GB2154481A

GB2154481A - Machine tool spindle and tool holder suitable therefor

Info

Publication number: GB2154481A
Application number: GB08500334A
Authority: GB
Inventors: Otto Eckle
Original assignee: Komet Stahlhalter und Werkzeugfabrik Robert Breuning GmbH; Komet Praezisionswerkzeuge Robert Breuning GmbH
Current assignee: Komet Stahlhalter und Werkzeugfabrik Robert Breuning GmbH; Komet Praezisionswerkzeuge Robert Breuning GmbH
Priority date: 1984-02-23
Filing date: 1985-01-07
Publication date: 1985-09-11
Also published as: CH666213A5; IT8519619A0; DE3406498C1; FR2560094A1; SE8500890D0; JPS60207736A; IT1200389B; FR2560094B1; JPH0431812B2; GB8500334D0; SE8500890L; SE459403B; DE8405489U1; GB2154481B

Abstract

The spindle (1) is provided at its spindle head (1a) with a frustoconical receiving bore (3a, 3b) for receiving a taper shank of a conventional tool holder and an annular end face (4) which is disposed around the receiving bore (3a, 3b). In the region of the frustoconical receiving bore (3a, 3b), the spindle head (1a) is provided with a cylindrical fitting bore (5) for selectively receiving a cylindrical fitting spigot portion (12) of a tool holder (11), the diameter (D) of the cylindrical fitting bore being somewhat smaller than the largest diameter (D1) of the frustoconical receiving bore (3a, 3b) and the axial length (L) thereof, as measured from the end face (4), being shorter than the axial length (L1) of the frustoconical receiving bore (3a, 3b). In the region of the cylindrical fitting bore (5), the spindle head (1a) has two diametrically oppositely disposed, radially extending female screwthreads (7, 8) each having a respective clamping screw (9, 10) provided with a conical projection (9a) or depression (10a). A clamping pin (14) is radially displaceable in a transverse bore (13) in the fitting spigot portion (12) and is provided at each of its two ends with a conical depression (14a) projection (14a) respectively co-operating with the clamping screws (9, 10). The spacing (a1) of the axis (A1) of the female screwthreads (7, 8) from the end face (4) is somewhat larger than the spacing (a2) of the axis (A2) of the transverse bore (13) from an annular surface (16) which extends around the fitting spigot portion (12) so that, when one of the clamping screws (9, 10) is tightened it acts on the clamping pin (14) so as to press the annular surface (16) and the end face (4) towards each other. <IMAGE>

Description

SPECIFICATION Machine Tool Spindle and Tool Holder Suitable Therefor The invention relates to a machine tool spindle and a tool holder which is suitable therefor, the spindle being provided at its spindle head with a frustoconical receiving bore for receiving a steepangle taper shank of a first tool holder, and an annular end face which surrounds the receiving bore.

It has been found that the connection which is most frequently used between the spindle head (DIN 2079) and the steep-angle taper shank (DIN 2080) of the tool holder is no longer ensures trouble free transmission of the full machine power of present-day high-output machine tools to the tool.

In the case of an ISO taper 50 in accordance with DIN 2080, the largest taper diameter is about 70 mm, while the taper shank is received in a spindle whose outside diameter is 128 mm. All transverse forces acting on the tool must be transmitted to the spindle by the taper shank which is comparatively thin in relation to the machine tool spindle. To ensure that the taper shank does not become loose in the frustoconical receiving bore, a very high level of retaining force must be produced by a retaining means which is disposed in the spindle and which pulls the taper shank into the receiving bore. For machines with automatic tool change, i.e.

machining centres, such retaining means must be capable of releasing the taper shank for the tool change operation. Consequently use is frequently made of diaphragm spring-actuated clamping claws which, when the diaphragm springs are relieved of load, close behind the head of a headed bolt which is disposed at the end of the taper shank, and with the residual force pull the taper shank into the receiving bore. When that operation is performed, even where there is a very high level of diaphragm spring bias, there is a considerable reduction in the pull-in force, and it may happen that a considerable, radially directed cutting force, acting at a tool which projects by a considerable distance from the spindle, may cause the taper shank to become temporarily loose in the receiving bore in the spindle. Chatter phenomena then occur.

Furthermore, the bending strength of the tool holder is determined by its smallest, unclamped diameter, and therefore is only depending on the largest diameter of the taper shank.

A drilling or boring tool is known (German patent specification No 3 108 439) wherein the head portion of the tool has a cylindrical fitting spigot portion which engages in a cylindrical fitting bore in the tool holder. In the region of the cylindrical bore, the tool holder has too diametrally oppositely disposed, radially extending female screwthreads, each having a clamping screw which is provided with a conical depression therein. A clamping pin is radially displaceable in a transverse bore in the fitting spigot portion, the clamping pin being provided at each of its two ends with a respective conical projection which co-operates with the conical depressions in the clamping screws.The axes of the female screwthreads and of the transverse bore are so arranged that, when one of the clamping screws is tightened, it acts on the clamping pin and presses an annular surface, which surrounds the spigot portion, against the end face of the tool holder. It has been found that that kind of connection has a high degree of installation accuracy and repetition accuracy, provides for the transmission of a high level of torque and also ensures that the connection between the parts of the drilling or boring tool has a very high level of bending strength. As however, in the known drilling or boring tool the tool holder itself has a steep-angle taper shank with which it can be fitted into the machine tool spindle, the disadvantages referred in the opening part of this specification arise in regard to the connection of the tool holder to the machine tool spindle.

The invention is based on the problem of so improving a machine tool spindle and a tool holder suitable therefor, of the kind set forth in the opening part of this specification, that the connection made between the machine tool spindle and the tool holder is resistant to bending and permits a high level of torque to be transmitted, while if required tool holders with a conventional steep-angle taper shank can be alternatively fitted into the spindle head.

According to the invention, that is achieved in that, in the region of the frustoconical receiving bore, the spindle head is provided with a cylindrical fitting bore for alternatively receiving a cylindrical fitting spigot portion of a second tool holder, the diameter of the spigot portion being somewhat smaller than the largest diameter of the frustoconical receiving bore and the axial length of the spigot portion, as measured from the annular end face of the spindle head, being shorter than the axial length ofthefrustoconical receiving bore, that, in the region of the cylindrical fitting bore, the spindle head has two diametrally oppositely disposed, radially extending female screwthreads each with a clamping screw provided with a conical projection portion of a conical depression, that a clamping pin is radially displaceable in a transverse bore in the fitting spigot portion, the clamping pin being provided at each of its two ends with a conical depression or a conical projection portion respectively co-operating with the conical projection portion or depression of a respective one of the clamping screws, and that the spacing of the axis of the female screwthreads from the annular end face is larger than the spacing of the axis of the transverse bore from an annular surface which surrounds the fitting spigot portion so that when one of the clamping screws is tightened, it acts on the clamping pin in the direction of pressing the annular surface and the end face towards each other.

The invention is therefore based on the concept of providing both a frustoconical receiving bore and a cylindrical fitting bore in the spindle head of a machine tool spindle so that a tool holder having a conventional steep-angle taper shank or a tool holder with a cylindrical fitting spigot portion and a clamping pin which is radially displaceably mounted therein can be selectively fitted into the spindle. The former has the advantage that the user of the machine tool can continue to use his conventional tools or tool holders with a steepangle taper shank, for operations in which the turning or bending moments which occur are not so high. However, he is also able selectively to use tools or tools holders of the novel design, which can be directly received by their cylindrical fitting spigot portion in the cylindrical fitting bore of the spindle head.That provides a connection between the spindle head and tool holder or tool, which is particularly resistant to bending and which also permits the transmission of high torques. More specifically, due to the axial displacement as between the axes of the clamping screws and the clamping pin, the latter is also moved in the axial direction by the axially effective force components, and thereby presses the annular surface with a high biasing force against the end face of the spindle head. Due to the annular surface and the end face being intensively and uniformly braced against each other, a high proportion of the torque is transmitted by frictional engagement, byway of those surfaces.

The remainder of the torque is transmitted by the clamping screws and the clamping pin. Another important consideration is that, when the annular surface bears firmly against the end face, the transverse forces acting on the tool are transmitted by those two surfaces to a comparatively large diameter which corresponds to the spindle diameter, so that the connection between the machine tool spindle and the tool holder is highly resistant to bending. Consequently, machining is even more accurate, the tool is less liable to oscillate, better transmission of the machine power to the tool is possible, and greater overhang or cantilever lengths in respect of the tool are also possible. As a result, higher levels of cutting efficency and shorter machining times can be attained.Another advantageous aspect is that all elements which are involved in the clamping action and which could possibly be subject to wear in the event of frequent tool changes, namely the clamping screws and the clamping pin, are readily replaceable.

Advantageous embodiments of the invention are characterised in the subsidiary claims.

The invention will now be described byway of example with reference to the accompanying drawings, in which: Figure 1 is a view in longitudinal section of part of a first embodiment of the invention, Figure 2 is a view in longitudinal section of part of a second embodiment of the invention, and Figure 3 is a view in longitudinal section of the machine spindle of Figures 1 and 2 with conventional steep-angle taper shank fitted therein.

The machine tool spindle 1 is rotatably mounted in the headstock 2. At its spindle head 1 a, the machine tool spindle has a frustoconical receiving bore 3a and 3b. The frustoconical receiving bore 3a and 3b is of a configuration corresponding to DIN 2079 or the corresponding ISO standard. The mouth of the receiving bore 3a, 3b is surrounded by a flat annular end face 4 which extends normal to the axis A of the spindle.

In the region of the frustoconical receiving bore 3a, 3b the spindle head 1 a has a coaxial, cylindrical fitting bore 5. The diameter D of the fitting bore 5 is somewhat smaller than the largest diameter D1 of the frustoconical receiving bore 3a, 3b. The axial length L of the bore 5, as measured from the end face 4, is shorter than the axial length L1 of the frustoconical receiving bore 3a, 3b.

The diameter D of the cylindrical fitting bore must be so selected that between the end face 4 and the beginning of the cylindrical fitting bore 5, there remains a portion 3a of the frustoconical receiving bore 3a, 3b, which is of sufficient length in the axial direction and is suitable for securely supporting the steep-angle taper shank 6 shown in Figure 3. It has been found desirable for the diameter D of the cylindrical fitting bore 5 to be about 4 to 10%, preferably about 6.5%, smaller than the largest diameter D1 of the frustoconical receiving bore. In the case of an ISO-50 steep-angle taper, the largest diameter D1 of the frustoconical receiving bore 3a, 3b is 69.85 mm.If the diameter selected for the cylindrical fitting bore 5 is 65.5 mm, the portion 3a of the frustoconical receiving bore 3a, 3b is about 14.9 mm in axial length. That is adequate for properly supporting the front end of the steep-angle taper shank 6.

So that the rear end of the steep-angle taper shank 6 is also supported in the spindle head 1 a, the fitting bore 5 may not extend over the entire length L1 of the frustoconical receiving bore. The axial length L of the fitting bore 5 should be about 1/2 to 2/3 of the axial length L1 of the frustoconical receiving bore, as measured from the end face. In that way, there remains a portion 3b of the frustoconical receiving bore 3a, 3b, which ensures adequate supportforthe rear end of the steep-angle taper shank 6.

Furthermore, in the region of the cylindrical fitting bore 5, the spindle head 1 a has two diametrally oppositely disposed, radially extending female screwthreads 7 and 8, in each of which a respective clamping screw 9, 10 can be radially screwed. The clamping screw 9 has a conical projection 9a and the clamping screw 10 has a frustoconical depression 1 ova. The axis Al of the female screwthreads 7 and 8 is at a spacing al from the end face 4.

The tool holder 11 has a cylindrical fitting spigot portion 12 which fits into the fitting bore 5 with a very small clearance (virtually without any clearance). The tool holder 11 carries at its free end 11 a for example a boring head, an inside turning tool, a milling tool, a reamer or broach, or the like, which is fixedly or interchangeably connected to the tool holder 11, possibly also with the interposition of intermediate members.

Provided in the fitting spigot portion 12 is a transverse bore 13 in which a cylindrical clamping pin 14 is radially displaceably mounted. At its one end, the clamping pin 14 has a conical projection portion 14a with which it engages into the frustoconical depression 1 Oa, while at its other end it has a frustoconical depression 14a into which the conical projection portion 9a engages. The spacing a2 of the axis A2 of the transverse bore 13 is somewhat less than the above-defined spacing al.

The tool holder 11 may also be surrounded by a coolant feed ring 15 which is arranged stationarily when the tool holder 11 is a rotary holder. The axial bore 15a of the tool holder is supplied by way of the coolant supply ring 15 with cooling fluid which is passed on to the cutting edges of the tool.

For the purposes of changing the tool, the clamping screw 9 only has to be released until the front end of its conical projection portion 9a no longer engages into the fitting bore 5. The clamping pin 14 can then be moved in the transverse bore 13 until its conical end portion 14a comes out of the conical depression 1 0a and the tool holder 11 can now be removed from the spindle head la, in a direction towards the left in the drawings.

The tool holder 11 of another tool is then fitted with its fitting spigot portion 12 engaging into the fitting bore 5. The portion 3a of the frustoconical receiving bore 3a, 3b facilitates the operation of inserting the fitting spigot portion 12 as the portion 3a increases outwardly from the diameter D of the fitting bore 5 to the diameter D1. When now the clamping screw 9 is screwed radially inwardly in the screwthread 7, the conical projection portion 9a moves the clamping pin 14 radially so that its conical projection portion 14a re-engages into the depression 10a in the clamping screw 10. The radially effective clamping force of the clamping screw 9 produces an oppositely directed reaction force of equal magnitude, at the clamping screw 10.

Due to the axial displacement of the axes Al and A2, each of the two clamping screws 9 and 10 generates an axially directed component of force, of equal magnitude. Accordingly, with a cone angle of 90% the clamping force of the clamping screw 9 causes the clamping forces to be doubled and presses the annular surface 16 of the tool holder 11 against the annular end face 4, with a force which is twice the radially directed clamping force. As can be seen from Figure 1, the outside diameter of the annular surface 16 is of the same size as the outside diameter of the end face 4 which approximately corresponds to the diameter of the spindle head 1 a.

The tool holder 11 is therefore supported at the spindle head 1 a over a very wide base, by way of the surfaces 16 and 4, and that is an aspect of substantial importance in regard to providing a connection between the two components, which is resistant to bending and which has little oscillatory movement.

The use of a respective clamping screw 9 with conical projection portion 9a and clamping screw 10 with conical depression 10a, and a corresponding clamping pin 14 which at one end has a conical projection portion 14a and at the other end a conical depression 14b has been found to be particularly advantageous in a practical situation. The arrangement however could possibly also be such that both clamping screws are provided with a respective conical depression, with the clamping pin accordingly having a corresponding projection portion at each of its two ends. Conversely, both clamping screws could also be provided with conical projection portions while the clamping pin then has conical depressions at both ends.

In the embodiment illustrated in Figure 2, the spindle head 1 a with receiving bore 3a and 3b and fitting bore 5 is of precisely the same configuration as in the embodiment illustrated in Figure 1. At its end which is towards the spindle head lathe tool holder 11' is also of the same configuration as the tool holder 11, for which reason the same reference numerals have been used and the foregoing description applies in corresponding fashion. At its front end however the tool holder 11' has a fitting bore 17 and two diametrally oppositely disposed female screwthreads 18 and 19 in the region of the bore 17. Clamping screws which correspond to the clamping screws 9 and 10 can be screwed into the female screwthreads 18 and 19.The diameter D1 selected for the fitting bore 17 is such that there engages thereinto the fitting spigot portion (not shown) of a milling tool, inside turning tool or boring head which is designed in accordance with German patent specification No 3 108 439, or the fitting spigot portion of an intermediate member which is possibly to be inserted between the tool and the tool holder. The tool holder 11' serves so-to-speak as an adapter between the machine tool spindle according to the invention and tools in accordance with German patent specification No 3108 439, the connecting dimensions of which have been established in the meantime.The tool holder 11' with its coolant supply ring 15 further has the advantage that one and the same tool holder 11' and one and the same coolant supply ring can be used for connecting different tools which have an internal coolant feed to the cutting edges.

Finally, Figure 3 shows the way in which a tool with a known tool holder 20 having a steep-angle taper shank, in accordance with DIN 2080, can be secured to the machine tool spindle according to the invention. For that purpose, the clamping screws 9 and 10 are removed and the two conventional, diametrally oppositely disposed entrainment members 21 are fitted into corresponding grooves 22 which are provided in the end face 4 in known manner. The entrainment members 21 engage into grooves 23 which are provided in the entrainment flange 20a of the tool holder 20. The steep-angle taper shank 6 is pulled into the frustoconical receiving bore 3a, 3b by a draw bar 25 which engages with a screwthread in the steep-angle taper shank or a spring-loaded clamping collet (not shown), with the shank 6 then being supported at the portions 3a and 3b of the receiving bore. A coolant supply ring 26 which is disposed concentrically around the tool holder can then serve to supply coolant.

Finally, it should also be mentioned that, instead of the fitting bore 17, the tool holder 11' could also have a second, forwardly projecting fitting spigot portion with a transverse bore and a clamping pin disposed therein. A tool holder of such a configuration is then suitable for receiving tools which, being a kinematic reversal of the principle disclosed in German patent specification No 3 108 438, instead of having a fitting spigot portion, have a fitting bore with two diametrally oppositely disposed female screwthreads. It has already been proposed that such tools be used in combination with tool change devices.

Claims

1. Amachine tool spindle and a tool holder which is suitable therefor, the spindle being provided at its spindle head with a frustoconical receiving bore for receiving a steep-angle taper shank of a first tool holder, and an annular end face which surrounds the receiving bore, characterised in that, in the region of the frustoconical receiving bore (3a, 3b), the spindle head (la) is provided with a cylindrical fitting bore (5) for alternatively receiving a cylindrical fitting spigot portion (12) of a second tool holder (11, 11'), the diameter (D) thereof being somewhat smaller than the largest diameter (D1) of the frustoconical receiving bore (3a, 3b) and the axial length (L) thereof, as measured from the end face (4), being shorter than the axial length (L1) of the frustoconical receiving bore (3a, 3b), that, in the region of the cylindrical fitting bore (5), the spindle head (lea) has two diametrally oppositely disposed, radially extending female screwthreads (7,8) each with a clamping screw (9, 10) provided with a conical projection portion (9a) or a conical depression (10a), that a clamping pin (14) is radially displaceable in a transverse bore (13) of the fitting spigot portion (12), the clamping pin being provided at each of its two ends with a conical depression (14a) ora conical projection portion (14b) respectively co-operating with the conical projection portion (9a) or depression (10a) of a respective one of the clamping screws (9, 10) and that the spacing (al) of the axis (Al) of the female screwthreads (7,8) from the annular end face (4) is largerthan the spacing (a2) of the axis (A2) of the transverse bore (13) from an annular surface (16) which surrounds the fitting spigot portion (12) so that when one of the clamping screws (9, 10) is tightened, it acts on the clamping pin (14) in the direction of pressing the annular surface (16) and the end face (4) towards each other.

2. A machine tool spindle according to claim 1 characterised in that the diameter (D) of the cylindrical fitting bore (5) is about 4 to 10% and preferably about 6.5% smaller than the largest diameter (D1) of the frustoconical receiving bore (3a, 3b).

3. A machine tool spindle according to claim 1 or claim 2 characterised in that the axial length (L) of the fitting bore (5), as measured from the end face (4), is about 1/2 to 2/3 of the axial length (L1) of the frustoconical receiving bore (3a, 3b).

4. A machine tool spindle according to claim 1, characterised in that the one clamping screw (10) has a conical depression (10a) and the other clamping screw (9) has a conical projection portion (9a), and that correspondingly the clamping pin (14) is provided with a conical projection portion (14a) at its one end and a conical depression (14b) at its other end.

5. A machine tool spindle and a tool holder substantially as described hereinbefore with reference to Fig. 1 or Fig. 2 of the accompanying drawings.