US2635396A - Portable rubbing machine - Google Patents

Description

April 2 1953 H. R. JOHNSON 2,635,396

PORTABLE RUBBING MACHINE Filed June 2, 1949 4 Sheets-Sheet l April 21, 1953 H. R. JOHNSON PORTABLE RUBBING MACHINE 4 Sheets-Sheet 2 Filed June 2,' 1949 www www uw mwN @N QW/df j? NNN Apri! 2L 1953 H. R. JOHNSON 2,635,396

PORTABLE RUBBING MACHINE Filed June 2, 1949 4 sheets-sheet 5 PI 21, 1953 H. R. JOHNSON 2,635,396

PORTABLE RUBBING MACHINE Filed June 2, y 1949 4 Sheets-Sheet 4 86 ZZ .7 l ./@3 Q7 Z9 @5 f77 175 ll JZ@ J70 Y 69 .1 -v i 1741 @a i. 12637 f 1 l s" /13 z? jge| l gz 73 l /1/2 70 L 1 72? mi 175 53 'w l 167 //////,//7,W//,/ d l" I *l a 156 a 7 172 Z? j! rif. I i

154/ fw' i fa Patented Apr. 21, 1953 PORTABLE RUBBING MACHINE Harold R. Johnson, Rockford, Ill., assignor, by

mesne assignments, to The Porter-Cable Machine Company, Syracuse, N. Y., a corporation of New York Application June 2, 1949, Serial No. 96,671

1 Claim. 1

l This invention relates to portable rubbing machines, and more particularly to such machines which are operated by fluid under pressure and adapted to manual manipulation for sanding, polishing and the like.

One of the objects of my invention is to provide a portable uid operated rubbing machine wherein the actuating parts are built into the body of the machine, and wherein tubes are cast into the body to provide fluid passages, thereby avoiding the necessity of a sizable number of relatively diicult and costly drilling operations.

As another object, my invention has within its purview the provision of a fluid operated rubbing machine having an actuating mechanism built into the body of the machine and so constructed and arranged that the machine body serves as an exhaust muilier.

My invention has for another object the provision of a piston actuated, uid operated rubbing machine in which the piston movements and energy are transferred directly to the rubbing surface.

It is a further object of the invention to provide a fluid operated rubbing machine embodying a valve having relatively few parts of rugged construction and which is mounted for ready and convenient access.

I have further provided, in the disclosed rubbing machine, a manually operable actuating element for controlling the operation f the machine, which actuating element is normally biased to a position such that the machine is shut off, and which is disposed and contoured relative to the portion of the machine normally gripped in use so that normal gripping pressures effect control of the machine operation with negligible conscious effort and no appreciable discomfort.

The structure of my rubbing machine adapts it to both wet and dry rubbing operations and is such that the liquid for wet rubbing operations is fed through the body of the machine and discharged at an eiective position relative to the rubbing surfaces by an attached jet, and in addition to which, the flow of liquid, as well as the operation of the machine may be controlled by a control member on the machine body.

It is further within the purview of this invention to provide relatively inexpensive, but effective and quickly operable clips for holding rubbing surface material in place on the rubbing shoes of my rubbing machine.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings in which similar characters of reference indicate similar parts throughout the several views.

Referring to the four sheets of drawings,

Fig. 1 is a perspective view taken from one end and to one side of a portable rubbing machine embodying a preferred form of this invention;

Figs. 2 and 3 are fragmentary end elevational views of a portion of the structure illustrated in Fig. 1 and wherein dierent positions of movable parts are illustrated;

Fig. 4 is a top plan view of the structure shown in Fig. 2;

Fig. 5 is a general and substantially central side sectional view of the portable rubbing machine illustrated in Fig. 1;

Fig. 6 is a fragmentary end View with a portion cut away and taken substantially at the position indicated by a line 6--6 in Fig. 5 when viewed as indicated by accompanying arrows;

Fig. 7 is a fragmentary side elevational view of a portion of the structure shown in Fig. 5 and wherein a part is cut away to illustrate certain details of internal structure;

Fig. 8 is an end elevational view taken substantially as indicated by a line 8 8 in Fig. '7 and accompanying arrows;

Fig. 9 is a sectional view taken substantially on a line 9 9 of Fig. 5 and viewed in the direction indicated by the arrows;

Fig. 10 is a sectional view taken substantially on a line l0-l0 of Fig. 5 and in the direction indicated by arrows;

Fig. 11 is a fragmentary, perspective, exploded view depicting certain preferred forms of parts and indicating their preferred order and arrangement in assembly for use in my portable rubbing machine;

Fig. 12 is a bottom plan View taken substantially at the position indicated by a line I2-I2 in Fig. 5 and in the direction of the accompany'- ing arrows; and

Figs. 13 and 14 are fragmentary top sectional views depicting different operating positions of parts of the structure which are illustrated in Fig. 11.

In general, the exemplary embodiment of my portable rubbing machine, which is shown in the accompanying drawings for illustrative purposes, includes a body 20 exteriorly contoured with smooth and rounded curves and with side indentations such as 22, so that the body, in addition to other purposes, serves as a hand grip by which the machine is manipulated in use.

At one end of the top of the body, an actuator 23 is movably mounted in recess 24 for controlling the operation of the machine. By preference, this actuator is nearly flush with the adjoining surfaces of the body and conforms generally to the body contours, so that it is not only accessible for operation by a convenient gripping action, but also so that its projection beyond the body surface is insuicient to cause damage to internal and associated parts in case the machine is dropped. The disclosed machine is adapted to operation by air under pressure, and is suited to either wet or dry rubbing operations. The body serves as a block or stationary part of an air operated motor including reciprocatingI parts to which rubbing shoes 25 and 26 are attached; the rubbing shoes 25 and 26 being normally in spaced relationship to one another and preferably driven in opposed cycles of reciprocating movements. A liquid jet 21 is secured to one side of the body and extends between theA rubbing shoes for applying liquid to the surface of the workpiece during wetrubbing operations.

The rubbing shoes 25 and 26 are alike in their structure, so that a description of one will suice for both. Each embodies a shoe plate 28 of generally rectangular shape and has a substantially plane bottom surface 29 to which a pad 30 of' a relatively soft material, such as rubber or felt, is secured for most rubbing operations. Sheet material 32, such as sand paper, is removably applied to the rubbing shoes, so that it covers the exposedk face of the pad and extends upwardly over the exposed opposite ends of4 theV rubbing shoes, as shown in Fig. 1. At thoseexposed opposite ends of each of the rubbing shoes, manually releasable clips 33 are utilized to secure the sheet material to the rubbing shoes.

As depicted in Figs. l to 4 inclusive, my preferred clip structure includes a block 34 and is secured to or integrally formed upon the top surface of the rubbing shoe plate. 'I'his block presents an end gripping surface 35 facing toward the adjacent end of the shoe plate and is preferably disposed in acute angular relationship to the top surface of the shoe plate. Also, the block is preferably disposed at a position such that the gripping surface 35 thereofis displaced inwardly from the adjacent end surface of the shoe plate. At a position spaced from the gripping surface 35, the block has a bearing bore 36 therein, the axis of which is substantially parallel to the gripping surface 35. A link 31 of elongated and generally rectangular shape has one side supported forV limited rotational movement in the bearing bore 36 of the block. The opposite side of the link is movably engaged by loops 38 and 39'Which are integrally formed at opposite ends of a substantially C-shaped clip element 40, which clip element is preferably made of formed sheet metal possessing some resilience.

A tab 42 is integrally formed on the clip element and projects upwardly from a position between the loops 38 and 39 to provide a handle for actuating the clip between the closed and open positions depicted in Figs. 2 and 3 respectively. The block, link and clip element are so disposed and proportioned that a gripping edge 43 of the clip element firmly and tightly engages a marginal portion of the sheet material when the link is swung to a position away from the gripping surface 35 of theblock and adjacent the top face ofthe shoe plate 28, whereby the sheet material is grippedebetween the gripping edge 43 and gripping surface35, as shown in Fig; 2. By swinging 4 the link upwardly with the aid of the tab 42, as shown in Fig. 3, the sheet material is quickly released. It may be noted that as the clip element moves toward its gripping position, it tends to draw the sheet material tautly across the face of the rubbing shoe pad 3U.

Referring more particularly to Figs. 5 to 10 inclusive, of the drawings, the body 2U of my portable rubbing machine is a block-like cast metal structure which is designed not only for neat and streamlined appearance and convenience in use, but also with a view to minimizing weight and materially lessening necessary machining operations such as drilling. A main block 44 has a longitudinal bore 45 extending therethrough from a plane end surface 46 to an opposed plane end surface41. At the ends of the longitudinal bore` 45, cylinder liners 48 and 49, in the form of cylindrical shells, are pressed into the bore to define coaxial cylinders 50 and 52. Internal cavities 53 and 54 in the main block 44. encompass top and side portions of the cylinder liners 48 and' 49 respectively to limit the weight of the body, aswell as to afford longitudinal balance; the cavity' 53 being larger than the cavity 54, whichV latter cavity is adjacent the recess 24 at one end of the block.

At the mid-portions of each of the cylinder lin-- ers 48 and 49, and at whatl is normally the bottomside of the machine, longitudinally elongated slots 55 and 56 extend through the cylindery liners.

Aligned with those slots, and alsov aligned longitudinally of the body, slots 51v and 58- extend through a bottom wall 59v of the main block. As depicted in Fig. 9, a passage 60 in the ymain blocky valve cavity having a substantially cylindrical' lower portion 63 and a threaded upper portionY 64. Coaxially with the valve cavity, a bearing bore 65 extends through the body in a direction lateral to the axis of the longitudinal bore 45. A sleeve bearing 66 is mounted in the former bore and extends across the mid-portion ofthev longitudinal bore between the cylinder linersv48 and 49.

In order to minimize drilling operations inthe main block and particularly in the instanceV of' longer passages and those having angularly1dls posed portions which would complicate the drilling of such passages, the disclosed structurer includes metal tubes which are positioned in the mold for the block, so that those tubes are cast' As depicted. in:

into the block when it is made. Figs. 6, '1 and 8, a tube 61 is cast into the main block to provide an air flow passage extendingfrom one side of the plane end surface 41 to-the cylindrical lower portion 63.of the valve cavity. Another tube 6B extends from the plane end surface 41 of the block to the mid-portion of one sideof the block near the bottom thereof toprovide a. passage for the ow of liquidutilized infwet rub-A bing operations. As shown'in Figs. 7,18 and 9, a third tube G9 extends from one end surface of the main block to the other in substantiallyI parallel relationship to the main bore 45. A drilled passage 10 provides communication for the ow of air from the lower surface of the valve cavity to the tube 69. Another drilled passage 1-2 extends from the lower surface of the valvecavityY to main bore 45 at the mid-portion of that main bore. Still another drilled passage 13 which commumcates with the` valve cavity, asshown in Fig.

5, adjoins an angularly disposed passage 14 'to provide communication between the valve cavity and the internal cavity 53 in the main block.

Pistons 15 and 16 are mounted for reciprocating movement and in opposed relationship in the cylinder bores 50 and 52 provided by the cylinder liners 48 and 49 at the opposite ends of the longitudinal bore 45. Piston rings 11 and 18 at opposite ends of each o the pistons, and mounted in ring grooves, serve to prevent leakage of air under pressure around the respective pistons. In order to minimize the vibration effected by rapid reciprooation of the pistons within the cylinder bores, as well as to improve mechanical efficiency and limit the overall weight of the machine, I prefer to use pistons of like structure having hollow end portions 19 and 80 which are closed at opposite ends of the pistons by metal disks 82 and 83 pressed into annular recesses B4 and 85 at the opposite ends of the respective pistons. The lengths and strokes of the pistons are s related to the lengths of the slots 55 and 56 in the cylinder liners that the pistons cover those slots at all points of their respective travel strokes. Midway between their respective ends, partitions 86, of substantial thickness, extend laterally across the pistons between their hollow end portions. These partitions have lateral bores 81 therethrough which are adapted to receive end portions of driving posts 88 and 89 with a running t; those driving posts preferably being secured in place with respect to the pistons by pins 90 and 92 extending through the posts and longitudinally of the piston partitions. The driving posts 83 and 89 extend outwardly of the main block through the slots 55 and 56 in the cylinder liners and through the aligned slots 51 and 58 in the block. At their exposed ends, the driving posts, in the disclosed structure, have slide receiving shank portions 93 and 94, as well as shoe supporting feet 95 and 95 integrally formed thereon.

Although the opposed cylinder bores for the respective pistons could be completely segregated from one another1 by a partition with separate air openings and valve ports to provide for the flow of air to and from the spaces at the ends of the two pistons, the valve structure is simplied and the number of required passages and ports minimized by eliminating such partition as in the disclosed structure, so that the air for operation is fed between and exhausted from the space between the opposed ends of the two pistons. It being my preference that the pistons shall move vthrough opposed cycles during operation, it may be readily understood that the introduction of 4air under pressure between thc opposed ends of the pistons effects their outward movements in opposite directions. At the opposite ends of the main block, the cylinder bores are closed by end caps S1 and 98. As shown in Fig. 7, the end caps 91 and 98 have channels 99 and |00 in their inner faces for providing communication between .the opposite ends of the tube 69 and the outer ends of the cylinder bores, whereby air under pressure fed through the tube 69 effects opposed and inward movement of the pistons, while outward movement of the pistons exhausts the air through that same tube.

As shown in Figs. 5 and 6, the end cap 98 of the disclosed structure has adjacent and substantially parallel valve ports |02 and |03 extending inwardly from a top recess |04 which forms a continuation of the recess 24 in the block.

The bottom of each recess communicates with a lateral bore,` such as I 05, extending to the' outside of the end cap and adapted to receive a threaded fitting such as |06 on a hose line or the like. Valve seats |01 and |08 are mounted within the ports |02 and |03 and are held in place therein by screw plugs |09 and ||0. Movable valve elements ||2 and ||3 are carried by the valve seats |01 and |08 and are biased by springs ||4 and |I5 to position such that they normally close passages IIB and ||1 in the valve seats. The valve seat |01 has a passage ||8 therein which communicates with the end 0f the tube 61, so that the valve is adapted to control the ilow of air therethrough to the valve cavity 62. Likewise, the valve seat |08 has a passage ||9 therein which communicates with one end of the tube 68 to control the ow of liquid through that tube during wet rubbing operations. Stems |20 and |22 extend from the movable Valve elements |2 and I3 through the screw plugs |09 and |'|0 and plroject into the recess |04 in adjacent relations 1p.

Although separate actuating members might be provided for eiecting manual control of the movable valve elements ||2 and ||3, I prefer to actuate both valves by the single actuator 23, so that the flow of liquid for wet rubbing operating is controlled simultaneously with the control of the air which effects operation of the rubing machine. The actuator 23, in the disclosed structure, comprises a shell having an exposed wall |23 which conforms to the general contour of the body, and side walls |24 which extend into the aligned recesses 24 and |04 in the block and end cap. A leaf |25 secured to the lower surfaces of the side walls |24 of the actuator hasacurved portion |26 at one end which engages a cross pin |21 at the inner end of the recess, so as to support the actuator for limited rocking movement within the recess. At the end of the leaf opposite the pin |21, that leaf engages the projecting ends of the stems |20 and |22. Intermediate the ends of the actuator, aligned slots |28 are provided in the side walls, which slots engage inwardly projecting studs |29 on opposite sides of the recess to guide the actuator and limit the outward movement thereof.v It may be observed that the valve springs ||4 and ||5, in addition to biasing the movable valve elements to their closed positions, normally bias the actuator to a position projecting outwardly somewhat from the walls of the body. Thus, inward movement of the actuator by the manual operation Aof pressure thereto opens both the air and liquid valves.

Externally of the body, the bottom wall 59 preferably presents a substantially plane surface |30. As illustrated in Figs. 5, 9, 10 and l2, that bottom wall 59 of the body is provided with grooves |32 and |33 which are equally spaced on opposite sides of the slots 51 and 58 and extend longitudinally of the body in substantially parallel relationship to the axis of the longitudinal bore 45. In the present instance, these grooves are arcuate in shape and are of a depth substantially less than a semi-circle. They carry slide bars |34 and |35 of circular section which are secured in place by end cross clamping strips |36 and |31 held in place by fastening means, such as screws |38. As shown in Figs. 5, 9, 10, 11 and l2, a slide |39 has parallel and arcuate grooves |42 and |43 therein which are adapted to fit for sliding movement at one end of the slide bars |34 and |35. Likewise, a slide |40 has parallel and arcuate grooves |44 and |45 therein which are adapted to` fit for sliding movement at the other ends of: the slide bars |34VV and |35. In the assembly; as depicted in Figs. and 9, openings |46 and |.41 in the slides fit onto the shank portions 93' and 94.V of the drive posts 88 and 891 and are secured inplace against the feet 95v and 96 on those. postsxby fasteningy means, such as screws. |48.

Substantially.: parallel. arms |49V and |5|l-` pro.- jectfromadjacent ends of the slides |39 and |.40,.respectively. and are normally disposed with their., end: portions in. adjacent andl side-by-side relationship. At their adjacentendsand inopposed relationship, thev arms: |49. and` |50 have lateral channels |52'and |53 therein, which'chan.- nels carry slide; blocks |518l and |55 for sliding movement in a= direction lateral to the sliding movementsofftheslides |,39 and |49. An oscillator shaft |56 is journalled in the sleeve bearing 66. AtV one end, thisoscillator shaft has a cross head |51 drivingly secured thereto, While the other end thereof extends into the valve cavity 6.2; At its opposite ends, the. cross head |51 has studs |58 and |59 projecting therefrom and extending into bearing bores |66 and |62 in the slide blocks |54 and |55 respectively. As depicted in Figs. and 12, the slide bars |313 and |35 have arcuate notches |63 and. |64 at their mid-portions,l that they clear the opposite ends' of" thecross head- |51. posts 88 and 89u are directly secured to the pistons -.and 16, reciprocating movement of those pistons. producessimilar reciprocating movements oftheslidesv |39 and |49. The arms |46 and |58 move with the-slide and in opposed directions to effect: oscillatory rotational movements'of the crosshead |51 and oscillator shaft |56; it being understoodA that the slide blocks |54 and |55 provide compensation between the linear movements of the armsl |49. and |58 and the ary cuate movements of the studs I 60v and |62 which are carried by cross head |51.

In addition to servingas guides for the movements of the rubbing shoes, the slides E39 and |48 act through the arms |49 and |50 to effect oscillating rotational movements of the oscillator shaft |56, the function of which shaft is to drive an. operating valve |65:which is disposed in the valvel cavity 62 for controlling the flow of air to and from the cylinder bores at opposite ends of the pistons in timed relationship to the piston movements. As shown in Figs. 1l, 13and 14, the'valve cavity 62 has a planeY bottom surface |614 throughv which the passages-10, 12 and 13 pass in' spaced relationship to one another. In the disclosed structure, the passages 10, 12 and 13 are concentrically disposed and are spaced at positions substantially 90 apart with respect to the axis of the oscillator shaft |56. In spaced relationship with respect to those openings, a pin |68 is mounted in an opening in the main block and projects into. the valve recess at a position spaced from the oscillator shaft.

In order to prevent wear on a portion of the block itself and so as to provide a replaceable and hardened wearing element, astationary valve plate |69 is mounted in the valve cavity against the plane bottom surface |61; that stationary valve plate having an opening |10 therein which fits snugly upon the pin |68 to hold it stationary. In alignment with the passages 19 and 12, the stationary valve plate has ports |12 and |13 extending axially therethrough, which ports preferably have straightl side edges to improve their closing and opening actions. At the center, the stationary valve plate has an opening |14 through Since the driving l...

8. which the oscillator shaft |56 extends. Between the ports |12 and |13 and in communica'.- tion with the passage 13, the stationary plate has an arcuate slot |15v therein.

A valve rotor |16 has a central opening |11 therein through which the oscillator shaft |56 extends for free rotational movement relative thereto. This valve rotor embodies an arcuate, channel |18 in its lower surface which is adapted to provide communication between the arcuate slot |15 and one or the other of the ports |12 or |13 in the stationary valve plate |69. The channel |18 does not extend through the movable valve rotor, because its primary purpose is to provide communication to the exhaust passage 13 through which air is released from one end of each of the pistons, while air under pressure isV fed to the other end thereof. On the other hand, notches |19 and |88 are provided at spaced positions separated from the ends of the channel |18 to control the flow of air to one or theV other of the ports 12 or |13. In respect to the use of the channel for controlling the now of air to the exhaust passage, as contrasted with the use of notches in the movable Valve plate for controlling the flow of air to the inlet ports, it is to be recalled that the valve cavity, during operation7 contains air under pressure which isk fed thereto through the tube 61. The two extreme positions of the movable valve plate are illustrated in Figs. 13 and 14. In Fig. 13, air under pressure from the passage provided by the tube 61 is being supplied to the outer ends of the cylinders through the passage 1D, while air is being exhausted from betweenA the pistons through the passage 'i2 and the passage 13. In the position shown in Fig. 14, the exhaust is from the ends of the cylinders, While the input of air under pressure is directed to the space between the pistons.

In connection with the exhausted air, it may be observedl that such air owing outwardly through the passage 13 in the valve cavity and passage 14, as depicted in Figs. 5 and 9, flows into the cavity 53 in the body. From that cavity, as shown in Fig. 9, it flows through the passage 60 into the slot 51, from which it escapes from the lower portion of the machine around the slides and adjacentthe shoes. Thus, the. body serves as a muffler for quieting the operation of the machine.

As has been explained, the oscillator shaft |56 is driven in timed relationship to the movements of the pistons. As shown in Figs. 5 and 11, the oscillator shaft has a notched end- |82 presenting-a flat driving surface within the valve cavity. This notched end fits into a correspondingly shaped opening |83 in a valve actuating cam |64. In the assembly of the valve, the movable valve plate |16 rests upon the stationary valve plate |59 and the valve camis disposed against the movable valve plate |16 while en gaging the notched end |82 of the oscillator shaft. Also, the movable valve plate 16 has a stud |85 projecting upwardly from the top surface thereof between the notches 19 and |80, which stud is disposed in a slot |86 in the cam |84. With this combination of structure, the movable valve part is driven in timed relationship to the piston movements and thereby effects an efficient and effective alternation of the iiow of pressure and exhaust air to and from the cylinders at opposite ends of the pistons, so as to produce reciprocating movements of the pistons in opposed cycles. In order to hold the valve parts inV their assembled relationship, as

shown in Fig. 5, as Well as for sealing the valve cavity, a valve cap |8| is threaded into the upper portion 64 of the valve cavity. A compression spring 19| is disposed between the valve cap |8| and the cam |84 in a recess 29| in that valve cap, whereby to urge the valve parts into rm engagement. The valve structure is readily disassembled by removal of the cap Iii, so that the spring and valve parts are readily accessible.

As shown in Figs. 5, 9 and 10, it is my preference to provide an apron |87 having side flanges |88 which t over lower marginal portions of the machine body, as well as a face portion |89 which covers the slides and has openings |90 and |92 therein for passage of the feet 95 and 96 therethrough. Pads |93, |94 and |95 of felt or the like are interposed between the face portion of the apron and the lower faces of the slides and arms. These pads, in addition to controlling the outward ow of exhaust air during operation of the machine, serve to prevent dust and dirt from getting into the operating parts of the machine.

In addition to the previously described shoe plates 28 and pads 30, each of the shoes 25 and 26 has a top plate |98 secured thereto by fastening means, such as rivets |91, as shown in Fig. 5. A shoe supporting stud |98 having a head portion |99 is held in place and extends upwardly from each of the shoes to serve as a mounting element for securing the shoes to the feet 95 and 96. A notch 200 is provided in one side of each of the studs. Also, the feet 95 and 96 have axial openings 202 therein which snugly nt the projecting studs. For securing the rubbing shoes in place, a set screw 203 is threaded into an outside end of each of the slides and has a tapered end adapted to engage the notch 200 in the stud to draw that stud inwardly as the screw is tightened. Aligned openings 204 and 205 in the apron and clamping straps provide access to the ends of the set screws for effecting the removal and installation of the shoes relative to the machine.

While I have illustrated a preferred embodiment of my invention, many modications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claim.

Having thus described by invention, what l claim as new and desire to secure by Letters Patent of the United States, is:

A portable rubbing machine adapted to operation by air under pressure and comprising, in combination, a cast body exteriorly contoured to provide a hand grip and having a longitudinal bore extending therethrough, a cylinder liner defining a cylinder and mounted in each end of the longitudinal bore, said body having cavities therein partially encompassing the mid-portions of the cylinder liners, said body and the cylinder liners also having aligned slots therein opening outwardly opposite the cavities and a passage providing communication from one of the cavities to one of the slots, double acting pistons mounted for reciprocating movement in the cylinders and covering the slots in all positions of the pistons, end caps secured to opposite ends of the body for closing the opposite ends of the cylinders, one of said end caps having an air ow passage therethrough and a valve therein for controlling the flow of air through the passage, said body having a valve cavity therein near the mid-portion of the longitudinal bore and normally closed by a removable cap to form a valve chamber, said body having passages therein for the flow of air from the air passage in said one of the end caps to the valve chamber and from the valve chamber to opposite ends of the cylinders, additional passages in the body for the flow of air from the valve chamber to the longitudinal bore at a position between the pistons and from the valve chamber to one of the cavities, a valve in said chamber for effecting air now in alternating sequence to the cylinders at opposite ends of the bore end and to the longitudinal bore between the pistons, the last mentioned valve also controlling the exhaust of air alternately from opposite ends of the cylinders to said one of the cavities, a slide and a rubbing shoe having substantially a direct and straight line connection to each of the pistons for actuation thereby, and means actuated by the slides for moving the last mentioned valve in timed relationship to the movements of the pistons, said last mentioned valve including a stationary plate having a single exhaust port and two inlet ports therein, a valve rotor engaging the stationary plate and having notches and a passage therein proportioned and disposed with respect to the exhaust and inlet ports in the stationary plate so as alternately to connect one of the inlet ports to the exhaust port while alternately exposing the other inlet ports to air under pressure in the valve chamber, a valve cam for actuating the valve rotor, and a shaft connected to the slides for eiecting oscillatory movement of the cam.

HAROLD R. JOHNSON.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,524,902 Anderson Feb. 3, 1925 1,700,115 Thompson Jan. 22, 1929 1,737,135 Windfelt Nov. 26, 1929 1,747,396 Scott Feb. 18, 1930 1,839,118 Plancq Dec. 29, 1931 2,214,189 Ahlskog Sept. 10, 1940 2,251,329 Ekstrom Aug. 5, 1941 2,477,807 Johnson Aug. 2, 1949 2,530,301 Hoy Nov. 14, 1950

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