referring to the drawings in detail , a novel micrometer lathe is shown in fig4 - 6 and generally designated by the numeral 10 . the lathe 10 is attachable to the top of standard pulp grinders , such as the great northern waterous grinder 12 shown in fig1 - 3 , and can be either a retrofit or an original equipment item . it is presently marketed under the trademark accuset ™ by montague industries , inc . of turners falls , mass . to understand the lathe 10 , it is necessary to first understand the environment in which it works -- namely , the pulp - grinding machines for which the invention was designed . as best shown in fig1 - 3 , these prior machines typically include a top chute or hopper 14 into which logs ( not shown ) are first loaded . from there the logs fall into an underlying pocket or grinding chamber 16 , where they are pressed against a rotating , cylindrical grinding stone 18 by a hydraulically operated piston 20 . the rotation of the porous , glass - matrix &# 34 ; pulp stone &# 34 ; 18 breaks down the logs into fibers ( not shown ). the fibers are mixed with water to form pulp . the &# 34 ; pulp stone &# 34 ; 18 has helical grooves ( not shown ) that extend the entire length of its grinding surface 22 . they spiral around the stone &# 39 ; s central , rotational axis 24 and are parallel to one another . during the stone &# 39 ; s rotation , helical cutting edges or shoulders of the grooves help to break down the logs . to assist in breakdown and to prevent undue wear of the shoulders , water is sprayed onto the grooves through nozzles 26 , 28 . this spray also mixes with wood particles ( not shown ) near the top of the stone . most of this mixture falls back into the grinding chamber 16 . however , some grit escapes . as shown by directional arrows 30 , 32 , this grit escapes out an upper opening of the great northern machine , where it contaminates any exposed components of overlying parts . over time , the grooves become subject to wear and need to be resharpened or &# 34 ; dressed &# 34 ;. to achieve this , the great northern 12 has previously used a hydraulic or electric lathe 34 . this lathe includes a dressing wheel or burr 36 . as seen in fig2 the wheel 36 rotates within a u - shaped housing 38 , which is part of an integral , vertically movable plunger 40 that is affixed to a spindle 42 , within a cylindrical carriage 43 . an overlying hand - operated bell crank 44 is attached to the top of the spindle 42 via interconnecting rod 45 . by turning the crank clockwise , the plunger 40 and dressing wheel 36 can be lowered to fit into the worn grooves on the surface of the grinding stone 22 . or , by turning the crank counterclockwise , the burr 36 can be raised away from the stone &# 39 ; s grinding surface . as shown in fig2 a calibrated disk 46 and integral rotatable position indicator 48 are located directly beneath the bell crank 44 to mark the exact position of the crank . the disk is calibrated to indicate a specific vertical distance of travel of the plunger 40 for each segment of axial rotation by the crank . to sharpen the grooves , an operator 49 ( see fig5 ) slowly lowers the dressing wheel 36 toward the rotating surface of the stone 22 by turning the ball crank 44 clockwise . the operator observes the descent of the wheel 36 and , when sparks ( not shown ) are observed ( at the &# 34 ; spark point &# 34 ;), the dressing wheel is raised a specific slight distance . the operator notes on the calibrated disk 46 the position of the crank 44 . particular burrs 36 are designed to crush a specific depth off of the grinding stone . the operator marks a setting on the calibrated disk 46 that corresponds to the proper burr depth plus the depth necessary to return to the contact or spark point . the operator then turns the crank 44 to the depth marked on the disk 46 , thereby lowering the dressing wheel to the approximate depth for sharpening the stone . when contact is made between the burrs on the wheel 36 and the surface of the stone 22 , the operator pulls operating lever 50 which activates an electric or hydraulic mechanism ( not shown ) that moves the lathe 34 horizontally on guide arms 52 , 54 along the surface of the grinding stone 22 . it is contemplated that the present invention &# 39 ; s most prolific use , at least initially , will be as a retrofit for converting the aforementioned , manually adjusted lathe 34 , into a unique electronically controlled one . accordingly , the invention 10 ( shown in fig4 - 6 ) will now be described in primarily &# 34 ; retrofit &# 34 ; terms . the accuset micrometer lathe 10 basically comprises a transducer 56 that is affixed to a top - end 58 of the pre - existing plunger 40 and generates electrical signals in response to mechanical vibrations ; a ball screw 60 that passes through a throughbore ( not shown ) in the top - end 58 of the plunger and is secured by nuts 62 , 64 captured within the throughbore , wherein axial rotation of the ball screw 60 moves the plunger 40 vertically ; a worm - gear box 66 coupled to a top - end 68 of the ball screw 60 that translates and gears down high - speed horizontal rotational force to low - speed vertical rotational force and minimizes backlash of the ball screw ; an encoder 70 , or electronic measuring means , attached to the worm - gear box 66 and also coupled to the top - end 68 of the ball screw 60 , which generates an electric signal in response to rotation of the screw and converts the signal into a measurement identifying the exact position of the plunger 40 ; an electric motor 72 mounted to the worm - gear box 66 that horizontally rotates a worm ( not shown ) within the gear box ; a programmable controller 74 , or electric signal processing means , ( see fig5 ) that receives and processes electrical signals from the transducer 56 and encoder ; and a variable frequency drive component 76 ( see fig5 ), electrically connected to the controller 74 and the motor 72 , which receives processed signals from the controller and converts the signals to the proper electrical current to activate the motor for precise operation . in converting the old , manually operated lathe 34 , a standard transducer 56 , such as an accelerometer , type 501m101 , manufactured by vibro - meter corp ., boston , mass ., is affixed to the top - end 58 of the plunger 40 . the top - end of the plunger is further modified to capture and secure a ball screw 60 and nut 62 , 64 assembly such as type # rp - 104 , model no . 8110 - 448 - 017 , by warner electric co . of south beloit , ill . after the ball screw assembly is secured a transducer electric wire 78 leads from the transducer 56 and is enclosed by a spiral wire protector 80 which spirals upward along the ball screw 60 . the plunger 40 fits within a standard cylindrical carriage 82 and the transducer wire 78 exits the interior of the carriage through an exit port 84 . a carriage top - plate 86 encloses the top of the carriage and is adapted to secure the ball screw 60 . a worm - gear box 66 , such as catalog no . f718 - 30 - b5 - h , 700 series , by boston gear of quincy , mass ., is affixed to the top - plate 86 and receives and engages top - end 68 of the ball screw . the top - end passes through the gear box 66 and is coupled to a standard encoder 70 such as rotary encoder model 845n - sjdn3 - cmy1 by allen bradley co . of highland heights , ohio . attached to the worm - gear box 66 is a standard electric motor 72 such as catalog no . vbm3542 , 56c frame , spec . 35e50 - 1864 - b , by baldor , co . of fort smith , ariz . it is mounted to the gear box 66 such that the rotational axis of the motor 72 is perpendicular to the rotational axis of the ball screw 60 . the motor rotates the worm ( not shown ) in the gear box which engages and rotates the top - end of the ball screw 68 . an encoder electric wire 88 and the transducer wire 78 both lead to , and transmit signals to , a standard programmable controller 74 such as model p . l . c . 2 - 05 by allen bradley co . of highland heights , ohio , with a signal conditioning component model 438 - d by vitec corp ., of cleveland , ohio . the signal transmitted from the transducer 56 is filtered by the signal conditioning component to filter out background signals produced by the transducer in response to vibrations resulting from ordinary operations . signals produced by the transducer in response to contact between the burr or dressing wheel 36 affixed to the plunger 40 and the surface of the grinding stone 22 have sufficiently large amplitude to pass through the filter and programmable controller 74 to a variable frequency drive 76 , such as model 1334 by allen bradley . the variable frequency drive 76 converts the electric signal received from the programmable controller 74 to the proper electrical current to drive the electric motor 72 a specific number of rotations , thereby causing the plunger 40 to move a specific distance . the encoder 70 transmits a signal to the programmable controller 74 identifying the position of the ball screw 60 and hence the position of the plunger 40 . the operator can program the programmable controller to signal the variable frequency drive 76 to stop moving the plunger 40 at specific , preset positions , identified by the encoder 70 . for example , in operation the operator 49 programs the controller 74 to have the plunger 40 descend in search of the surface 22 of the grinding stone 18 . upon contact between the rotating surface and the burr affixed to the plunger , a resulting vibration causes the transducer to signal the motor 72 , via the programmable controller 74 and the variable frequency drive 76 , to instantaneously stop , and then withdraw the plunger a specific , minute distance to stop the contact . the encoder 70 identifies the position of the plunger via measurements of the rotational position of the top - end 68 of the ball screw 60 , and transmits the position identity to the controller 74 . the operator can then program the controller to make the plunger descend the precise distance to again make contact plus an additional distance dependent upon the specific &# 34 ; crush dressing &# 34 ; depth requirements of the burr 36 being used . the operator then initiates the final plunger descent and , when the sharpening or dressing depth is reached , activates the horizontal pass of the lathe 10 across the surface 22 of the grinding stone 18 . the next time sharpening is required , typically one day later , the programmable controller 74 has stored in its electronic memory the positions utilized by the plunger for the previous sharpening . consequently , the operator 49 can save time by avoiding a time - consuming contact point search . a search can be commenced from the contact position identified by the encoder 70 during the previous sharpening cycle . plunger 40 positions can also be identified by the encoder and set in the programmable controller 74 , in the same manner described above , for minimum and maximum depth settings . these settings serve to prevent damage to the lathe in the event a plunger descends accidentally when no stone 18 is under the plunger . a minimum depth setting serves to automatically shut off the motor 72 when the plunger 40 ascends to a point near the carriage top plate 86 , to avoid accidental damage to the lathe 10 . similarly , a maximum depth setting automatically shuts off the motor if the plunger descends too far . in the event the programmable controller 74 or encoder 70 fail , proximity switches 90 , 92 such as model e2a12 , catalog 871c , manufactured by allen bradley co ., serve as electro - mechanical minimum and maximum plunger - positions stop . they shut down the motor 72 if triggered by the plunger 40 , thereby serving to reduce the risk of accidental damage to the lathe . it should be understood by those skilled in the art that obvious structural modifications can be made without departing from the spirit of the invention . for example , the same lathe position identifying and controlling apparatus and process described hereinabove for sharpening pulp - grinding stones can be used for any lathe . accordingly , reference should be made primarily to the accompanying claims rather than the foregoing specification to determine the scope of the invention .