GB2094191A

GB2094191A - Boring tool shank

Info

Publication number: GB2094191A
Application number: GB8203502A
Authority: GB
Original assignee: Komet Praezisionswerkzeuge Robert Breuning GmbH
Current assignee: Komet Praezisionswerkzeuge Robert Breuning GmbH
Priority date: 1981-03-06
Filing date: 1980-02-08
Publication date: 1982-09-15
Also published as: IT8219431A0; DE3108439C1; CH656335A5; FR2501093B1; GB2094191B; SE447352B; DE8106317U1; SE8200525L; JPS5851004A; HK55190A; IT1149731B; FR2501093A1; JPS6055241B2

Abstract

A boring bar has a head portion 3 carrying two cutter plates 4, and a tool holder 1 which can be secured to the spindle of a machine tool. The head portion 3 is connected to an intermediate member 5 which has a cylindrical fitting plug portion 6 which is coaxial with the boring tool and surrounded by an annular surface 7 normal to the tool axis B. The tool holder 1 has a fitting bore 8 surrounded by an annular end surface 9. The fitting plug portion 6 has a transverse bore 10 containing a connecting pin member 11 which is displaceable and has at each end a tapered projection portion 12 or a tapered recess. First and second retaining screws 13 are screwed into the tool holder 1 coaxially and diametrically opposite with respect to one another. The two retaining screws 13 bear against opposite ends of the connecting pin members 11 by means of respective tapered recesses 14 or tapered projection portions. The two axes C, D, of the projection portions and recesses are spaced apart in the tool axis direction to provide an axial clamping affect. The head portion 2 is connected to the intermediate member 5 in the same way. <IMAGE>

Description

SPECIFICATION Improvements in boring tools The present invention relates to a boring tool, in particular a boring bar, comprising a head portion having at least one cutter plate, and a tool holder which can be secured to the spindle of a machine tool, wherein, at its rearward end which is towards the tool holder, the head portion has a cylindrical fitting portion which is concentric to the axis of the boring tool and which is surrounded by an annular surface extending normal to the axis of the boring tool, and the tool holder ha a fitting bore which is surrounded by an annular end surface, for receiving the said fitting portion, and a radially screwable retaining screw in the region of the fitting bore, which screw acts on the fitting gudgeon portion by way of a tapered projection portion and a tapered recess, the two axes of which are displaced relative to each other in the direction of the axis of the boring tool, and the tool comprising at least one intermediate member which can optionally be inserted between the head portion and the tool holder and the two ends of which are provided with connecting means which fit to the connecting means of the head portion and the tool holder.

As on the one hand the tool mounting means on the spindles of boring and milling machines are of very widely differing kinds, including special arrangements, in addition to tapered tool receiving means with a very wide range of different taper angles, and as on the other hand the intention is that the boring tools are to be adapted to performing the widest possible range of different machining operations, it is usual for boring tools to comprise two or more parts, in the manner of modular system. In that case, the appropriate head portion of each given machining operation is picked out and connected to a tool holder which is adapted to the respective tool receiving means. Boring tools of different lengths can be set up, by interposing connecting members of different lengths, or also a plurality of connecting members.

In a known boring tool of the type defined hereinbefore, the fitting portion has a tapered recess in its cylindrical peripheral surface. A tapered projection portion on the retaining screw engages into the tapered recess. When the retaining screw is tightened, the axial displacement of the axis of the tapered recess relative to the axis of the tapered projection portion causes the annualar surface to be pressed against the annular end surface. However, due to the retaining screw being disposed at one side, and because of the inevitable clearance between the fitting portion and the bore, the abovementioned pressing effect between the two surfaces is also one-sided.As moreover the retaining screw only acts on the fitting portion from one side, the fitting portion is pressed against the part of the wall surface of the fitting bore, at one side thereof, which lies opposite the retaining screw. By virtue of this one-sided pressing effect, the axis of the head portion is no longer precisely aligned with the axis of the tool holder, and that results in inaccuracies in machining. Furthermore, the tapered recess in the fitting portion is subjected to a very high pressure which under some circumstances can result in wear phenomena. This high pressure is not just caused by tightening the retaining screw, but also by the torque which in part must be transmitted to the recess by the retaining screw.When this occurs, a high pressure per unit of surface area occurs, for the tapered projection portion is in contact with the recess, which is also tapered, only along a line or at any event at a very narrow surface. In addition, in order to make the firm connection required between the head portion and the tool holder, the retaining screw must be com pa ratively fi rm ly tig htened, and under some circumstances this can result in damage to the thread on the screw or the female thread which is provided in the tool holder for the retaining screw.

The invention is based on the problem of providing a boring tool of the type defined hereinbefore, wherein the connection between the head portion and the tool holder or any intermediate members which may be fitted therebetween is not subjected to a loading on one side, which provides an improvement in the manner in which the annular surface and the annular end surface are pressed against each other, and wherein connecting means which are subjected to a heavy loading can be easily replaced.

According to the invention, this is achieved in that the said fitting portion has, in the region of the retaining screw, a transverse bore with a connecting pin member which is displaceable therein and which has at each end either a tapered projection portion or a tapered recess, and that a second retaining screw is arranged screwably in the tool holder coaxially with respect to the first said retaining screw and diametrically opposite thereto, wherein both retaining screws bear against opposite ends of the connecting pin member, by means of the respective tapered recess or tapered projection portion.

In a tool embodying the invention, there are two retaining screws which are disposed diametrically opposite to each other but which do not act directly on the said fitting portion but instead act on a connecting pin member which is displaceable therein. As the two retaining screws act on the connecting pin member by way of tapered recesses and tapered projection portions, the two retaining screws apply forces at diametrically opposite ends of the connecting pin member, the components of such forces pressing the annular surface against the said end surface, at diametrically opposite regions. This arrangement ensures that the two surfaces are pressed against each other in a more uniform fashion. In addition, no pressure is applied against the said fitting portion at one side thereof, when the retaining screws are tightened, as the connecting pin member can move in the transverse bore.This arrangement always ensures that the axis of the head portion is coaxial with respect to the axis of the tool holder or any interposed intermediate members. Furthermore, the stressing force as betweeen the annular surface and the end surface is doubled, for a tapered projection portion and a tapered recess are in engagement with each other at each of the two ends of the connecting pin member. Finally however, all connecting means which are subjected to a heavy loading, namely the two retaining screws and the connecting pin member, can be easily replaced if it is found that those components are worn.

The invention will now be described in greater detail, solely by way of example with reference to the accompanying drawings in which: Figure 1 is a side view, partly in longitudinal section, of a boring tool embodying the invention; Figure 2 is a view in cross-section at a line Il-Il in Figure 1; and Figures 3 and 4 are partial longitudinal sections of two further embodiments.

In Figure 1 there is shown a tool holder 1 which can be fitted by means of its taper portion 2 into the tool receiving means of a machine tool. Instead of the taper portion 2 illustrated, the tool holder 1 may have a taper portion with a different taper angle, a cylindrical shank portion or a flange or can be fitted in some other manner to the tool receiving means on the spindle of the machine tool (not shown).

The boring tool, which is a boring bar, has a head portion 3 which is provided for example with two diametrically oppositely disposed cutter plates 4.

The head portion 3 is to be connected to the respective tool holder 1 directly or by way of an interposed intermediate member 5. Instead of the head portion 3 illustrated, other head portions which are adapted to the respective machining operation to be performed are also to be connectible to the most widely varying tool holders and intermediate members. So that the system enjoys the maximum variability, the connecting means described hereinafter on the head portion 3 and on the tool holder 1, and on the intermediate member 5, are each of the same kind. The following description relating to the connection between the intermediate member 5 and the tool holder 1 also applies in corresponding manner to the connection between the head portion 3 and the forward end of the intermediate member 5.

At its rearward end 5a which is towards the tool holder 1, the intermediate member 5 is provided with a cylindrical fitting plug portion 6 which is concentric to the axis B of the boring tool. The plug portion 6 is surrounded by an annular surface 7 which extends normal to the axis B of the boring tool. The tool holder 1 is provided with a fitting bore 8 which is also concentric with respect to the axis B of the boring tool and which serves to receive the fitting plug portion 6. The bore 8 is surrounded by an annular end surface 9.

The plug portion 6 has a transverse bore 10 in which a connecting pin member 11 is displaceably mounted. The connecting pin member 11 desirably has tapered projection portions 12, at its two ends.

The tool holder 1 is provided with two radially screwableretaining screws 13 which are disposed diametrically opposite to each other and which are provided in the regin of the transverse bore 10. Each of the retaining screws 13 has a tapered recess 14 corresponding to the tapered projection portion 12.

The arrangement of the retaining screw 13 and the transverse bore 10 is such that the distance A of the axis C of the retaining screw 13 from the end surface 9 is somewhat greater than the distance a of the axis D of the transverse bore 10 from the annular surface 7. In practice, the two axes C and D are displaced relative to each other for example by 0.3 to 0.5 mm in the direction of the axis B of the boring tool.

This arrangement provides that the two retaining screws 13, upon being tightened, each act on the connecting pin member 11 from a respective side of the arrangement, in the direction P, and tend to drive the connecting pin member 11 towards the right as shown in Figure 1. This causes the annular surface 7 to be pressed against the end surface 9. As the forces Pact on the connecting pin member 11 at both ends thereof, the two surfaces are pressed against each otherwith a uniform annular contact area. In addition, the pressing forces are doubled as there are two tapered portions 12 engaged with the tapered recesses 14 adapted thereto, at the same time.

Forces acting on the plug portion 6 on one side thereof are eliminated by virtue of the connecting pin member 11 being displaceable in the transverse bore 10.

It would also be possible, as shown in Figure 3, for the connecting pin member 11' to be provided with tapered recesses 14' at both ends and for tapered projection portions 12' to be mounted on both retaining screws 13', to engage in the tapered recesses 14' in the connecting pin member 11'.

Furthermore, in the embodiment of Figure 4, the connecting pin 11" can be provided at one end with a tapered projection 12 which engages with the tapered recess 14 of a retaining screw 13, and at its other end with a tapered recess 14' in which a tapered projection 12' of the other retaining screw 13' engages.

It is also desirable for the length L of the connecting pin member to be somewhat less than the diameter dofthe fitting plug portion 6. In that case, the connecting pin member 11 can always remain in the transverse bore 10 when dismantling and assembling the arrangement.

In order for the connecting pin member 11 not to come out of the transverse bore 10 and be lost when the components are dismantled, the connecting pin member 11 is provided in its peripheral surface with a longitudinal groove 15 which is closed at both ends and in which there engages a screw 16 screwed into the plug portion 6. The length of the screw 16 is such that under no circumstances does it jam the connecting pin member 11 in the transverse bore 10. The length of the longitudinal groove or slot 15 is such that the connecting pin member 11 can come out of the transverse bore 10, at a maximum only by the length of one of its two tapered projection portions 12. This ensures that, when assembling or dismantling the components of the boring tool, the connecting pin member 11 can never jam but is always pressed into the transverse bore 10 by its tapered projection portions 12.

Boring tools often also have coolant bores through which coolant can be supplied from the tool holder 1, out of the cutter plates 4. The head portion 3, the intermediate member 5 and the tool holder 1 of the illustrated embodiement are also provided with coolant bores 17 of this kind. In this case, it is desirable for the connecting pin member 11 also to be provided with a coolant bore 18 which extends in the direction of the axis B of the boring tool and which is sbstantially aligned with the coolant bore in the plug portion 6.

In most cases it is also important for the head portion 3 to be disposed in a predetermined angular position relative to the tool holder 1. To ensure that the components always take up that predetermined angular position, an index pin 19 which extends parallel to the axis B of the boring tool is provided in the end surface 9. The index pin 19 engages in a corresponding longitudinal bore 20 in the annular surface of the head portion 3 of the intermediate member 5 respectively. With such an arrangement, that connection can also be made with a greater clearance of about 0.1 mm. The index pin 19 may transmit a part of the torgue.

The tip angle oc of the tapered projection portions 12 and the tapered recesses 14 is about 90 in the illustrated embodiment. If the pressing force applied between the annular surface 7 and the end surface 9 is to be greater than in the illustrated embodiment, a smaller angle oc would have to be used.

Claims

1. A boring tool comprisng a head portion having at least one cutter plate, and a tool holder which can be secured to the spindle of a machine tool, wherein the head portion is coupled to the tool holder by connecting means including a cylindrical fitting portion which is coaxial with the boring tool and which is surrounded by an annular surface extending normal to the axis of the boring tool, and a fitting bore, which is surrounded by an annular end surface, for receiving the said fitting portion, and a radity screwable retaining screw in the region of the fitting bore, which screw acts on the fitting portion by way of a tapered projection portion and a tapered recess, the two axes of which are displaced relative to each other in the direction of the axis of the boring tool, characterised in that the said fitting portion has, in the region of the retaining screw, a transverse bore with a connecting pin member which is displaceable therein and which has at each end either a tapered projection portion or a tapered recess, and that a second retaining screw is arranged screwably in the tool holder coaxially with respect to the first said retaining screw and diametrically opposite thereto, wherein both retaining screws bear against opposite ends of the connecting pin member, by means of the respective tapered recess or tapered projection portion.

2. A boring tool accordiang to claim 1, wherein the length of the connecting pin member is somewhat less than the diameter of the said fitting portion.

3. A boring tool according to claim 2, wherein the connecting pin member is provided, in its peripheral surface, with a longitudinal groove which is closed at both ends and into which engages a screw screwed in the said fitting position.

4. A boring tool according to claim 3, wherein the connecting pin member has a coolant bore which extends in the direction of the axis of the boring tool and which is substantially aligned with a coolant bore in the said fitting portion.

5. A boring tool according to any preceding claim, werein an index pin is provided in the end surface of the tool holder and extends parallel to the axis of the boring tool and engages in a corresponding longitudinal bore in the annular surface of the head portion.

6. A boring tool according to any preceding claim, wherein the tip angle of the tapered projection portions and the tapered recesses is about 90".

7. A boring tool comprising a head portion equipped with at least one cutter plate, a tool holder which can be secured in a machine tool, and means connecting the head portion to the tool holder, the connecting means including at least one connection comprising a cylindrical fitting portion coaxial with the boring tool and surrounded by a first annular surface normal to the tool axis, a fitting bore receiving the fitting portion and surrounded by a second annular surface normal to the tool axis, a transverse bore through the fitting portion, a connecting pin member displaeably located in the transverse bore, and first and second coaxial and diametrically opposed retaining screws screwed into the walls defining the fitting bore and bearing against opposite ends of the connecting pin member, the retaining screws and the connecting pin member being provided with cooperating tapered projecting portions or recesses at their ends whereby the first and second annular surfaces are clamped together.

8. A boring tool according to claim 7, wherein there are two of the said connections, one of the respective cylindrical fitting portions being provided on the head portion, one of the respective fitting bores being formed in the tool holder, and the other respective fitting portion and the other respective fitting bore being provided by an intermediate member constituting part of the said connecting means.

9. A boring tool substantially as described hereinbefore with reference to and as shown in Figures 1 and 2, or Figures 3 or4, of the accompanying drawings.