Motor with cutting tool mounting opening
The motor design with a labyrinth seal and concentric grooves addresses the issue of cutting oil and powder ingress, enhancing motor durability by containing contaminants and preventing seal damage, thus reducing insulation and grounding issues.
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- HARMONIC DRIVE SYST IND CO LTD
- Filing Date
- 2007-06-20
- Publication Date
- 2026-06-03
AI Technical Summary
Existing motors used in cutting processes are prone to rapid degradation due to the ingress of cutting oil and metal cutting powder, which causes insulation and grounding issues, particularly when flexible contact seals are damaged by direct contact with the metal cutting powder.
A motor design featuring a cylindrical housing with a through-opening, a motor shaft with a recess and tool fastening opening, a bearing, an annular holder plate, a flexible contact seal, a rigid sealing plate, and a labyrinth seal to prevent the ingress of cutting oil and contaminants, using concentric and extremely narrow circular grooves to contain cutting powder and oil.
The design effectively prevents cutting powder from reaching the contact seal, minimizing damage and extending the motor's service life by containing contaminants within the labyrinth seal, thereby reducing grounding defects and insulation problems.
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Abstract
Description
Technical field
[0001] The present invention relates to a motor for the rotational driving of a cutting tool, which is securely coupled to a tool mounting opening, wherein the tool mounting opening is formed in a shaft end portion of a motor shaft exposed at an end face of a motor housing. More specifically, the present invention relates to a motor with a cutting oil-resistant design such that cutting oil containing cutting powder or chips is prevented from penetrating the motor during a cutting process from the area between the motor housing and the shaft end portion of the motor shaft. State of the art
[0002] In document WO 2005 / 013 463 A1, the applicant provided a flat, hollow brushless servomotor for performing a cutting operation in which a cutting tool is attached to both ends of a motor shaft and a workpiece is subjected to pressure from both sides.
[0003] Document JP 2001 268 859 A discloses a high-speed rotary spindle with a motor shaft and a mounting opening for a cutting tool and a labyrinth seal to prevent the ingress of cutting oil, wherein the labyrinth seal is formed between an annular sealing plate and a shaft end part of the motor shaft.
[0004] In a workpiece cutting tool using a brushless motor of this configuration, the cutting process is performed by the cutting tool while cutting oil is supplied to the workpiece in a position close to the motor. This makes it easy for the cutting oil to penetrate the motor from a shaft end. The cutting oil contains a significant amount of metal cutting powder generated by the cutting process. When this metal cutting powder mixes with the cutting oil and enters the motor, motor winding ground faults, insulation problems, and other adverse events occur more rapidly than under normal operating conditions. Therefore, an oil seal or other flexible contact seal is appropriate between the motor shaft and the motor housing to prevent the unwanted combination of metal powder and other contaminants with the cutting oil.
[0005] In this case, however, the metal cutting powder comes into direct contact with the contact area between the contact seal and the outer circumferential surface of the motor shaft. As a result, the area of the contact seal (lip) in contact with the motor shaft quickly suffers abrasion and damage due to contact with the metal cutting powder, thus drastically reducing its service life. Disclosure of the invention
[0006] In view of the circumstances described, one objective of the present invention is to create a motor with a cutting tool mounting opening in which the ingress of metal cutting powder and other contaminants into the interior can be prevented.
[0007] Another objective of the present invention is to create a motor with a cutting tool mounting opening in which the adhesion of metal cutting powder to an oil seal or other contact seal integrated between the motor shaft and the motor housing can be prevented.
[0008] To achieve the objectives described above, a motor with a cutting tool opening according to the present invention is characterized by the following: A cylindrical motor housing that is tightly sealed at both ends in the axial direction; a through-opening formed in the middle of at least one end plate area of the motor housing; a motor shaft in which a shaft end part is exposed through the through-hole and a circular recess is formed in the shaft end part; a tool fastening opening which is formed in the central area of an end face of the shaft end part in the motor shaft; a bearing for supporting the motor shaft in such a way that the motor shaft can rotate relative to the end plate area, wherein the bearing is located between an inner circumferential edge end of the through-hole in the end plate area and an outer circumferential surface area of the shaft end part of the motor shaft; an annular holder plate for holding the cutting tool, wherein the annular holder plate has an annular area which is coaxially fixed in the circular recess formed in the shaft end part of the motor shaft, such that a circular groove of a certain width is formed between a circular inner circumferential surface at the open side of the circular recess of the shaft end part of the hollow motor shaft and a circular outer circumferential surface of the annular holder plate; wherein the annular holder plate furthermore has an annular plate area which extends radially outwards from the outer circumferential edge of the outer end surface of the annular area; an annular contact seal with a flexible material for sealing the space between the inner circumferential edge of the through-hole and the outer circumferential surface area of the shaft end part at a position axially outside the bearing; an annular sealing plate made of a rigid material, which is fixed at the end plate area at a position axially outside the contact seal to cover the space between the inner circumferential edge end of the through-hole and the shaft end part, wherein the sealing plate has a radially spreading annular plate area and a cylindrical area which is bent at right angles from an inner circumferential edge of the annular plate area and extends axially into the circular groove formed between the circular inner circumferential surface at the open side of the circular recess of the shaft end part of the hollow motor shaft and the circular outer circumferential surface of the tool holder plate; and a labyrinth seal to prevent the ingress of cutting oil, wherein the labyrinth seal is formed between the sealing plate and the shaft end part of the motor shaft.
[0009] In the motor with a cutting tool mounting opening according to the present invention, a labyrinth seal is arranged on the outside of the contact seal to prevent the ingress of cutting oil. In cases where cutting oil, in combination with metal cutting powder or other cutting powder, penetrates the motor interior along the outer circumferential surface of the motor shaft, the labyrinth seal reliably contains the cutting powder, particularly cutting powder of a comparatively large size. In this way, the occurrence of adverse effects can be prevented or minimized where cutting oil containing comparatively large cutting powder particles reaches the oil seal or another contact seal, and contact with the cutting powder causes rapid damage to the contact seal.
[0010] In cases where a circular inner circumferential end surface coaxially surrounds the circular outer circumferential surface area of the shaft end part of the motor shaft, the labyrinth seal can be formed using an extremely narrow circular groove formed between the circular inner circumferential end surface and the circular outer circumferential surface area, extending in the axial direction.
[0011] With a labyrinth seal of this configuration, comparatively large cutting powder particles and other contaminants contained in the cutting oil can be removed, while the cutting oil that has penetrated from the outside of the engine passes through the extremely narrow annular groove.
[0012] The following configuration is preferably used for the labyrinth seal to ensure that ultrafine cutting powder and other contaminants contained in the cutting working oil do not pass through the labyrinth seal along with the cutting working oil and reach the contact seal.
[0013] The sealing plate comprises an annular plate area extending radially and a cylindrical area extending axially at a right angle from the inner circumferential edge of the annular plate area. A circular groove of fixed width, through which the cylindrical area of the sealing plate passes coaxially, is formed in the shaft end of the motor shaft. An extremely narrow circular groove for guiding the cutting oil along the axial direction in a first direction is formed on the inner circumferential side of the cylindrical area inserted into the circular groove. An extremely narrow circular groove for guiding the cutting oil along the axial direction in a second direction, opposite to the first, is formed on the outer circumferential side of the cylindrical area inserted into the circular groove.These circular grooves communicate with each other via a connecting groove that is wider than the circular grooves.
[0014] In the case of a labyrinth seal with two concentric and extremely narrow circular grooves, cutting oil that has passed through one annular groove along the axial direction then passes through the other extremely narrow annular groove in the opposite axial direction. In this way, even ultrafine cutting powder is reliably retained within the labyrinth seal. As a result, it is prevented or suppressed that ultrafine cutting powder can penetrate the contact seal and enter the motor interior. This minimizes or eliminates grounding defects in the motor winding, insulation problems, and other harmful effects caused by cutting powder ingress into the motor, thus extending the motor's service life.
[0015] A labyrinth seal with two annular grooves of the type described can be configured as follows using the shaft end part of the motor shaft and an annular holder plate attached to it for holding the cutting tool.
[0016] The sealing plate comprises an annular plate section extending radially and a cylindrical section that curves at right angles from the inner circumferential edge of the annular plate section towards the interior of the motor and extends axially. An annular retaining plate for holding the cutting tool is coaxially fixed to the shaft end of the motor shaft. Furthermore, a circular groove of fixed width, through which the cylindrical section of the sealing plate passes coaxially, is formed between the shaft end and the annular retaining plate.
[0017] An extremely narrow circular groove for directing the cutting oil in a first direction along the axial direction is formed on the inner circumferential side of the cylindrical area inserted into the circular groove, an extremely narrow circular groove for guiding the cutting oil along the axial direction in a second direction, which is opposite to the first direction, is formed on the outer circumferential side of the cylindrical area inserted into the circular groove, these circular grooves being connected to each other via a connecting groove which is wider than the circular grooves.
[0018] A configuration can be used in which a circular groove extending radially and wider than the extremely narrow cylindrical grooves extending axially is formed between the annular holder plate and the sealing plate, and the radially extending circular groove is connected to one of the extremely narrow circular grooves extending axially. Brief description of the drawings
[0019] The drawings show: Fig. 1A a schematic sectional view showing a brushless DC servomotor in which the present invention is applied; Fig. 1B an end face view of the motor of the Fig. 1A; Fig. 1C an end face view showing the end face on the opposite side of the motor Fig. 1A; Fig. 2. An enlarged fragmentary cross-sectional view to illustrate the central area of the engine. Fig. 1A; Fig. 3 A fragmentary enlarged cross-sectional view to illustrate a further magnification of the area in which in Fig. 2 the labyrinth seal is formed; and Fig. 4 An enlarged fragmentary sectional view to illustrate another example of the formation of the motor shaft end part. Best way to implement the invention
[0020] In the following, exemplary embodiments of a motor with the cutting tool mounting opening, in which the present invention is applied, are described with reference to the drawings.
[0021] Fig. Figure 1A shows a schematic sectional view of a brushless DC servomotor having a cutting tool mounting opening according to the present embodiment. Fig. 1B and Fig. Figure 1C shows end-surface representations of this. Fig. Figure 2 shows a partially enlarged cross-sectional view, in which an enlargement of the central area of this is shown.
[0022] A brushless DC servomotor 1 according to the present embodiment has a flat cylindrical motor housing 2 which is tightly sealed at both ends. A stator assembly 3 and a rotor assembly 4 are arranged concentrically inside the motor housing 2.
[0023] The stator assembly 3 comprises a toroidal core 31 made of a magnetic material and a drive winding 33 wound around a pronounced pole region of the toroidal core 31 via an insulator; furthermore, the stator assembly 3 is coaxially mounted on the inner circumferential surface of a flat cylindrical body 21 of the motor housing 2. The stator assembly 3 has, for example, a configuration with 20 poles and 24 slots.
[0024] The rotor assembly 4 is arranged concentrically on the inside of the stator assembly 3. The rotor assembly 4 has a hollow motor shaft 41 (rotor shaft) and a ring magnet 42, which is fixed to the circular outer circumferential surface of the hollow motor shaft 41. The ring magnet 42 is positioned opposite the stator assembly 3, facing across a small gap. A through-opening 43 is formed in the center of the hollow motor shaft 41. A narrow annular connecting element 44 on the outer circumferential surface projects radially outward from the center of an axial direction 1a, and a wide magnet mounting element 45, to which the ring magnet 42 is attached, is formed at the outer circumferential end of the annular connecting element 44.
[0025] Circular through-openings 22a, 23a are formed in the center of end plate regions 22, 23 on both sides of the motor housing 2. Circular inner circumferential edges 22b, 23b of the end plate regions 22, 23, which form the circular through-openings 22a, 23a, have cross-sectional shapes that project in a direction facing the annular connecting part 44 of the hollow motor shaft 41. Ball bearings 46, 47 are arranged between the circular inner circumferential edges 22b, 23b and circular outer circumferential surface regions 411, 412, which face these edges on the side of the annular connecting part 44 in the hollow motor shaft 41. The hollow motor shaft 41 is rotatably mounted through the left and right end plate regions 22, 23 via the ball bearings 46, 47.Ring-shaped oil seals (contact seals) 48, 49 are attached to the outer sides of the ball bearings 46, 47 between the circular inner circumferential edges 22b, 23b of the left and right end plate areas 22, 23 and the circular outer circumferential surface areas 411, 412 of the hollow motor shaft 41.
[0026] Ring-shaped tool holder plates 51, 52 are coaxially fixed to shaft end parts 413, 414 on both sides of the hollow motor shaft 41 by fastening screws 50. Tool fastening hexagonal openings 51a, 52a are formed in the center of the tool holder plates 51, 52.
[0027] Ring-shaped metal plates 53, 54 (sealing plates) are arranged coaxially between the respective shaft end sections 413, 414 of the hollow motor shaft 41 and the tool holder plates 51, 52. A labyrinth seal 55, preventing cutting oil from penetrating the motor interior from the outside, is formed between the shaft end section 413 of the hollow motor shaft 41, the tool holder plate 51, and the metal plate 53. Similarly, a labyrinth seal 56 is formed between the other shaft end section 414, the tool holder plate 52, and the metal plate 54.
[0028] As described above, the motor housing 2 has the flat cylindrical body 21 as well as the end plate section 22 and the end plate section 23, which tightly seal the two ends of this body; furthermore, the circular through-openings 22a, 23a are formed in the center of these end plate sections 22, 23. The tool holder plates 51, 52, which are fixed to the shaft end sections 413, 414 of the hollow motor shaft 41, are freely accessible through these circular through-openings 22a, 23a.
[0029] In the outer surfaces of the left and right end plate areas 22 and 23 of the motor housing 2, a first and a second workpiece insertion recess 24, 25 of a specific depth are formed, which have circular regions concentrically containing the circular through-openings 22a, 23a, as well as regions that extend from these circular regions and radially to the outer circumferential edges of the end plate areas, as shown in the Fig. 1B and Fig. Figure 1C shows that these workpiece insertion recesses 24, 25 are formed by reducing the thickness of the end plate regions 22, 23 to a specific width. The length of the hollow motor shaft 41 in the axial direction 1a is equal to or less than the thickness between the bottom surfaces of these workpiece insertion recesses 24, 25, and in the present example, the shaft end surfaces on the sides of the hollow motor shaft 41 substantially coincide with the bottom surfaces of the recesses 24, 25.
[0030] A lead wire routing area 6 is attached to the outer circumferential surface of the cylindrical body 21 of the motor housing 2 for routing a lead wire from the drive winding 33 and a sensor (not shown) to the outside of the motor. The lead wire routing area 6 projects radially outwards from the outer circumferential surface of the cylindrical body 21 of the motor housing 2 and has a thickness that can be accommodated within the thickness dimension in the axial direction 1a of the motor housing 2.
[0031] The motor housing 2 of the present example has a design in which the cylindrical body 21 and the end plate region 23 are formed integrally, and the end plate region 22 is fixedly attached to an annular end surface of the cylindrical body 21. A mounting flange 27 extends radially from the outer circumferential surface region of the cylindrical body 21 to the outside, and the motor 1 is attached to a fixed side region (not shown) by the mounting flange 27. Furthermore, an outer surface 23c of the end plate region 23 is a heat dissipation surface on which an uneven surface is formed radially.
[0032] Fig. Figure 3 shows a partially enlarged sectional view to illustrate a section of the labyrinth seal 55, which is formed in the shaft end 413 of the hollow motor shaft 41. The design of the labyrinth seal 55 is described with reference to the Fig. 2 and Fig. 3 described. The other labyrinth seal 56 has a symmetrical design, but a description of this is omitted.
[0033] The labyrinth seal 55 is formed between the shaft end 413 of the hollow motor shaft 41, the tool holder plate 51, and the metal plate 53. A circular recess 415 is located in the shaft end 413 of the hollow motor shaft 41, through which the tool holder plate 51 is coaxially mounted from the side of the end face of the shaft end.
[0034] The tool holder plate 51 has an annular area 511, which is mounted in the circular recess 415, and an annular plate area 512, which extends radially from the outer circumferential edge of the outer end surface of the annular area 511. In this state, with the tool holder plate 51 mounted, a circular groove 550 of a specific width is formed between a circular inner circumferential surface 416 on the open side of the circular recess 415 of the shaft end 413 of the hollow motor shaft 41 and a circular outer circumferential surface 513 of the tool holder plate 51.
[0035] The metal plate 53 has a thick annular projection 531, a thin annular plate area 532 extending radially inwards from the inner circumferential surface of the projection 531, and a cylindrical area 533 angled at a right angle to the inside of the motor from the inner circumferential edge of the annular plate area 532 and extending along the axial direction 1a. The projection 531 is fixedly attached to the outer peripheral end surface area of the inner circumferential edge 22b in the end plate area 22 of the motor housing 2 by a fastening screw 57.
[0036] The annular plate area 532 of the metal plate 53 is arranged opposite the inner end surface of the annular plate area 512 of the tool holder plate 51 across a defined gap. The cylindrical area 533, extending away from the inner circumferential edges of the annular plate area 532, is inserted coaxially into the circular groove 550 formed between the tool holder plate 51 and the shaft end 413 of the hollow motor shaft 51.
[0037] The circular outer circumferential end surface of the annular plate area 512 of the tool holder plate 51 extends to the vicinity of the projection 531 of the metal plate 53, forming an extremely narrow first circular groove 551 between them, which runs in the axial direction 1a. A second circular groove 552, which is wider than the first circular groove 51 and runs radially, is formed between the annular plate area 512 of the tool holder plate 51 and the annular plate area 532 of the metal plate 53 facing the plate area 512, and the outer circumferential end of the second circular groove 552 is in contact with the first circular groove 551.
[0038] An extremely narrow third circular groove 553, extending in the axial direction 1a, is formed between the circular outer circumferential surface 513 of the annular region 511 of the tool holder plate 51 and the cylindrical region 533 of the metal plate 53, and the axially outer end of the third circular groove 553 is in contact with the inner circumferential end of the second circular groove 552. A fourth circular groove 554, wider than the third circular groove 553 and extending radially, is formed between the circular distal end face of the cylindrical region 533 and the circular end face that forms the bottom face of the circular groove 550, the fourth circular groove 554 being in contact with the inner end of the third circular groove 553.
[0039] Furthermore, an extremely narrow fifth circular groove 555, extending in the axial direction 1a, is formed between the circular outer circumferential surface of the cylindrical section 533 and the circular inner circumferential surface 416 of the shaft end part 413. The inner end of this fifth circular groove 555 is connected to the fourth circular groove 554. A sixth circular groove 556, which is wider than the fifth circular groove 555 and extends radially, is formed between the inner end surface of the annular plate section 532 of the metal plate 53 and the annular end surface of the shaft end part 413 facing the first end surface, with the sixth circular groove 556 being connected to the outer end of the fifth circular groove 555. The sixth circular groove 556 is connected to the area in which the oil seal 48 is located.
[0040] The labyrinth seal 55 is formed by the six circular grooves 551 to 556 with the design described above.
[0041] In the brushless DC servomotor 1 according to the present embodiment, design components of the motor are integrated into the flat cylindrical motor housing 2, and a cutting tool (not shown) can be directly attached to the tool mounting openings 51a, 52a of the tool holder plates 51, 52 which are exposed from the through-holes 22a, 23a of the end plate areas 22, 23 and are attached to the shaft end areas 413, 412 of the hollow motor shaft 41.The workpiece insertion recesses 24, 25 are further formed in the outer surfaces of the end plate areas 22, 23 of the motor housing 2, so that an area with a small thickness in the axial direction 1a is formed in the motor housing 2, and a workpiece (not shown) with an opposite area in a gap that is narrower than the axial width of the motor housing 2 can be inserted into the end areas (the places machined by the cutting tool) of the motor mounting openings 51a, 52a from the outside of the motor 1 in a radial direction.
[0042] Furthermore, the thickness of the end plate area 22 of the motor housing 2 is reduced, a recessed groove 26 is formed for routing a supply wire, and the supply wire routing area 6 is accommodated within the thickness dimension of the motor housing 2. In this way, an extremely flat, hollow, brushless DC servo motor can be achieved.
[0043] When the workpiece undergoes a cutting operation, the cutting tool performs the operation near the outer surface of the shaft end 413 of the hollow motor shaft 41, and the shaft end 413 is thus exposed to a large quantity of cutting oil. If a large quantity of cutting powder is absorbed into the cutting oil and the cutting powder penetrates the interior of the motor, grounding defects and insulation problems in the drive winding 33 can easily occur.
[0044] However, the labyrinth seal 55 with the configuration described above is formed in the shaft end section 413. The extremely narrow third circular groove 553 and fifth circular groove 555, which run in the axial direction, are formed concentrically in the labyrinth seal 55. In cases where the cutting oil containing the cutting powder penetrates from the outside, the powder material flows from the first circular groove 551 via the second circular groove 552 into the third circular groove 553. The cutting oil, flowing along the third circular groove 553 in the axial direction 1a, flows via the fourth circular groove 554 into the outer fifth circular groove 555, where the oil then flows in the opposite direction along the axial direction 1a. The oil then passes through the sixth circular groove 556 and reaches the area where the oil seal 48 is located.As the cutting oil travels along this route, the cutting powder contained in the cutting oil is trapped in the circular grooves. A large portion of the cutting oil is also prevented from penetrating before it reaches the oil seal 48.
[0045] As a result, it is reliably prevented that the cutting oil containing the cutting powder reaches the oil seal 48 and that the lip 48a of the oil seal 48, which is in contact with the hollow motor shaft 41, is quickly damaged by the cutting powder. Furthermore, it is reliably prevented that the cutting oil penetrates the interior of the motor and reaches, for example, the ball bearings 46 or the like. (Other embodiments)
[0046] Fig.Figure 4 shows a partial sectional view of another example of the present invention. The essential configuration of the brushless DC motor 1A shown in this drawing is identical to the case described above, and corresponding components are therefore designated with the same reference numerals and are not explained. In the motor 1A of the present example, the metal plates 53A, 54A are not provided with cylindrical areas. Therefore, the labyrinth seals 55A, 56A each include a second circular groove 552A, a single extremely narrow circular groove 557 extending in the axial direction 1a, and a sixth circular groove 556A. The arrangement of the labyrinth seals 55A, 56A with this configuration is also effective in preventing the ingress of cutting oil containing cutting powder, and in particular in preventing large cutting powder particles from reaching the oil seal.
Claims
[1] Motor (1) with a cutting tool attachment opening (51a, 52a), comprising: a cylindrical motor housing (2) which is tightly closed at both ends in the axial direction; a through-opening (22a, 23a) which is formed in a center of at least one end plate area (22, 23) of the motor housing (2); a motor shaft (41) in which a shaft end part (413, 414) is exposed through the through-opening (22a, 23a), wherein a circular recess (415) is formed in the shaft end part (413, 414); a cutting tool attachment opening (51a, 52a) which is formed in a central area of an end surface of the shaft end part (413, 414) of the motor shaft (41); a bearing (46, 47) for supporting the motor shaft (41) in such a way that the motor shaft (41) can rotate relative to the end plate region (22, 23), wherein the bearing (46, 47) is located between an inner circumferential edge end of the through-hole (22a, 23a) in the end plate region (22, 23) and an outer circumferential surface region (411, 412) of the shaft end part (413, 414) of the motor shaft (41); an annular holder plate (51, 52) for holding the cutting tool, wherein the annular holder plate (51, 52) has an annular region (511) which is coaxially fixed in the circular recess (415) formed in the shaft end part (413, 414) of the motor shaft (41), such that a circular groove (550) of a certain width is formed between a circular inner circumferential surface (416) at the open side of the circular recess (415) of the shaft end part (413) of the hollow motor shaft (41) and a circular outer circumferential surface (513) of the annular holder plate (51, 52); wherein the annular holder plate (51, 52) furthermore has an annular plate region (512) which extends radially outwards from the outer circumferential edge of the outer end surface of the annular region (511); an annular contact seal (48, 49) with a flexible material for sealing a space between the inner circumferential edge end (22b, 23b) of the through-hole (22a, 23a) and the outer circumferential surface area (411, 412) of the shaft end part (413, 414) at a position axially outside of the bearing (46, 47); an annular sealing plate (53, 54) of a rigid material, which is fixed at the end plate region (22, 23) at a position axially outside the contact seal (48, 49) to cover a space between the inner circumferential edge end of the through-hole (22a, 23a) and the shaft end part (413, 414), wherein the sealing plate (53, 54) has a radially extending annular plate region (532) and a cylindrical region (533) which is bent at a right angle from an inner circumferential edge of the annular plate region (532) and extends axially into the circular groove (550) that is located between the circular inner circumferential surface (416) at the open side of the circular recess (415) of the shaft end part (413, 414) of the hollow motor shaft (41) and the circular outer circumferential surface (513) of the tool holder plate (51, 52) is formed; and a labyrinth seal (55) to prevent the ingress of cutting oil, wherein the labyrinth seal (55) is formed between the annular sealing plate (53, 54) and the shaft end part (413, 414) of the motor shaft (41). [2] Motor (1) with a cutting tool mounting opening (51a, 52a) according to claim 1, characterized by , that the sealing plate (53, 54) has a circular inner circumferential end surface that coaxially surrounds the circular outer circumferential surface area (411, 412) of the shaft end part (413, 414) of the motor shaft (41); and that the labyrinth seal (55) has an extremely narrow circular groove formed between the circular inner circumferential end surface and the circular outer circumferential surface area (411, 412) and extending in the axial direction. [3] Motor (1) with a cutting tool mounting opening (51a, 52a) according to claim 1, characterized by , that an extremely narrow circular groove (555) is formed for guiding the cutting oil in a first direction along the axial direction in an inner circumferential side of the cylindrical area (553) inserted into the circular groove (550); that an extremely narrow circular groove (553) for guiding the cutting oil along the axial direction in a second direction opposite to the first direction is formed on an outer circumferential side of the cylindrical area inserted into the circular groove (550); and that the labyrinth seal (55) has the two circular grooves (553, 555) as well as a connecting groove (554) which is wider than the circular grooves (553, 555) and connects these circular grooves (553, 555) together. [4] Motor (1) with a cutting tool attachment opening (51a, 52a) according to claim 3, characterized by, that the labyrinth seal (55) between the annular retaining plate (51, 52) and the sealing plate (53, 54) has a circular groove (552) which extends radially and is wider than the extremely narrow cylindrical grooves (553, 555) extending axially; and that the radially extending circular groove (552) is connected to one of the extremely narrow circular grooves (553, 555) extending axially.