JPH0752017A - Grinding device and method, and manufacture of prism - Google Patents

Abstract

PURPOSE:To provide a grinding device and its method capable of grinding plural faces to be machined of a workpiece in a short time and with high accuracy. CONSTITUTION:A multistage grinding wheel 15 where plural ring-shaped grinding wheels 31, 32 are concentrically fixed, is rotated and moved along the face S to be machined of a workpiece P, and the face S to be machined of the workpiece P is ground-machined by the outside and inside ring-shaped grinding wheels 31, 32 projected in order toward the side of the face S to be machined. Further, the workpiece P is rotated through a specified angle in order for other faces S to be machined of the workpiece P to be directed to the multistage grinding wheel 15, and thus plural faces S to be machined of the workpiece P are sequentially ground-machined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grinding apparatus and method for grinding a work piece made of a brittle material such as fine ceramics or glass by using a grindstone. The present invention relates to a method for manufacturing a prism in which a prismatic material is ground using a grindstone.

[0002]

2. Description of the Related Art FIG. 10 is an explanatory view of a jig or the like for manufacturing a color separation prism for a VTR, for example. In FIG. 10, the fixing jig 100 has three V grooves 100a on the upper surface.
And a plurality of cut grooves 100b orthogonal to this are formed. In the V groove 100a of this fixing jig 100,
A glass work P, which is a prismatic prismatic material (triangular prismatic material), is horizontally supported. This glass work P is
It is positioned horizontally on the fixing jig 100 with the processed surface, which is one of the side surfaces of the prismatic material, facing upward.

FIG. 11 is an explanatory view of a conventional manufacturing process of the color separation prism. First, in the jig attaching step E1, the glass work P is adhesively fixed in the V groove 100a of the fixing jig 100 with the first processing surface S1 facing upward. Next, in the grinding step E2, the first processed surface S1 of the three glass works P on the fixing jig 100 is ground to a predetermined surface roughness (for example, Rmax is about 10 μm) by using a predetermined grinding wheel. To be done.

Subsequently, in the lapping process E3 and the polishing process E4, the first processed surface S1 of the glass work P after the grinding process is subjected to the lapping process and the polishing process using fine abrasive grains or the like. At the end of the polishing process, the surface roughness of the first processed surface S1 of the glass work P is Rmax 0.01 μm (Ra 0.05).
μm), the flatness is 0.3 μm / surface or less, and the angular accuracy is plus or minus 30 (seconds) or less.

Next, in a peeling step E5, the glass work P is peeled off from the fixing jig 100. Then, in the next jig attaching step E1, the glass work P is processed into the second processed surface S.
The adhesive 2 is fixed in the V groove 100a of the fixing jig 100 with 2 facing upward. Subsequently, the second processed surface S2 of the glass work P is processed with a predetermined accuracy through a grinding step E2, a lapping step E3, and a polishing step E4.

Next, in a peeling step E5, after the glass work P is peeled from the fixing jig 100, the next third processed surface S3 of the glass work P is similarly processed.
In this way, when the processing of the three surfaces of the glass work P is completed, the glass work P on the fixing jig 100 is cut into the cut groove 1.
A color separation prism is completed by cutting the film to a predetermined thickness along 00b.

[0007]

In the above-described conventional method of manufacturing a prism, one processed surface S of the glass work P is processed.
In order to process, the grinding process E2, the lapping process E3,
Three steps of polishing step E4 are required. Therefore, the operator needs to use a grinding device, a lapping device, and a polishing device for each processing surface S. Therefore, if there are many processed surfaces S of the glass work P, there is a problem that the setup work becomes complicated and the processing work takes time.

Further, in the above-described conventional method for manufacturing a prism, since the finishing accuracy in the grinding step E2 is low, the processing amount in the lapping step E3 and the polishing step E4, which are the post-steps, increases. However, since the lapping process and the polishing process are constant pressure processes using fine abrasive grains and the like, the processing amount (processing speed) per time is very small. Therefore, it takes a lot of time to finish the processed surface S in the subsequent process, and there is a problem that the processing time becomes long as a whole.

Incidentally, electrolytic impro dress grinding and MEEC
If (Mechanical Electro Discharge) is used, it is possible to perform highly accurate grinding of the machined surface including surface roughness and the like.
However, these grinding methods have a problem that the processing speed is slow.

In view of the above points, it is a first object of the present invention to provide a grinding apparatus and a grinding method capable of highly accurately processing a plurality of processed surfaces of a workpiece in a short time. Also,
A second object of the present invention is to provide a method for manufacturing a prism, which can grind a plurality of processed surfaces of a prismatic prismatic material in a short time with high accuracy.

[0011]

According to the present invention, the above-mentioned first object is to provide a support means for supporting both ends of a workpiece having a plurality of processing surfaces and a plurality of ring-shaped grindstones having different functions. A multi-step grindstone that is fixed in a concentric shape, and that is closer to the center of the plurality of ring-shaped grindstones so as to project toward the processing surface of the workpiece, a rotating means that rotates the multi-step grindstone, and the multi-step grindstone. Moving means for moving the grindstone along the processing surface of the work piece and the supporting means for rotating the work piece by a predetermined angle, and sequentially turning the work surface of the work piece toward the multi-step grindstone side. And a rotary positioning means for controlling the rotation position.

Preferably, a back surface supporting means for supporting the workpiece is provided on the opposite side of the processing surface of the workpiece supported by the supporting means.

Further, according to the present invention, the first object is to rotate a multi-step grindstone in which a plurality of ring-shaped grindstones are concentrically fixed, and to rotate the multi-step grindstone so that both ends of the multi-step grindstone are supported. By moving along the processing surface, by the ring-shaped grindstone that sequentially protrudes from the outside to the inside on the processing surface side, the processed surface of the workpiece is ground, then,
The workpiece is rotated by a predetermined angle, the other machining surface of the workpiece is directed toward the multi-step grindstone, and the multi-step grindstone is used to sequentially grind a plurality of machined surfaces of the work piece. This is achieved by the grinding method described above.

Further, according to the present invention, the second object is to rotate a multi-step grindstone in which a plurality of ring-shaped grindstones from an outer rough grindstone to an inner finish grindstone are concentrically fixed,
This multi-step grindstone is moved along the processing surface of the prism-shaped prismatic material whose both ends are supported, and the processing surface is mirror-finished by the ring-shaped grinding wheel protruding from the outside to the inside in order. Then, the prismatic material is rotated by a predetermined angle, and another machining surface of the prismatic material is directed toward the multi-step grindstone side, and then the multi-step grindstone sequentially grinds the prismatic material. This is achieved by the prism manufacturing method that is performed.

[0015]

According to the above construction, the machined surface of the workpiece is ground by the multi-step grindstone which moves while rotating along the machined surface via the rotating means and the moving means. in this case,
The machined surface is first ground by an outer ring-shaped grindstone of a multi-step grindstone fixed concentrically.

Next, the machined surface is sequentially ground by the ring-shaped grindstone inside the multi-stage grindstone protruding toward the machined surface side. Therefore, in one step of the multi-step grindstone, the processing surface of the workpiece is ground by the number of ring-shaped grindstones.

Next, when the grinding of one working surface of the workpiece is completed, the workpiece is rotated by a predetermined angle by the rotary positioning means via the supporting means. And
The other processed surface of the work piece is positioned on the multi-step grindstone side, and similar processing is continuously performed by the multi-step grindstone.

Further, by supporting the opposite side of the work surface of the work piece by the back surface supporting means, it is possible to prevent the work piece from being deformed during the grinding process by the multi-step grindstone.

Further, according to the above construction, the plurality of processing surfaces of the prismatic prismatic prism material are mirror-finished in a short time by the multi-step grinding wheel having the ring grindstones from the rough grindstone to the finishing grindstone. It

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to FIGS. It should be noted that the examples described below are suitable specific examples of the present invention, and therefore, various technically preferable limitations are given, but the scope of the present invention particularly limits the present invention in the following description. Unless otherwise stated, the present invention is not limited to these modes.

FIG. 1 shows an embodiment of a grinding apparatus for manufacturing a prism to which the present invention is applied. In FIG. 1, a grinding device 10 includes a chuck 11, a tailstock 12, a rotary encoder 13, a chuck rotation motor 14, a multi-step grindstone 15, an air spindle 16, and a high frequency motor 1.
7, a back support device 18, a support 19, a spindle support 20, a base 21, and a support moving motor 22.
And an air spindle moving table motor 23.

The glass work P to be processed is a prismatic glass prism material (trigonal prism material).
It has three processing surfaces S having a size L = 100 mm and W = 30 mm. The glass work P has a pin P1 attached to one end and a center hole P2 formed at the other end. The chuck 11 is the standing portion 1 of the support base 19.
It is attached to 9a and holds the pin portion P1 on one end side of the glass work P.

The tailstock 12 presses the center 12a against the center hole P2 of the glass work P to rotatably support the other end of the glass work P. And this tailstock 12
The chuck 11 constitutes a supporting means for the glass work P. The glass work P is attached to the upright portion 19a of the support table 19.
The rotary encoder 13 and the chuck rotation motor 14, which are the rotation positioning means, are attached. The chuck rotation motor 14 rotates the chuck 11 by a predetermined angle determined by the rotary encoder 13.

On the processing side B of the glass work P, a multi-step grindstone 15 is arranged in a state of being supported by one end of a rotary shaft 16a of an air spindle 16. As will be described later, the multi-step grindstone 15 has a processing surface S facing the processing side B of the glass work P.
It moves while rotating along with, and the processed surface S is mirror-finished at one time by a plurality of grindstones.

On one side of the air spindle 16, a high frequency motor 17 as a rotating means for rotating the multi-step grindstone 15 via the air spindle 16 is attached.
Further, the air spindle 16 is moved in the arrow A direction with respect to the spindle support 20 by a support moving motor 22. Therefore, the multi-step grindstone 15 can move back and forth with respect to the processing surface S facing the processing side B of the glass work P.

On the non-working side B of the glass work P, a back support device 18 is arranged. The back surface support device 18 supports the back surface of the glass work P on the opposite side of the processed surface S by two pairs of upper and lower (four) support members 18a to prevent deformation of the glass press during grinding. The support member 18a is moved by an air cylinder or the like in the direction of arrow C, which coincides with the direction of arrow A, so that the glass work P can be easily supported and released.

The support 19 is a chuck 11 and a tailstock 1.
2. Supports the back support device 18, etc. This support 1
9 is moved in the arrow B direction orthogonal to the arrow A direction with respect to the base 21 by the operation of the support base moving motor 22. Therefore, the multistage grinding stone 15 can be moved along the processing surface S of the glass work P by driving the support base moving motor 22.

Next, details of the multi-step grindstone 15 will be described. FIG. 2 shows the basic configuration of the multi-step grindstone 15. Figure 2
In, the multi-step grindstone 15 is a grindstone base 30 made of a metal material attached to the rotary shaft N (in this case, the rotary shaft 16a of the air spindle 16), and fixed to the grindstone base 30 concentrically with the rotary shaft N. A ring-shaped roughing grindstone 31,
A ring-shaped finishing grindstone 32 is concentrically fixed to the inside of the roughing grindstone 31.

The finishing grindstone 32 protrudes from the roughing grindstone 31 toward the processing surface S of the glass work P, for example, by an amount (for example, 30 to 50 μm) corresponding to the finishing allowance. The rough grinding wheel 31 on the outer side has, for example, a particle size of 100 to 200 μm.
The diamond abrasive grains of No. 10 are hardened with resinoid bond, and the inner finishing grindstone 32 has, for example, a grain size of 10 to 2
The diamond abrasive grains of 0 μm are hardened with resinoid bond.

While rotating, the multi-step grindstone 15 is fed in a direction along the processing surface S with a predetermined cut amount with respect to the processing surface S of the glass work P. As a result, the roughing grindstone 31 first proceeds while roughing and grinding the processed surface S of the glass work P to form the rough processed surface Sa. Subsequently, the inner finishing grindstone 32 advances while performing finish grinding, and forms a mirror-like finished surface Sb.

In this case, the finished surface Sb has, for example, a flatness of 1 μm / surface or less and an angular accuracy of plus or minus 20.
(Sec) or less, the surface roughness is 0.5 μm of Rmax (Ra 0.
0 μm) or less. Further, in this case, if the cutting amount of the multi-step grindstone 15 is, for example, 1 mm / time, the size of the processing surface S is W = 30 mm and L = 100 mm, and thus the processing amount by the multi-step grindstone 15 is 3 cubic centimeters / Times.

Therefore, the moving speed of the multi-step grindstone 15 is 100
In the case of mm / min, the multi-step grindstone 15 can achieve a processing rate of 3 cubic centimeters / min. The value of 3 cubic centimeters / min is an extremely large value as the processing amount speed of the glass work P or the like.

The specific construction of the multi-step grindstone 15 is shown in FIGS. 3 and 4. In the multi-step grindstone 15 shown in FIG. 4, a rough-working grindstone 31 and a finishing grindstone 32 are integrally joined to a grindstone base 30 having a through hole 30a for the rotation axis N in the center.

In the multi-step grindstone 15 shown in FIG. 4, a roughing grindstone 31 and a finishing grindstone 32 are joined on support rings 33 and 34 made of a metal material. The support rings 33, 34 are attached to the grindstone base 30 with bolts 35. The bolt 35 is used for each support ring 33, 3
4 are arranged at several positions in the circumferential direction. It is preferable that the support rings 33, 34 are counterbored so that the heads of the bolts 35 do not project above the support rings 33, 34.

Next, the operation of the grinding device 10 will be described with reference to FIGS.
Along with this, description will be made with reference to FIG. First, as shown in FIG. 1, both ends of the glass work P are supported by the chuck 11 and the tailstock 12, and the glass work P is attached to the grinding device 10.

Next, the glass work P is rotated by the operation of the chuck rotation motor 14, and the processing surface S of the glass work P is accurately positioned vertically on the processing side B. Next, the support base moving motor 22 is activated, and the support base 1
9 moves in the direction of arrow B1 to move the glass work P to the position shown in FIG.
Positioning is performed at the processing start position C shown in (a). At the same time, the four support members 18a of the back surface support device 18 are pressed against the back surface side of the glass work P and locked. As a result, the back surface side of the glass work P is supported by the back surface support device 18.

Continuing, as shown in FIG.
The multi-step grindstone 15 is positioned at the processing position E of the tailstock 12. At this processing position E, the roughing grinding stone 31 and the finishing grinding stone 32 of the multi-step grindstone 15 are positioned such that a predetermined cut amount is formed on the processing surface S side of the glass work P. Next, the multi-step grindstone 15 is rotated via the air spindle 16 and the high frequency motor 17. Further, the support base moving motor 22 operates to move the support base 19 in the direction of arrow B2 at a predetermined speed.

As a result, the multi-step grindstone 15 is relatively moved in the direction of the arrow B1 and, as shown in FIG. 2, the roughing grindstone 31 and the finishing grindstone 32 simultaneously work the working surface S of the glass work P. Done. Then, as shown in FIG. 5B, when the glass work P moves to the processing end position D where the end surface P3 of the glass work P reaches the edge portion 31a of the roughing grindstone 31, the support base moving motor 22 stops, The grinding of the processed surface S is completed.

In this case, the processed surface S has a flatness of 1 μm / surface or less and an angular accuracy of plus or minus 20 as described above.
(Sec) or less, the surface roughness is 0.5 μm (Ra 0.0
5 μm) or less, and is mirror-finished. Also,
In this case, the processing amount speed of the processing surface S by the multi-step grindstone 15 is about 3 cubic centimeters / min as described above.

Next, the air spindle moving base motor 23 operates in the reverse direction, and the air spindle 16 moves in the direction of arrow A2. Then, as shown in FIG. 5B, the multi-step grindstone 15 moves to a standby position that is away from the glass work P by a predetermined distance. Subsequently, the support base moving motor 22 operates in the reverse direction, and the support base 19 moves to the machining start position C in the direction of arrow B1 as shown in FIG. 5 (a). And
The lock of the support member 18a of the back support device 18 is released, and the support member 18a is separated from the glass work P.

Next, the chuck rotation motor 14 is activated to move the chuck 1 by the amount indicated by the rotary encoder 13.
1 is rotated and the next processing surface S1 of the glass work P is accurately positioned vertically on the processing side a. Continuing,
While the multi-step grindstone 15 is rotated, the support base 19 is moved in the direction of the arrow B2 at a predetermined speed, and a new work surface S is ground. Then, when the grinding of the third processed surface S of the glass work P is completed, the grinding of the glass work P is completed.

As described above, in the grinding apparatus 10, the multi-step grindstone 15 can be used to simultaneously perform rough finishing and finishing, and the finished surface S can be finished with high precision in a short time. In this case, since rough finishing and finishing are performed at the same time, a large error does not occur in the flatness of the finished processing surface S. Further, in this case, since the processing amount by the subsequent lapping processing or polishing processing can be reduced, it is possible to reduce the total process time of the prism manufacturing.

Further, since the plurality of processing surfaces S of the glass work P are sequentially positioned on the processing side B by the rotary positioning means, all the processing surfaces S of the glass work P can be continuously ground. . Therefore, even if the glass work P has a plurality of processed surfaces S, all the processed surfaces S of the glass work P can be continuously ground by one setup, and the grinding can be speeded up. You can

Here, in this grinding apparatus 10, the multi-step grindstone 15 may be one in which a medium working grindstone 36 is mounted between a rough working grindstone 31 and a finish working grindstone 32, as shown in FIG. Good.

In this case, for example, the grindstones 31, 32, 36 are respectively support rings 33, 34, 3 arranged concentrically.
It is joined to 7. And each support ring 33, 34, 3
7 are formed so as to be pressed by the outer support rings, and the outermost support ring 33 is formed by the bolt 3
It is fixed to the whetstone base 30 at 5. In addition, each grindstone 31, 32,
36 is sequentially projected from the outer side toward the inner side toward the processing surface.

In this grinding apparatus 10, the glass work P may be supported at both ends by the method shown in FIG. That is, as shown in FIG.
The pin portions P1 may be attached to both ends of the glass work P and both ends may be supported by the chuck 11. Here, the chuck 11 may be a 3-jaw chuck, a 4-jaw chuck, or a collet chuck.

Further, as shown in FIG. 7B, center holes P2 may be formed at both ends of the glass work P so that both ends of the glass work P are supported by projecting centers. In this case, in order to prevent the glass work P from rotating,
It is also possible to form a detent hole P3 on one end side of the glass work P and engage the detent member with the detent hole P3.

Further, in this grinding apparatus 10, the glass work P may be back-supported by the back-supporting apparatus 18 having, for example, four pairs (8) of upper and lower supporting members 18a.

Further, as shown in FIG. 8A, during the grinding process, the movement track of the multi-step grindstone 15 with respect to the glass work P has a convex shape in the vicinity of the support part of the glass work P, but the support part It changes to a concave shape in the part far from.

Therefore, as shown in FIG.
The movement path of the multi-step grindstone 15 is changed to a concave shape in the vicinity of the supporting portion of the glass work P, and is changed to a convex shape in a portion far from the supporting portion. As a result, the final movement trajectory of the multi-step grindstone 15 becomes closer to a flat surface, and the flatness of the processing surface S can be further improved.

Further, the work piece of the grinding apparatus 10 is
The prism work is not limited to the glass work P, and may be any prism-shaped one made of a brittle material such as glass or fine ceramics and having a plurality of processed surfaces.

Next, the whole process of manufacturing the prism will be described with reference to FIG. First, the glass work P of the triangular prism is
In the pre-processing step D1, the center hole P2 is formed at the end or the pin portion P1 is attached. Next, the glass work P for which pre-processing has been completed is
The three grinding surfaces 10 are mirror-ground by the grinding device 10. Then, the processed surface S has the above-mentioned accuracy (flatness 1
μm / surface or less, surface roughness Rmax 0.5 μm (Ra 0.05
(μm) or less, angular accuracy plus or minus 20 (seconds) or less)
Is finished. In this case, the flatness and angular accuracy are almost finished to meet the requirements of the prism. Further, the surface roughness can be finished with higher accuracy than the conventional manufacturing method.

Next, the glass work P for which the mirror surface grinding has been completed
Is lapped in the lapping step D3. The lapping process is performed by fixing the glass work P on a lapping machine such as a tin surface plate. That is, the lap is slid between the processed surface S of the glass work P and the lap and the processed surface S is processed by sliding the lap. In this case, the processed surface has a surface roughness of Rmax 0.05 μm (Ra 0.005 μm) or less.

Next, the glass work P that has undergone the lapping process is subjected to a polishing process in a polishing step D4. The polishing process is performed by fixing the glass work P on a pitch surface plate similar to the above. That is,
Between the processed surface S of the glass work P and the polisher, the processed surface S is processed by sliding the polisher while interposing, for example, cerium oxide of ultrafine particles. In this case, the processed surface S has a surface roughness Rmax of 0.01 μm (Ra 0.005 μm).
m) Finished below.

Next, the glass work P that has been subjected to the polishing process is cut at a predetermined pitch in the longitudinal direction of the glass work P in the cutting D5 to form prism pieces Q1. In this case, the dimensional accuracy between the cut surfaces of the prism piece Q1 is maintained at, for example, ± 50 μm or less, and the perpendicularity of the cut surface is maintained at 20 μm or less.

Subsequently, in the chamfering step D6, the prism piece Q1 is chamfered at the corners, and then the cleaning step D1.
Washed at 7. And finally, the flatness is 0.3μ.
m / surface or less, surface roughness Rmax 0.01 μm (Ra 0.0
05μm) or less, angular accuracy plus or minus 30 (seconds)
The following three-sided prism Q2 is formed.

[0057]

As described above, according to the present invention, it is possible to provide a grinding apparatus and a grinding method capable of highly accurately processing a plurality of processed surfaces of a workpiece in a short time. Further, according to the present invention, it is possible to provide a method of manufacturing a prism that can grind a plurality of processed surfaces of a prismatic prismatic material with high accuracy in a short time.

[Brief description of drawings]

FIG. 1 is a perspective view of a grinding apparatus according to a preferred embodiment of the present invention.

FIG. 2 is a diagram showing a basic configuration of a multi-step grindstone in the grinding apparatus of FIG.

FIG. 3 is a diagram showing a specific configuration of the multi-step grindstone of FIG.

FIG. 4 is a diagram showing another specific configuration of the multi-step grindstone of FIG.

FIG. 5 is an explanatory view of the operation of the grinding device of FIG.

FIG. 6 is a view showing a modified embodiment of the multi-step grindstone in the grinding apparatus of FIG.

FIG. 7 is a diagram illustrating another method of supporting the glass work in the grinding device of FIG.

FIG. 8 is an explanatory diagram relating to rear surface support of a glass work in the grinding apparatus of FIG.

FIG. 9 is a diagram showing a manufacturing process of a prism.

FIG. 10 is a perspective view of a fixing jig for manufacturing a prism.

FIG. 11 is a diagram showing a conventional prism manufacturing process.

[Explanation of symbols]

 10 Grinding device 11 Chuck 12 Tailstock 13 Rotary encoder 14 Chuck rotation motor 15 Multi-step grindstone 16 Air spindle 17 High frequency motor 18 Backside support device 22 Support stand moving motor 31 Roughing grindstone 32 Finishing grindstone P Glass work S Machining surface

Claims (4)

[Claims] 1. A support means for supporting both ends of a workpiece having a plurality of processing surfaces, and a plurality of ring-shaped grindstones having different functions are concentrically fixed,
Further, a multi-step grindstone configured such that the one closer to the center of the plurality of ring-shaped grindstones is projected toward the processed surface of the work piece, a rotating means for rotating the multi-step grindstone, and the multi-step grindstone for the work piece. Of moving means for moving along the machining surface, and rotation positioning means for rotating the machining object by a predetermined angle via the supporting means and sequentially orienting the machining surface of the machining object toward the multi-step grindstone. A grinding device comprising: 2. A back surface supporting means for supporting the workpiece is provided on the opposite side of the processing surface of the workpiece supported by the supporting means.
The described grinding device. 3. A multi-step grindstone in which a plurality of ring-shaped grindstones are concentrically fixed is rotated, and the multi-step grindstone is moved along a work surface of a work piece whose both ends are supported. The machined surface of the work piece is ground by the ring-shaped grindstone that sequentially protrudes from the outer side to the inner side, and then the work piece is rotated by a predetermined angle. A grinding method characterized in that a plurality of machined surfaces of an object to be machined are sequentially machined by the multi-step grindstone with a machined surface facing the multi-step grindstone. 4. A prism for forming a prism in which both ends are supported while rotating a multi-step grindstone in which a plurality of ring-shaped grindstones from an outer rough grindstone to an inner finish grindstone are concentrically fixed. The work is moved along the machined surface of the material, and the machined surface is mirror-finished by the ring-shaped grindstones protruding from the outer side to the inner side of the machined surface side. A method of manufacturing a prism, which comprises rotating the prismatic material by an angle, directing another machining surface of the prismatic material toward the multi-step grindstone, and then sequentially grinding the prismatic material with the multi-step grindstone.