JP3046370B2 - Screw grinder with opposed wheel head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread grinder, and more particularly to a thread grinder suitable for grinding a long screw shaft.

[0002]

2. Description of the Related Art Conventionally, a long screw having a single diameter has a low rigidity. When grinding with a screw grinder, chattering occurs or a workpiece is elastically deformed, and the axis of the screw is displaced during grinding. Accuracy, especially variation in screw diameter, is likely to occur. In the case of thread grinding such a work piece having no rigidity, an anti-sway is generally used.

[0003]

Since a screw shaft whose length is significantly larger than its diameter has no rigidity, a shoe is applied to the outer diameter portion of the screw shaft to oppose the grinding force. The screw shaft is hardened by turning the screw with grinding allowance by turning and has high hardness. Then the shoe touches the screw crest,
The shoe exerts a large pressure due to the grinding force. for that reason,
The shoe is easily worn, and the top of the screw and the corner of the flank where the width of the screw top is narrowed move in the axial direction due to the rotation of the screw shaft, so that the shoe is easily shaved. Therefore, it is necessary to drive and match the shoes during processing, which involves adjustment of the shoe position of the anti-sway. Since the number of such anti-skids increases as the length of the workpiece increases and supports the workpieces, it takes time to adjust the anti-sway during processing. This point is generally described in a little more detail in the processing of a long workpiece, and a workpiece is subjected to a grinding force obtained by combining a main component force and a back component force of the grinding resistance. A two-point anti-sway device having a shoe that receives the main component and a shoe that receives the component by a back force is generally used. In this case, the shoe subjected to the back force directly affects the grinding accuracy and must be sent to a predetermined position with respect to the workpiece. Further, since a large force is applied to the shoe which receives the main component force, the shoe can be placed at a retreated position to some extent by utilizing the elasticity of the workpiece in consideration of the wear resistance. Therefore, in the case of the anti-sway adjustment, the shoes subjected to the back force are simply independent of the workpiece diameter.
Although the same position may be used, the shoe receiving the main component force needs to adjust the feeding amount to the workpiece in accordance with a mode in which each of the cleats arranged in the axial direction supports the workpiece. For the reasons described above, it is time-consuming to adjust the anti-sway. Therefore, the number of anti-skids is kept to the minimum necessary, and the cutting amount of the grinding wheel is limited.

[0004] Since the above-mentioned thread grinding is performed, the amount of cut is small, and the processing time is remarkably increased due to the anti-sway adjustment. It is necessary to adjust two shoes having different directions to one wobble in association with each other, and it is very difficult to improve the grinding accuracy because it requires a very high degree of skill because the positions of the shoes are related to each other.

The present invention has been made in view of the above points, and an object of the present invention is to provide a screw grinding machine which can improve grinding accuracy, reduce the number of anti-skids, and have good grinding efficiency.

[0006]

The first invention of the present invention has a long
In a screw grinder provided with a screw grinding feed means for keeping the ratio of the rotation of the work of the scale and the relative movement of the grinding wheel and the work in the axial direction constant, the machine base and the machine base are reciprocally movable. Table, table drive and table on table
Workpiece and headstock and tailstock with opposite parallel lines in the direction of reciprocation of the Le, on each machine frame on both sides of the workpiece
Two supported via a turning position adjustment device whose center of rotation is a vertical axis passing through the center line of the workpiece and perpendicular to the machine base
And slides in the workpiece supported by headstock and tailstock
Workpiece substantially the same position as cord passes in the vertical axis
And two wheel head which faces with the retractably slides toward the workpiece on both sides of a thread grinding machine provided with a counter wheel head with a grinding wheel head driving device.

A second invention of the present invention is the rotation of a long workpiece.
The ratio of the relative movement of the grinding wheel and the workpiece in the axial direction is constant
In a screw grinding machine equipped with a screw grinding feed means
A table, a table reciprocally movable on the machine base, and a table
Of the table and the reciprocating direction of the table on the table
Workpiece headstock and tailstock provided facing each other on parallel lines
And at a position away from the workpiece on both sides of the workpiece, respectively
The position of the workpiece in the axial direction can be adjusted on the machine base.
Swiveled saddle and vertical axis perpendicular to machine
Two wheels provided on the saddle so that the turning position can be adjusted as the center
Supported by two swivel slides, headstock and tailstock
Swivel on both sides of the workpiece at approximately the same location on the workpiece
Opposite on the slide so that it can move back and forth toward the workpiece
Opposed whetstone with two whetstone heads and a whetstone head drive
It is a screw grinder equipped with a table .

[0008] A third invention of the present invention is to move the grinding wheel head to the retracted position.
Equipped with a grindstone correction device that acts on the grindstone in
Place a grindstone correction tool on the opposite side of the
According to the first or second aspect of the present invention,
It is a screw grinder equipped with an opposed wheel head.

According to a fourth aspect of the present invention, the two grinding wheels are individually machined.
It is provided on a slide that moves back and forth toward an object, and the slide is
A sensor driven by a numerical controller via a screw feeder
A first motor driven by a servomotor.
Equipped with the opposed grinding wheel head according to the second or third invention.
This is a screw grinder.

[0010] A fifth invention of the present invention is a grinding wheel rotation of both wheel heads.
The first to fourth emission sources, wherein the directions are the same.
A thread grinder provided with the opposed wheel head according to any one of the preceding claims.
It is.

[0011] A sixth invention of the present invention is a grinding wheel rotation of both wheel heads.
The directions are opposite to each other.
A screw provided with the opposed wheel head according to any one of the fourth inventions
It is a grinding machine.

[0012] A seventh invention of the present invention relates to a whetstone head of both whetstone heads.
At least one of the main motors for driving the grinding wheel
The first to fourth inventions are characterized in that they can be reversed.
A screw grinder provided with the opposed wheel head according to any one of the above.
You.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a plan view, and FIG. 2 is a side view of FIG. 1 (a servomotor for driving a lead screw and a bearing are removed).

A table 3 slides on a so-called V-palm guide 2 provided on the machine base 1, and the table 3 can reciprocate on the machine base 1. This table 3 has a feed nut 4
A lead screw 5 parallel to the guide 2 is screwed into the feed nut 4.

A work headstock 6 is fixed on the table 3 in the direction in which the table 3 reciprocates, and a tailstock 9 is fixed to the work headstock 6 so that the position of the tailstock 9 can be adjusted. The workpiece headstock 6 is input from the upper electric motor 10 via the belt device 11 and is supplied via the internal reduction gear to the workpiece spindle 8.
The rotation is transmitted to. The workpiece W is supported by a center 12 that fits into the workpiece spindle 8 and a center 14 that fits into a sleeve 13 whose entry and exit are adjusted to the tailstock 9. The workpiece W is rotated by a driving tool 16 engaged with a screw 15 fixed to the workpiece W. The driving tool 16 is fixed to the workpiece spindle 8.

Slides 17 and 18 are provided on opposite sides of the grindstone heads 18 and 118 which are diagonally opposed to the workpiece W supported on the workpiece headstock 6 and the tailstock 9 so as to be able to reciprocate obliquely toward both sides at substantially the same position in the axial direction.
117. For this reason, slides 17, 117
The guides 2 of the machine base 1 are provided with guides 19, 119 in the cross direction in the guide 2 of the machine base 1.
9 is slipping. Grinding wheel shafts 22 and 122 orthogonal to the guides 19 and 119 are rotatably supported on the wheel head main bodies 21 and 121, respectively. The main motors 23 and 123 provided on the wheel head main bodies 21 and 121 and the wheel shafts 22 and 122 are connected by belt devices 24 and 124. Whetstone shaft 22, 12
Grindstones 25 and 125 having a radial cross section corresponding to the shape of the thread valley formed on the workpiece W are attached to the workpiece 2.
The grindstones 25 and 125 are on opposite sides of the diameter of the workpiece W, and a grinding action portion is provided at a position separated by half a pitch of a screw formed on the workpiece W in the axial direction of the workpiece W. The slides 17 and 117 are provided with driving devices for the grindstone stands 18 and 118.

The drive units for the wheel heads 18, 118 are servomotors 26, 126 fixed to the slides 17, 117 and guides 19, 11 connected to the servomotors 26, 126, respectively.
The cutting feed screws 27, 127 parallel to 9 and the cutting feed screws 27, 127 are screwed into the grindstone main bodies 21, 12.
1 comprises feed nuts 28 and 128 fixed at 1.

As shown in FIG.
9 is provided on the slides 17,117. The two grindstone correction devices 29 and 129 face the grindstone correction tools 31 and 131, and the respective grindstones 2, 125 from the back of the grindstones 25 and 125.
5, 125, and has the same configuration, so that the grindstone correcting device 29 will be described. The grindstone correction tool 31 is a rotary dresser. The grindstone correction tool 31 is fixed to a grindstone correction tool table 32 on a rotating shaft (not shown) parallel to the grindstone shaft 22, and is rotated by a motor built in the tool table 32. The grindstone correction tool base 32 is fixed to the slides 17 and 117 so that its position can be adjusted in directions parallel and orthogonal to the grindstone shaft 22.

The slides 17, 117 are rotatably fitted to arc guide strips 33, 133 provided on the machine base 1. The arc guide strips 33 and 133 have the same center O. Center O
1 corresponds to a perpendicular passing through the intersection of a straight line passing through the center of the workpiece W and the center in the width direction of the grindstones 25 and 125 in FIG.

An arc-shaped angle scale 34, 134 is provided along the arc guide strip 33, 133, and the slide 17,
At 117, readers 35 and 135 for the angle scales 34 and 134 are attached. Also, arc guide strip 3
Worm wheel segment 36,1 concentric with 3,133
The worm 37 is fixed to the slides 17 and 117 and engages with the worm wheel segments 36 and 136.
137 is a bearing 3 whose shafts 38, 138 are provided on the machine base 1.
9, 139, and lead angle adjustment handles 41, 141 are attached to the shaft ends of the shafts 38, 138.

In order to obtain the feed amount of the table 3 corresponding to the thread pitch of the workpiece W by rotating the workpiece W, the lead screw 5 and the workpiece spindle 8 are rotated at a constant rotation ratio so as to obtain a desired thread pitch. Rotate with. Therefore, a well-known numerical controller, a replaceable gear box, or a combination thereof is used for this part. In this example, an example by numerical control will be described. The output shaft of the Z-axis servo motor 7 fixed to the machine base 1 is connected to the lead screw 5. An encoder 43 is connected to the workpiece spindle 8. The rotation of the workpiece spindle 8 causes the encoder 43 to rotate.
Is input to the numerical controller 44, which rotates the lead screw 5 of the Z-axis servomotor 7 at a fixed rate with respect to the rotation of the work spindle 8. In order to obtain the thread pitch of the workpiece W, the workpiece spindle 8 is rotated by a numerically controlled servomotor, and a linear scale is provided on the machine base 1 or on the table 3 in the longitudinal direction of the table 3. By providing the linear scale reading device in the machine base 1, the rotation angle of the workpiece spindle 8 may be made to correspond to the position of the table 3 to be read.

Next, the operation of the above configuration will be described.

First, a program for a thread pitch, a thread length, a cutting depth, and a grinding cycle to be cut is input to the numerical controller 44. Next, a lead angle corresponding to the screw pitch is calculated. When the lead angle adjusting handles 41, 141 are rotated, the worm shafts 38, 138 are rotated, and the worms 37, 13 are rotated.
7 is rotated. The worms 37, 137 rotate the worm wheel segments 36, 136. Since the worm wheel segments 36 and 136 and the slides 17 and 117 are fixed, the slides 17 and 117 are
3,133 to be tilted in a horizontal plane. When the angle scales 34 and 134 are read by the angle readers 35 and 135 so as to obtain a lead angle, the grindstones 25 and 1 are read.
The horizontal line connecting the centers in the width direction of 25 is inclined at a required lead angle with respect to the axis of the workpiece W.

The cut into the workpiece W is shown in FIG.
Shown in The blank of the workpiece W is provided with a grinding allowance and the lower screw is cut, and the outer diameter D0 is usually turned and hardened. The amount of cutting in the radial direction of the grindstone 25 (the following cutting is described as the amount of cutting in the radial direction of the workpiece W, and is simply referred to as the amount of cutting) is t1, and the amount of cutting of the grindstone 125 is t2. Assuming that the rotation direction of the work W is clockwise in FIG. 4, the normal grindstones 25 and 125 are clockwise, and the moving direction of the circumferential surface of the work W and the moving direction of the circumferential surface of the grindstones 25 and 125 are opposite directions. is there. When not using the anti-slip, cut t1,
t2 is selected so that the main components of the grinding resistance of the grindstones 25 and 125 are substantially equal.

As described above, in order to set the grinding wheel cutting amounts t1 and t2, the grinding wheel correction devices 29 and 129 are used as a reference. The grinding wheel correction tools 31 and 131 are diamond rolls, and the wear amount is extremely small. Therefore, the grinding wheel correction tool 3 for practical use
The 1,131 grinding action surfaces can be considered to be in a fixed position. The rotational positions of the servo motors 26 and 126 for moving the grindstone stands 18 and 118 through the feed screws 27 and 127 and the feed nuts 28 and 128 are given by the numerical controller 44 to the grindstones 25 and 125, so that the grindstones 25 and 125 are adjusted.
Is calculated, the amount of movement of the grindstone stands 18, 118 for cutting and feeding of the grindstones 25, 125 is also calculated with reference to the origin position.
It is possible to determine t2.

A screw 15 is attached to the blank of the work W, and the center 12 of the work headstock 6 and the center 1 of the tailstock 9 are mounted.
The workpiece W is mounted between the four, and the driving tool 16 and the turn 15 are engaged. When the main motors 23 and 123 rotate, the grindstone shafts 22 and 122 rotate through the belt devices 24 and 124, respectively, and the grindstones 25 and 125 rotate. The numerical controller 44 is operated to urge the Z-axis servomotor 7 to rotate the lead screw 5, move the feed nut 4 to feed the table 3, and come off the tailstock side end of the workpiece W. Origin position 25, 12
The table 3 is moved so as to reach the position No. 5 and then the start button of the numerical controller 44 is pressed.
6 is urged to rotate the cut feed screws 27, 127,
Move the feed nuts 28, 128 to move the grindstones 18, 118
Are brought close to each other, the cutting amount of the grindstone 25 becomes t1, the cutting amount of the grindstone 125 becomes t2, and the servomotors 26, 1
26 stops and the grindstones 25 and 125 stop moving.
The cut amount is set as shown in the figure. Subsequently, the electric motor 10 on the workpiece headstock 6 is assisted by the auxiliary function of the numerical controller 44 according to the program input to the numerical controller 44.
Is energized. The rotation of the electric motor 10 is transmitted to the workpiece spindle 8 via the belt device 11, and the driving tool 16, the screw 15
Workpiece W is rotated via.

The rotation of the work spindle 8 causes the encoder 43 to rotate.
Detects the rotation angle of the workpiece spindle 8, that is, the rotation angle of the workpiece W, and sends it to the numerical controller 44. The numerical controller 44 rotates the Z-axis servomotor 7 at a fixed ratio with respect to the rotation angle of the encoder 43 to rotate the lead screw 5 and sends the table 3 so as to obtain the input thread pitch of the workpiece W. The workpiece W to the right in the axial direction. Thereby, the workpiece W
Grinding is performed.

When the left end of the thread portion of the workpiece W in FIG. 1 comes to the position of the grindstones 25 and 125, the numerically controlled motor 10
Stops, the Z-axis servomotor 7 stops, the servomotors 26 and 126 are energized, the grindstones 25 and 125 retract and stop, and the Z-axis servomotor 7 is energized to move the table 3 to the left. , The workpiece W is moved to the original position on the Z axis and stopped. In the second grinding, the grindstones 25 and 125 are further cut, and the same cycle is repeated. Whetstone 2
Correction of the grinding surface of 5,125 is performed by the grindstone correcting tools 31 and 131 by retracting the grindstones 25 and 125 and urging the grindstone correcting devices 29 and 129.

After the grindstones are corrected, the numerical control device 44 gives the cutting amounts of the grindstones 25 and 125 to the grindstone correction tools 31 and 131. Therefore, the numerical control device 44 corrects the cutting amounts and corrects the work W The amount of cutting of the grindstones 25 and 125 into the wheel is always calculated.

As shown in FIG. 4, the grinding resistance applied to the workpiece W is such that the grinding resistance of the grindstone 25 is the main component force F1, the back component force F2, and the grinding resistance of the grindstone 125 is the main component force 101, the back component force F102. , The main component force F1 ≒ F101 and the back component force F2 ≒ F102.

As described above, since the grinding resistance of the grindstones 25 and 125 can be balanced, a bending force is hardly applied to the workpiece W. Therefore, even if the workpiece W is elongated, the workpiece W can be machined without the anti-skid, and the anti-skid is used. In this case, the number is extremely small as compared with the conventional case. The anti-sway device is a V-block 73 that moves up and down from below the workpiece W as shown in FIG. 5, or a metal support 7 that moves up and down from below the workpiece W as shown in FIG.
4 may be used.

Next, another embodiment will be described. FIG. 7 is a plan view corresponding to FIG. 1 of the previous embodiment. The points different from the previous embodiment are as follows.
8, 118 are carried on a swivel slide device movable in the Z-axis direction, and since these are arranged symmetrically on both sides of the workpiece W, mainly only one side will be described. A guide 51 is provided on the machine base 1 in parallel with the guide 2.
Is guided to the saddle 52. A circular guide (not shown) provided on the upper surface of the saddle 52 has a swivel slide 53.
Are rotatably guided, the grindstone table 18 is guided by a guide 19 provided on a swivel slide 53, and the grindstone shaft 22 and the guide 19 are orthogonal to each other.

A feed screw 50 rotatably provided on the machine base 1
And a screw feeder 54 having a feed nut (not shown) into which the feed screw 50 fixed to the saddle 52 is screwed. The feed screw 50 of the screw feeder 54 has a Z-axis provided with a micrometer device 55. It is fixed to the feed handle 56.

A worm wheel segment 57 is coaxially fixed to the swivel slide 53, and a worm 58 meshes with the worm wheel seg cement 57. The worm shaft 59 of the worm 58 is supported by a bearing 61 provided on the saddle 52, and has an angle handle 62 at the shaft end. The angle scale 63 provided on the swivel slide 53 is read by a reading device 64 provided on the saddle 52.

The operation different from that of the previous embodiment is the adjustment of the tilting position of the grinding wheel head. When the angle handle 62 is rotated, the worm shaft 59 is rotated, and the worm 58 is rotated, and the worm wheel segment 57 is rotated. As a result, the swivel slide 53 rotates, the grindstone table 18 rotates, and the grindstone 25 is inclined with respect to the workpiece W. Angle scale 63 is read by angle reading device 6
4 is read and adjusted to the lead angle of the workpiece W. Similarly, the grindstone 125 is inclined at the same angle as the grindstone 25. Next, when the Z-axis feed handle 56 is rotated, the saddle 52 moves via the screw feed device 54, so that the workpiece W of the grindstones 25 and 125 is moved.
Adjust the axial position of. Then, the line passing through the center of the width of the grindstones 25 and 125 is aligned with the straight line in FIG. The same operation is performed with respect to the opposing grindstone table 118.

FIG. 8 is a front view of still another embodiment. In the figure, a grinding wheel base 18 on the near side exists above the portion where the machine base 1 has been cut, but it is not shown in the drawing for the sake of cutting, and only the grinding wheel base 118 on the rear side is shown. The difference from the above embodiment is that the relationship between the rotation angle of the workpiece W and the position of the table 3 is obtained by the exchange gear box 71. The work spindle 8 and the lead screw 5 supported by bearings 72 at both ends of the table 3 are connected to each other via a replacement gear box 71. A group of gears that are selectively engaged in accordance with the screw pitch are provided in the exchange gear box 71, and a gear train is selected by operating a lever (not shown). Some of the gear pairs can be replaced manually to prepare for a special pitch or the like. Since the exchange gear box 71 is well known in general-purpose lathes, detailed description is omitted. In this case, the feed nut 4 into which the lead screw 5 is screwed is fixed to the machine base 1.

[0037]

The first and second aspects of the present invention are as follows: (1) Since the cutting depth of the grinding wheel can be increased, the grinding ability is significantly increased. (2) Even if the cutting depth of the grinding stones is increased, the bending moment applied to the workpiece can be reduced by canceling the grinding resistance of the two grinding stones.
Alternatively, the number of steady rests can be reduced. (3) Since the force applied to the workpiece at the same depth of cut is smaller than that of a conventional thread grinder, the dimensional error and the shape error of the workpiece due to the deformation of the workpiece are reduced. (4) The anti-sway device has a simple structure because it only needs to support the workpiece in one direction, and the adjustment is performed quickly.

According to a third aspect of the present invention, when the distance between the grindstone correction tool of each grindstone correcting device and the grindstone in a cut state to the workpiece is made equal, each grindstone table is retracted by the same distance.
The grinding wheel can be modified. For example, when a molded rotary diamond dresser is used, there is almost no wear of the modified tool. Therefore, the diameter of the grinding wheel is cut evenly, and the dimensional control of the grinding wheel is easy.

According to the fourth aspect of the present invention, each wheel head is driven by a numerical controller by a separate feeder.
It is possible to set a cutting difference between both whetstones, so that simultaneous cutting action can be easily performed.

According to the fifth aspect of the present invention, since both grinding wheels rotate in the same direction, the moving directions of the peripheral surfaces of the two grinding wheels are both the same direction or the opposite directions to the moving direction of the workpiece peripheral surface. Can be.

According to the sixth aspect of the present invention, since both wheels rotate in opposite directions, both wheels have the same circumferential direction with respect to the direction of movement of the workpiece circumferential surface, and the circumferential surface of the other wheel has the same direction. Moves in the opposite direction. That is, upcut grinding and downcut grinding can be combined.

According to the seventh aspect of the present invention, since either one of the two grindstones rotates forward and backward, both grindstones can rotate in the same direction and both grindstones can rotate in mutually opposite directions. Therefore, any of the grinding methods according to the fourth and fifth aspects can be selected.

[Brief description of the drawings]

FIG. 1 is a plan view of an embodiment of the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 1;

FIG. 4 is a side view perpendicular to a workpiece showing a grinding cut example.

FIG. 5 is a side view of the steady rest.

FIG. 6 is a side view of the steady rest.

FIG. 7 is a plan view of another embodiment.

FIG. 8 is a front view showing a partial cross section of still another embodiment.

[Explanation of symbols]

Workpiece 1. Machine stand 2. Guide 3. Table 4. Feed nut 5. Lead screw 6. Workpiece headstock 7. Z-axis servo motor 8. Workpiece spindle 9.
・ Tailstock 10 ・ ・ Electric motor 11 ・ ・ Belt device 12
・ ・ Center 13 ・ ・ Sleeve 14 ・ ・ Center 15 ・
・ Spindle 16 ・ ・ Drive device 17,117 ・ ・ Slide 18,118 ・ ・ Whetstone stand 19,119 ・ ・ Guidance 2
1,121 ・ ・ Whetstone base 22,22 ・ ・ Wheel axis
23, 123 ··· Main motor 24, 124 · · · Belt device 25, 125 · · Grinding wheel 26, 126 · · Servo motor 27, 127 · · · Feed screw 28, 128 · · · Feed nut 29, 129 · · · Grinding wheel correction device 31 , 131
..Wheelstone correction tool 32..Wheelstone correction tool table 33,13
3 ··· Arc guide 34, 134 · · Angle scale 3
5,135-reader 36,136-worm wheel segment 37,137-worm 38,
138 ··· Shaft 39,139 ··· Bearing 41,141 ·
・ Lead angle adjustment handle 43 ・ ・ Encoder 44 ・
· Numerical control unit 51 · · Guide 52 · · Saddle 53
..Swivel slide 54.Screw feeder 55.
・ Micrometer device 56 ・ ・ Z axis handle 57 ・
・ Warm wheel segment 58 ・ ・ Warm 59
..Warm shaft 61.Bearing 62.Handle 6
3. Angle scale 64 Angle reader 71 Replacement gear box 72 Bearing 73 V block 74
・ Receipt.

Claims (7)

(57) [Claims] 1. A screw grinder provided with a screw grinding feed means for making a ratio of rotation of a long workpiece and relative movement of a grinding wheel and a workpiece in an axial direction constant, a machine base and a machine base. and reciprocating freely with tables, and a drive device of the table, and the workpiece headstock and tailstock with opposite parallel line to the reciprocating direction of the table on the table, you on both sides of the workpiece
On each machine , passing through the center line of the workpiece
Two slides supported via a turning position adjustment device having a vertical vertical axis as a rotation center, and a position where the center line of the workpiece supported by the headstock and the tailstock passes through the vertical axis. A screw grinding machine comprising two opposed wheel heads provided on a slide so as to be able to advance and retreat toward a workpiece on both sides of a workpiece at the same position, and an opposed wheel head provided with a driving device of the wheel head. 2. A screw grinding machine provided with a thread grinding feed means for making a ratio of rotation of a long workpiece and relative movement of a grinding wheel and a workpiece in an axial direction constant, a machine base and a machine base. A table provided reciprocally, a table driving device, a workpiece headstock and a tailstock provided on the table so as to face a line parallel to the reciprocating direction of the table, and workpieces on both sides of the workpiece. A saddle that is provided on the machine base at a position away from the machine so that the position of the workpiece in the axial direction can be adjusted, and a saddle that can adjust the turning position with the vertical axis perpendicular to the machine as the center of rotation Two swivel slides provided, and two opposing grinding wheels provided on the swivel slide on both sides of the workpiece at substantially the same position of the workpiece supported by the headstock and the tailstock so as to be able to advance and retreat toward the workpiece. And a drive unit for the grinding wheel head. Screw grinder equipped with a facing wheel head. 3. A grindstone correcting device which acts on a grindstone at a retracted position of a grindstone base, and a grindstone correcting tool is disposed at a position opposite to a position where each grindstone acts on a workpiece. Or a screw grinder provided with the opposed grinding wheel stand according to 2. 4. The apparatus according to claim 1, wherein each of the two wheel heads is provided on a slide that advances and retreats toward the workpiece, and the slide is driven by a servomotor driven by a numerical controller via a screw feeder. Item 4. A screw grinder provided with the opposed grindstone head according to Item 1, 2 or 3. 5. The screw grinding machine according to claim 1, wherein the grinding wheels rotate in the same direction. 6. The screw grinder according to claim 1, wherein the rotating directions of the grinding wheels are opposite to each other. 7. The opposed grindstone according to claim 1, wherein at least one of the grindstone driving main motors provided on the grindstone heads of the two grindstone heads is capable of normal and reverse rotation. Screw grinder with table.