BACKGROUND OF THE INVENTION 
     The present invention relates to gas-shielded welding tip reconditioning apparatus, and particularly to improvements therein useful in robotic MIG welding operations. “Welding” in the context of the present invention relates to the co-joining of two or more metal parts. The quality of the weld is affected by a number of factors, including the selection of any given welding technology, the competency of the operator, and of particular importance in the present context, the condition of the welding equipment. With regard to the condition of the equipment, the condition of the welding tip is often important. In the case of resistance welding equipment, for example, there are a variety of devices useful in connection with welding electrode maintenance—including surface reconditioning apparatus those disclosed in the following patents: U.S. Pat. No. 4,682,487; U.S. Pat. No. 4,856,949; U.S. Pat. No. 4,916,931; and U.S. Pat. No. 4,921,377. 
     Another well known welding technique is ARC welding—which differs from resistance welding in that ARC welding electrodes are deliberately consumed during the welding process so that the electrode material becomes an integral component of the finished weld. As a result, the problem of electrode reconditioning that is associated with resistance welding equipment, is not a problem in ARC welding. 
     MIG (and acronym for “metal-inert-gas”) arc welding is an arc welding technique in which a relatively fine wire electrode is fed continuously from a large spool mounted on by a variable speed drive whose speed is controlled to optimise arc length and burnoff rate. During the welding process, the electrical arc that extends between the electrode and the metal surfaces that are being welded, is shielded within a gas flow. Typically argon or other gases having suitable characteristics, or mixtures thereof are used—with carbon dioxide often being the gas of commercial choice. 
     In gas shielded welding the wire electrode and the gas are generally channelled through a so-called “torch”, which includes a central, electrically charged “tip”. The tip directs the wire electrode toward the weld site, and a concentrically arranged metal gas shield (that is electrically insulated from the tip), acts as a hood to direct and maintain a coaxial flow of the inert gas in surrounding relation about the wire. The quality of the weld is contingent on both consistent and continuous gas flow and arc patterning. Anything that interferes with the gas flow or redirects or otherwise militates against the desired electrical arc pattern, will diminish the quality of the weld. 
     MIG welding, when properly executed, permits high welding speeds, and necessitates less operator training than is required in the case of other welding techniques. In applications where one or the other or both of these benefits are sought, the weld quality is especially sensitive to those variations that are attributable to adverse gas flow or anything which could negatively influence the desired arc pattern. 
     Gas flow in MIG welding can be adversely effected as a consequence of molten metal deposition. This arises as a result of backsplash splatter on the respective mutually opposed surfaces of the tip and the hood, within the interior of the torch. Similarly, (since the dielectric strength of the gas flow is otherwise a constant), the accumulation of such backsplash splatter decreases the physical and hence “electrical” distance between the charged tip and the electrically insulated hood. If the distance decreases sufficiently, the voltage differential will exceed the dielectric strength of the intervening gas flow, and the arc will jump between the tip and the hood. This results in a diminished amount of electrical energy being delivered to the weld site and a concomitant compromise in weld quality. 
     In view of the foregoing, it is important that MIG welding torches be cleaned regularly, in order to avoid these two latter mentioned problems. A variety of devices are available for this purpose, and many if not most involve mechanical devices such as torch clamps and reaming tool drives, that can be exposed to and damaged by the debris that is dislodged from the torch. The present invention is intended to help remedy or at least reduce the incidence/severity of such damage. 
     SUMMARY OF THE INVENTION 
     The present invention relates generally to a MIG welding torch reconditioning apparatus including a pneumatic supply line; vent; and a mechanical transmission shaft. The pneumatic supply line supplies air to the vent which in turn then vents a directed debris-scattering air-flow against the mechanical transmission shaft proximal to exposed seals thereon. This arrangement is particularly advantageous as part of a combination in which the MIG welding torch reconditioning apparatus has a pneumatic supply line that is connected to supply a pneumatically driven mechanical means, and to vent “spent-drive” air that exits from the mechanical means, through vent means as described above. 
     In a more specific embodiment, a MIG welding torch reconditioning apparatus according to the present invention includes a pneumatic supply line for supplying pneumatic rotary drive means, as well as a drive vent means for venting the directed debris-scattering air-flow towards a mechanical transmission shaft proximal to seals thereon. Preferably, this transmission shaft is a rotary drive shaft that is arranged in driven relation to the pneumatic drive means. The transmission shaft is also connected, in turn, in driving relation to a reaming tool that is adapted to be aligned and inserted within a torches gas-shield and to be operable therein to remove at least some of any back-splash deposits laid down on interior surfaces of the gas-shield. In an especially preferred embodiment of this aspect of the invention, the transmission shaft is an extensible rotary drive shaft, adapted to be retractably extended past a seal to position the reaming tool within said gas shield. 
     In an alternative aspect of the present invention there is provided a MIG welding torch reconditioning apparatus which includes a pneumatic supply line for supplying pneumatic lift means and wherein lift vent means is included, for venting a directed debris-scattering air-flow towards a mechanical transmission shaft proximal to seals thereon. In a preferred form of this particular embodiment, the transmission shaft is an extensible shaft, adapted to be retractably extended past said seals to position a reaming tool within a gas shield. An especially advantageous embodiment of this aspect of the invention involves the transmission shaft being a rotary drive shaft arranged in driving relation with a reaming tool to be aligned and inserted within a torches gas-shield and to be operable therein to remove at least some of any back-splash deposits laid down on interior surfaces of said gas-shield. 
     In a general sense, the present invention relates to MIG welding torch reconditioning apparatus comprising: a pneumatic supply line; pneumatic lift means powered from said supply line, pneumatic rotary drive means powered from said supply line; a mechanical transmission shaft that is connected in rotary driven relation to paid drive means and is retractably extensible on operation of said lift means. In this type of embodiment, an exhaust vent supplied by one of: air directly from said supply line; exhausted air flow from said lift means; exhausted air from said rotary drive means; or a combination of any of the forgoing. This exhaust vent is operable to vent a directed debris-scattering air-flow from these various sources, towards a said transmission shaft proximal to seals thereon. In an especially preferred form this exhaust vent is supplied at least in part by exhausted air from the rotary drive means. 
     In another embodiment, there is generally provided a MIG torch reconditioning apparatus which comprises an in-line, direct-drive arrangement of a motor, a mechanical transmission shaft, and chuck for receiving a reaming tool. A pneumatic lift means is provided to lift the direct drive arrangement into reaming tool engagement, (wherein the tool is positioned within a torches gas shield and operable to remove at least some of any back-splash deposits laid down on interior surfaces of said gas shield). Preferable, embodiments of this aspect of the invention include a pneumatic motor as part of the direct drive means. 
     In a preferred form, the direct-drive arrangement is movably arranged as a piston within a channel in a housing, and the pneumatic lift means is operable to introduce a supply of air under pressure into the channel to move the piston arrangement there-along. In an exemplary embodiment of this aspect of the present invention the direct-drive arrangement includes a cradle for supporting said pneumatic motor within the channel. The cradle comprises surfaces that are adapted to cooperate with interior channel surfaces of the housing, to form a sliding air-tight seal there-between. Typically, these cradle surfaces will include sealing rings. In addition, it is preferable in embodiments where the channel is cylindrical, that the cradle be mounted in slidably positionable relation along an at least one guide rail that is arranged within the channel. The longitudinal axis of the guide rail is oriented parallel to the channels longitudinal axis, and the rail located in an axially offset relation from the direct drive arrangement. In this way, the guide rails serves to resist reactionary rotation of the cradle within the channel during the operation of the direct drive means. 
     In a particularly preferred embodiment, the apparatus according to the present invention further includes a pneumatic retractor means. This retractor is operable to retract the direct drive arrangement from out of reaming tool engagement within the torches gas shield, once the tool has removed at least some of any back-splash deposits that may have been laid down on interior surfaces of the gas shield. 
     A preferred embodiment of the present invention includes a cradle which comprises at least two, mutually spaced apart sealing surfaces. A space is defined there-between which is otherwise also bounded by adjacent cradle and channel surface portions. A pneumatic inlet is provide through the housing and opens up into that space. In addition, the cradle includes a pneumatic (conduit) passage communicating between the space and an air inlet into the pneumatic motor. In this arrangement, air that is supplied through the housing inlet is deliverable to the motor through the above mentioned “space” and the “passage” over a range of positions in which the inlet is in register between the spaced apart sealing surfaces. In this way, the motor can be powered over a range of its axial positioning, relative to the introduction and retraction of the reaming tool into and from a gas shield. 
     Moreover, it is also preferred that the cradle include a port for exhausting drive air from the motor. Such a port can comprise, for example, a telescoping snorkel adapted to channel drive air exhaust exteriorly of the housing. 
     In yet another embodiment of the present invention, there is generally provided a MIG welding torch reconditioning apparatus which comprises means adapted to hold a reaming tool to be aligned and inserted within a torches gas-shield. The reaming tool is itself adapted to be operable within the confines of the gas-shield to remove at least some of any back-splash deposits laid down on interior surfaces of said gas-shield. 
     When the apparatus is in use the motor-driven reaming tool is operable in intermittently driven relation. More specifically, when an incipient stall condition arises, (i.e. a condition in which the torque available from the motor is insufficient to properly rotate the reaming tool against loads occasioned by contact of the reaming tool against welding deposits within the gas-shield), then the apparatus responds by causing the motor to discontinue driving the reaming tool until sufficient motive force can be brought to impact through the reaming tool and in turn against the contacted deposits. This in turn, is intended to allow the apparatus to return to it normal reaming operation. 
     The advantages of this apparatus are particularly applicable to small pneumatic motors. Accordingly, in a contemplated embodiment of the present invention the torch reconditioning apparatus described above, might include a pneumatic motor and its drive would be suspended as contemplated above, by the specific means of a feed-back operated valve in a pneumatic supply line to the motor. This valve would be operative in response to feed-back signaling an incipient stall condition, to interrupt an air supply from driving the motor. It would then suddenly reconnect the air supply to provide sufficient motive force to impact through the reaming tool against the contacted deposits, to allow the apparatus to return to normal reaming operation. 
     Although this arrangement may provide some of the benefit associated with the present invention, there is every reason to believe that more efficacious results might be realized through the use of clutch means to selectively uncouple and re-couple the motor (whether pneumatic or otherwise) from driving relation with the reaming tool. The clutch would be thereby operable when the motor encounters an incipient stall condition, to responds by causing the motor to discontinue driving the reaming tool. Such discontinuity would persist until sufficient motive force can be brought upon re-engaging said clutch, to impact through the reaming tool and in turn against the contacted deposits. 
     A clutch within the present contemplation might, without limiting the generality of the explicit function, be mechanical, electrical, pneumatic or hydraulic in its operation. 
     Generally speaking, therefore, it is preferable for the purposes of the present invention that the MIG welding torch reconditioning apparatus comprise torch reconditioning means adapted to hold a reaming tool to be aligned and inserted within a torches gas-shield; and, to be operable therein to remove at least some of any back-splash deposits laid down on interior surfaces of said gas-shield, and wherein said torch reconditioning means includes an intermittent drive coupling arranged intermediate between a motor and said reaming tool, and operable there between to uncouple a reaming tool transmission side of said coupling from a motor-powered drive side of said coupling when, in operation, the torque available from the motor is insufficient to properly rotate the reaming tool against loads occasioned by contact of the reaming tool against welding deposits within the gas-shield, whereupon the motor rotates the drive side of the coupling under unloaded-motor conditions until the drive coupling re-couples through complementary mating surfaces thereof to thereby transmit the resulting impact force through the reaming tool and against and contacted deposits. 
     In a particularly preferred form of the present invention, there is provided a MIG welding torch reconditioning apparatus comprising, torch reconditioning means adapted to hold a reaming tool to be aligned and inserted within a torches gas-shield; and, to be operable therein to remove at least some of any back-splash deposits laid down on interior surfaces of said gas-shield, and wherein said torch reconditioning means includes a mechanical, impact-clutch intermittent drive coupling arranged intermediate between a motor and said reaming tool, and operable there between to uncouple a reaming tool transmission side of said coupling from a motor-powered drive side of said coupling when, in operation, the torque available from the motor is insufficient to properly rotate the reaming tool against loads occasioned by contact of the reaming tool against welding deposits within the gas-shield, whereupon the motor rotates the drive side of the coupling under unloaded-motor conditions until the drive coupling re-couples through complementary mating surfaces thereof to thereby transmit the resulting impact force through the reaming tool and against and contacted deposits. 
     Again, this apparatus is particularly useful in combination with a pneumatically driven motor. Particular versatility can be realized when the coupling is reversibly operable and the motor is a reversible pneumatically driven motor. 
     In an especially preferred form, the present invention comprises a MIG welding torch reconditioning apparatus comprising, torch reconditioning means that is adapted to hold a reaming tool to be aligned and inserted within a torches gas-shield. When so held, the reaming tool is operable to remove at least some of any back-splash deposits laid down on interior surfaces of said gas-shield. 
     In addition, the torch reconditioning means includes an impact-clutch intermittent drive coupling arranged intermediate between a motor and the reaming tool. The drive coupling is operable in two modes. 
     In a first mode, it operates to uncouple a reaming tool transmission side of said coupling from a motor-powered drive side of said coupling. This it accomplishes through disengagement of complementary hammer and reception block surfaces of the coupling which it does under predetermined high motor-load conditions. 
     In a second mode, the drive coupling operates to re-couple the drive and transmission sides of the coupling, which it does by impacting the hammer and reception block surfaces against one another. 
     Thus, when this latter embodiment is in operation, and the torque available from the motor is insufficient to properly rotate the reaming tool against loads occasioned by contact of the reaming tool against welding deposits within the gas-shield, then the drive coupling uncouples the tool from the motor. Once uncoupled from the reaming tool loading, the motor rotates the drive side of the coupling freely under unloaded-motor conditions. This forces the hammer and reception block surfaces to impact against one another and to thereby transmit the resulting impact force through the reaming tool and against the contacted deposits and greatly increases the instantaneous forces that are available to dislodge that material. 
     In still another embodiment of the present invention, a clamp is provided for engaging a cylindrical body between a pair of generally orthogonally-offset faces of a “V”-block and respective gripping surfaces on gripping surface members of a pair of opposed jaws. The jaws are arranged on respective jaw pivots and also include respective lever arms which extend beyond the pivots. Each such lever arm supports respective cam followers in spaced apart relation from their respective jaw pivots. The clamp also includes movable cam surfaces which are adapted to act on the cam followers in such a way as to rotate the lever arms and associated jaws about their pivots. This translates in turn, into movement of the gripping surfaces in and out of a three-way engagement of the cylindrical body between said surfaces and the “V”-block (or more specifically, the above mentioned “faces” thereof. 
     In a preferred form of the clamp, each of the orthogonally-offset faces are arranged in generally parallel, mutually-opposed relation to a corresponding gripping surface on a gripping surface member. The “V”-block in this clamp, is mounted on a “V”-block pivot and is rotatable about same to permit the cylindrical body to be engaged in a self-centering relation between the “faces” and the “surfaces” of the jaws and the “V”-block, respectively. 
     Preferably, the cam surfaces are side walls of a milled track arranged in a slide plate which is selectively movable between positions corresponding to the gripping surfaces being, respectively, in and out of the three-way clamp engagement of the cylindrical body. 
     In an additionally preferred feature of the invention, the cam surfaces are comprised of a primary portion that is configured to direct the cam followers and to translate the motion thereof through the lever arms, to move the jaws rapidly towards engagement with a lower mechanical advantage. A secondary portion of the cam surfaces are configured to direct the cam followers and thereby translate the motion thereof through the lever means, to move the jaws more slowly into engaged relation with the cylindrical body, with greater mechanical advantage. 
     The plate is preferably selectively driven by a pneumatic piston. 
     The clamp according to the present invention is desirably arranged such that the plate, the lever arms, and the cam followers are enclosed within a housing, while the “V”-block and the gripping surface members arranged externally thereof. A central resilient cylindrical seal is arranged generally tangentially against the jaws, between and proximal to the jaw pivots, to thereby reduce ingress of debris into the housing. Respective ones of outboard cylindrical seals are arranged adjacent the pivots and generally tangentially between corresponding ones of the jaws, and adjacent portions of the housing, to thereby reduce ingress of debris into the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 of the appended drawings is a front-quarter perspective view of a preferred MIG welding torch reconditioning apparatus according to the present invention; 
     FIG. 2 is a view of the apparatus illustrated in FIG. 1, from a rear-quarter with the rear casing shown in partial phantom, to reveal interior workings of the apparatus; 
     FIG. 3 is an exploded view of drive components as arranged within the embodiment depicted in FIGS. 1 and 2; 
     FIGS. 4 a ,  4   b  and  4   c , depict an impact drive mechanism in various drive states; 
     FIG. 5 depicts a preferred lift mechanism in accordance with the embodiment depicted in the preceding figures; 
     FIG. 6 depicts an elevated side view of the clamping mechanism that is adapted to engage a welding torch; 
     FIG. 7 depicts a top down view of the clamping mechanism shown in FIG. 6; and 
     FIGS. 8 a  and  8   b  depict end and top views of portions of the clamping mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the appended Figures generally, (except as otherwise specified from time to time), there is depicted a preferred MIG welding torch reconditioning apparatus  1 , embodying the present invention, and comprising a preferred torch reconditioning means that is indicated generally by reference numeral  2 . 
     Torch reconditioning means  2  is adapted to hold a reaming tool  3 , so that said tool can be aligned and inserted within a gas shield of a torch. The shield being designated by reference numeral  4  in FIG.  6 . When so positioned, the tool is operable to remove at least some of any back-splash deposits laid down on the interior surfaces of shield  4 . 
     In this preferred torch reconditioning means  2  the motor-driven reaming tool is operable in intermittently driven relation, such that when an incipient stall condition arises in which the torque available from the motor  5  is insufficient to properly rotate the reaming tool  3  against loads occasioned by contact between the reaming tool and welding deposits adhering to shield  4 , then apparatus  1  responds by causing the motor  5  to discontinue driving the reaming tool until sufficient motive force can be brought to impact through the reaming tool and in turn against the contacted deposits, to allow the apparatus  1  to then return to normal reaming operation cycle. 
     Motor  5  is a pneumatic motor. Note that in an alternative embodiment of the present invention (not shown in the appended drawings), it is contemplated that the drive of the pneumatic motor could be suspended by a mechanism comprising feed-back operated valve in a pneumatic supply line to said motor, the said valve being operative in response to feed-back signaling an incipient stall condition. In operation, this would interrupt an air supply from driving the motor, and then suddenly reconnect the supply to provide sufficient motive force to impact (through the reaming tool) against the contacted deposits, to dislodge same under the suddenly applied force, and to allow the apparatus to return to normal reaming operational cycle. However, such an alternative embodiment is not presently preferred. 
     Instead, the mechanism of the presently preferred embodiment of the MIG welding torch recondition apparatus of the present invention comprises a clutch (indicated generally by reference numeral  6 ). Clutch  6  is provided to selectively uncouple and re-couple motor  5  from driving relation with reaming tool  3 . In this way, clutch  6  is operable when motor  5  encounters incipient stall conditions to respond to the incipient stall condition by uncoupling the motor from the reaming tool, causing motor  5  to discontinue driving the reaming tool until sufficient motive force can be brought on by the re-coupling of the clutch  6  to impact through the reaming tool  3  and in turn against the contacted deposits, to dislodge same and allow the apparatus to return to normal reaming operational cycle. 
     Although the clutch could be mechanical, electrical or hydraulic in nature, clutch  6  is preferably mechanical, as shown. More particularly, in accordance with the depicted preferred embodiment of the present invention, clutch  6  is operable under incipient stall conditions, such that the motor rotates the drive side of the clutched coupling between the motor  5  and reaming tool  3 , under unloaded-motor conditions. This mode of operation continues until the drive coupling re-couples through complementary mating surfaces (referenced generally at  7 ) thereof (i.e. of clutch  6 ) to thereby transmit the resulting rotary-impact force through a simple and direct coupling (see for example, FIG. 3 of the appended drawings) with rotatable mechanical transmission shaft  12  to the reaming tool  3  and against any contacted deposits. 
     Accordingly, in this particular embodiment of the present invention, clutch  6  includes a mechanical impact-clutch intermittent drive coupling  8  that is arranged intermediate between motor  5  and reaming tool  3 . As mentioned above, this arrangement is operable to uncouple a reaming tool transmission side (indicated generally by  8   a ) of coupling  8  from a motor-powered drive side (indicated generally by  8   b ) thereof. When, in the course of a normal operational cycle, the torque available from motor  5  is insufficient to properly rotate the reaming tool against loads occasioned by contact of the reaming tool against welding deposits within the shield  4 , the motor rotates the drive side of the coupling under unloaded-motor conditions until the drive coupling re-couples through complementary mating surfaces thereof to thereby transmit the resulting impact force through the reaming tool and against and contacted deposits. 
     In accordance with the preferred aspects of the present invention as embodied in the illustrated features herein, motor  5  is a pneumatically driven motor; and both the coupling  8  and motor  5  are reversibly operable. 
     As regards impact mating surfaces  7 , these are comprised of complementary hammer  9  and reception block  10  surfaces of coupling  8 . 
     Impact drive devices are generally known—including that disclosed in U.S. Pat. No. 5,887,666 which is incorporated herein by reference. The impact drive illustrated in the appended drawings was obtained from Campbell Hausfeld, of Harrison, Ohio. 
     Referring now in particular, but not exclusively, to FIGS. 3 and 5 of the appended drawings, there is illustrated a MIG torch reconditioning apparatus  1  comprising an inline, direct-drive arrangement  11 , of a motor  5 , a mechanical transmission shaft  12 , and chuck means  13  for receiving a reaming tool  3 . Pneumatic lift means  14  is provided to lift the direct drive arrangement  11  to engage reaming tool  3  with torch gas shield  4 , so that tool  3  is operable to remove at least some of any back-splash deposits laid down on interior surfaces of gas shield  4 . 
     Direct-drive arrangement  11  is movably arranged as a piston  15  within a channel  16  in a housing  17 , and said pneumatic lift means  14  is operable to introduce a supply of air under pressure into channel  16  to move piston  15  therein. Direct-drive arrangement  11  includes a cradle  18  for supporting pneumatic motor  5  within channel  16 . Cradle  18  comprises surfaces  19  adapted to cooperate with interior channel ( 16 ) surfaces  20  of housing  17 , to form sliding air-tight seals  21  there-between. These include sealing rings  22 . 
     In this preferred embodiment, channel  16  is cylindrical and cradle  18  is mounted in slidably positionable relation along an at least one guide rail  23  that is arranged within channel  16  and parallel to the channels longitudinal axis. Rail (or rails, as in the present case)  23 , is offset from direct drive arrangement  11  and operable to resist rotation of cradle  18  within channel  16 . Additionally, MIG torch reconditioning apparatus  1  further includes pneumatic retractor means (including pneumatic inlet  24  into housing  17 ) operable under pneumatic control to retract direct drive arrangement  11  from out of reaming tool engagement within torch gas shield  4  after tool  3  has removed at least some of any back-splash deposits laid down on interior surfaces thereof. 
     Cradle  18  comprises two, mutually spaced apart, sealing surfaces  21  defining a space  25  there-between which is otherwise bounded by adjacent cradle and channel surface (reference numerals  19  and  20 , respectively) portions  19   a  and  20   a . A pneumatic inlet  26  through housing  17  communicates into space  25 , and cradle  18  includes a pneumatic passage  27  communicating between space  25  and an air inlet  28  into pneumatic motor  5 . Air supplied through housing inlet  26  is delivered to motor  5  through space  25  and passage  27  throughout a range of cradle positions over which inlet  26  is in register between respective top and bottom sealing surfaces  21 . Cradle  18  includes a port  29  for exhausting drive air from motor  5 . Port  29  comprises a telescoping snorkel  30  that is adapted to channel drive air exhaust exteriorly of housing  17 . 
     In accordance with the present invention, MIG welding torch reconditioning apparatus  1  includes vent means  31  for venting a directed debris-scattering air-flow from housing  17  and against a portion  32  of the mechanical transmission shaft proximal to exposed seals  33  thereon. Portion  32  of the transmission shaft is an extensible rotary drive shaft, adapted to be retractably extended past seals  33  to position reaming tool  3  within shield  4 . 
     As illustrated in FIG. 5, the pneumatic inlet  26 , space  25 , pneumatic passage  27 , air inlet  28 , port  29  and snorkel  30  broadly define a pneumatic supply line for directing debris-scattering air-flow to the vent means  31 . However, it is understood that the pneumatic supply line may be a direct flow path from the inlet  26  to the vent means  31 , bypassing the motor  5 , or any other indirect flow path that directs air from the inlet  26  to the vent means  31 . It is also contemplated that the pneumatic supply line may include a passage  52  through which air is delivered to the pneumatic lift means  14  for driving the lift means, and may further include an exhaust vent (not shown) for exhausting air from the lift means and directing the air to the vent means  31 . 
     Referring now to FIGS. 6,  7  and  8  in particular, although not exclusively, there is depicted a clamp  34  for engaging a cylindrical body (e.g. the torch shield  4 ) between a pair of generally orthogonally-offset faces  35   a  and  35   b  of a “V”-block  35  and respective gripping surfaces  36   a  and  37   a  on gripping surface members  36  and  37  (respectively) of a pair of opposed jaws  38 . Jaws  38  are arranged on respective jaw pivots  38   a  and  38   b . Jaws  38  further include respective lever arms  38   c  and  38   d  extending beyond pivots  38   a  and  38   b . Each lever arm ( 38   c  and  38   d ) support respective cam followers  39   a  and  39   b  in spaced apart relation from their respective jaw pivots  38   a  and  38   b . Clamp  34  further includes movable cam surfaces  40   a  and  40   b  which are adapted to act on cam followers  39   a  and  39   b  to rotate lever arms  38   c  and  38   d  and associated jaws  38  about pivots  38   a  and  38   b  to move gripping surfaces  36   a  and  37   a  in and out of a three-way engagement in which the cylindrical body of torch shield  4  is engaged between surfaces  36   a  and  37   a  and orthogonal faces  35   a  and  35   b  of “V”-block  35 . 
     Note that respective ones of the orthogonally-offset faces  35   a  and  35   b  is arranged in generally parallel, mutually-opposed relation to a corresponding gripping surface  36   a  and  37   a , and that “V”-block  35  is mounted on a “V”-block pivot  41  around which “V”-block  35  is rotatable. This arrangement permits the cylindrical body of torch shield  4  to be engaged in self-centering relation by clamp  34 . 
     Also note that cam surfaces  40   a  and  40   b  are side walls of a milled track  42  that is arranged in a slide plate  43 . Slide plate  43  is selectively movable between positions corresponding to said gripping surfaces being, respectively, in and out of the above mentioned three-way engagement with the torch shield  4 . 
     Track  42  is milled in such a way that the cam surfaces comprise primary portions  44   a  and  44   b  respectively, that are configured to translate (through cam followers  39   a  and  39   b  and lever arms  38   c  and  38   d ), to rapidly move jaws  38  towards engagement with a certain but relatively lower, mechanical advantage. Cam surfaces also comprise secondary portions,  45   a  and  45   b , that are configured to translate through motion to more slowly move jaws  38  into engagement, with relatively greater mechanical advantage. 
     Plate  43  is selectively driven on a pneumatic piston,  46 , which travels along rails  47  milled into housing  48 . Plate  43 , lever arms  38   c  and  38   d , and cam followers  39   a  and  39   b  are enclosed within housing  48 , while “V”-block  35  and gripping surface members  36  and  37 , are all arranged externally thereof. A central resilient cylindrical seal  49  is arranged generally tangentially against jaws  38 , between jaw pivots  38   a  and  38   b , to thereby reduce ingress of debris into the interior of housing  48 . In addition, respective ones of outboard cylindrical seals  50   a  and  50   b  are arranged generally tangentially between corresponding ones of jaws  38 , and adjacent portions  51   a  and  51   b  of housing  48 , to thereby further reduce ingress of debris into housing  48 . 
     In general operation, (and referring to the drawings in general) torch shield  4  is approximately positioned relative to apparatus  1 , (and under robotic welder control), for cleaning in accordance with some predetermined schedule or other direct or indirect criteria for maintaining welding performance. With torch shield  4  so positioned, pneumatic piston,  46  is actuated (in response to control signals not detailed herein—but for which the programming and mechanisms are generally well known in the relevant arts), and begins its transit along rails  47 , carrying plate  43  along with it. As plate  43  moves, portions  44   a  and  44   b  of the cam surfaces  40   a  and  40   b  of milled track  42 , act against cam followers  39   a  and  39   b . The resulting movement of cam followers  39   a  and  3   9   b  then in turn translates into initial and relatively rapid movement of lever arms  38   c  and  38   d  about pivots  38   a  and  38   b  —and corresponding movement of the balance of jaws  38  translates into movement of members  36  and  37  such that gripping surfaces  36   a  and  37   a  advance towards respective offset faces  35   a  and  35   b , with torch shield  4  interposed there between. This action continues until piston  46  extends to the point where cam followers  39   a  and  39   b  begin to track against respective secondary surface portions  45   a  and  45   b . The change in the rate of displacement of the cam followers  39   a  and  39   b  as they track along these secondary surface portions  45   a  and  45   b , reduces the rate of rotation of jaws  38  about jaw pivots  38   a  and  38   b —slowing the progress of the gripping surfaces in the direction of shield  4 , but increasing the relative mechanical advantage with which these surfaces engage shield  4 . Ultimately shield  4  is brought into contact with surfaces  35   a  and  35   b , during which time “V”-block  35  rotates passively to receive and position shield  4  into the requisite alignment above reaming tool  3 . Clamp  34  completes its engagement and holds shield  4  in clamped relation between the respective faces of “V”-block  35  and surface members  36  and  37  of jaws  38 , throughout the balance of the reaming operation. 
     With shield  4  aligned and clamped, the pneumatic supply line provides an air flow into pneumatic inlet  26  (which extends through housing  17 ) and from there into space  25 . The air then flows from space  25  though a pneumatic passage  27  in cradle  18 , and from there into air inlet  28  to drive pneumatic motor  5 , which in turn spins reaming tool  3 . Air is also supplied through passage  52  to drive pneumatic lift means  14 , lifting piston  15  within channel  16  of housing  17 , to extend reaming tool  3  into the interior of shield  4 . During the reaming operation, spent air is vented from motor  5 , through passage  29  and snorkel  30  and ultimately through vent means  31 , to prevent accumulation of seal damaging debris on transmission shaft seals. 
     In addition, and also during the reaming operation, the impact drive cuts in under incipient stall conditions. In such circumstances, the mechanical impact-clutch intermittent drive coupling  8  operates to uncouple a reaming tool transmission side (indicated generally by  8   a ) of coupling  8  from a motor-powered drive side (indicated generally by  8   b ) thereof. Referring now in particular to FIGS. 4 a ,  4   b  and  4   c , there is shown views of the coupling  8  in pre-impact, impact and post-impact positions, respectively. 
     Once the reaming activity is completed, clamp  34  releases shield  4 , and the robotic welding control takes over in returning the torch to productive application. Other variations on the present invention will be apparent to persons skilled in the art(s) in view of the disclosure and teachings contained herein or following here-from, and the scope of the present invention is therefore constrained only by the definitions thereof as provided in the claims that ultimately issue on the basis hereof.
A method and apparatus for reconditioning a MIG welding torch of the type having a gas shield through which gas is exhausted from the torch comprises inserting a reaming tool within an opening of the gas shield. The reaming tool is moved relative to the gas shield within the opening into contact with deposits adhered to the gas shield within the opening. An impact force is applied through the reaming tool against the deposits in the event that movement of the reaming tool relative to the gas shield is substantially inhibited by any of the deposits.