FIELD OF THE INVENTION The present invention relates to a three-jaw tightening chuck. a method and a device for cutting teeth of the gripping jaws, that can be used in machines operating with rotating tools such as drills, multiflute drills, countersink drills, reamers, as well as hand held drilling machines, NC machines, etc.

STATE OF THE ART A three-jaw tightening chuck for securing rotating tools is known. the shuck comprising a body with a main hole for coupling to the rotating driving machine and with three openings, the axes of which are inclined with respect to the longitudinal axis of the body. Gripping jaws are accommodated in the openings, one of the surfaces of the jaws being formed as a tooth sector engaged with the conical thread of a gear wheel.

The tightening of the tool is carried out bv rotating the gear wheel either manually or by key. The gripping jaws are characterised in that the teeth of the tooth sector have a pitch and a shape that match the conical thread of the engaged gear wheel. Besides, each tooth of the rack of the gripping jaws has a different curvature and an angle of inclination.

Another three-jaw tightening chuck for securing drills and other rotating tools is known (2). the chuck having design similar to the design of the above described chuck. In order to improve the accuracy in gripping and to prevent the rotation of the jaws around their axes the teeth in the tooth sectors of the gripping jaws have different characteristics from those of the previously described chuck. More important characteristics are the form of the surface on which the teeth are cut. the surface <BR> <BR> <BR> being determined bV ils radis and ihe position of) ts axis Wtth

respect to the axis of rotation during cutting and the axis of rotation of the cutting tool ; the curvatures of the teeth. determined bv their radii of rotation and the angles of inclination with respect to the longitudinal axis.

A three-jaw tightening chuck is also known for securing drills and other rotating tools (3) the chuck having design similar to the design of the above described chucks. The difference consists in the shape of the teeth in the tooth sector.

The teeth are formed as a part of a cylindrical screw surface and their pitch and the shape of their profile match the conical thread of the engaged driving gear wheel. The teeth in the tooth sectors have constant angles of inclination which are equal to the angle of elevation of their cylindrical thread.

The above described known constructions of three-jaw tightening chucks are not effective enough with respect to the precision of gripping and rotating of the tool, as well as to the smooth movement of the jaws in locking or releasing of the tool. The above mentioned drawbacks are caused main, by the constructive design of the teeth in the tooth sectors.

As it was already stated, the curvature of the teeth and the angle of inclination of each tooth are different. therefore in motion the teeth of the gripping jaws contact stepless the screw surfaces of the conical thread, having constant pitches and different curvatures and angles of inclination in each section.

As a result the engagement between the rack and the conical thread of the gear wheel changes during the stroke of the gripping jaws and the contact areas are disposed on a curved spatial line inclined with respect to the midnormal of the gripping jaw. the midnormal starting at the middle of the first tooth near the contact side of the jaw and ending at the right end of the last tooth in the tooth sector. The above described manner of contacting between the tooth sector and the conical

thread of the gear wheel leads to an unbalanced loading of the teeth. which are subjected to the negative influence of a torque with respect to the longitudinal axis of the gripping jaw. thus worsenine the contact with the tightened tool. respectively the accuracv of rotation. Another disadvantage is the rapid losing of the initial accuracy of rotation of the chuck caused bv the unbalanced loading and by the wearing of the contacting parts.

A method for cutting teeth in the tooth sectors is known. the method comprising the following steps: a set of jaws is placed in a mandrel, the axes of the jaws being inclined with respect to the axis of rotation of the mandrel; a cutting tooi. for example bobbing cutter is fed. the axis of rotation of the cutter being parallel to the axis of the gripping jaws: the cutting tool moves until the entire height of the teeth is cui: the mandrel rotates at one and one quarter revolutions, and all of the teeth in the tooth sector are cut byaxially,pitchby pitch forward motion of the cutter.

A method for cutting teeth in tooth sectors is also known. which differs from the above described method in that a cylindrical thread is cut on the jaws gripped in the mandrel.

An arrangement for carrying out the above described method is known. the arrangement containing a special machine <BR> <BR> <BR> <BR> -universal lathe. The mandrel with the set of jaws to be cut is fixed on the spindle of the lathe. The rotating means of the cutting device is secured on the slide of the machine, and the axis of rotation of the cutting device is inclined with respect to the axis of rotation of the machine. A particular feeding mechanism ensures the synchronisation between the rotation of the spindle and the feeding motion of the cutting too ! by one pitch parallel to the axes of the jaws to be cut.

The above described known constructions of the teeth of the gripping jaws and their geometric characteristics, as well as the methods and the devices for cutting teeth do not provide such forming of the teeth in order to achieve a high accuracy for gripping of the rotating tool, a smooth motion of the gripping jaws in locking and in releasing of the tool. and permanent maintaining of the initial accuracy of rotation of the chuck. In order to keep the standard requirements for accuracy for the three-jaw tightening chuck it is necessary its composite parts to have high classes of accuracy. which considerably increases the production expenses and the cost of the article.

Another drawback of the known three-jaw chucks is that the accuracy for gripping and rotation of the tightened tool become lower because of the rotation of the gripping jaws around their longitudinal axes caused by different reasons.

SUMMARY OF THE INVENTION In view of the above stated. it is an object of the present invention to provide an improved construction of a three-jaw tightening chuck, which is distinguished by a smooth motion of the gripping jaws, a higher reliability for tightening of the tool and precision of rotation and a longer period of maintaining the initial accuracy, excluding at the same time the possibility of lowering the accuracy in gripping and rotating of the tool caused bv the rotation of the gripping jaws around their longitudinal axes. An object of the invention is ro provide a method and a device for cutting teeth with reduced manufacturing costs ; satisfying at the same! ime the standard requirements for the accuracy of the tightening chucks.

A further object of the invention is to provide a method and a device for cutting teeth in the tooth sectors, which achieve a informingteethofthegrippingjaws,sufficientaccuracy

These objects of the invention are achieved by providing a three-jaw tightening chuck for securing rotating tools, the shuck comprising a body with a main hole for coupling to the rotating driving machine, and three openings, the axes of which are inclined with respect to the longitudinal axis of the body.

Tightening jaws having tooth sectors on their outer surface engaged with the conical thread of a gear wheel are accommodated in the openings. At the opposite side of the tooth sectors there is an inclined contact surface for contact with the tightened tool.

According to the invention all teeth in the tooth sectors of the gripping jaws have identical pitches and shapes of the profile similar to these of the conical thread of the gear wheel, to which they are engaged. The teeth are formed on a cylindrical surface, the axis of which is parallel to the axis of the gripping jaw. Both axes lie in one plane passing their midperpendicular. The radius of the cylindrical surface is equal to the minimal internal radius of the conical thread. The teeth are arch-cut with a curvature determined by the rotation of the jaw around an axis at an angle with respect to the axis of the gripping jaw. The curvature has a radius equal to the minimal outer radius of the conical thread.

The angle of inclination of the teeth with respect to the longitudinal axis of the gripping jaw is equal to the angle of elevation of the conical thread, determined by its middle radius.

According to one embodiment of the invention the teeth in the tooth sector are perpendicular to the longitudinal axis of the gripping jaw.

The above described design of the teeth in the tooth sectors of the gripping jaws is achieved bv a method for cutting teeth on gripping jaws. The method includes positioning of the

gripping jaws, advancing them to a cutting tool, forward motion of a feeding forming mechanism and rotatable motion of the cutting tool, where the axis of rotation of the cutting tool is parallel to the axis of the jaw to be cut.

The inventive method includes the following steps: positioning of one jaw along its longitudinal axis in the feeding forming mechanism, the axis of rotation of which is orientated at an angle with respect to the axis of the jaw to be cut, where the forward motion of the feeding forming mechanism is a rotatable oscillating motion at a certain angle; advancing of the jaw to be cut towards the cutting tool; cutting of the first tooth space; stopping of the advanced motion; axially moving of the jaw to be cut to a distance equal to one pitch of the conical thread ; reversing of the forward rotating motion and cutting of the second tooth space ; stopping of the forward rotating motion; and axially moving of the jaw to a distance at one pitch of the conical thread.

The repeating of the above described sequence of operations leads to cutting of all teeth in the tooth sector with uniform radius of rotation with respect to the axis at an angle of the feeding forming mechanism.

The above described method for cutting teeth on gripping jaws is carried out boy a device for cutting of uniform teeth, the device including a casing on which feeding forming mechanisms connected to cutting mechanisms are mounted. the mechanisms being controlled bv a hvdraulic and an electric svstems.

According to the invention there are three pairs of mechanisms on the casing, each pair containing one feeding forming mechanism and one cutting mechanism. The feeding forming mechanism is disposed in such a way that its axis and the axis of rotation of the cutting tool lie in one plane, and the arrangements of the base support elements of the feeding

forming mechanisms with respect to the front parts of the cutting tools for the second and for the third pair of mechanisms differ from that for the first pair bv one third and two thirds, respectivelv. of the pitch of the conical thread.

According to one embodiment of the inventive device there is only one pair of mechanisms mounted on the casing, the pair including one feeding forming mechanism and one cutting mechanism.

The feeding forming mechanism includes a carrier body with a built-in cylindrical tailstock barrel, to which base positioning movable and immovable elements are fixed. A driving cylinder is axially mounted to the tailstock barrel and is immovably connected to a pitch dividing mechanism, and the carrier body is accommodated in a bearing case with a build-in feeding group.

The positioning elements: a tightening cylinder, an immovable base support. an immovable base support having a semicvlindrical hole and a movable base support formed as a prism are all arrange on the tailstock barrel. The disposition of the base supports determines the position of the axis of the jaw to be cut and the angle of inclination of the teeth to be cut.

According to one embodiment of the invention the axis of the base positioning elements of the feeding forming mechanism lies in one plane with the axis of the cutting tool and the axis of the feeding forming mechanism.

The pitch dividing mechanism includes a casing, in which a pitch templet connected to a piston rod of a driving cylinder and to a cylindrical tailstock barrel is mounted.

The feeding group of the feeding forming mechanism is <BR> <BR> <BR> <BR> mounted in a bearing case. in which a rack js built-in to the piston rod of a driving cylinder, the rack being engaged to a gear wheel fixed on a bearing journal.

The cutting mechanism includes a casing attached to a base plate by means of guides. A spindle resting on bearings within the casing and having a cutting tool mounted on is driven by an electric driving group. The cutting mechanism allows longitudinal and transversal motion of the cutting tool with respect to the axis of the spindle.

The three-jaw tightening chuck according to the invention is an improved construction, which provides an increased strength for gripping and higher accuracy of rotation of the rotating tool.

The specific design of the gripping jaw in relation to the tooth sector and especially the forming of the teeth having geometric parameters according to the invention provides uniform contact areas of all teeth in their engagement with the helical surface of the conical thread. The contact areas are disposed on the midnormal of the rack and determine an uniformly-distributed loading of the teeth in tightening. This leads to a higher precision of rotation of the tightened tool ; more smooth motion of the gripping jaws and a longer period of maintaining of the initial accuracy. By applying of the invention it is possible to manufacture the elements of the chuck at a lower class of accuracy with keeping the standard requirements for accuracy for the tightening chucks, thus reducing considerably the manufacturing costs. At the same time by using of the proposed construction of the tightening chuck the possibility of lowering the accuracy in gripping and rotation of the tool caused by the rotation of the eripping jaws around their longitudinal axis is excluded.

The proposed method and device for cutting teeth on gripping jaws allow cutting teeth at a sufficient accuracy and precision, where further grinding operstion for the complete

treatment of the teeth to be cut is possible. Thus the class of accuracy of the chuck is increased at the same time decreasing the frictional factor in engaging the teeth in the rack with the conical thread of the gear wheel.

The above described constructive features of the chuck result in increased tightening strength of the tool at reduced forces applied for tightening and releasing of the rotating tool.

BRIEF DESCRIPTION OF THE DRAWINGS An exemplary embodiment of the three jaws tightening chuck according to the invention is shown with reference to the accompanying drawings, wherein: Figure 1 is a longitudinal section of a tightening chuck; Figure 2 is a cross-sectional view of a tightening chuck ; Figure 3 is a longitudinal section of a conical gear wheel- nut; Figure 4 is a side view of the gripping jaw ready for cutting of the teeth ; Figure 5 is a cross-sectional view taken on line M-M of Figure 4 ; Figure 6 is a side view of a jaw with cut teeth; Figure 7 is a cross section taken on line N-N of Figure 4; Figure 8 is a top view of the teeth in the gripping jaw; Figure 9 is a front view of a device for cutting teeth in a gripping jaw : Figure l 0 is a side view of partial sections of a feeding forming mechanism: Figure 11 is a cross section taken on line A-A of Figure 10; Figure 12 is a cross section taken on line B-B of Figure 10: Figure 13 is a cross section taken on line C-C of Figure 10; Figure 14 is a front view of the cutting mechanism: Figure 15 is a view on lire F of Figure 10 ; Figure 16 is a view on line D of Figure 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT Further in the description an exemplary embodiment of the invention is shown, the invention concerning a three-jaw tightening chuck with a specific construction of the teeth in the gripping jaws, a method for cutting teeth of the jaws and a device for carrying out the method.

According to the invention the three-jaw tightening chuck <BR> <BR> <BR> <BR> comprises a main body 1 with three openings 2, the axes of which are inclined with respect to the longitudinal axis of the body 1. Gripping jaws 3 are accommodated in the openings 2, the jaws 3 being provided with contact surfaces 4. Tooth sectors are formed on the outer surfaces of the jaws, and the teeth of the tooth sectors engage the conical thread of a gear wheel 5. to which a sleeve 6 is immovably attached.

All teeth of the gripping jaws have identical pitch and shape of the profile similar to these of the conical thread to which they are engaged. The teeth are formed on a cylindrical surface 7 (Figure 4), the axis of which is parallel to the axis 8 of the gripping jaw 3. Both axes lie in one plane through their midperpendicular. The radius of the cylindrical surface 7 is equal to the minimal radius of the conical thread. The teeth are arch-cut with a curvature 9, (Figure 8) determined by the rotation of the jaw 3 around an axis at a certain angle with respect to the axis 8 of the gripping jaw 3. the curvature 9 having a radius equal to the minimal outer radius of the conical thread and an angle of inclination with respect to the longitudinal axis 8 of the jaw 3 equal to the angle of elevation of the conical thread, corresponding to its middle radius.

According to one embodiment of the invention the teeth of the gripping jaws 3 are cut perpendicularly to the axis 8 of the gripping jaw 3. i. e. without an inclination.

In order to achieve a high precision of rotation a smooth motion of the gripping jaws and to retain the initial accuracy

for a longer period, and to exclude the possibility of lowering the accuracy in gripping and rotation of the tool caused by the rotation of the gripping jaws around their longitudinal axes, there is provided a tightening chuck with teeth in the gripping jaws preferably incorporating the technical solution described in Bulgarian patent application ser. No 102 424.

The above described gripping jaws having specific designed teeth are cut according to a method for cutting of uniform teeth, where only one jaw is located and locked in a feeding forming mechanism. The jaw is advanced to a cutting mechanism simultaneously with the rotation of the cutting tool. According to the invention the cutting is carried out by a forward rotatable feeding of the feeding forming mechanism. After cutting of the first tooth space the rotating feed of the feeding forming mechanism is stopped and the jaw is axially moved at a distance equal to one pitch of the conical thread. The second <BR> <BR> <BR> <BR> tooth space is cut in a reversible rotating feed followed by stopping and again moving of the jaw to a distance of one pitch of the conical thread.

The above described sequence of operations repeats until all teeth are cut, the teeth having uniform radius of rotation with respect to the axis of the feeding forming mechanism: after that the ready jaw is released and is dismantled from the device either automatically or manually.

The above described method for cutting of uniform teeth on the gripping jaws 3 according to the invention is accomplished by a device for cutting uniform teeth. the device including a casing 10. on which three pairs of mechanisms are mounted.

Each pair contains one feeding forming mechanism II and one <BR> <BR> <BR> <BR> cutting mechanism 12. the feeding forming mechanism 11 being disposed in such a wav that its axis 13 and the axis of rotation

14 of the cutting tool lie in one plane. The arrangements of the base supports 22 and 23 of the feeding forming mechanisms 11 with respect to the front parts of the cutting tools 15 for the second and for the third pair of mechanisms differ from that for the first pair by one third and by two thirds, respectively, of the pitch of the conical thread.

The base supports 21,22,23 determine the disposition of the axes of the jaws to be cut 3 and the angle of inclination of the teeth, which is equal to the angle of elevation of the conical thread identified by its middle radius.

The feeding forming mechanism 11 includes a carrier body 16 with a built-in cvlindrical tailstock barrel 17 and a tightening cylinder 18 mounted on it.

The tightening of the jaws to be cut 3 is achieved by its tightening between the head 19 of the piston rod 20 and the immovable base support 21, the immovable base support with semicylindrical hole 22 and the movable base support 23, the last being vertically orientated by means of a spring 24. A driving cylinder 25 is built-in along the axis of the tailstock barrel 17, and the piston rod 26 of the cylinder 25 passes through a cover 25 and is immovably connected to a pitch dividing mechanism 28.

The pitch dividing mechanism 28 includes a casing 29, where a pitch templet 30 is dismountably connected to a piston rod 31 of a hydraulic cylinder 32, the pitch templet 30 being closed bv means of covers 33,34,35. The carrier body 16 of the feeding forming mechanism 11 rests on bearing journals 36, 37 in bearing cases 38,39. A feeding arrangement 40 is built-in the bearing case 39. the feeding arrangement 40 including a driving cylinder 41 and a rack 42 mounted on the piston rod of the driving cvlinder 41. The rack 42 is engaged with a gear wheel 43 immovably fixed in the bearing journal 37. The

feeding arrangement 40 is closed by a cover 44. A pusher 45 is provided at one end of the carrier body 16 for forced transposition of the movable base support 23 when the cylindrical tailstock barrel 17 is at a front end position.

The cutting mechanism 12 includes a casing 46, in which a spindle 47 is placed resting on bearings. The cutting tool 15 is <BR> <BR> <BR> <BR> mounted on the spindle 47, and the casing 46 is attached to a base plate 48 by means of guides 49. The cutting mechanism 12 is adjusted by means of a screw 50 and built-in nut 51, the screw 50 being driven by a flywheel with vernier 52. The cutting tool 15 is driven by a motor 53 immovably mounted on the casing 46 and by a common transmission, i. e. a belt 54 and a pulley 55 fixed on the spindle 47.

The above described construction of the cutting mechanism allows for longitudinal and transversal displacement of the cutting tool 15 in order to achieve an uniform situating with respect to the jaw to be cut 3. The proposed constructive design is not limited in relation to variant technical solutions providing similar possibilities.

A further embodiment of the device includes a casing 10 containing only one pair of feeding forming mechanism 11 and a cutting mechanism 12, which can be adjusted to cut a set of jaws for one chuck.

When the teeth are cut at an angle with respect to the longitudinal axis 8 of the jaw 3, the axis of the base supports 21, 22, 23, which determines the position of the axis 8 in the feeding forming mechanism 11 is inclined with respect to the plane, in which the axis 13 of the feeding forming mechanism 11 and the axis 14 of the cutting mechanism 12 lie.

The device for cutting teeth on gripping jaws 3 is provided with a hydraulic system 56 and a lubricating system 57 shown

schematically in the drawings. The entire electric control of the operations, especially the synchronisation of the motion of the working groups and mechanisms for cutting of the gripping jaws 3 is carried out by means of an electric system, not shown.

APPLICATION OF THE INVENTION The three-jaw tightening chuck is used as follows: the tightening chuck is secured in a known manner to the spindle of the operating machine through the main hole in its body 1. The tightened tool is engaged in the opening formed between the jaws 3, and the conical gear wheel 5 is driven by means of a suitable locking key inserted in the body 1. As a result of the engagement between the conical thread and the teeth of the gripping jaws 3 the jaws move linearly in the inclined openings 2 and engage and hold the tightened tool by their contact surfaces 4. Due to the fact that the teeth have uniform geometric characteristics and the teeth of the rack and of the conical thread have identical profiles and pitches, the engagement is in steady contact areas disposed along a midnormal of the rack, providing at the same time a constant and an uniformly-distributed loading of the teeth.

The device for cutting teeth of gripping jaws performs the sequence of operations already revealed in relation to the inventive method. The gripping jaws 3 are located either manually or automatically on the immovable base support 21 and by means of the head 19 of the piston rod 20 of the tightening cylinder 18 are tightened and fixed in the base supports 22,23. The thus locked jaw 3 is transferred by means of the cylindrical tailstock barrel 17 to an initial position for cutting teeth. The cutting tool 15 is put in rotating motion and simultaneously the feeding forming mechanism 11 rotates forwardly at a preset angle and thus the first tooth space is cut.

After that the forward motion of the feeding forming mechanism 11 stops and the pitch template 30 moves at one pitch by means of the piston rod 31 of the hydraulic cylinder 32. The gripping jaws 3 move to a distance of one pitch in order to cut the second tooth space by a reversible motion of the feeding forming mechanism 11. After that the forward rotating motion is stopped and the jaws 3 are transferred at one pitch. The above described sequence of operations repeats until all teeth of the rack are cut.

After completing the cutting of all teeth the tailstock barrel 17 returns to its initial position by means of the driving cylinder 25, and the pusher 45 moves the vertically orientated movable base support 23, formed as a prism. The piston rod 20 of the tightening cylinder 18 automatically releases the gripping jaw 3, having teeth cut on its external surface.

When the device includes only one pair of mechanisms for the cutting of each jaw 3 from the set of jaws for one chuck, the position of the front part of the cutting tool 15 is correspondingly adjusted with respect to the base prism of the feeding forming mechanism 11.