INTERNAL CHUCK

Abstract: An internal chuck especially for use in cutting external threads on small pipe pieces, where the pipe piece is placed on a mandrel (2) which is rotatably connected to a fixable mandrel (1) and provided with preferably three axially extending and rotatably embedded dogs (9) having a plane surface (10). The fixable mandrel (1) has activating members (14) which make the dogs (9) rotate via mutual rotation of the two mandrels (1, 2) such that the edge of the plane surface (10) is pressed against the interior wall of the pipe piece.

Description: INTERNAL CHUCK TECHNICAL FIELD This invention relates to an internal chuck to be used particularly for cutting external threads on small pipe pieces and of the type where a cylindrical mandrel intend¬ ed for insertion in the pipe piece has at least two, pre¬ ferably three, axially-running cylindrical sockets placed, in the cylinder surface at uniform angle distance, the depth of said sockets being less than their diameter, but larger than or equal to their radius, and in which cylin¬ drical dogs are rotatably embedded having a plane surface parallel to the axis, said surface substantially covering- the same angle ' as ...the openings of the sockets. BACKGROUND ART An internal chuck of this kind is known from GB-PS No. 408,777. In said chuck the dogs, via a toothed seg¬ ment, are activated by a spring to the active position in which the pipe piece is securely held, the dogs being em¬ bedded in a fixable body part. However, said internal chuck has some disadvantages, as its action is based on a " certain friction between the dogs and the interior surface of the work piece, so that this friction results in a further rotating of the dogs for gripping the work piece. However, if the interior* surface of the pipe piece is smooth there is a danger of reduced friction and the pipe OMPI /., IPO ^ piece cannot be securely held unless the spring action is exceedingly strong. But, this would involve difficulties in placing the pipe piece on the mandrel as, in that case, the dogs are rotated so that they project substantially beyond the interior circumference of the pipe piece. DISCLOSURE OF INVENTION It is the object of the present invention to provide an internal chuck in which the above disadvantages are re moved and which, consequently, is considerably easier to operate. This is achieved by the internal chuck according to the invention which is characteristic in that the said mandrel (2) is rotatably connected to a fixable mandrel(l provided with activating members (14) at its end surface (13) facing aforementioned mandrel (2), said members (14) being arranged to make the dogs (9) rotate via mutual ro¬ tation of the two parts (1,2). By making the dogs rotate via mutual turning of the two mandrels a steadily increasing pressure of the abut- ting of the dogs against the interior surface of the pipe piece is obtained. In a preferred embodiment of the internal chuck ac¬ cording to the invention the ends of the dogs extend down wards into a housing secured to the mandrel, in which housing the end of the fixable mandrel is rotatably embed ded and fixed axially. This results in the activating members being completely enclosed and protected against outer influence. According to the invention the activating members can be designed so that each of the dogs at its end part ex¬ tending into the housing is provided with a radially ex¬ tending arm, and that the fixable mandrel at its end sur¬ face is provided with a number of pins corresponding to the number of dogs, said pins protruding in between said arms. When the two mandrels are rotated conversely,they wil cause the pins to move against the arms and thereby mak the dogs rotate, and during this operation the pins will slide along the arms. By reversing the rotation of the mandrels, the dbgs will rotate back, releasing the secured pipe piece. The axis of the arms forms an angle preferably of 30° with the plane surface of the dogs. In a particularly appropriate embodiment the length of the arms of the. dogs is adapted so that they abut on the • interior wall of the housing when the plane part of the dogs flush with the cylindrical surface of the mandrel. Thus the mandrel with the dogs can always be adjusted to neutral position in which the pipe piece freely can be placed on the mandrel or removed therefrom. In yet another embodiment of the internal chuck ac¬ cording to the invention the arms are placed on the dogs in such a manner that the plane part of the dogs flush with the cylindrical surface of the mandrel, when the arms abut on a neighbouring dog or on a part fixed to same. By this is achieved that the pins activated by the arms slide inwards along these so that the moment of force on the arms approaches the axis of rotation of the dogs. The embodiments hitherto mentioned are intended for __ threading in one direction only. In a special embodiment suited for threading in both directions, i.e. cutting of both right-handed threads and left-handed threads, the end of the dogs protruding into the housing is provided with mainly oval plates, the one end of each of said plates be¬ ing secured to the dogs and the other end provided with a hollow in which the pins placed on the fixable mandrel slidingly engage. In order to be able to fix the dogs in the neutral po¬ sition, the plates are provided with indentations at the ends facing away from the hollows, a bushing of an elastic, yielding material being placed centrally between the plates and engaging in said indentations. BRIEF DESCRIPTION OF THE DRAWING The invention is explained further in the following by some embodiments with reference to the drawings in which OMPI Λ, WIPO ^ FIG.l shows a side view of an internal chuck according to the invention, FIG.2 shows the internal chuck of FIG.l seen from above, FIG.3 shows an exploded view of an embodiment of the internal chuck according to the invention, FIG.4 shows a section of the embodiment of FIG.3 along the line IY - IT of FIG.l in a larger scale, FIG.5 shows a corresponding section of another embodi¬ ment, and FIG.6.shows a corresponding section of a third embodi¬ ment. BEST MODE OF CARRYING OUT THE INVENTION The internal chuck consists of mandrels 1 and 2 placed coaxially and conversely rotatable. The fixable mandrel 1 is intended for fixing in a thread lathe and is therefore provided with a shoulder 3 serving as a stop device. This fixable mandrel 1 is rotatably embedded in a cylindrical housing 5 by an expanded part 4, said housing being secur¬ ed to the other mandrel 2 and having an interior annular groove 6 for receiving a resilient locking ring 7 which firmly holds the expanded part 4 of the fixable mandrel 1 in the housing 5- The mandrel 2 of the embodiment shown has .three cylin¬ drical sockets 8 extending parallel to. the axis of said body, and the depth of which is less than their diameter, so that the sockets 8 are open outwards radially. In the sockets 8 are placed cylindrical dogs 9 having substantial ly the same diameter as the sockets 8, so that the dogs 9 are rotatable in said sockets 8. The dogs 9 have a plane surface 10 parallel to the axis, said surface 10 covering the same angle as the openings of the sockets 8. The dogs 9 protrude downwards into the housing 5 where in the embodiment of FIG.3 they are provided with a bottom part 11 from which an arm 12 projects radially. Said arm 1 is cylindrical and its axis forms an angle of 30° with the plane surface 10 of the dog 9. Three pins 14 are placed at equal angle distance on the end surface 13 of the expanded part 4 of the fixable mandrel 1 close to the circumference of said end surface. The pins 14 are provided with annu " arms 12. The function of this embodiment of the internal chuck is explained in connection with FIG. 4. In the neutral po- sition shown by solid lines the plane surface 10 of the dogs 9 flush with the cylindrical surface of mandrel 2, and the end surface 16 of the arms 12 abut on the interior wall of the housing 5. The pins 14 are secured on the end surface 13 of the fixable mandrel 1, and if the two mandrels are rotated conversely to each other the pins 14 will move towards the arms 12 along the arrow 17 ' " by which the arms 12 and the dogs 9 will rotate to the position shown in dotted lines. A pipe placed on mandrel 2 and having an interior diameter corresponding to that of said mandrel will be held fast by the edges on the dogs 9, which edges are pressed against the interior wall of the pipe. Releasing of the pipe takes place by turning the man¬ drels 1,2 in the opposite direction, so that the pins 14 move towards the opposite side of the arms 12, as shown by the arrow 18 and the position of the pin 14 shown by the dotted line. Upon continuing the turning the arms 12 will assume the position shown in -solid lines, and the pipe can be removed. Rotation of one mandrel in relation to the other can be achieved by rotating the housing 5, the exterior'surfa¬ ce of which may be knurled. However, normally the fixable mandrel 1 will be fixed in a lathe and the pipe piece that is to be provided with a thread is placed over the mandrel 2. When the mandrels are then put into rotation and the threading die is pressed against the pipe, said mandrels will by themselves rotate conversely to each other and thereby the pipe will be held firmly on mandrel 2, as ex¬ plained above. FIG.5 . shows a modification of the internal chuck shown in FIG.4 having the same reference numbers for correspond¬ ing parts. In this case the arms 12 are placed on the bot¬ tom part 11 of the dogs substantially diametrically oppo- OMPI w site to the position of the arms in FIG.4. When the dogs are in neutral position the arms 12 abut on the bottom part 11 of the neighbouring dog. In order to turn the dog 9, the pins 14 are moved towards the arms 12 along the ar row 17' and by the contact of the arms against the interi wall of the housing the rotation of the dogs is limited t 45°. Reversion to neutral position takes place by means o another pin that is moved along the arrow 18'. By this em bodiment the arms 12 receive a reduced stress because the pins 14 during their movement, to fixing position are led inwards towards the arms' connection with the dogs 9. FIG.6 is a schematic view of another embodiment of th internal chuck according to the invention. In this case t dogs 9 are provided with a bottom part 21 v/hich has an ov design and v/hich protrudes to a point close to the interi wall of the housing 5. At the end facing the housing 5 there are hollows 22 corresponding to the pins 14 leaving a possibility of a slight displacement of said pins in said hollows 22. The activated position of the bottom part 21, pin 14 and dog 9 is shown in dotted -lines. The bottom parts 21 are adjusted in relation to e ' ach other so that by rotatio they move towards * each other without the pins 14 disengag¬ ing the hollows 22. In order that the dogs 9 can be placed in neutral po¬ sition, i.e. in which the plane part 10 of the dogs flush with the surface of the mandrel 2, the bottom parts 21 ca be provided with an indentation 23 at the end facing the axis of the mandrel, and in this case a bushing 24 of spring steel is placed between the bottom parts, the axial edges of said bushing overlapping each other without inter connection, said bushing engaging the indentations of the bottom parts.. The embodiment of FIG. .6 can be applied for both righ handed and left-handed threading, while the embodiment of FIG. 4 and FIG.5 only can be applied for threading in one direction, as the arms 12 have to extend on the other sid of pins 14 for threading in the other direction. ^-^ RE f OMP In all three embodiments the activating members on-the fixable mandrel 1 are shown as pins 14. However, other forms of activating members could also be imagined, for example, on the fixable mandrel 1 a toothed wheel could " be placed centrally engaging toothed segments on the dogs 9, as sketched in 19 of FIG. 4. INDUSTRIAL APPLICABILITY As mentioned, the " internal chuck can be used for cut¬ ting threads on small pipe pieces for producing pipe nipples. However, the internal chuck according to the in¬ vention can also be used for other types of work pieces having a cylindrical boring. Contrary to the previously mentioned known internal chuck, the work piece or the pipe piece is held fast in the present internal chuck in a self- increasing gripping, as in case of threading or other sort of working the two mandrels are turned conversely with a steadily increasing force whereby the activating members are further rotated and press the dogs against the interior wall surface of the work piece. OMPI

Claims: CLAIMS 1. An internal chuck especially for use in cutting ex¬ ternal threads on small pipe pieces and of the type where a cylindrical mandrel intended for insertion in the pipe piece has at least two, preferably three, axially-running cylindrical sockets placed in the cylinder surface at uni¬ form angle distance, the depth of said sockets being less than their diameter, but larger than or equal to their radius, and in which cylindrical dogs are rotatably embed- ded having a plane surface parallel to the axis, said sur¬ face substantially covering the same angle as the openings of the sockets, c h a r a c t e r i z e d in that the said mandrel (2) is rotatably connected to a fixable mandrel (1) provided with activating members (14) at its end surface (13) facing aforementioned mandrel,- said members (14) being arranged to make the dogs (9) rotate via mutual rotation of the two mandrels (1,2). 2. An internal chuck according to claim 1, c h a r a c ¬ t e r i z e d in that the ends of the dogs (9) extend downwards into a housing (5) secured to the mandrel (2), in which housing the end part -(4) of the fixable mandrel (l) is rotatably embedded and fixed axially. 3. An internal chuck according to claim 2, c h a r a c ¬ t e r i z e d in that each of the dogs (9) at its end ex- tending into the housing is provided with a radially extend¬ ing arm (12), and that the fixable mandrel (1) at its end surface is provided with a number of pins (14) correspond¬ ing to the number of dogs (9), said pins (14) protruding in between said arms (12). 4. An internal chuck according to claim 3, c h a r a c ¬ t e r i z e d in that the axis of the arms (12) form an angle of 30° v/ith the plane surface (10) of the dogs (9). 5. An internal chuck according to claim 4, c h a r a c¬ t e r i z e d in that the length of the arms (12) of the dogs is adapted so that they abut on the interior wall of OMPI the housing (5) when the plane part (10) of the dogs (9) flush with the cylindrical surface of the mandrel (1). 6. An internal chuck according to claim 3, c h a r a c- t e r i z e d in that the arms (12) are placed on the dogs (9) in such a manner that the plane part (10) of the dogs flush with the cylindrical surface of the mandrel (2) when the arms abut on a neighbouring dog (9) or on a part (11) fixed to said dogs (9). . 7. An internal chuck according to claim 2, c h a r a c- t e r i z e d in that the end of the dogs (9) protruding into the housing is provided with mainly oval plates (21) the one end of each of said plates (21) being secured to the dogs (9) and the other end provided with a hollow (22) in which the pins (14) placed on the fixable mandrel (1) slidingly engage. 8. An internal chuck according to claim 7, c h a r a c¬ t e r i z e d in that the plates (21) are provided with indentations (23) at the end opposite the end with the hollows (22), and that a bushing (24) of an elastic yield- ing material is placed centrally between the plates (21), said bushing engaging the said indentations (23). ■< REAtT OMPI

Inventors: CARLSEN P, NIELSEN K
Applicants: CARLSEN P, NIELSEN K
Application year: 1980
Main classification: B23B31
IPC codes: B23B31