Patent Publication Number: US-9427840-B2

Title: Honing tool holder with a feed system powered by through-the-spindle coolant pressure and actuated by spindle rotation

Description:
This application is submitted under 35 U.S.C. 371 claiming priority to PCT/US2011/52618, filed Sep. 21, 2011, which application claims the benefit of U.S. Provisional Application No. 61/384,966, filed Sep. 21, 2010. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to a honing tool holder, and more particularly, that is adapted for mounting in a rotatable spindle of a machine tool or machining center lacking a feed system, but as is common, does have a means to deliver pressurized coolant through the center of the spindle, the holder being capable of holding and automatically operating an in-process adjustable feed honing tool for honing a work piece to a desired diameter or other characteristic, using the coolant pressure to deliver a constant force to the wedge element of the honing tool. 
     BACKGROUND ART 
     U.S. Provisional Application No. 61/384,966, filed Sep. 21, 2010, is incorporated herein by reference in its entirety. 
     Machine tools and machining centers, hereinafter sometimes jointly referred to by the term “machine tool”, including, but not limited to, milling machines and the like, include rotatable spindles configured for holding tools such as milling cutters, drills, reamers, and the like, for performing machining operations, such as but not limited to, milling, drilling, boring, and reaming. Such tools are typically removably held in the spindle by tool holders, which allow quickly changing the tools, for instance, by an automatic tool changing apparatus. Honing is a machining operation that can impart a much more precise size, shape, and finish to work piece bores, but many traditional honing tools require a feed mechanism or system for adjusting a feed position and/or feed force of honing elements, e.g., abrasive stones, of the tool, in process, as those elements are urged against the surface of a bore of a work piece for honing the bore. Known machine tools and machining centers lack the required feed system or mechanism, and thus the traditional in process adjustable feed honing tools have not been used on machine tools. But many machine tools and machining centers have through-the-spindle coolant delivery systems operable for directing a flow of liquid coolant from a port or orifice in the spindle, into a mating port or orifice of a tool holder held by the spindle. 
     There exist several honing tools designed for use in machine tools that utilize through-the-spindle coolant pressure to directly or indirectly force the abrasive stones of the honing tool into the surface of the bore. Reference in this regard, Hyatt, et al. U.S. Pat. No. 5,800,252, which describes a honing tool designed for use in a machine tool having through-the-spindle coolant. In the Hyatt, et al. tool, by means of passages the coolant pressure is supplied directly to chambers under the abrasive stones providing direct force. However, an observed shortcoming is that this type of tool allows each abrasive stone to feed independently which will not reliably improve the roundness of a bore, which is often a goal of the honing process. Usually, roundness is accomplished by having abrasive stones fed by a single wedge that keeps all stones advancing and retracting in unison. 
     U.S. Pat. No. 6,739,949 B2, Becksvoort, et al. and U.S. Pat. No. 7,070,491 B2, Becksvoort et al, both describe a honing tool with a wedge that is fed by the pressure of coolant delivered through the machine tool spindle. Both of these tools, however, rely on an internal helical spring to retract the tool. Spring force naturally is increased as the abrasive stones are fed outward. The net force delivered to the wedge is the coolant force minus the spring force. This results in a variation of the feeding force supplied to the wedge. Although in theory this could be compensated for by adjusting the coolant pressure, a reliable feedback loop would be required to do so, and in absence of such a feedback loop the feed force will be diminishing over time as the abrasive stones wear. Even during the travel of a single honing cycle the net feed force will drop as the wedge feeds against the retraction spring. 
     As an additional limitation, none of the known prior art discussed above includes a means to detect when the honing operation has achieved the desired bore size. Honing is typically performed for a set period of time, or some external means of in-process bore gauging must be employed. 
     As another observed limitation, none of the above referenced prior art discloses a manner of using traditional in-process adjustable feed honing tools on the spindle of a machine tool or machining center. 
     Thus, what is sought is a honing tool holder that provides a capability for automatically feeding the honing elements or stones when in the bore of a work piece, and for automatically stopping the feeding when a particular condition such as a bore size, is reached, to enable use of an in-process adjustable feed honing tool in a machine tool, machining center, or the like, lacking a feed mechanism or system, but including a through-the-spindle coolant delivery system. 
     SUMMARY OF THE INVENTION 
     What is disclosed is a honing tool holder that utilizes a through-the-spindle coolant delivery system, for automatically uniformly feeding the honing elements or stones when in the bore of a work piece, and for automatically stopping the feeding when a particular condition such as a bore size, is reached, to enable use of an in-process adjustable feed honing tool in a machine tool, machining center, or the like, lacking a feed mechanism or system. 
     According to a preferred aspect of the invention, the tool holder has a body having a mounting element for cooperatively mounting the tool holder on a spindle of a machine tool for rotation therewith about a rotational axis therethrough, and a tool holding element opposite the mounting element configured and operable for cooperatively holding a honing tool for rotation about the rotational axis. The tool holder has a feed system carried on the body, configured to connect to a feed element of a honing tool held by the tool holding element, the feed system including a biasing element configured and operable upon occurrence of a predetermined condition, to automatically direct pressure from a pressurized fluid flow received from the spindle to exert a feed force against the feed element to urge honing elements of the tool radially outwardly relative to the tool, and apparatus configured and operable to automatically prevent radial movement of the feed element of the honing tool past a limit. The condition is preferably rotation of the tool holder, and the movement is preferably prevented by preventing the pressurized fluid flow from acting on the biasing element in a feed direction. This is accomplished with a valve mechanism that is centrifugally actuated by the rotation of the tool holder. 
     As an advantage of the invention, the tool holder allows honing tools to be interchangeable between a honing machine and another type of machine tool not specifically designed for honing, providing the non-honing machine the capability of using honing tools that have already been optimized for the honing process. 
     As another advantage, the honing element or elements of the honing tool can be uniformly fed, in the same manner as if used on a dedicated honing machine having a conventional feed system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a representative machine tool having a rotatable spindle with through-the-spindle coolant delivery, and a honing tool holder of the invention for installation in the spindle of the machine tool, and showing a representative honing tool held in the holder; 
         FIG. 2  is an enlarged perspective view of the honing tool holder of  FIG. 1 , showing the honing tool removed therefrom to reveal mounting and feed elements thereof; 
         FIG. 3  is an enlarged sectional view of the tool holder, without a honing tool held therein, and in a non-rotated state; 
         FIG. 4  is another enlarged sectional view of the tool holder, in a first pressurized state representative of when installed in a spindle and rotated; 
         FIG. 5  is another enlarged sectional view of the tool holder, showing a feed rod assembly of the holder adjusted to a different length; 
         FIG. 6  is still another sectional view of the tool holder, showing an alternative orifice configuration; 
         FIG. 7  is an exploded perspective view of upper elements of the tool holder; 
         FIG. 8  is a continuation of  FIG. 7 , showing lower elements of the tool holder; and 
         FIG. 9  is a simplified schematic side view of the tool holder of the invention, in operation holding a honing tool and stroking the tool in a bore of a work piece. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, in  FIG. 1 , a conventional computer numerical control or “CNC” machine tool  10  is illustrated, including a vertical spindle  12  of well-known construction and operation. Spindle  12  is automatically controllably rotatable about a vertical rotational axis Z, and movable upwardly and downwardly along axis Z, by a controller  14  of machine tool  10 , in the well-known manner. Machine tool  10  additionally includes a table  16  controllably movable horizontally along an X axis and a Y axis by controller  14 , and configured and operable for supporting one or more or fixtures  18  for holding a work piece or work pieces on which work operations will be performed by machine tool  10 . Controller  14  is of conventional construction and operation, and is a microprocessor controlled device automatically operable for executing a machining program for controlling spindle  12  and table  16  for performing the machining operations in the well-known manner. Such operations conventionally include, but are not limited to, milling, drilling, boring, reaming, threading, and the like. The respective operations are performed using tools specialized for the operations, which are held by tool holders insertable into and held by spindle  12 , also in the well-known manner. Machine tool  10  will additionally usually include a tool changer (not shown) configured and operable for automatically inserting the respective tools into spindle  12  for commencement of operation, and removing of the tools after the operation is complete, also under control of controller  14 . A honing tool holder  20  constructed and operable according to the teachings of the present invention, is illustrated as being insertable into spindle  12  for rotation and upward and downward movement thereby. Honing tool holder  20  is illustrated holding a honing tool  22 . Here, it should be noted that although rotational axis Z is illustrated as a vertical axis, the present invention is also configured for operation and other orientations, including, but not limited to, a horizontal axis. 
     Referring also to  FIG. 2 , honing tool  22  is representative of a wide variety of in-process adjustable feed honing tools including an elongate, hollow mandrel  24  which receives and carries a feed or wedge element  26  for longitudinal movement therein. Wedge element  26  has one or more wedge surfaces (not shown) located within mandrel  24  and which bear against mating wedge surfaces (also not shown) on honing elements  28  extending through slots  30  through the sides of mandrel  24  at angularly spaced locations thereabout. In operation, movement of wedge element  26  longitudinally into mandrel  24  (downwardly as depicted by arrow F in  FIG. 2 ) will cause sliding relative movements of the wedge surfaces, which, in turn, will cause uniform radial outward movement or feed of honing elements  28 , as denoted by the small arrows emanating radially from elements  28 . Movement of the wedge element longitudinally outwardly relative to the mandrel (opposite of direction F) will allow the honing elements to radially retract. If in a work piece bore, once the honing elements are radially moved outwardly so as to contact the surface of the bore, application of a force in direction F against the wedge element, commonly referred to as a feed force, will act to transmit a radial outward force against the honing elements, which will be exerted against the surface of the work piece bore. The honing elements will comprise an abrasive substance, in the form of a stone or layer of abrasive particles, selected to achieve a desired honing or bore finishing effect, such as, but not limited to, a particular bore size, surface finish, trueness or concentricity, shape, or the like. 
     Honing tool  22 , like many other in-process adjustable honing tools, has a mounting end  32  of a standard shape and size suitable for insertion into and retention by a honing machine spindle. At the same time, a wedge coupler  34  on the end of wedge element  26  is connectable to a feed rod of a feed mechanism located within the spindle of the honing machine and controllably movable in direction F and the opposite direction. In typical operation, at an appropriate time or times in the honing cycle or operation, the feed rod of the honing machine will be moved in direction F relative to the mandrel of the honing tool, to bring the honing elements into contact with the surface of the bore of a work piece in which the tool is located, and the feed force applied, during relative rotation and stroking of the tool and work piece, to effect honing the bore surface. Upon completion of a desired honing step or operation, the feed rod will be moved in the opposite direction, to remove the feed force and the tool can be withdrawn from the bore, or another honing operation performed. 
     Feed mechanisms similar to those of conventional honing machines as just described, are not present in the spindles of other machine tools, such as milling machines, machining centers, and the like, such as representative machine tool  10  illustrated. As a result, in-process adjustable feed honing tools such as tool  22  are normally not usable with a conventional, non-honing type machine tool or machining center such as machine tool  10 . However, many machine tools such as machine tool  10  will include a through-the-spindle coolant delivery system that pumps pressurized coolant fluid, such as, but not limited to, a commercially available water or oil based liquid coolant, through spindle  12 , so as to be discharged from a port P within the spindle, in a well-known manner. 
     Honing tool holder  20  remedies the above shortcoming with regard to a lack of a feed system, by including an integrated feed system which has a capability to utilize the pressure of the through-the-spindle coolant feed to provide feed force, and which will automatically initiate feeding of the honing elements at a desired point in the honing process, and stop the feeding when a limit is reached. Honing tool holder  20  also has the capability to automatically output a signal indicating the reaching of the limit, such that the honing cycle or operation can be halted, altered, or other step taken.  FIGS. 1 and 2  show that the tool holder  20  has a relatively large body  36  including a mounting end  38  having a tapered shank  40  made to a standard connection specification (such as, but not limited to, CAT, HSK, etc.) so as to be installable in the manner of a conventional tool holder in a matching collet of the spindle of a machine tool or machining center including a through-the-spindle coolant delivery system, but not including a feed system or mechanism, as represented by spindle  12  of machine tool  10 . Mounting end  38  of tool holder  20  additionally includes a flange  42  about mounting end  38  adjacent to tapered shank  40  and adapted for engagement with a conventional tool changer operable for installing and removing tool holder  20  from a spindle, such as spindle  12 . When installed in a spindle, such as spindle  12 , a central axis A of tool holder  20  will be coaxial with a rotational axis of the spindle (here, rotational axis Z), and tool holder  20  will be rotatable and movable upwardly and downwardly with the spindle. 
     Referring also to  FIGS. 3 through 9  which show elements of tool holder  20 , within the top of body  36 , disposed within flange  42  and adjacent mounting end  38 , are elements of a feed system  44  completely contained on tool holder  20  and configured to receive pressurized fluid coolant from in-the-spindle port P of a spindle to which the holder is mounted (here, spindle  12 ), and connect or couple to and operate a feed element of a honing tool held by the tool holding element (here, wedge element  26  of honing tool  22  via connection with coupler  34 ). Feed system  44  includes a fluid pressure operated biasing element  46  configured and operable upon occurrence of a predetermined condition, to automatically direct a pressurized fluid flow received from port P of spindle  12  as a feed force against the feed element (wedge element  26  of tool  22 ) via a feed rod assembly  100  (described in detail below) to urge honing elements  28  of the tool radially outwardly relative to the tool. Feed system  44  also includes apparatus configured and operable to automatically prevent the radial movement of the feed element of the honing tool and thus honing elements  28  past a limit. Still further, feed system  44  additionally includes a release mechanism  48  configured and operable to utilize the fluid pressure to automatically hold the feed element in a retracted position and prevent the exertion of the feed force against wedge element  26  until a predetermined condition occurs, which here is initiation of rotation of tool holder  20 , as will be explained. 
     Biasing element  46  of feed system  44  includes a feed piston assembly  50  which consists of a piston  52  carried in a cylinder bore  54  of a cylinder housing  56  carried in body  36 . An upper first end of cylinder bore  54  is covered by an orifice plate  58  which also bounds and defines the lower extent of a radially extending release valve passage  60  within body  36  which is a part of release mechanism  48 . The upper extent of valve passage  60  is bound by a flange  62  having a threaded receptacle which threadedly receives a lower end of shank  40 . Shank  40  includes a connecting passage  64  therethrough which, when installed in a spindle such as spindle  12  having through-the-spindle coolant delivery, connects via an inlet orifice  66  with release valve passage  60  on the lower end and with port P of the spindle on the upper end, as evident in  FIGS. 4, 5, and 6 . 
     Release mechanism  48  is preferably centrifugal force operated and includes a release valve element  68  disposed in release valve passage  60  and movable radially between a first position ( FIG. 3 ) adjacent and slightly eccentric to the axial center, and thus to the center of rotation, of tool holder  20 , and a second position ( FIGS. 4, 5, and 6 ) radially outwardly of the first position and thus more eccentric to the axial center. Valve element  68  is biased toward the first position by a biasing spring  70  disposed between a portion of body  36  enclosing the radial end of passage  60  and valve element  68 . Suitable spacer blocks  72  ( FIG. 7 ) define the lateral sides of passage  60 . Valve member  68  is a two way valve member and includes a first passage  74 , and a second passage  76 , therethrough. 
     When in the first position, which comprises a retract mode of release mechanism  48 , first passage  74  is aligned with and connects inlet orifice  66  with a bypass port  78  extending through orifice plate  58  and cylinder housing  56  to a lower end  80  of cylinder bore  54 , below piston  52 . A ball check valve  82  is located in port  78 , oriented to allow flow to lower end  80 , but not in the opposite direction. When in the second position, which comprises a feed or release mode of mechanism  48 , second passage  76  is aligned with inlet orifice  66  and a feed port  84  through orifice plate  58  in an upper end  86  of cylinder bore  54 . A connecting port  86  extends through piston  52  or another suitable path between lower end  80  and upper end  86  of cylinder bore  54 , and includes a ball check valve  90  operable to allow flow from upper end  86  to lower end  80 , but not in the reverse direction. 
     When release valve element  68  is in the first position, the pressurized fluid from port P of the spindle will fill and pressurize port  78  and lower end  80  of cylinder bore  54 , to maintain piston  52  in an upper position, shown in  FIGS. 3 and 4 . 
     When valve element  68  is in the second position, the fluid from port P will fill and pressurize the upper end  86  of bore  54 . The pressurized fluid will also be able to flow, and the pressurization will be communicated, through check valve  90  and connecting port  88  from upper end  86  to lower end  80 . Thus, the pressurized condition will exist in bore  54  on both ends of piston  52 . 
     Here it should be observed that piston  52  has a lower axially facing surface  92  in lower end  80  of bore  54  having an annular shape with an outer diametrical extent bounded by the surface of bore  54 , and an upper axially facing surface  94  that is circular, but of the same outer diametrical extent as lower surface  92 . The lower end of piston  52  additionally includes a downwardly projecting portion that serves as an upper feed rod  96  of feed rod assembly  100 . As a result, it can additionally be observed that lower axially facing surface  92  has a smaller sectional area than upper axially facing surface  94 , which will be important for reasons discussed below. The check valve  90  may be configured upon assembly, via an inversion of the seat  144  below the check ball, to be permanently in a closed position. In this case the second position described in the previous paragraph will result in only the top side of piston  52  being pressurized. This will allow for a greater force to be applied to the feed rod assembly  100 . The decision regarding whether check valve  90  is installed as active or as permanently locked is dependent on the feed force requirements of the honing application. Users of this device, with training on proper disassembly and assembly of the device may thereby change the feed force range of the tool holder from one of lower force capability to one of higher force capability. 
     Feed rod assembly  100  additionally includes a lower feed rod  98  that extends downwardly through an inner passage of tool  20  to a coupler  104  for coupling to wedge coupler  34  of a tool such as tool  22  held by holder  20  on the lower end. An access hole  148  is preferably provided at this location that allows an operator to insert a tool to release coupler  104  for honing tool installation and removal. 
     The invention preferably includes apparatus operable to automatically prevent radial movement of the honing elements of the tool and thus the final honed size, past a limit. This apparatus additionally preferably enables adjusting the final honed size or other characteristic, and/or adjusting for the wear of the abrasive honing elements of the honing tool. In a preferred embodiment to provide these capabilities, lower feed rod  98  is mounted to upper feed rod  96  by a feed adjusting element  102 . The upper end of lower feed rod  98  is telescopingly receivable in a passage  106  extending axially upwardly from the lower end of upper feed rod  96  and into piston  52 . Feed adjusting element  102  has a threaded hole  108  therethrough aligned with passage  106  and threadedly receives the upper end of lower feed rod  98  which is threaded for this purpose. Adjusting element  102  additionally has an adjusting gear  110  about its outer circumference, and a retaining flange  112  on its upper end. Retaining flange  112  rotatably attaches adjusting element  102  and gear  110  to the lower end of upper feed rod  96 . Gear  106  engages a pinion  114  that in turn engages a ring gear  116  at its lower end. Ring gear  116  is fastened to a feed position adjustment nut  118  rotatably disposed about the lower end of body  36 , so that a measured turn of nut  118  will rotate ring gear  116  to rotate pinion  114 , which in turn will rotate adjusting gear  110 , to threadedly engage lower feed rod  98  to move it upwardly or downwardly within and relative to feed adjusting element  102 . Adjusting element  102  is connected to upper feed rod  96 , such that the upward and downward movement of lower feed rod  98  will also be relative to upper feed rod  96 , so as to effectively shorten or lengthen feed rod assembly  100 , which will translate to adjustment movements of a wedge element  26  coupled to lower feed rod  98  via coupler  104 , which will adjust final bore size achieved by honing elements  28  of a tool held by holder  20 . 
     To provide coolant flow to a honing tool, it can be observed that piston  52  has an additional, optional passage  120  therethrough, connecting with passage  106 . Lower feed rod  98  additionally includes an optional passage  122  therethrough (plugged in  FIGS. 3, 4, and 5 ) connecting passages  106  and  120  with coupler  104 . As a result, when unplugged, as shown in  FIG. 6 , a continuous flow path will exist from the upper end  86  of the cylinder bore to a tool held by holder  20 . This path can be used to communicate the pressurized fluid in the bore to the tool for cooling, lubricating, and flushing purposes. This path can also optionally have a restricting orifice  124  therein, to restrict or meter the flow of coolant, if desired, and help maintain a desired feed force. 
     As another feature of the invention, a window  126  in the side of tool holder exposes an LED  128  (visible or infrared), or a radio frequency transmitter. When feed adjusting element  102  reaches a position corresponding with the final bore size, a limit switch  130  will change state. Switch  130  is part of a sealed unit  132  located within body  36  and containing batteries  134 , a circuit  136  and LED  128 , configured and operable for outputting a signal, denoted by arrow S, indicative of feed system  44  having reached a predetermined settable feed limit. When switch  130  is contacted by element  102  it closes the circuit  136  to provide power from batteries  134  to the LED (and/or optionally an RF transmitter) to send the signal S to a receiver of, or in connection with, controller  14  of machine tool  10  as an indication that the final size and/or other characteristic of a bore  138  of a work piece  140  being honed ( FIG. 9 ) located in a fixture  142  has been reached. Controller  14  then stops the honing cycle, e.g., by stopping spindle rotation and by withdrawing honing tool  22  from the work piece bore, or performs some other programmed command. 
     As the abrasive stones or other honing elements wear, feed rod assembly  100  must be adjusted. As explained above, adjustment nut  118  on the outside of tool holder  20  can be turned relative to body  36  of the tool holder to lengthen or shorten the effective length of feed rod assembly  100 . This can be accomplished by programmed operation of machine tool  10  which will move table  16  and spindle  12  as required to set tool holder  20  into a “nest” including parallel planes  146  ( FIG. 2 ) that mate with parallel sides of nut  118 . (e.g. like a traditional open-end wrench fixed to some location on the machine tool table.) Machine tool  10  will then rotate spindle  12  (with the tool holder  20 ) by a precise angle corresponding to the amount of feed adjustment required. 
     The complete operation of tool holder  20  is best seen by examination of  FIGS. 3, 4, and 5 .  FIG. 3  illustrates the state of tool holder  20  when not loaded in a spindle, and when located in a spindle but not rotating. In this state, if held in a spindle, such as spindle  12 , and through-the-spindle coolant is supplied via port P of the spindle, the fluid will flow from port P through connecting passage  64  through shank  40  and inlet orifice  66 , to centrifugally actuated release valve element  68  of release mechanism  48 . Because tool holder  20  is not sufficiently rotating at this time, release valve element  68  will have no centrifugal force acting against it, and thus will be held by biasing spring  70  in the first or retracted position shown. This aligns first passage  74  with bypass port  78 , such that the pressurized fluid will be communicated to lower end  80  of cylinder bore  54 . Feed port  84  is thus not directly connected to port P of the spindle. This pressure creates a retracting force RF, which urges piston  52 , feed rod assembly  100 , and a wedge element of a honing tool held by the holder, upwardly toward their retracted positions, which serves to also retract the honing elements of the tool. This mode has utility, for instance, when not honing, and when inserting the honing tool into a work piece bore. 
       FIGS. 4 and 5  illustrate the state of tool holder  20  when rotated sufficiently to automatically centrifugally actuate release mechanism  48 . In this state, the rotation generates sufficient centrifugal force, denoted by arrow CF, acting on release valve element  68  to urge it radially outwardly to its second or feed position shown. Now, second passage  76  of the valve element is aligned with inlet orifice  66  and feed port  84  in connection with upper end  86  of cylinder bore  54 . Bypass port  78  is now disconnected from direct communication with inlet orifice  66  and port P of the spindle. In this configuration, the pressurized fluid is communicated from port P of the spindle directly to the upper end  86  of the bore. Additionally, the pressurized condition may be communicated via connecting port  88  to lower end  80  of the bore, as determined by the assembled configuration of check valve  90 . Because of the difference in size of axially facing surfaces  92  and  94  of piston  52  (upper surface  94  is larger) acted on by the pressurized fluid in lower end  80  and upper end  86 , respectively, of bore  54 , a differential feed force is exerted against piston  52  in the downward direction. This is transmitted through feed rod assembly  100  as feed force F acting against wedge element  26  of tool  22  coupled thereto, which in turn serves to urge honing elements  28  of the tool radially outwardly as depicted by the small arrows in  FIG. 2 . If in the bore of a work piece such as bore  138  of work piece  140  shown in  FIG. 9 , this will provide the required feed force for honing the surface of the bore. 
     In  FIG. 6 , the plug is removed from passage  120  of piston  52 , to allow the fluid to flow through the piston to passage  122  downwardly through the feed rod assembly  100 , as denoted by arrow FF. This fluid is delivered through coupler  104  to the honing tool, and can travel through internal passages of the tool to provide cooling and lubrication, and can exit through coolant ports (not shown) of the tool and/or slots  30  ( FIG. 2 ), to cool the work area and flush particles, in the well known manner. 
     During the honing operation, piston  52  and feed adjusting element  102  move slowly downward as the abrasive honing elements are radially expanded by the feed force F. Eventually, element  102  will advance to limit switch  130 . Switch  130  is encased in sealed unit  132  which is automatically operable to energize LED  128  to output a signal indicative of the position of element  102  to controller  14 , and thus the position of honing elements  28  connected thereto. 
     Machine tool  10  will be programmed for performing the reciprocating motion and relative rotation of the tool and work piece of a typical honing cycle. That programmed cycle will be allowed to continue until the signal is received from the transmitter (e.g., LED  128  on tool holder  20 , or RF signal, etc.). Additionally, the program should include logic to stop a cycle after a maximum time has been reached as an indication that the abrasive honing elements are worn out or no longer in a condition to cut effectively. 
     The control program should also allow for bore size compensation as follows: A manually entered tool comp value would be used by the program to adjust the tool size accordingly. A known approximate honing element or stone wear rate entered by the operator would result in an automatic adjustment of the tool by that amount before each honing cycle. An external gauging device (air gauge, or similar) could feed back information to the machine control system for purposes of adjusting tool size and possibly adjusting the stroke of the honing cycle. 
     The routine of adjusting the tool size will include some programmed machine motions. As one example, adjustment nut  118  of tool holder  20  can automatically be brought into engagement with a set of parallel planes  146  and then the spindle rotated by a proper amount for effecting a change in the overall length of feed rod assembly  100 , as evidenced by the different lengths of  FIGS. 4 and 5 . The control system will need to have a value representative of the wedge angle of the tool and ratio of the internal gearing to accurately calculate the proper rotation angle. 
     As a side note to this, the tool holder with a tool installed may be large enough that it may not be able to be kept in the machine&#39;s magazine. It may need to reside in a nest on the table that is away from the work piece but reachable by the spindle. Such a nest could be designed to include parallel planes  146  or similar apparatus to engage adjustment nut  118  on the tool holder, so that any tool size compensation could be made by a programmed spindle rotation just after it has grasped the tool holder but before it has removed it from its nest. 
     Advantages 
     Although they would not be necessary in all applications, the embodiment of tool holder  20  shown includes a pair of check valves that allows for lower feed forces to be obtained without the need to install an additional pressure regulator on the machine tool. In absence of these check valves, the coolant would be supplied to the top side of the piston for feeding and to the bottom side for retracting. However the area of the top side of the piston might be too great to achieve low levels of feed force even at the minimum pressure supplied by the machine. To achieve lower feed force coolant can be supplied to both sides of the piston as in the present embodiment. This creates a feed force F that is equal to the pressure times the difference between the axially facing top piston area and the bottom piston area, as explained above. 
     As also explained above, when the spindle is not rotating and the coolant is turned on, the pressurized coolant is routed to the bottom of the piston which keeps the feed rod in the retracted position (up). When the spindle rotates at sufficient velocity, then centrifugal force acting on the off-center release valve element will automatically switch the coolant path. The two check valves will change their positions under influence of the coolant pressure and coolant will be supplied to both sides of the piston. This will initiate the feed motion. 
     After final size is reached, as transmitted by LED  128 , the machine tool control system will stop the spindle rotation. Biasing spring  70  will then change the coolant path back to the original state and the piston will retract the feed rod assembly, and the wedge element and honing elements of the attached honing tool. The tool can then be withdrawn from the work piece. 
     An additional feature is that there are no mechanical seals between the piston and its cylinder. This minimizes any friction between the two. Feed forces can be low and the piston will generally move very slowly during honing. Any friction/stick-slip in the system will detract from the constancy of the feed force. Also the centrifugal valve will actuate at lower spindle velocity if it is free to move without friction. Therefore the cylinder and piston will be made with very minimal clearance to minimize leakage past the piston and the valve will also be made with minimal clearance. Since this tool holder will operate in an environment where coolant is sprayed/splashed in all directions, some leakage of the fluid paths inside the tool holder should be of no consequence. The tool holder has sufficient openings to allow the escape of coolant that has leaked out of the pressurized path. 
     Honing Process Control 
     To use this device effectively the machine tool must have some control of coolant pressure. Ideally this would be via existing controls and hardware already in the machine tool. In the absence of that it could be possible to retrofit a pressure regulating device to the coolant delivery system that is either adjusted manually or preferably by a machine output signal. 
     The invention offers the following benefits over the prior art: A constant feed force will be maintained over the full travel of the honing tool and over the life of the abrasive stones. 
     The tool holder has an integral system for sensing a final feed position and sending a signal immediately when that position is reached. The feed position is equivalent to the wedge position in the honing tool and therefore implies a consistent final bore size. When used with honing elements such as abrasive stones that have minimal or consistent stone wear, this will produce close bore size control. 
     The tool holder&#39;s connection to the honing tool is identical to honing machine spindles so that any tools may be used interchangeably in a honing machine or any other machine tool equipped with this tool holder. 
     In light of all the foregoing, it should thus be apparent to those skilled in the art that there has been shown and described a novel HONING TOOL HOLDER WITH A FEED SYSTEM POWERED BY THROUGH-THE-SPINDLE COOLANT PRESSURE AND ACTUATED BY SPINDLE ROTATION. However, it should also be apparent that, within the principles and scope of the invention, many changes are possible and contemplated, including in the details, materials, and arrangements of parts which have been described and illustrated to explain the nature of the invention. Thus, while the foregoing description and discussion addresses certain preferred embodiments or elements of the invention, it should further be understood that concepts of the invention, as based upon the foregoing description and discussion, may be readily incorporated into or employed in other embodiments and constructions without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown, and all changes, modifications, variations, and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is limited only by the claims which follow.