Claims
1. A downhole machining system (1) for machining a casing (2) in a borehole
(3) in a well having a top, comprising:
- a first tool part (4) having an axial extension (5) and an anchoring section (6),
- a second tool part (7) adapted to rotate and move axially in relation to the first tool part, the second tool part comprising a machining bit (8) which is movable in a direction (9) radial in relation to the axial extension,
- a first actuator (10) comprising an electrical motor (HA) for axially moving the second tool part in relation to the first tool part,
- a second actuator (12) comprising an electrical motor (11B) for rotating the second tool part In relation to the first tool part, and
- a third actuator (14) comprising an electrical motor (11C) for rotating the bit,
wherein at least one of the actuators comprises a gear (15) for changing a rotational speed of a rotor (16) of the motor.
2. A downhole machining system according to claim 1, wherein the gear is a reduction gear.
3. A downhole machining system according to any of the preceding claims, wherein the first tool part is arranged closer to the top of the well than the second tool part.
4. A downhole machining system according to any of the preceding claims, wherein the system comprises a second anchoring section (6, 6A, 6B), and the anchoring sections are arranged with a mutual axial distance between them, both anchoring sections being arranged closer to the top of the well than the second tool part and the bit.
5. A downhole machining system according to claim 4, wherein one anchoring section is axially movable in relation to the other.
6. A downhole machining system according to any of the preceding claims, wherein the gear of the third actuator is a bevel gear.

7. A downhole machining system according to any of the preceding claims, wherein the gear of the second actuator is a planetary gear.
8. A downhole machining system according to any of the preceding claims, wherein the gear of the first actuator is a planetary gear.
9. A downhole machining system according to any of the preceding claims, wherein the bit is moved radially in relation to the axial extension by means of an electrical motor and/or hydraulics.
10. A downhole machining system according to any of the preceding claims, wherein the bit is moved radially by means of a hydraulic cylinder.
11. A downhole machining system according to claim 10, wherein the bit forms a piston of the hydraulic cylinder.
12. A downhole machining system according to any of the preceding claims, wherein the first actuator comprises a hydraulic cylinder instead of the motor.
13. A downhole machining system according to any of the preceding claims, wherein the system comprises a control unit (17) for controlling the actuators.
14. A downhole machining system according to any of the preceding claims, wherein the system further comprises a pinching or cutting tool (18) projectable through an opening (19) in the casing provided by the machining bit.
15. A downhole machining system according to any of the preceding claims, wherein the bit is moved radially in a bit housing (34), the bit has a sharp end (32) facing the casing and a piston end (33), and the bit is moved radially in relation to the axial extension by means of an electrical motor (31) driving a hydraulic cylinder (30) which is in fluid communication with the bit housing pressing onto the piston end.
16. A downhole machining system according to any of the preceding claims, further comprising a fluid cleaner (43) for cleaning up cuttings from the machining process.

17. A downhole machining system according to any of the preceding claims, further comprising a plug setting tool (44) for subsequently setting a plug.
18. A downhole machining system according to any of the preceding claims, further comprising a pinching or cutting tool (18) adapted to project through an opening in the casing provided by the bit.
19. A machining method comprising the following steps:
- Inserting the downhole machining system according to any of the preceding claims into the casing,
- anchoring the system in the casing,
- moving the second tool part in relation to the first tool part,
- moving the machining bit radially in relation the axial extension, and
- machining the casing by means of the bit.

20. A machining method according to claim 19, further comprising the step of moving the second tool part and the bit axially and/or rotate the second tool part and the bit during the machining step in order to provide an opening in the casing, said opening being larger than a diameter of the bit.
21. A machining method according to claim 19 or 20, wherein the machining step Is performed to provide an opening in the casing, and the method further comprises the step of projecting an operation tool into the opening.