Abstract:
A plurality of fixing holes are made in the upper and side faces of a hollow rectangular prism block body at least the top and four side faces of which are quartz glass or monocrystalline quartz rectangular plates. A plurality of reference members, each having a reference measuring face with which the fore end of a probe of a measuring apparatus is brought into contact, are inserted into the fixing holes, respectively, and secured in place. An inspection master block ensuring a high inspection accuracy by minimizing the effect of ambient temperature variation and a method for producing the same are thereby provided.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application is the national stage under 35 U.S.C. §371 of international application PCT/JP01/00965, filed Feb. 13, 2001 which designated the United States, and which application was not published in the English language. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a testing master block so called an interim testing artifact for inspection or correction of the accuracy of a measuring apparatus such as a three dimensional measuring machine so called a coordinate measuring machine. 
     DESCRIPTION OF THE RELATED ART 
     In the past, for the measurement of the dimensions of machine parts such as automobile engines or transmission cases, the measuring apparatus such as coordinate measuring machines, which measure dimensions by bringing the front end of a probe into contact with a measured object set on a measurement table (bed), have been used generally. 
     This type of measuring apparatus is maintained in accuracy of measurement by using a measurement master finished to a high accuracy to periodically inspect the accuracy or correct measurement error. 
     The measurement master is provided with a reference measurement plane to which a probe of the measuring apparatus may be brought into contact. By comparing the actually measured data of the reference measurement plane obtained by the measuring apparatus with a reference value, it is possible to inspect or correct the accuracy of the measuring apparatus. 
     As this type of measurement master proposed in the past, there is for example the measurement master disclosed in Japanese Unexamined Patent Publication (Kokai) No. 11-44527. Measurement hole members are provided respectively at the four corners of each of the top surfaces, one of the side surfaces and the front surface of a cubic hollow box made of cast iron. 
     Each of these reference hole members is shaped as a cylinder provided with a flange at one end and is bolted to the box with the flange. Further, the inner surface of the cylindrical portion is shaped as a circular hole finished to a high accuracy and forms a reference hole for measurement. 
     Further, in the master measuring apparatus disclosed-in Japanese Unexamined Patent Publication (Kokai) No. 4-160301, rods formed of a glass material with a coefficient of linear expansion of a value of about 0 are assembled into a grid and fastened to the outside of a cube-shaped or box-shaped hollow support block comprised of a low expansion material. The two end surfaces of the rods form the reference measurement planes, and at least three balls formed by a glass material etc. for setting reference coordinates are attached to the top surface of the support block. 
     In the inspection master disclosed in the above mentioned Japanese Unexamined Patent Publication (Kokai) No. 11-44527, since the reference hole members are attached to a hollow box made of cast iron, if a portion of the cast iron box expands or contracts due to a change of the ambient temperature, the distance or angle between the reference hole members changes slightly and it will be caused some defects on the inspection accuracy. 
     Further, in the master measuring apparatus disclosed in Japanese Unexamined Patent Publication (Kokai) No. 4-160301, by using glass material having a linear expansion coefficient of a value of about 0 for rods having two end surfaces as reference measurement planes or balls for setting the coordinates, it is being attempted that the inspection accuracy is improved by holding minimum expansion or contraction of the rods or balls themselves due to a change of the ambient temperature. 
     However, since the rods or balls are supported by a cast iron box, there are some problems that changes in the dimensions of the parts or warping of the shape of the box due to temperature changes of the box gives a bad influence on the inspection accuracy, the structure becomes complicated and the cost of manufacturing becomes higher. 
     DISCLOSURE OF THE INVENTION 
     An objective of the present invention is to provide a testing master block and manufacturing method of the same able to solve the above problems in the prior art and obtain high inspection accuracy by eliminating, as much as possible the effects due to changes in ambient temperature. 
     To achieve the above objective, the first aspect of the testing master block of the present invention is characterized by being provided with a hollow box-shaped block body with at least a top surface and four side surfaces comprised of quartz glass or single crystal quartz rectangular plates and a plurality of reference members each fastened by insertion to a plurality of mounting holes formed in the top surface and side surfaces of the block body and each having a reference measurement plane to which the front end of a probe of a measuring apparatus may be brought into contact. 
     Note that the term “rectangular” as used in this specification includes “square” and the term “box-shaped” includes a “cube”. 
     The second aspect of the testing master block of the present invention is characterized by being provided with a hollow cylindrical block body comprised of a side surface of a quartz glass or single crystal quartz cylindrical tube and at least a top surface of a quartz glass or single crystal quartz disk and a plurality of reference members each fastened by insertion to a plurality of mounting holes formed in the top surface and side surface of the block body and each having a reference measurement plane to which the front end of a probe of a measuring apparatus may be brought into contact. 
     The third aspect of the testing master block of the present invention is characterized by being provided with a block body having at least a top surface and side surfaces and fabricated by being cut out from a single piece of quartz glass or single crystal quartz and a plurality of reference members each fastened by insertion to a plurality of mounting holes formed in the top surface and side surface of the block body and each having a reference measurement plane to which the front end of a probe of a measuring apparatus may be brought into contact. 
     In the first to third aspects of the testing master block, a reference member comprised of a ceramic ball with a surface serving as a reference measurement plane and a bushing holding the ceramic ball and fastened by insertion into a mounting hole of the block body may be used. 
     The first aspect of a manufacturing method of a testing master block of the present invention is characterized by comprising a first step of forming mounting holes at predetermined positions of rectangular plates comprised of quartz glass or single crystal quartz, a second step of forming at least a top surface and four side surfaces of a hollow box-shaped block body by joining a plurality of quartz glass or single crystal quartz rectangular plates so that the rectangular plates formed with the mounting holes in the previous step are positioned at least atone of the four side surfaces and the top surface, and a third step of fastening reference members to which the front end of a probe of a measuring apparatus may be brought into contact by insertion into the mounting holes after the second step. 
     The second aspect of the manufacturing method of a testing master block of the present invention is characterized by comprising a first step of forming mounting holes at predetermined positions of a quartz glass or single crystal quartz disk and a quartz glass or single crystal quartz cylindrical tube, a second step of forming a hollow cylindrical block body by joining a disk formed with mounting holes at the previous step to at least the top surface of the cylindrical tube, and a third step of fastening reference members to which the front end of a probe of a measuring apparatus may be brought into contact by insertion into the mounting holes after the second step. 
     A third aspect of the manufacturing method of a testing master block of the present invention is characterized by comprising a first step of cutting out a block body having at least a top surface and side surfaces from a single piece of quartz glass or single crystal quartz, a second step of forming mounting holes at predetermined positions of the top surface and side surfaces of the block body formed at the first step, and a third step of fastening reference members to which a front end of a probe of a measuring apparatus may be brought into contact by insertion into the mounting holes after the second step. 
     In the first to third aspects of the manufacturing method of a testing master block, the reference members after the third step may be finished into reference measurement planes to which a front end of a probe of a measuring apparatus may be brought into contact. 
     In the testing master block of the present invention (hereinafter referred to as the “master block”), a plurality of reference members formed by a material with a small coefficient of linear expansion such as nonshrinking steel are attached to a block body made of quartz glass or single crystal quartz and reference measurement planes to which a probe of a measuring apparatus may be brought into contact are formed at these reference members. 
     The block body may be formed using rectangular plates made of quartz glass or single crystal quartz for at least the top surface and the four side surfaces and joining these plates into a hollow box or may be formed using a cylindrical tube and a disk made of quartz glass or single crystal quartz for the side surfaces and at least the top surface and joining these cylindrical tube and disk into a hollow cylinder. 
     Note that a commercially available instantaneous adhesive is suitable for joining the rectangular plates or the disk and the cylindrical tube. 
     Further, these reference members are fastened by insertion into mounting holes formed in the rectangular plates or the disk and cylindrical tube by a jig borer or other machine tool in advance before the assembly of the block body. 
     Further, the block body may be fabricated by being cut out into a block shape or tubular shape from a single piece of quartz glass or single crystal quartz using a diamond tool etc. 
     After the outer shape of the block body is cut out, mounting holes for insertion of the reference members are formed in the top surface and side surfaces of the block body by a jig borer etc. 
     Note that the block body cut out from the single material is preferably a hollow shape having a cavity with an open bottom in order to reduce its weight. 
     On the other hand, these reference members may be fastened by screws or other fastening means to the block body, but at this time, it is preferable to adhere the reference members to the mounting holes by applying an adhesive between the peripheral edges of the mounting holes and the reference members so that the fastening positions of the reference members do not shift. 
     Further, it is possible to affix the reference members to the mounting holes of the block body by just an adhesive without using screws or other fastening means. 
     Further, by finishing the reference measurement planes after affixing the reference members to the block body, it is possible to enhance the accuracy of the mounting angles or mounting positions of the reference measurement planes. 
     Note that the reference members may also be comprised using the surfaces of ceramic balls finished to a high accuracy as the reference measurement planes. 
     A quartz glass or single crystal quartz material has an extremely small coefficient of linear expansion, so the distance between the reference measurement planes of the reference members attached to the block body and the orientation of the reference measurement planes are almost completely free of the effect of changes in the ambient temperature and a high accuracy can be maintained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the state of setting a testing master block according to the first embodiment of the present invention in a coordinate measuring machine; 
     FIG. 2 is a perspective view of a first embodiment of a testing master block of the present invention; 
     FIG. 3 is a disassembled perspective view of a first embodiment of a testing master block of the present invention; 
     FIG. 4 is a partial sectional view of a structure for mounting a reference member to an upper plate; 
     FIG. 5 is a perspective view of a second embodiment of a testing master block of the present invention; 
     FIG. 6 is a disassembled perspective view of a second embodiment of a testing master block of the present invention; 
     FIG. 7 is a longitudinal sectional view along the line A—A of FIG. 5; 
     FIG. 8 is a partial sectional view of a structure for mounting a reference member to an upper plate; 
     FIG. 9 is a partial sectional view of a structure for mounting a reference member to a cylindrical tube; 
     FIG. 10 is a partial sectional view of another aspect of a reference member; 
     FIG. 11 is a perspective view of a third embodiment of a master block body of the present invention; 
     FIG. 12 is a disassembled perspective view of the third embodiment of a master block body of the present invention; 
     FIG. 13 is a plane view of the third embodiment of a master block body of the present invention; 
     FIG. 14 is a longitudinal sectional view along the line B—B of FIG. 13; 
     FIG. 15 is a bottom view of the third embodiment of a master block body of the present invention; and 
     FIG. 16 is a partial sectional view along the line C—C of FIG.  15 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Next, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 shows a first embodiment of a master block of the present invention. The master block  1  in the embodiment is fastened to a jig pallet  4  placed on a measurement table  3  of a coordinate measuring machine  2  and is used for inspection or correction of its accuracy. 
     The coordinate measuring machine  2  is comprised of a gantry-type movable frame  5  supported at the two sides of the measurement table  3  slidably in the X-direction shown in the figure, a head portion  6  slidably supported at the movable frame  5  and slidable in the Y-direction perpendicular to the X-direction, and an elevation shaft  7  supported to be vertically movable in the vertical direction, that is, the Z-direction of the figure, and can move and position the probe  8  fastened to the bottom end of the elevation shaft  7  in three-dimensional directions. 
     The front end of the probe  8  is comprised of a hard material having wear resistance such as artificial ruby or ceramic formed into a high accuracy spherical shape. In normal measurement work, the coordinate measuring machine  2  brings the front end of the probe  8  into contact with the finished surface of an engine block or other workpiece placed on the measurement table  3 , measures the displacement of the probe  8  from the reference position, and inspects if the workpiece is being finished to the prescribed dimensions. 
     On the other hand, when inspecting the accuracy of the coordinate measuring machine  2  itself, the front end of the probe  8  is brought into contact with the reference measurement plane of a reference member  9  made of nonshrinking steel provided at the master block  1  instead of a workpiece, and the distance between the reference measurement planes of two reference members  9  provided at the master block  1  is actually measured and compared with a reference value so as to investigate the error between the actually measured value and the reference value or calibrate the coordinate measuring machine based on the actually measured error. 
     As shown in FIG. 2, the master block  1  is comprised of a substantially box-shaped block body  1 A and reference members  9  attached to the top surface and the side surfaces. 
     The block body  1 A is comprised of a top plate  10 , side plates  11 , and a bottom plate  12  made of quartz glass and formed into substantially rectangular shapes bonded together by an adhesive (commercially available instantaneous adhesive etc.) 
     FIG. 3 is a disassembled perspective view of the master block  1 . The top plate  10  and the four side plates  11  are formed with mounting holes  13  for mounting the reference members  9  at the four corners passing through the plates in the thickness direction. 
     Further, air holes  14  are formed for circulation of air between the inside and outside of the master block  1  at three locations at the top plate  10  and two locations of each of the side plates  11 . 
     Note that these air holes  14  are for preventing a difference in air pressure between the inside and outside of the block body  1 A and warping of the block body  1 A due a change of the temperature. It is sufficient if an opening is formed for circulation of air in the bottom plate  12 . 
     On the other hand, a circular through hole  15  is formed at the center portion of the bottom plate  12 . A small diameter portion  16 A of a circular fastening plug  16  is fit into that through hole  15 . 
     The fastening plug  16  is formed with a pair of threaded holes  18  into which two bolts  17  may be engaged. 
     These bolts  17  are inserted from the bottom into a pair of bolt through holes  20  of a fastening plate  19  provided at the sides of a jig pallet  4  (see FIG. 1) and engaged with the threaded holes  18  of the fastening plug  16  to fasten the master block  1  to the fastening plate  19 . 
     Note that the fastening plug  16  is desirably fabricated by nonshrinking steel or another material resistant to expansion and contraction or warping due to temperature. 
     Further, each of these reference members  9 , as shown in FIG. 4, is comprised of a cylindrical portion  9 A having an outer diameter conforming with the mounting holes  13  formed in the top plate  10  or side plates  11  and a flange portion  9 B with a diameter larger than the mounting holes  13 . A threaded hole  9 C into which a bolt  21  may be engaged is formed in the center of the end surface of the cylindrical portion  9 A. 
     The cylindrical portion  9 A of the reference member  9  is formed to a length whereby it partially projects out to the rear side of the top plate  10  or the side plates  11  when inserted from the outside of the top plate  10  or the side plates  11  until the flange portion  9 B abuts against the peripheral edge of a mounting hole  13 . 
     A collar  22  made of elastic urethane is fit over the projecting portion. 
     The collar  22  is formed to a length in the axial direction when not subject to compressive force in the axial direction somewhat longer than the length of the projecting portion of the cylindrical portion  9 A. When a washer  23  is fastened to the end surface of the cylindrical portion  9 A by a bolt  21 , the collar  22  is elastically compressed and gripped between the top plate  10  or the side plate  11  and the washer  23 , whereby the reference member  9  is fastened to the top plate  10  or the side plate  11 . 
     Note that when fastening a reference member  9  by a bolt  21  to the top plate  10  or a side plate  11 , an adhesive (commercially available instantaneous adhesive etc.) may be coated between the contacting portions of the two to prevent a shift of the fastening position of the reference member  9  with respect to the top plate  10  or the side plate  11 . 
     Further, the end surface S 1  of the flange portion  9 B of a reference member  9  and the inside circumferential surface S 2  of the circular depression formed at the center of the end surface S 1  are finished to a high accuracy as a reference measurement plane to which the front end of the probe  8  (see FIG. 1) may be brought into contact. 
     Next, explaining the manufacturing method of the master block  1  configured in the above way, first, six plates, that is, the substantially square top plate  10 , side plates  11 , and bottom plate  12 , made of quartz glass or single crystal quartz shown in FIG. 3 are fabricated. Of these, the top plate  10  and the four side plates are formed with mounting holes  13  for the reference member  9  and air holes  14  by a jig borer or other machine tool. Further, the bottom plate  12  is similarly formed with a circular through hole  15  at its center by a jig borer etc. 
     Next, the four side plates  11  are assembled into a square tubular shape by adhering one end surface of each to an edge of a rear surface adjoining the end surface at the opposite side of that end surface by an adhesive. 
     Further, the top surface  10  and the bottom surface  12  are adhered by an adhesive to the upper and lower end surfaces of these four side plates to assemble the block body  1 A (see FIG.  2 ). 
     Next, the cylindrical portions  9 A of the reference member  9  are inserted into the mounting holes  13  from the outside of the block body  1 A and fastened by an adhesive. Further, the collars  22  and washers  23  are fit over the reference members  9  as shown in FIG.  4  and the members fastened to the plates  10  and  11  by the bolts  21 . 
     In this way, the reference members  9  are firmly fastened to the block body  1 A by the adhesive and the bolts  21 . 
     Note that the work of fitting the collars  22 , washers  23 , and bolts  21  to the reference members  9  may be performed by inserting the hand or a box spanner or other fastening tool from the through hole  15  formed in the bottom plate  12  inside of the block body  1 A. Further, the fastening plug  16  has to be inserted into the block body  1 A in advance before the block body  1 A finishes being assembled. 
     After fastening the reference members  9  to the block body  1 A in this way, the small diameter portion  16 A of the fastening plug  16  is fit into the through hole  15  of the bottom plate  12  and fastened to a jig pallet of a not shown machine tool by the bolts  17  shown in FIG.  3 . 
     Up to this point of time, the end surface S 1  of the flange portion  9 B of each of the reference members  9  shown in FIG.  4  and the inner circumferential surface S 2  of the circular depression formed in the end surface S 1  were left unprocessed. The machine tool is used to precision machine the end surfaces S 1  and the inner circumferential surfaces S 2  of the depressions to precisely form the distances between the inner circumferential surfaces S 2  of the depressions of the adjoining reference members  9  to a reference value and to form them so that the angles between the end surfaces S 1  of the reference members  9  fastened to the surface perpendicular to the block body  1 A becomes precisely 90 degrees, whereby the manufacturing method of the master block  1  is ended. 
     Next, FIG. 5 is a perspective view of a second embodiment of a testing master block of the present invention, while FIG. 6 is a disassembled perspective view of the same. The master block  31  of the present embodiment is provided with a block body  31 A comprised of a cylindrical tube  32  formed with a cylindrical inner surface and made of quartz glass or single crystal quartz, a top plate  33  having a diameter substantially equal to the outside diameter of the cylindrical tube  32 , and a bottom plate  34  having a diameter larger than the cylindrical tube  32 . 
     As shown in FIG. 5, the top surface and side surfaces of the block body  31 A are provided with reference members  35  and  36  made of nonshrinking steel. Reference members  35  are attached at four locations at equal intervals in the circumferential direction near the outer circumference of the top plate  33 . Further, reference members  36  are attached at four locations in the circumferential direction of the cylindrical tube  32  corresponding to the reference members  35 , two each in the upper and lower directions, for a total of eight locations. 
     As shown in FIG. 6, the four mounting holes  37  to which the reference members  35  are attached are formed passing through the top plate at equal intervals in the circumferential direction. Threaded through holes  38  are formed in the top plate  33  at positions shifted  45  degrees each in center angle from the mounting holes  37 . 
     On the other hand, a through hole  39  is formed in the center portion of the bottom plate  34 . Further, around the through hole  39 , threaded through holes  40  are formed at positions corresponding to the mounting holes  37  formed in the top plate  33  directly above. 
     As shown in FIG. 7, the top plate  33  and the bottom plate  34  are connected by the two ends of four connecting rods  41  passing through the cylindrical tube  32  and formed by nonshrinking steel. That is, the connecting rods  41  are shaped symmetrically in the vertical direction and are formed with threaded portions  41 A at the upper and lower ends. 
     These threaded portions  41 A are inserted into the threaded through holes  38  and  40  formed at facing positions of the top plate  33  and bottom plate  34 . Collars  42  made of urethane polymer and having elasticity are attached to the portions projecting upward from the top plate  33  and portions projecting downward from the bottom plate  34  and are fastened by engagement by nuts  43 . The top plate  33  and the bottom plate  34  are connected integrally across the cylindrical tube  32 . 
     Note that the portions of the connecting rods  41  other than the threaded portions  41  at the two ends have lengths which are substantially equal to the length of the cylindrical tube  32  in the axial direction and have outer diameters which are formed larger than the threaded through holes  38  and  40  formed at the top plate  33  and the bottom plate  34 . 
     Further, each of the connecting rods  41  is formed with threaded holes  41 B at two locations separated from each other in the longitudinal direction in a direction perpendicular to the longitudinal direction. Positioning bolts  44  are engaged with these threaded holes  41 B. 
     These positioning bolts  44  face the outside in the radial direction in the cylindrical tube  32  and abut against the inner circumferential surface of the cylindrical tube  32  at their front ends, whereby the center of the cylindrical tube  32  is matched with the center of the top plate  33  and the bottom plate  34 . 
     Further, lock nuts  45  are engaged with the positioning bolts  44 . These lock nuts  45  fasten the engagement position of the positioning bolts  44  adjusted in position with respect to the connecting rods  41 . 
     Next, FIG. 8 is a partial sectional view of the mounting structure of a reference member  35  to the top plate  33 . The reference member  35  is comprised of a threaded portion  35 A which is passed through a mounting hole  37  formed in the top plate  33  and a flange portion  35 B having an outside diameter larger than the diameter of the mounting hole  37  exposed at the surface of the top plate  33 . 
     The reference member  35  is formed with a through hole at its center across the total length in the axial direction. The end surface S′ 1  of the flange portion  35 B and the inner circumferential surface S′ 2  of the through hole are finished to a high accuracy as reference measurement planes to which the front end of a probe  8  (see FIG. 1) may be brought into contact in the same way as the reference member  9  in the first embodiment. 
     Further, the threaded portion  35 A has a length projecting out to the rear surface of the top plate  33  at the position inserted into the mounting hole  37  up to where the flange portion  35 B abuts against the front surface of the top plate  33 . An urethane polymer collar  46  having elasticity and a washer  47  are fit over the projecting portion. Further, the reference member  35  is fastened to the top plate  33  by engagement of a nut  48 . 
     Note that in the reference member  35  in the present embodiment, in the same way as the reference member  9  of the first embodiment, the contact portions of the top plate  33  and reference member  35  are adhered by an adhesive so as to prevent a shift in position of the reference member  35  fastened to the top plate  33 . 
     Next, FIG. 9 is a partial sectional view showing the mounting structure of a reference member  36  to the cylindrical tube  32 . The reference member  36  has a shape similar to the reference member  35  and is comprised of a threaded portion  36 A and a flange portion  36 B. A through hole is formed in the center through the entire length in the axial direction. The end surface S″ 1  of the flange portion  36 B and the inner circumferential surface S″ 2  of the through hole are finished to a high accuracy as reference measurement planes. 
     The threaded portion  36 A of the reference member  36  is inserted into a mounting hole  49  formed passing through the cylindrical tube  32  in the radial direction and fastened by engagement of a nut  50  from the inside of the cylindrical tube  32 . To deal with the curvature of the inner and outer circumferential surfaces of the cylindrical tube  32 , an outer collar  51  and inner collar  52  formed at the centers with holes through which the threaded portion  36 A may pass are arranged at the outside and inside of the cylindrical tube  32 . 
     The surfaces of the outer collar  51  and the inner collar  52  abutting against the inner and outer circumferential surfaces of the cylindrical tube  32  are formed by a concave curved surface and a convex curved surface conforming to the radii of curvature of the inner and outer circumferential surfaces so that no bending stress is generated inside the cylindrical tube  32  due to the fastening by the nut  50  engaged with the threaded portion  36 A. 
     These outer collar  51  and inner collar  52  are fabricated from nonshrinking steel. The outer collar  51  and the flange portion  36 B of the reference member  36  and the outer collar  51  and the cylindrical tube  32  are adhered by an adhesive. 
     Next, explaining the manufacturing method of a master block  31  comprised as mentioned above, first a cylindrical tube  32 , top plate  33 , and bottom plate  34  made of quartz glass or single crystal quartz as shown in FIG. 6 are fabricated. 
     Here, the mounting holes  49  of the cylindrical tube, the mounting holes  37  and the threaded through holes  38  of the top plate  33 , and the through hole  39  and the threaded through holes  40  of the bottom plate  39  are formed by a jig borer or other machine tool. 
     Note that the threaded through holes  38  of the top plate  33  and the threaded through holes  40  of the bottom plate  34  are desirably formed with the top plate and the bottom plate  34  superposed concentrically so as to prevent deviation of the machining position. 
     Next, four connecting rods  41  fabricated in advance are inserted into the cylindrical tube  32  in the state with the positioning bolts  44  and the lock nuts  45  attached. The threaded portions  41 A of the two ends of each are inserted into the threaded through holes  38  of the top plate  33  and the threaded through holes  40  of the bottom plate, fitted with washers  42 , and loosely fastened by nuts  43 . 
     Next, the front ends of the positioning bolts  44  are made to abut against the inside circumferential surface of the cylindrical tube  32  and are precisely adjusted in position so that the cylindrical tube  32 , the top plate  33 , and the bottom plate  34  become concentric and are fastened by lock nuts  45  at the adjusted position so that the positioning bolts  44  do not turn. 
     Next, nuts  43  are fastened to integrally connect the cylindrical tube  32 , the top plate  33 , and the bottom plate  34  to complete the assembly of the block body  31 A. 
     Note that an adhesive is preferably coated to adhere the top and bottom end surfaces of the cylindrical tube  32  and the top plate  33  and bottom plate  34 . 
     After the assembly of the block body  31 A is completed, the reference members  35  and  36  are attached to the mounting holes  37  of the top plate  33  and the mounting holes  49  of the cylindrical tube  32 . At that time, the threaded portions  35 A of the reference members  35  are inserted from the outside from the mounting holes  37  of the top plate  33 , then the flange portions  35 B and peripheral edges of the mounting holes  37  of the top plate are adhered by an adhesive. 
     Further, the collars  46  and washers  47  are fit to the threaded portions  35 A from the inside of the top plate  33  as shown in FIG.  8  and fastened by engagement with nuts  48 . 
     Further, the threaded portions  36 A of the reference members  36  to which the outer collars  51  are fit as shown in FIG. 9 are inserted from the outside into the mounting holes  49  of the cylindrical tube  32 . The outer surfaces and the inner surfaces of the outer collars  51  are adhered by an adhesive to the outer circumferential surfaces of the flange portion  36 B and the cylindrical tube  32 . 
     The inner collars  52  are fit over the threaded portions  36 A projecting to the inside of the cylindrical tube  32  and fastened by engagement with nuts  50 . 
     Note that the work of fitting the collars  46 , washers  47 , and inner collars  52 , nuts  48  and  50  over the reference members  35  and  36  in the block body  31  may be performed by inserting the hand or a box spanner or other fastening tool from the through hole  39  formed in the bottom plate  34  inside of the block body  31 A in the same way as the through hole  15  formed in the bottom plate  12  of the first embodiment explained above. 
     Further, the through hole  39  serves also as an air hole for preventing a difference of air pressure between the inside and outside of the block body  31 A and deformation of the block body  31 A due to changes in the ambient temperature. 
     After the reference members  35  and  36  finish being attached to the block body  31 A, the portion of the bottom plate  34  of the block body  31 A projecting outside the cylindrical tube  32  in a flange manner is fastened to the fastening member of the jig pallet of a not shown machine tool. Further, the still not yet finished end surfaces S′ 1  and inner circumferential surfaces S′ 2  of the through holes of the flange portions  35 A of the reference members  35  and the end surfaces S″ 1  and inner circumferential surfaces S″ 2  of the through holes of the flange portions  36 A of the reference members  36  are precision machined, thereby completing the manufacturing method of the master block  31 . 
     Note that in the present embodiment, the end surfaces S′ 1  of the reference members  35  and the end surfaces S″ 1  of the reference members  36  are finished to form precisely right angles with each other. Further, they are finished so that the center positions of the inner circumferential surfaces S′ 2  of the through holes of the reference members  35  and the inner circumferential surfaces S″ 2  of the through holes of the reference members  36  are arranged at every 90 degrees center angle with respect to the center of the block body  31 A. 
     Next, FIG. 10 shows another example of a reference member. The reference member  53  shown in the figure is comprised of a hollow bush  53 C having a threaded portion  53 A and flange portion  53 B and a ceramic ball  53 D. 
     The ceramic ball  53 D uses the surface as a reference measurement plane and is finished precisely to a predetermined diameter. It is fastened by an adhesive to a fastening seat “a” formed at part of the spherical surface of the bush  53 C conforming to the ceramic ball  53 D. 
     In the same way as the master blocks  1  and  31  of the above embodiments, the threaded portion  53 A of the reference member  53  is inserted from the outside into the mounting hole  55  of the quartz glass or single crystal quartz plate  54  comprising the block body, an elastic urethane polymer collar  56  is fit over the threaded portion  53 A from the rear side of the plate  54 , and this is fastened by engagement of a nut  57 . 
     Note that in the master blocks  1  and  31  of the embodiments discussed above, the block bodies  1 A and  31 A are provided with bottom plates  12  and  34  comprised of quartz glass or single crystal quartz, but these bottom plates  12  and  34  may also be omitted and portions other than the bottom plates such as the side plates  11  or cylindrical tube  32  may be fastened directly to the jig pallet etc. 
     Next, FIG. 11 is a perspective view of a third embodiment of a testing master block of the present invention, FIG. 12 is a disassembled perspective view of the same, and FIG. 13 is a plane view. The master block  61  of the present embodiment is provided with a block body  61 A fabricated by being cut out from a single piece of quartz glass or single crystal quartz. 
     The block body  61 A has a smooth top surface  62  and has flat surfaces  64  at four locations in the circumferential direction extending from the top end to close to the bottom end of the cylindrical outer circumference  63 . Further, inside, to reduce the weight, is formed a space opened at the bottom as shown in FIG.  14 . 
     The block body  61 A is formed with mounting holes  65  at four locations in its top surface  62  and at two locations each above and below in each of its four flat surfaces  64 . Reference members  66  are fastened to these mounting holes  65 . 
     These reference members  66  have tubular parts  66 A and flange parts  66 B. They are similar to those used in the above embodiments, but the reference members  66  of this embodiment are fastened by just an adhesive in the state with the tubular parts  66 A inserted into the mounting holes  65 . 
     FIG. 15 is a view of the block body  61 A seen from below. As shown in the figure, the bottom surface  67  of the block body  61 A is formed at three locations at equal intervals in the circumferential direction with projecting legs  68  with smooth bottom surfaces for stable placement of the block body  61 A on the measurement table of a coordinate measuring machine. 
     As shown in FIG. 16, the bottom surface  67  is formed with shallow recesses  69  at two facing locations in a single diametrical direction of the block body  61 A. Each of these recesses  69  is formed with a positioning hole  70  for insertion of a positioning pin projecting out at a measurement table side of the coordinate measuring machine. 
     In the master block  61  of the present embodiment, below a facing two of the four flat surfaces  64  formed by partially cutting away the cylindrical outer circumference  63  of the block body  61 A, pairs of holding grooves  71  are formed in parallel with these flat surfaces  64 . 
     These pairs of holding grooves  71  are for insertion of supporting forks mounted to a setting device for moving and setting the master block  61  at a measurement position on a measurement table of a coordinate measuring machine. The master block  61  is lifted by the supporting forks of the setting device, moved from a retracted position to the measurement position on the measurement table, and lowered on to the measurement table there at the time of inspection of the accuracy of the coordinate measuring machine. 
     At that time, the master block  61  is supported at a fixed position on the measurement table by the three legs  68  formed on the bottom surface  67  in the state positioned with respect to the measurement table by insertion of the positioning pins projecting out from the measurement table side into the pair of positioning holes  70  formed in the block body  61 A. 
     Note that as such a setting device, it is possible to use the one already proposed by the present inventor and filed for in Japanese Patent Application No. 2000-017583. 
     Further, as the master block  61  of the present embodiment, it is possible to use one having ceramic balls instead of the reference members  66  as shown in FIG.  10 . 
     Next, explaining the manufacturing process of the above master, block  61 , first, the outer shape of the block body  61 A is cut out from a single piece of quartz glass or single crystal quartz by a machine using a diamond tool etc. At that time, to lighten the block body  61 A, a cavity with an open bottom is formed. 
     Next, mounting holes  65  for mounting the reference members  66  are formed by a jig borer or other machine in the top surface  62  and side surfaces  64  formed at the block body  61 A. 
     After forming the mounting holes  65 , the tubular members  66 A of the reference members  66  are inserted into the mounting holes  65  until their flange parts  66 B abut against them. 
     At that time, an adhesive is used between the inner circumferences of the mounting holes  65  and the tubular parts  66 A of the reference members  66  or between the top surface  62  or side surfaces  64  of the block body and the flange parts  66 B of the reference members  66 , or both, to adhere the reference members  66  to the block body  61 A. 
     After adhering the reference members  66  to the block body  61 A in this way, the measurement planes of the reference members  66  are finished to predetermined accuracies to complete the master block  61 . 
     INDUSTRIAL APPLICABILITY 
     Summarizing the effects of the invention, as explained above, according to the aspect of the invention set forth in claim  1 , since a hollow box-shaped block body is comprised by rectangular plates made of quartz glass or single crystal quartz and since a plurality of reference members having reference measurement planes to which the front end of a probe of a measuring apparatus may be brought into contact are fastened by insertion into mounting holes formed in the top surface and side surfaces, there is almost no expansion or contraction of the block body due to changes in the ambient temperature, it is possible to maintain the distance or angle of the reference measurement planes of the reference members constant at a high accuracy, and it is possible to improve the inspection accuracy. 
     According to the aspect of the invention set forth in claim  2 , in the same way as the aspect of the invention set forth in claim  1 , there is almost no expansion or contraction of the block body due to changes in the ambient temperature, it is possible to maintain the distance or angle of the reference measurement planes of the reference member constant at a high accuracy, and it is possible to improve the inspection accuracy. Further, due to the use of a quartz cylindrical tube for the side portion of the block body, the assembly becomes easier and the manufacturing cost can be reduced. 
     According to the aspect of the invention set forth in claim  3 , since the block body to which the reference members are fastened is fabricated by being cut out from a single piece of quartz glass or single crystal quartz, the block body has a high rigidity and is substantially free from expansion or shrinkage due to changes in temperature. Therefore, it is possible to maintain the intervals or angles between the reference measurement planes of a plurality of reference members at a higher accuracy. 
     Further, according to the aspect of the invention of claim  4 , in addition to the effects of the aspects of the invention as set forth in claims  1  to  3 , since the reference member is comprised by a ceramic ball having its surface as a reference measurement plane and a bushing fastened by insertion into a mounting hole of the block body, the wear of the reference measurement plane is reduced and a high accuracy can be maintained over a long period. 
     Further, according to the aspect of the invention of claim  5 , since at least the top surface and four side surfaces of the hollow box-shaped block body are formed by joining rectangular plates comprised of quartz glass or single crystal quartz, even if an expensive material such as quartz glass or single crystal quartz is used, it is possible to fabricate the body relatively inexpensively, it is possible to lighten the weight of the block body, and it is possible to facilitate the assembly and reduce the cost of manufacture. 
     Further, according to the aspect of the invention of claim  6 , due to the use of a quartz cylindrical tube, the assembly of the block body becomes easier and the manufacturing cost can be reduced compared with the manufacturing method of the aspect of the invention set forth in claim  5 . 
     Further, according to the aspect of the invention of claim  7 , since the mounting holes of the reference members are formed after cutting out the block body from a single piece of quartz glass or single crystal quartz, it is possible to further improve the accuracy of the positions or angles of the mounting holes compared with a block body assembled by joining a plurality of portions formed in advance with mounting holes. 
     Further, according to the aspect of the invention of claim  8 , it is possible to form a reference measurement plane of a reference member with a high accuracy without being influenced by the processing accuracy of the mounting holes formed in the block body. 
     In this case, when forming the block body by cutting it out from a single piece of quartz glass or single crystal quartz, since the block body with the reference members fastened to it is high in rigidity, it is possible to finish the reference measurement planes with a higher accuracy. 
     While the invention has been described with reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.