US2811877A

US2811877A - Pneumatic drill construction

Info

Publication number: US2811877A
Application number: US486495A
Authority: US
Inventors: Degroff William Brooks
Original assignee: Aro Equipment Corp
Current assignee: Aro Equipment Corp
Priority date: 1955-02-07
Filing date: 1955-02-07
Publication date: 1957-11-05
Anticipated expiration: 1974-11-05

Description

Nov. 5, 1957 A w. B. DE GROFF 2,811,877

,A PNEUMATIC DRILL CONSTRUCTION Filed Feb. 7, 1955 v 2 Sheets-Shea?I l vnf /70 f6 INVENTOR: A

ATTORNEYS.

Nov. 5, 1957 w. B. DE- GROFF PNEUMATIC DRILL CONSTRUCTION 2 Sheets-Sheet 2 Filed Feb. 7, 1955 United States Patent Oice 2,811,877 Fatented Nov. 5, 1957 PNEUMATIC DRlLL CONSTRUCTION William Brooks DeGroif, Bryan, Ohio, assignor to Aro Elilpment Corporation, Bryan, Ohio, a corporation o io Application February 7, 1955, Serial No. 486,495

3 Claims. (Cl. 77-33.5)

The present invention relates to a portable automatic drill of the pneumatically operated type.

It is a primary object of this invention to provide an improved drill construction, wherein pneumatic means serve to effect power drive of the drilling tool, and to effect both forward and reverse reciprocation thereof.

lt is another object to provide an air motor driven and air reciprocated drill construction, wherein oil dash-pot and by-pass valve means serve to adjustably regulate the speed of forward drilling movement.

It is a further object to provide oil dash-pot means for a pneumatically operated drill, wherein by-pass port means operatively responsive to the forward position of the drilling tool and variably adjustable closure means limiting the operability of said port means serve to permit initial rapid traverse of said drilling tool for a predetermined distance followed by slow forward movement thereafter, whereby the work may be approached quickly and the actual drilling performed more slowly.

It is still another object to provide auxiliary oil reservoir and valve means serving to automatically replenish the main oil supply of the dash-pot means of an automatic drill, thereby obviating the need for frequent oil replenishment during normal drill operation.

It is still a further object -to provide an automatic drill of the air operated type which is readily adaptable to different stroke length, thereby eliminating the necessity for a range of tools to perform a Variety of working operations.

It is yet another object to provide an automatic drill of the air operated type having a removably detachable arrangement of parts providing interchangeable gearing assemblies to permit a variety of different drill speeds with a single drill by simple interchange of gearing units.

Further objects and advantages of this invention will become apparent as the following description proceeds and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

A preferred embodiment of the invention is shown in the accompanying drawing, in which:

Figure 1 is a side elevational view, partly broken away and in section, showing a portable automatic drill of the air-operated type embodying the features of the present invention;

Figure 2 is a transverse cross-sectional view taken substantially as indicated by the line 2-2 on Figure 1;

Figures 3 and 3A together constitute a longitudinal cross-sectional view of the portable automatic drill of Figures 1 and 2, wherein Figure 3 illustrates the rear portion of the drill and Figure 3A is a continuation thereof illustrating the forward portion of the drill;

Figure 4 is a transverse cross-sectional view taken substantially as indicated by the line 4 4 on Figure 3A.

Figure 5 is a fragmentary view of a portion of combined Figures 3 and 3A,'illustrating the operation of the adjust-V able rapid traverse means.

Referring now more particularly to Figure 1 of the drawing, I have shown a portable pneumatic drill comprising the major structural components of an oil chamber and air motor section 12, an air piston section 14, a control valve section 16, a nose housing 18, and a rear sleeve guard 20.

The oil chamber and air motor section 12 comprises an oil chamber housing 22 and an air motor housing 24, -as best seen in Figures 3 and 3A. The

housings

22 and 24 are co-axially and concentrically aligned in spaced relation to define therebetween the main chamber 26 of an oil dash-pot means.

The air motor housing 24 encloses an air motor assembly indicated generally at 2S. The air motor 28 is of the wellknown type comprising a plurality of vanes 30 carried by a drive shaft 32 mounted for rotation about a longitudinal axis by means of suitable bearing assemblies 34 and 36. The forward end of the drive shaft 32 is splined at 33 for operative connection in readily detachable manner to a gearing assembly indicated generally at 33.

An oil retaining sleeve 40 is disposed outwardly of the air motor housing 24- in surrounding relation thereto, and is screw-threadedly carried by the inner wall portions of the oil chamber housing 22. Suitable O-

ring seals

44 and 46 provide a fixed oil-tight seal and a slidable oiltight seal, respectively.

An oil screw 48 is screw-threadedly received within a tapped hole provi-ding an oil Vent port S6 which extends through the oil chamber housing 22 for communication between the oil chamber 26 and the exterior. A suitable 0-ring seal 52 is provided for oil-tight closure lof the port 50 by the screw 4S.

The forward end of the oil retaining sleeve 40 is screwthreaded at 56 to mountingly receive the nose housing 18 thereon. A wiping seal 58 is provided inwardly of the sleeve 40 for sliding cooperation with the reciprocably movable air motor housing 24, as will hereinafter become apparent.

The splined forward end 33 of the motor drive shaft iixedly carries a drive gear 6b (see Figures 3A and 4), which meshes with a surrounding pair of planet gears 62 and 64. The gears 62 and 64 are rotatably supported by means of suitable needle bearings 66 `on a pair of drive pins 68 and 7i), respectively.

rfhe drive pins

68 and 70 are received within a drive fitting 72 which is rotatably supported by means of bearings '74 within a iixedly positioned sleeve member 76. The sleeve 76 provides stationary gear teeth internally thereof which mesh with the planet gears 62 and 64. An end cap Sil is screw-threaded onto the sleeve member 76 to retain the various parts of the gearing unitin assembled relation. ln this manner, driving rotation of the air motor drive shaft 32 is transmitted to provide driving rotation of the fitting 72 at a predetermined speed.

The forward terminal end of the drive fitting 72 receives thereon a slinger ring 82 which abuts against a thrust ring 84, and is screw-threaded for xedly carrying a drill chuck assembly 86 thereon. A suitable drilling tool carried by the chuck assembly 86 may thereby be driven by the air motor 23.

The rear end of the air motor housing 24 is enlarged in a radially outward manner to provide a dash-pot piston 90 which slidably engages the internal surface of the oil chamber housing 22, and abuts in its rearmost position against an internal shoulder portion 23 of the housing 22. An O-ring seal 92 maintains oil-tight contact between the dash-pot piston 9? and the housing 22, thereby defining the length of the main oil chamber 26 between the oil retaining sleeve 4i) and the dash-pot piston 90. Rearward of the piston 90, the air motor housing 24v terminates in an end collar 94, which is externally screwthreaded. Inwardly thereof, the housing 24 provides a central bore terminating in a screw-threaded recess 96.

The air piston section 14 of the drill extends rearwardly of the oil chamber and air motor section 12, and includes` an air piston inner sleeve 100 which is screwthreaded onto the end collar 94 of the air motor housing 24. A hollow air feed tube 102 is screw-threadedly received within the recess 96, and provides a liow conduit for supplying compressed air from a suitable source of supply, as regulated byV valve control means, to the air motor 28. A pair of O-ring seals 104'are provided between the inner sleeve 166 and the oil chamber housing 22. An air bleed-off passage 106 communicatesrfrom the interface between sleeve 188 and housing 22 to the exterior, thereby permitting trapped air to be bled-olf. An O-ring seal S is also provided at the interface between the air feedtube 102 and the air motor housing 24'..

The. rearward end ofy the air piston section 14.is rigidly coupled to the control valve section 16 which provides a valve head assembly 120. An air piston 122 is slidably carried on the air feed tube 102, and provides an acting face 124 for forward drill feed and an acting face 126 for reverse drill movement. A forwardly extending collar portion 128 of the air piston 122 is externall ly screw-threaded to receive the rear end of the air piston inner sleeve 108. Suitable O-ring seals 130'and 132 are provided for oil-tight engagement at the interfaces between the air piston collar 128 and the air feed tube 102 and inner sleeve 100.

An air piston outer sleeve 134 is screw-threadedly attached at its forward end to the oil chamber housing 22 and at its rearward end to the valve head assembly 120. An O-ring seal 135 is provided at the interface between the relatively movable air piston 122 and the outer sleeve 134 to provide an air-tight seal between a reversing air space 136 and a forward feeding air space 138.

Suitable valve means having both manual and automatic control actuators are provided within the valve head assembly 120 substantially in accordance with the teachings set forth in my co-pending application, Serial No. 476,317, filed December 20, 1954. The details of the air motor valve means and actuators do not form a-part of the present invention and have not been described in detail herein, reference being invited to the aforesaid'copending application for details of construction.

During operation, the valve head assembly 120 will serve to provide air pressure at the forward acting surface 124A of the air piston 122 to effect forward sliding movement will serve to provide air pressure at the reverse acting face 126 of the air piston 122,- thereby moving the air piston rearwardly, as well as the various parts carriedl thereby including the air motor.

An oil piston 140 is slidably carried on the air feed tube 102, and effects oil-tight engagement at the interfaces I with the air feed tube'102 and the air piston inner sleeve 100, O-ring seals 142 and 144 being provided therefor. A loading spring 146 is biased in compressionA between the oil piston 140 and the collar portion 128 of the'air piston 122. The spring 146 serves to maintaina force against the oil piston 140 tending to move its forwardly along the air feed tube 102. An oil screw 148 effects an oil-tight closure of a tapped hole forming al passageway 149extending through the oil piston 140.

An auxiliary oil reservoir or chamber 150 is defined forwardly of the oil piston 140, and is normally filled-to capacity with oil. A flow conduit 152 provides communication from the auxiliary oil chamber'150 through the air motor housing 24 to the main chamber 26. A spring-loaded ball valve 154 is interposed in the conduit 152; The normal'closing vbias of the valve 154' is sufficientlysmall so that a pressure differential between the

chambers

26 and 150, resulting from'alowered pressure inthe chamber 26 due to loss of oil therefrom, will effect an' opening ofthe valve 154'and a consequent ow of oil fromV the chamber to chamber 26 by the loading force of the oil piston 140, thereby replenishing the main chamber oil loss.

A passageway 158 is provided through the dash-pot piston 90, and a one-way slide valve 160 is disposed therein. The valve 160 is arranged so that pressure thereagainst during forward movement of the piston 90 through the main chamber'26 will effect closure of the passageway 158, while rearward movement will effect valve opening,

to permit'free ow therethrough.

As best seen in Figure 2 of the drawing, an adjustable by-pass valve 166 is provided to permit oil ow from one side of. the-dash-pot piston 90 to theV other during reciprocation thereof withinthe main chamber 26. The by-pass valve 166 is screw-threadedly received within a transverse bore 168 formed in the oil chamber housing 22. The valve 166 is of reduced diameter at 170 for receiving a key pin 172 to effect locking of the valve 166 against removal from the bore 168 while permitting lengthwise adjustment. A lock washer 174 is also provided for securely iixingthe by-pass valve 166 in position.

The valve 166 is formed with a reduced diameter forward end 176. An 0-ring seal 178 engages the bore 168- toprovide an oil-tight seal while permitting lengthwise movement of the valve 166 therein. A valve oil chamber is defined between the'forward end of the valve 166 and the walls of the bore '168.

The valve chamber 180 communicates with apassageway 182k (see Figure 3) leading to a forward `acting face 184-of the dash-pot piston 9). The valve chamber 180 also-communicates with a passageway 186 (see Figure 2) whichrextends in a transversely outward direction to an elongated axial passageway 188 (see Figures 2, 3, and 3A). The axial passageway 188 communicates at its-forward end witha -transversely inwardly directed passageway 190 (see Figure 3A) which leads to the chamber 26 for flow communication with a reverse acting surface 192 of the `piston 90. -It will be app-arent that the

passageways

190, 188, 186 provide communication with the valve chamber 180 at the reverse side of thepiston 90, and the passageway 182 .provides communication with the valve chamber 180 at the forward side of the piston 90.

The/bypass valve 166 terminates at its inner end ina tapered closure pin 194, which cooperates with Ithe pas-- sageway, 186v at itsl point of communication with the valve chamber 180to determine the size of the annular orifice formed therebetween.- In this way, the rate of flow from one side of the dash-pot piston 90 to the other side may be adjustably variedby rotating the valve '166 so as to screwv it'forwardly or rearwardly of its length to vary the orifice size. vIt will be clearly apparent that by providing. a relatively large orifice size the resistance pressure-load in the, dash-pot main chamber 26 will be reduced so as to permit the piston 90 to be more readily reciprocated therethrough, resulting in more rapid forward dri-ll feeding movement. Conversely, close restriction of the `orifice ysize by the tapered pin 194 will result in increased resistance to by-passing flow around the piston 90 during forward movement thereof, and a consequent slower rate of forward movement of the drill.

predetermined by the operator.

The main oil chamber 26 and the auxiliary oil reservoir 150 are initially filled with hydraulic fluid in the following manner. The drill 10 is held in a generally horizontal position and the air piston is run forward a short distance so as to free the air piston face 124 and the dash-pot piston face 18410 permit the various inner drill parts to Vturn freely.

The rear sleeve guard 20 and the nose housing 18 are first removed. The valve head yassembly 120 is then unscrewed from the air piston section 14 and removed. The air-piston outersleeve 134 may then be unscrewed from the oil chamber lhousing 22 an-d removed. The air--pis-v `In this' fway, the speed of drill feed may be readily and-simply ton 122 is now fully exposed and may be unscrewed from the air piston inner sleeve 100 and slid olf the rear end of the hollow air feed tube 162. The spring 146 is also removed.

The oil level in the main oil chamber 26 should next be checked. The drill is held in a vertical position with its forward or tool end upward, and the following steps taken. The oil Iscrew 418 .and O-ring seal 52 are removed from the port 50 of the oil chamber housing' 22. The oil retaining sleeve assembly 40 is then unscrewed and removed from the housing 22. The oil level in the main `oil chamber 26 should be level with the port 50. If the oil level is below this point, it is necessary to replenish the supply of oil to raise the level to the de? The oil retaining sleeve assembly 40 may then be replaced. Excess oil and entrapped air will bleed sired point.

outwardly through the port 50 as the sleeve assembly 40 is screwed into the housing 22. The oil screw 48 and O-ring 52 may then be replaced.

The position `of the drill 10 is then reversed and held in a vertical position with the nose or tool end of the drill pointed downwardly. The oil screw 148 and its O-ring are removed from the passageway 149 fof the oil piston 140. Suit-able means may then be inserted into the tapped hole 149 to enable the oil piston 140 to be slid upwardly and olf .of the air feed tube 102. The bore between the air feed tube 102 and the air piston inner sleeve 100 is then fully exposed to permit access to the auxiliary reservoir 150. A predetermined quantity of hydraulic oil may then be poured in to ll the auxiliary oil chamber 150 with the necessary quantity of fluid. In the particular drill construction which I have illustrated, about 3 ounces `of hydraulic fluid are required.

The oil piston 140 may then be replaced. The oil piston 140 is slidY downwardly along the air feed tu-be 102 until the oil within the reservoir 150 begins to bleed upwardly through the tapped hole 149. In this way, entrapped air within the oil reservoir 150 is eliminated. The oil screw 148 may then be replaced. The spring 146 is then returned to its proper position, and the air piston 122 slid onto the -air feed tube 102 and screwed into the air piston inner sleeve 100. The air piston outer sleeve 134 and the valve head assembly 120 are then replaced. The sleeve guard 20 and nose housing 1'8 may then be returned to position, thereby completing reassembly of the drill 10.

The main oil chamber 26 will now be completely filled with oil. The auxiliary oil reservoir will also lbe completely lled with oil and subjected to -a loading pres# sure by the spring biased oil piston 140. As normal leakage occurs from the main oil chamber 26 during oper-ation of the drill, the spring loaded ball valve 154 will be unseated in response to demand to per-mit a replenishing supply 4of oil to be introduced to the m-ain chamber 26 from the auxiliary oil reservoir 150. In this Way, a substantial quantity of replenishing oil will be continuously and automatically yavailable for maintaining the main oil chamber 26 lled at all times. The drill 10 may be subjected to continuous operation over substantially long periods of time, without any necessity for withdrawing the drill from use and disassembling it for oil replenishment. Whereas drills of this type now employed must be serviced at frequent intervals, usually weekly, the provision of an auxiliary oil supply in the manner disclosed herein permits continuous drill openation for periods of time in excess of one month without any necessity for oil replenishment.

I have also provided rapid traverse adjusting me'ans to permit the drilling tool to be initially moved forvvardly toward the work at a relatively high rate of speed, and thereafter fed forwardly during the drilling operation at a substantially lower rate of speed as predetermined rby the -adjustment ,of the by-.pass valve 166. For this purpose I provide a by-pass passageway 200 formed in the oil chamber housing 22 (see Figure 3). The passageway 200 terminates at its rear end in a cross port 202 closely adjacent the interface between the piston and .an abutment surface 23 of the oil chamber housing 22. A plurality of rapid traverse adjustment ports 204 Iare provided between the dash-pot chamber 26 and lthe'lby-pass passageway 200 forwardly of the piston 90 when in its rear position of engagement against the hou-sing abutment -shoulder 23.

A slidable pin 206 is received within the by-pass passageway 200 and is of suicient length to effect closure of all the ports 204, as shown in Figure 3. It will be apparent that with all the ports 204 obstructed by the slidable pin 206, the speed of movement of the dash-pot piston 90 through the chamber 26 will be determined solely by the adjustment of the by-pass valve 166.

A knob 208 is screw-threadedly received within an enlarged head end 210 of the slidable pin 206. The knob 208 may be tightened to effect a locking of the head 210 in position, thereby xedly determining the relation of the pin 206 to the ports 204. A guide slot 212 extends forwardly within the oil chamber housing 22 to permit the pin 206 to be adjustably positioned for exposing one or all of the ports 204. In this Way, by-pass ow through the ports 204, passageway 200 and port 202 may be provided to permit rapid forward traverse of the piston 90.

In Figure 5 of the drawing, I have shown a position of adjustment wherein several of the ports 204 have been exposed. It will be apparent that as the piston 90 moves forwardly from its rearmost position, oil within the main chamber 26 will be rapidly by-passed, and the rate of forward movement will be relatively rapid. When the piston 90 has reached a forward position overlying all of the exposed ports 204, by-pass iiow therethrough will be discontinued, and the by-pass adjustment of the valve 166 will then determine the speed of forward feeding movement. It is possible, therefore, to permit the drill to move rapidly forward to the work, and then to continue movement at a substantially slower rate of speed for actual drilling operation. Such rapid traverse adjustment permits a substantial saving of operator time by minimizing the usual waiting time for running the drilling tool forwardly up to the work.

As seen in Figure 1, a plate 214 is externally mounted on the drill adjacent the knob 208, and is provided with suitably calibratedindicia for indicating the predetermined distance of initial rapid traverse movement.

It will be understood that when forward drilling move-- ment is terminated, and the drill is reversed for withdrawal or return movement, the one-way valve is opened by the pressure force of the oil within the dashpot chamber 26 to permit ow directly through the piston 90, thereby resulting in relatively rapid drill movement in the reverse direction. A practical mounting of the drill 10 for working operation is shown in Figure 1. An adaptor cap 220 is screw-threadedly received within the nose housnig 18 and serves to carry a hanged connector member 222 which cooperates with a bayonet slot formed in a complementary mounting member 224 which is fixedly secured to a piece of work 226. A drill bit or tool 228 is carried by the drill chuck, and may be fed forwardly and thereafter Withdrawn to provide a drilled hole 230 in the work 226.

It will be apparent that the conventional use of various fittings and mounting elements for xedly positioning the drill relative to the work results in a substantial distance between the end of the drill tool 22S and the surface of the work 226. If this distance is, say, 21/8 inches, the knob 208 of the traverse adjusting means will be slid forwardly by the operator and locked in position at the marking on plate 214 designated 2l/s. This adjustment will serve to expose a predetermined number of by-pass ports 204, resulting in oil by-pass to permit the dash-pot piston 90 to move forward rapidly through the main chamber 26 for an initial distance of nearly 2%; inches. At this point, the previously exposed ports 204 will`be fully closed 'by the piston 90, and further forward? movement ofthe drilling tool will thenjbeA governed byth'eY predetermined 'rate of drilling-speed;controlled byithe b'y-pass valve 166. Upon reversal of drill movement; theY dash-pot.pistonltlJ will return through' the main chambern 26,V and the valve 160 will open to permit oil flow-through the piston for rapid return movement.

As best seen in Figure 3A of' the drawing; it` Will'be' apparent that the entire gearing assembly 38" may-be readily removed from the motor driveshaft 32 as asingle integral unit. lcontemplate by the present invention the provision of various other gearing assemblies providing a variety of motor speeds for interchangeable mounting on the air motor shaft 32.' Both singlereductionA anddouble reduction gearing units may be employed.y For large ratio reduction units, the gearing assemblies'may be of substantially greater length than that illustrated. In such casesit may be necessary to replace the nose housing 13 with an alternative nose housing to accommodate the different gearing assembly size'andv position of` the drill chuck assembly.

By using various gearing assemblies, which mayv be readily interchanged, it is possible to employl the same' single drill unit for a wide variety of working operations. For example, I may provide gearing assemblies permitting available drilling speeds-of 350, 650, 1200, 2500, and 4600 R. P; M with the same drill unit.

In order to effect change from one gearing assembly to another it is merely necessary to remove the nose housing 1S, drill chuck assembly 86 and slinger ring'82. The entire gearing assembly 38 may then be axially slidA forwardly off the splined end 33 of the motor drive shaft 32. The gearing assembly of requiredspeedmay then be replaced on the motor shaft, and the slinger ring, drill chuck, and nose housing returned'to their former positions.

Changes may be made in the construction and arrangement of the parts of my pneumatic drill construction without departing from the real spirit and purpose of my invention, and it is my intention to cover by theV claims any modiied forms of structure or use of mechanical improvements which may be reasonably included withintheir scope.

What I claim as new and desire to obtain by Letters Patent of the United States is:

l. A pneumatic drill comprising a casing forming av pair of elongated chambers arranged in longitudinally spaced relation, longitudinally aligned air piston means reciprocably mounted for forward and reverse movement within said casing, the forwardend of said air piston means carrying within the forward chamber an air motor adapted to elfect driving rotation of a tool, the rear end of said piston means carrying within the rear charnber a double-acting piston adapted to effect reciprocation of said air piston when actuated, hydraulic piston means carried by said air piston means within said forward chamber and cooperating with hydraulic nid contained' therein to provide dash-pot means for regulating the speed of reciprocation of said air motor, valve means carried by said dash-pot piston and operative to regulate` forward and reverse ow of hydraulic fluid therethrough4 to effect relatively slow forward movement and relatively rapid reverse movement of said air motor when reciprocated, and an auxiliary fluid reservoir disposed withinsaid air piston means and having passage means communicating with said forward chamber, said passage including valve means and said reservoir being pressure loaded for cooperation with said valve means to automatically etfectreplenishment ofhydraulic iluid'losses from said one chamber during/drill operation:

2'; A pneumatic'drill comprisingaI casing forming a'pairl yof elongated chambers arranged in longitudinally spaced relation, an airA motor reciprocably mounted for forward andreverse movement withinone of vsaid chambersandV pot meansforregulating thespeed of reciprocation ofsaid airmotor, supplemental regulating means operative in responsev to the' forward-position of said air-motorl to elect'control of'said dash-p otmeans for providing' rapid traverse'of said air motor'through a-predetermined initialV distance, saidsupplemental regulating means comprising longitudinally elongated port meansformed within.A saidcasing'l forwardlyl ofv saiddash-'pot piston when. in4 its rearmost position, said port means providingflowr com'- munication through by-pass conduit means' from they forward to the reverseside of'said'dash-pot piston; and longitudinally elongated closure means axially^ slidable along said Icasing for fully closing said port means and fory opening said port means progressivelyforwardly to permit selective predetermining of the extent of' initial rapid traverse, thereby adapting-said drill to providea range of operating strokes;

3.v A pneumatic drill comprising acasing forming'a pair of elongated chambers' arrangedn inV longitudinally' spacedrelation, an airv motor'reciprocably mountedfor y forward ,and 'reverser movement-withinA one of said chambers and adapted toeffect'driving rotation ofa tool, double-acting vpiston` means disposedwith'insaid other chamber and operatively connected to saidair motor-to effect reciprocation thereof when-actuated, piston means carried by'said airmotorwithin said one chamber and cooperating with'. hydraulicY fluid contained' therein to provide dash-pot'means; for regulatingv the speed' of re,-

ciprocation of. saidA air., motor,p supplemental regulatingv means operativein response to` theforwardlposition of saidair motor to4 eiect control of 'saiddash-potimeans for providing rapid` traverseof` said air motor-throughla predetermined' initial distance', said supplemental regulat; ing means comprising an axially aligned plurality of longi= tudinally spacedv ports formed. within' saidcasing forwardly ofY said'dash-pot piston when in-,its rearmost position, each ofssaid ports providingow'communication' through bypass conduit means from the forward -to the' reverse sideof said dash-pot piston, longitudinally elongated closurev means axiallyv slidable along said casing for fully. closing'` said ports and.t'or opening saidports successivelyforwardly to permit selective predetermining of. thev extent of initial rapid traverse, thereby' adapting said drillto .provide a range of operating strokes, and'.

variablyI adjustable orice means in said by-pass conduit means for regulating the rate of by-pass ow therethrough tolpermit control' of initial .rapid traverse speed.

References-Citerlin the iile'of4 this patent f UNITED STATES PATENTS 630,439 Barrett Aug. 8; 1899. 889,619 Kilgore .lunef25` 1908 2,406,482 Tuckeriv Aug. 27, 1946 2,604,759 Smith'l Iuly' 29; 1952 2,657,595 Shaft" Nov. 3,l 1953