Drill or milling head

Details Drill or milling head Drill or milling head

2000-09-08

2001-11-13

Briggs, William (Department: 3722)

Gear cutting, milling, or planing

Milling

With cutter holder

C279S050000, C279S074000, C279S134000, C408S240000

Reexamination Certificate

active

06315507

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a drilling or milling head with a collet chuck operated by a quick-change mechanism and a drive shaft connected to a motor, the collet chuck being opened by axial displacement with respect to a clamping sleeve and the force necessary therefor being transferred through a friction clutch, and having a transmission for driving the collet chuck. In particular, this drill or milling head is suitable for machines which serve for the production of fine structures such as circuit-board milling machines and engraving machines.
In the as yet unpublished patent application Ser. No. 197 48 735.1 a drilling or milling head of this kind is described. In this drilling or milling head a drive shaft of the motor is connected by a coupling to a drive shaft of the collet chuck. Thus, the rotatory speed of the chucked tool is always equal to the motor speed.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a drilling or milling head of this kind in which the rotation of the motor drive shaft can be transferred with a gear ratio to the drive shaft of the drilling or milling head by means of a transmission based on simple means.
This object is achieved by the invention as described and claimed hereinafter. In the drilling or milling head according to the invention, the driving part of the transmission is a ball bearing whose balls are driven concentrically about a common axis by means of a driving part fastened on a drive shaft of the motor. The balls are mounted between two bearing surfaces of circular cross section aligned concentrically with the axis, and engaged in an at least partially force-transmitting manner with them. One of the bearing surfaces is rotatable about the axis while the other bearing surface remains fixed. Also, the bearing surfaces are aligned substantially parallel to the axis and concavely curved in the axial direction symmetrically to one another, the maximum distance of the curves from one another being approximately equal to the diameter of the balls. A force is applied axially to the balls by the driving part.
The transmission is based on the principle that the balls move simultaneously relative to two concentric circumferential surfaces serving as bearing surfaces, which are circular in cross section and have different radiuses. The result is different angular velocities of the motor drive shaft and the driven bearing surface, corresponding to the ratio of the radiuses of the bearing surfaces.
Thus a drilling or milling head is provided with a transmission that is space-saving and subjected hardly at all to wear. Since it is based on simple means, the transmission can also be manufactured at low cost. Since the bearing surfaces are aligned substantially parallel to the axis and concavely curved in the axial direction, and indeed such that the curvatures are symmetrical with one another, i.e., with respect to the axis passing through the balls about which the balls rotate, and furthermore since the balls are subjected to a force by the driving part, the balls are urged against an area of the curves in which the distance of the curves from one another is less than the diameter of the balls. In this manner a force-transmitting engagement of the balls with the bearing surfaces is achieved, resulting in a simple form of a slipping coupling.
Inasmuch as the bearing surfaces are concavely curved, the axial travel of the driving part is especially short—shorter, for example, than in the case of the surfaces tapering in the axial direction. Due to the curvature of the bearing surfaces the balls come very quickly into engagement with the bearing surfaces.
The driving part can be biased by a spring which is fastened on the motor drive shaft between a motor housing and the driving part. The spring absorbs the reaction force upon engagement and simultaneously offers protection against overload due to excessive heating of the balls and the races. The spring force is to be adjusted accordingly when the transmission is assembled.
The transmission can be used both for increasing speed and for reducing speed. To achieve a speed increase, the bearing surface having the greater radius is fixed. In this manner the part that forms the bearing surface having the smaller radius is caused to rotate. This part can directly be a section of the drive shaft of the drilling and milling head, or it can also be joined to this drive shaft through a coupling.
The bearing surfaces can be formed by a bearing inner ring or a bearing outer ring. The bearing outer ring, if it is fixed, can be inserted in a housing of the transmission. The bearing inner ring can be pressed on the driven part.
Preferably the driving part fastened on the motor drive shaft is a toothed flange whose teeth are engaged between the balls. Provision can be made for pressing seats in the axial direction into the toothed flange for the balls of the ball bearing. The toothed flange is preferably made from wear-resistant material. Sintered bronze, preferably impregnated with oil, is especially suited to the purpose.
The friction clutch of the drilling or milling head preferably is comprised of a part that can be moved axially and relative to the drive shaft of the drilling or milling head and a part that is axially displaceable and affixed to the drive shaft of the drilling or milling head, the two parts having faces which conform to one another which come in contact when the quick change mechanism is operated. Provision is made for the two parts each to be supported on the tool side against the force of a spring. This assures that in a state of rest, the two parts will be spaced a distance from one another, and in case the part of the drilling or milling head affixed to the drive shaft rotates only friction will occur between the surfaces, which does not result in damage to the drilling or milling head.
According to a preferred embodiment of the drilling or milling head, the part that can be moved relative to the drive shaft of the drilling or milling head is cylindrical and is arranged concentrically with this drive shaft, and has on the end toward the motor an annular shoulder. The part of the drilling or milling head that is affixed to the drive shaft is a sleeve with a circumferential flange. The conforming surfaces are formed on the annular shoulder and on the circumferential flange planar and perpendicular to the shaft.
Since the force necessary for the axial shifting of the collet chuck is transmitted by a friction clutch, it is impossible for an accidentally still rotating collet chuck when opened to come into locking engagement with a non-rotating part. The axial displacement force is instead transferred in a positive manner through the friction clutch to the collet chuck, or to the drive shaft to which the collet chuck is attached.
The quick change mechanism can be operated manually through a hand actuator. Provision can also be made for the hand actuator to be locked in the position in which the collet chuck is open. This has the advantage that the operator has both hands free to manipulate the drilling or milling tool.
The hand actuator can be, for example, a lever which has a handle section and a functional section disposed within a housing of the drilling or milling head. It is anticipated that in the rest position this functional section of the lever will form an inclined angle to a horizontal plane and in the actuated position it will assume a right angle to the drive shaft of the drilling or milling head, and furthermore lies against an immovable surface of the drilling or milling head and, on the tool side, against the part that is movable relative to the drive shaft. When in the actuated position the functional section of the lever has a greater maximum length in the axial direction than in the rest position. Thus, moving the lever from its rest position to its active position causes the part of the friction coupling that can move relative to the drive shaft to be displaced toward the tool end of the drilling or milling head, and at

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