all of the rollers has been exerted by springs reacting against fixed parts of the machine.

The present invention is based upon a recognition that, in prior wide abrasive belt planing machines, the use of springs to impart downward bias to the in-feed pressure shoe which engages the workpiece as it enters the abrasion zone, has been responsible for requiring the drive motor for the conveyor belt to be considerably larger and more powerful (and, therefore, more expensive) than it really needed to be. The heretofore unappreciated relationship between the power of the motor driving the conveyor belt and the character of the in-feed pressure shoe biasing means arises from the fact that the workpieces generally rough lumber have a substantial variation in thickness from point to point along their length. To understand how this thickness variation in workpieces affects the requirements for the power of the conveyor belt motor, consideration mut be given to the character of the biasing force which a spring exerts. As a spring is flexed or loaded, the force that it exerts is in substantially linear relation to the extent of its deformation. Thus, when a vertically movable pressure shoe is urged downwardly by a spring, the force required to lift the shoe is least when the shoe is near the bottom limit of its permitted movement, and increases as the shoe is raised.

Hence, if a workpiece of varying thickness along its length is carried beneath a spring biased pressure shoe on a conveyor belt, the shoe exerts the least downward pressure upon the thinnest portions of the workpiece and the greatest downward pressure upon its thickest portions. Therefore, as the thicker portions of the workpiece pass beneath the pressure shoe, there is an increase in friction between the shoe and the workpiece, requiring more work from the motor to keep the workpiece moving under the shoe at a constant speed. However, the work that must be performed by the motor increases more than proportionally to the increased friction between the shoe and the workpiece, owing to the character of the conveyor belt. As the shoe applies increased downward force to the workpiece, such force is transmitted through the workpiece onto the conveyor belt which is thus forced more tightly down against its supporting platen. As a consequence, the friction between the conveyor belt and the platen is increased and decreased simultaneously with, and in substantially direct proportion to, changes in friction between the shoe and the workpiece.

While the art has heretofore recognized that increases in thickness of the workpiece as it passes under the in-feed pressure shoe raises the load on the motor driving the conveyor belt, this appreciation has taken the form of a sort of intuitive understanding that the power rating of the conveyor drive motor had to be appraised on the basis of an allowance for a substantially large safety factor, for it was well understood that if the motor was not oversized to a considerable extent, it could be expected to stall whenever a portion of a workpiece that was approaching the contact drum was substantially thicker than the nominal thickness for which the machine was set.

What seems not to have been appreciated isthat this need for oversizing the conveyor drive motor arose from the character of the biasing forcethatwas apin frictional drag that resulted from changes in biasing force.

With the foregoing observati rmn mind, it is the general object of this invention to provide a wide abrasive belt planing machine of the character described which has a substantially ower horsepower conveyor drive motor than machines of equivalent capacity heretofore in use, but which nevertheless achieves uniformly steady motion of workpieces past the contact drum, despite very substantial variations in thickness of the workpieces along their length.

More specifically, it is an object of this invention to provide means for so biasing a pressure shoe in a wide abrasive belt planing machine that frictional drag between the shoe and a workpiece engaged thereby remains substantially constant despite relatively large variations in thickness of the workpiece along its length, and whereby friction between the conveyor belt that carries the workpieces and a platen that the belt supportingly overlies, likewise remains substantially constant.

With the above and other objects in view which will appear as the description proceeds, this invention resides in a novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of a physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a view in side elevation ofa wide belt sanding machine embodying the principles of this invention;

FIG. 2 is a vertical sectional view through the contact drum and the pressure shoes of the machine, showing the relationships of those parts to one another and illustrating the principles of this invention more or less diagrammatically.

FIG. 3 is an enlarged view generally similar to FIG. 1, but with portions of the machine housing broken away to illustrate details of construction;

FIG. 4 is an end view of the in-feed pressure shoe and its associated structure, said view being taken on the plane of the line 4-4 in FIG. 5; and

FIG. 5 is a view in elevation of the structure shown in FIG. 4, taken from the right-hand side of FIG. 4, but with portions broken away to illustrate details of construction.

Referring now more particularly to the accompanying drawings, the numeral 5 designates generally the abrading head of a wide abrasive belt lumber planing machine, which head comprises, in general, a wide endless abrasive belt 6 trained around a lower contact drum 7 and an upper tension roll 8. The contact drum is journalled on the frame 9 of the machine for rotation on a fixed axis and is driven in the customary manner by a powerful motor (not shown). The tension roll 8 is mounted in a known manner for limited bodily up and down motion and is biased upwardly to maintain tension on the abrasive belt.

workpieces are carried beneath the abrasive head, to be abraded thereby, by means of a conveyor which is designated generally by the numeral 12 and which comprises a supple endless belt 13 trained around horizontally spaced apart rollers 15 and 16 with a straight upper working stretch 17 extending between those rollers. The roller 15 is driven by an electric motor connected therewith through an appropriate transmission system, as more or less diagrammatically illustrated in FIG. 1 at 19. In this manner, orbital motion is imparted to the conveyor belt in the direction to move its upper stretch from right to left, as viewed in the drawings.

As is more or less conventional, the upper stretch of the conveyor belt is supported by idler rollers 20 and a flat smooth surfaced platen 21, located directly beneath the contact drum. The distance between the bottom of the contact drum-supported abrasive belt and the top surface of the platen thus determines the amount of stock that is removed from a workpiece fed through the machine, and since the machine must be capable of handling a wide range of workpiece thicknesses, that distance must be adjustable. To this end, the entire conveyor is mounted on the machine frame in a known manner for bodily up and down adjustment.

As already explained, it is important that the workpiece be held in firm engagement with the platensupported conveyor belt directly adjacent to the zone of abrading action, and especially just as it enters that zone. The necessary downward force for this purpose is applied to the workpiece by an in-feed pressure shoe 24 and an out-feed pressure shoe 25. The downward force which these pressure shoes exert on the workpiece must be applied as close as possible to the zone of engagement between the abrasive belt and the workpiece and, for this reason, the pressure shoes are shaped to have toe portions 26 that project inwardly under the contact drum, as best seen in FIG. 2. Essentially, only these toe portions of the shoes engage the workpiece.

The

pressure shoes

24 and 25 extend across the full width of the conveyor belt and are mounted on

cross shafts

27 and 27 which have their ends received in coaxial bores in vertical mounting brackets 28 that are rigidly fixed to the main frame of the machine, only one of these brackets being shown in the drawings. The pressure shoes are preferably castings and have flat parallel end walls 29. Between these end walls the cross sectional shape of the shoes is essentially uniform and defined by a concave front surface 30 and a convex back surface 31 which is stepped, as at 32, to define the heel of the shoe. Forwardly of this heel the bottom surface 33 of the shoe slopes downwardly to join the botto n st rface34 of the toe of the shoe.

The end walls 29 of the shoes have coaxial bores to receive the

cross shafts

27 and 27 whereby each shoe is rockably supported by its respective cross shaft. For the out-feed shoe 25 which requires no bodily vertical adjustment, the cross shaft 27 and the bore in the end walls 29 of this shoe are coaxial; but in the case of the in-feed shoe 24 which must be bodily vertically adjustable, the connection between each of its end walls 29 and the cross shaft 27 includes an eccentric 35 keyed to the shaft and journalled in the end wall of the shoe. The eccentrics at the opposite ends of the shoe are, of course, coaxial and being keyed to the cross shaft it follows that by rotation of the shaft the axis about which the shoe rocks can be raised and lowered between limits determined by the throw of the eccentrics. The need for such vertical adjustment of the axis about which the shoe 24 rocks arises from the variations in the level of the lowermost surface of the abrasive belt occasioned by differences in grit size. Rotation can be imparted to the shaft 27 to effect this adjustment by means of a wrench applied to the head of a cap screw 36 that is threaded into one end of the shaft, or, if desired, a handle could be fixed to the shaft.

Since the shaft 27 on which the out-feed shoe is rockably mounted does not have to turn, it is fixed with respect to the mounting brackets 28 by which it is supported. The cross shaft 27, however, must turn both with respect to the mounting brackets and the shoe. Axial displacement of this shaft is precluded by collars 37 (only one being shown) clamped to the shaft just inside the end walls 29 of the shoe. This secures the shaft against shifting axially with respect to the shoe, and the confinement of the shoe between the two mounting brackets (one at each side of the machine) completes the securement of the shaft against endwise movement.

Another collar 38 on the extreme end of the shaft into which the cap screw 36 is threaded provides for securing the shaft in a selected position of rotary adjustment. For this purpose, the collar is keyed to the supporting bracket 28, as at 39, and is releasably clamped to the shaft.

Since the out-feed pressure shoe 25 engages the workpiece surface after it has been abraded, so that the elevation of that surface is fairly uniform, it is entirely satisfactory to use a compression spring 40 one at each end of the shoe to impart force to the shoe in the direction to press its toe portion against the workpiece.

As explained hereinbefore, the inevitable variations in the cross-sectional dimensions of nominally the same size rough lumber results in corresponding variations in the elevation of the top surface of the workpieces moving through the machine. To accommodate those varying conditions, the in-feed pressure shoe 24 must be capable of up and down motion. While the prior art use of springs to force the in-feed shoe down onto the workpiece did not preclude such up and down motion, it often resulted in the exceptionally severe friction loads referred to hereinbefore, which sometimes were so great that they stalled the conveyor drive motor. To prevent this from happening, a higher horsepower motor was used. This, of course, entailed a significant increase in the cost of the machine, not only because the motor was more expensive, but also because the transmission system had to be capable of handling the increased loads.

This invention eliminates these objectionable consequences of blindly following the deeply entrenched prior practice of using spring force to hold both pressure shoes down, by employing regulated fluid pressure to hold the in feed shoe down onto the workpiece. Specifically, an air pressure cylinder 41 is mounted at each end of the in-feed shoe by being secured to a bracket 42 that is welded to the inner face of the adjacent frame'carried mounting bracket 28. These air cylinders are preferably of the conventional diaphragm type, having a plunger 43 connected to and projecting from one side of a diaphragm 44 to be forced outwardly of the cylinder by air pressure manifested at the opposite side of the diaphragm.

The outer end of the plunger 43 bears against an upwardly projecting arm 45 on the pressure shoe 24, and to accommodate arcuate motion of this arm, the plunger applies its thrust to the arm through a swivel connection 46.

Uniformity in the pressure applied to the workpiece by the in-feed shoe 24, regardless of variations in thickness of the workpiece, is assured by the incorporation of a pressure regulator valve 47 in the air pressure line leading to the cylinder. As will be understood, this valve maintains the pressure in the cylinder at the selected value throughout the full range of diaphragm motion that accompanies the rocking movement of the pressure shoe. Hence, no matter what the distance might be between the underside of the toe of the shoe and the platen-supported conveyor belt, the load on the drive motor remains the same.

An adjustable stop 48 limits downward rocking movement of the toe portion of the pressure shoe. This stop consists simply of the head of a bolt that passes freely through a hole in the bracket 42 and is threaded into the upper portion of the shoe. Lock nuts on the bolt secure it against loss of adjustment.

As is customary in machines of this type, there are spring urged hold-down idler rolls 50 that maintain the workpieces in firm engagement with the conveyor belt in the conventional way, but a feature of the invention is the utilization of the structure that rockably mounts the two

pressure shoes

24 and 25 to also mount two of the idler rolls namely, those nearest the shoes. Thus, each of these rolls is freely rotatably mounted on a cross shaft 52, the ends of which are secured to and connect a pair of arms 53 that are located beyond the ends of the rolls. These arms are pivotally mounted on the cross shafts that rockably mount the pressure shoes and project beyond the back sides of the shoes. At the free ends of the arms 53 there are extensions 54 into which bolts 55 are threaded to project upwardly therefrom and have their headed ends pass through holes in horizontal ledges 56 that are welded to the mounting brackets 28 and to the adjacent brackets 42.

Compression springs 57 encircling the bolts 55 are confined between the underside of the ledges 56 and nuts 58 threaded onto the bolts, to yieldingly maintain the idler rolls at a predetermined level tangent to the plane containing the underside of the toe portions of the pressure shoes when no workpiece is present.

Although the drawings show only the structure at one side of the machine, it will no doubt be understood that the illustrated structure is essentially duplicated at the other side of the machine.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

1. A wide abrasive belt lumber planing machine having a frame, a contact drum rotatably mounted in the frame, a conveyor belt that has a horizontally extending Working stretch which is solidly supported by frame carried means including a platen beneath the contact drum, and by which workpieces are carried under the drum to be abraded by an orbitally moving abrasive belt trained around it, and power drive means for the conveyor belt, said machine also having a pressure shoe near the contact drum, a portion of which engages workpieces to confine them tightly against the conveyor belt directly before they are engaged by the abrasive belt, said machine being characterized by:

A. means mounting the pressure shoe on the machine frame for rocking movement about a horizontal axis transverse to the direction workpieces are carried through the machine by said conveyor belt, whereby the workpiece engaging portion of the shoe can move arcuately up and down;

B. pneumatic force-applying means fixedly mounted on the machine frame at a level above the pressure shoe and having a plunger which is movable substantially horizontally;

C. a rigid arm projecting upwardly from the pressure shoe and constrained to rock therewith, said arm having a pad which is engaged by said plunger whereby the plunger transmits to the pressure shoe the force which is applied by the pneumatic force-applying means; and

D. means including a pressure regulating valve for supplying compressed air to said pneumatic forceapplying means in such manner that the force produced thereby remains substantially constant.

2. A wide abrasive belt lumber planing machine having a frame, a contact drum rotatably mounted in the frame, a conveyor belt that has a horizontally extending working stretch which is solidly supported by frame carried means including a platen beneath the contact drum, and by which workpieces are carried under the drum to be abraded by an orbitally moving abrasive belt trained around it, and power drive means for the conveyor belt,

said machine also having a pressure shoe near the contact drum, a portion of which engages workpieces to confine them tightly against the conveyor belt directly before they are engaged by the abrasive belt,

said machine being characterized by: A. means mounting the pressure shoe on the machine frame for rocking movement about a horizontal axis transverse to the direction workpieces are carried through the machine by the conveyor belt, with the work engaging portion thereof spaced from said horizontal axis and located closely adjacent to the lowermost portion of the contact drum to move arcuately up and down and hold a workpiece down on the conveyor belt; and B. pneumatic biasing means acting on the pressure shoe in a direction to urge its workpiece engaging portion downward towards the conveyor belt with a yielding force that remains constant irrespective of the distance between said portion of the shoe and the conveyor belt, said pneumatic biasing means comprising v 7' V I. an air cylinder mounted on a fixed part of the machine at an elevation above that of said horizontal axis with the axis of the cylinder substantially horizontal, the air cylinder having a plunger which is projected axially from the cylinder by air pressure therein,

2. an arm fixed with respect to the pressure shoe and projecting upwardly from said horizontal axis about which the pressure shoe rocks,

said plunger bearing against said arm whereby pressure in the pneumatic cylinder forces the work engaging portion of the pressure shoe downward; and

C. a pressure regulating valve through which air under pressure is supplied to the air cylinder.

3. The machine of claim 2, wherein said means that rockably mounts the pressure shoe on the machine frame includes a shaft extending across the machine with its end portions journalled in bearings in the machine frame, and on which the pressure shoe is rockably supported,

and further characterized by:

A. a hold-down roll to hold workpieces down on the conveyor belt as they approach the pressure shoe;

B. a pair of arms rockably mounted on said shaft and projecting substantially horizontally therefrom and upstream of the work advancing travel of the conveyor belt,

said pair of arms having the hold-down roll journalled therein; and

C. biasing means reacting between each of said pair of arms and the machine frame to yieldingly force the hold-down roll downward.

7' 4. The machine of claim 1, further characterized by: lost motion connection means connected between said rigid arm and a part fixed with respect to the frame of the machine for defining a limit of downward motion of the workpiece engaging portion of the pressure shoe.

5. The machine of claim 1, further characterized by:

said means for rockably mounting the pressure shoe including an eccentric, rotation of which provides for up and down adjustment of the axis about which the pressure shoe rocks.

6. The machine of claim 5, wherein:

A. said means for rockably mounting the pressure shoe comprises a cross shaft supported at its opposite ends from fixed parts of the machine, and having the shoe rotatably mounted thereon with its workpiece engaging portion spaced horizontally in one direction from the cross shaft; and further characterized by:

B. a pair of roll carrying arms also mounted on said cross shaft for swinging motion about the shaft and for bodily up and down adjusting motion, said roll carrying arms extending horizontaly from the shaft in the direction away from the workpiece engaging portion of the shoe;

C. a roll freely rotatably mounted on the free end portion of said arms for bodily up and down movement with swinging motion of said arms;

D. spring means reacting between the roll carrying arms and the machine frame to bias the roll carrying arms downwardly; and

E. motion limiting means connected between the machine frame and the said arms for maintaining said roll at not less than a predetermined distance above the platen.

Claims

1. A wide abrasive belt lumber planing machine having a frame, a contact drum rotatably mounted in the frame, a conveyor belt that has a horizontally extending working stretch which is solidly supported by frame carried means including a platen beneath the contact drum, and by which workpieces are carried under the drum to be abraded by an orbitally moving abrasive belt trained around it, and power drive means for the conveyor belt, said machine also having a pressure shoe near the contact drum, a portion of which engages workpieces to confine them tightly against the conveyor belt directly before they are engaged by the abrasive belt, said machine being characterized by: A. means mounting the pressure shoe on the machine frame for rocking movement about a horizontal axis transverse to the direction workpieces are carried through the machine by said conveyor belt, whereby the workpiece engaging portion of the shoe can move arcuately up and down; B. pneumatic force-applying means fixedly mounted on the machine frame at a level above the pressure shoe and having a plunger which is movable substantially horizontally; C. a rigid arm projecting upwardly from the pressure shoe and constrained to rock therewith, said arm having a pad which is engaged by said plunger whereby the plunger transmits to the pressure shoe the force which is applied by the pneumatic force-applying means; and D. means including a pressure regulating valve for supplying compressed air to said pneumatic force-applying means in such manner that the force produced thereby remains substantially constant.

2. A wide abrasive belt lumber planing machine having a frame, a contact drum rotatably mounted in the frame, a conveyor belt that has a horizontally extending working stretch which is solidly supported by frame carried means including a platen beneath the contact drum, and by which workpieces are carried under the drum to be abraded by an orbitally moving abrasive belt trained around it, and power drive means for the conveyor belt, said machine also having a pressure shoe near the contact drum, a portion of which engages workpieces to confine them tightly against the conveyor belt directly before they are engaged by the abrasive belt, said machine being characterized by: A. means mounting the pressure shoe on the machine frame for rocking movement about a horizontal axis transverse to the direction workpieces are carried through the machine by the conveyor belt, with the work engaging portion thereof spaced from said horizontal axis and located closely adjacent to the lowermost portion of the contact drum to move arcuately up and down and hold a workpiece down on the conveyor belt; and B. pneumatic biasing means acting on the pressure shoe in a direCtion to urge its workpiece engaging portion downward towards the conveyor belt with a yielding force that remains constant irrespective of the distance between said portion of the shoe and the conveyor belt, said pneumatic biasing means comprising

2. an arm fixed with respect to the pressure shoe and projecting upwardly from said horizontal axis about which the pressure shoe rocks, said plunger bearing against said arm whereby pressure in the pneumatic cylinder forces the work engaging portion of the pressure shoe downward; and C. a pressure regulating valve through which air under pressure is supplied to the air cylinder.

3. The machine of claim 2, wherein said means that rockably mounts the pressure shoe on the machine frame includes a shaft extending across the machine with its end portions journalled in bearings in the machine frame, and on which the pressure shoe is rockably supported, and further characterized by: A. a hold-down roll to hold workpieces down on the conveyor belt as they approach the pressure shoe; B. a pair of arms rockably mounted on said shaft and projecting substantially horizontally therefrom and upstream of the work advancing travel of the conveyor belt, said pair of arms having the hold-down roll journalled therein; and C. biasing means reacting between each of said pair of arms and the machine frame to yieldingly force the hold-down roll downward.

4. The machine of claim 1, further characterized by: lost motion connection means connected between said rigid arm and a part fixed with respect to the frame of the machine for defining a limit of downward motion of the workpiece engaging portion of the pressure shoe.

5. The machine of claim 1, further characterized by: said means for rockably mounting the pressure shoe including an eccentric, rotation of which provides for up and down adjustment of the axis about which the pressure shoe rocks.

6. The machine of claim 5, wherein: A. said means for rockably mounting the pressure shoe comprises a cross shaft supported at its opposite ends from fixed parts of the machine, and having the shoe rotatably mounted thereon with its workpiece engaging portion spaced horizontally in one direction from the cross shaft; and further characterized by: B. a pair of roll carrying arms also mounted on said cross shaft for swinging motion about the shaft and for bodily up and down adjusting motion, said roll carrying arms extending horizontaly from the shaft in the direction away from the workpiece engaging portion of the shoe; C. a roll freely rotatably mounted on the free end portion of said arms for bodily up and down movement with swinging motion of said arms; D. spring means reacting between the roll carrying arms and the machine frame to bias the roll carrying arms downwardly; and E. motion limiting means connected between the machine frame and the said arms for maintaining said roll at not less than a predetermined distance above the platen.