Description

A portable threading machine

Technical Field

This invention relates to a portable threading machine.

In particular, the invention relates to a portable threading machine normally used to cut right-hand or left-hand threads of any pitch both in blind and through holes without having to place the parts to be threaded on fixed or conventional machine tools.

Background Art

This need is felt especially strongly when cutting threads in holes, mounting assemblies, connectors, flanges and all parts of fixed installations (ship engines, nuclear reactors, etc) where the parts to be threaded are difficult to dismantle and transport.

For this purpose, twin motor threading machines are known. One motor rotationally drives the threading tool while the other feeds the threading tool as it rotates.

A typical example of prior art threading machines is that of threading machines where rotational drive is imparted to the threading tool by belt transmission means, such as, for example, elastic belts equipped with belt tensioners to ensure correct belt tension. These threading machines are extremely complex because the two motors must be perfectly synchronized to guarantee the correct combination of rotational and translational feed motion of the threading tool.

Moreover, even in the case of a threading machine with a transmission belt and a belt tensioning device, drive timing mist be frequently checked and adjusted so that the rotational motion of the threading tool is always perfectly synchronized with its translational feed motion.

It should also be noticed that the transmission belts generate vibrations that lead to stress on the transmission parts, thus contributing significantly to the above mentioned loss of synchronization.

Disclosure of the Invention

The aim of this invention is therefore to provide a portable threading machine that is free of the above mentioned disadvantages.

In particular, this invention has for an aim to provide a portable threading machine that does not require special maintenance to restore the synchronization between the rotational and translational feed motion of the threading tool.

Another aim of the invention is to provide a portable threading machine that offers a high level of versatility.

These aims and others are achieved by a portable threading machine comprising the technical characteristics described in one or more of the appended claims.

Brief Description of the Drawings

Further characteristics and advantages of the invention are more apparent in the detailed description below, with reference to a preferred, non-limiting embodiment of a portable threading machine, illustrated in the accompanying drawings, in which:

- Figure 1 is a perspective view of a portable threading machine according to the invention; - Figure 2 is a partly cut-away perspective view of the portable threading machine of Figure 1;

- Figure 3 is an exploded view of the threading machine of Figure 1; and

- Figure 4 is a cross section through the plane IV-IV of a detail of the machine of Figure 1.

Detailed Description of the Preferred Embodiments of the Invention

With reference to the accompanying drawings, the numeral 1 denotes in its entirety a portable threading machine according to this invention.

The machine 1 is designed to cut right-hand and left-hand threads of any pitch both in blind and through holes.

Further, the machine 1 can cut the thread directly on the part without having to remove the part from its operating position.

For this purpose, the machine 1 comprises a customary mounting unit 2, not further described, which enables the machine 1 to be firmly attached to the workpiece 100, as illustrated in Figures 1 and 2.

The machine 1 also comprises a containing structure 3 to which the main parts of the machine itself are connected.

In the preferred embodiment illustrated in the accompanying drawings, the containing structure 3 has a substantially tubular, elongated shape and is hollow to receive and house a shaft 4 that transmits motion to a threading head 5. The latter is positioned at a front end 6 of the shaft 4 and is designed to cut a thread in a hole in the workpiece 100.

The machine 1 is equipped with means 7 for rotationally driving the shaft 4 (and hence the threading head 5) and means 8 for translationally feeding the shaft 4 (and hence the threading head 5).

Advantageously, both the means 7 for rotationally driving the shaft 4 and the means 8 for translationally feeding the shaft 4 are driven by a single motor 9 which, in the preferred embodiment, is an electric motor.

Alternatively, the motor 9 might be a hydraulic or pneumatic motor.

This ensures easy synchronization between the rotational motion and the translational feed motion of the shaft 4. In particular, the motor 9 acts directly only on the means 7 for rotationally driving the shaft 4, while it acts indirectly on the means 8 (or vice versa).

In the preferred embodiment, as illustrated in Figures 1 and 2, the motor 9 is integral with the containing structure 3 and is mounted at a first end 10 of the structure itself. A suitable guard 11 mechanically connects the motor 9 to the containing structure 3.

As shown by the cross section of Figure 4, the guard 11 houses the means 7 for rotationally driving the shaft 4. These means 7 comprise a cylindrical tubular element 12 that is rotationally driven by the motor 9 and, more specifically, by an output shaft 13 forming part of it (shown in Figure 3). The cylindrical tubular element 12 is fitted over a portion of the shaft 4, constraining the latter to rotate while at the same time leaving the shaft 4 free to slide translationally.

To achieve this type of coupling, the cylindrical tubular element 12 comprises a protrusion, or key, 14 which extends from a lateral inside surface of it in a radial direction towards the centre of the element 12 itself and which engages a longitudinal groove 15 formed on the shaft 4.

The groove 15 runs along a good part of the length of the shaft 4.

Thus, the cylindrical tubular element 12 is rotationally driven as one with the shaft 4 which, at the same time, is slidable relative to the element 12. The coupling between the cylindrical tubular element 12 and the motor output shaft 13 is, in the preferred embodiment illustrated in Figure 3, provided by a helical gear wheel 16 that is keyed to the outside surface of the element 12 and

meshes with a worm screw 17 of the motor output shaft 13.

In an alternative embodiment that is not illustrated, the motor output shaft 13 ends with a bevel gear wheel that meshes with a corresponding bevel gear wheel to which the tubular element 12 is keyed. In yet another alternative embodiment, also not illustrated, the outside surface of the tubular element 12 has a cylindrical gear wheel that meshes with a corresponding cylindrical gear wheel on the output shaft 13.

In all the embodiments described, the axis of rotation of the output shaft 13 and the axis of rotation of the shaft 4 are skew to each other, preferably perpendicular, where the term perpendicular means substantially transversal.

As illustrated in Figure 4, the cylindrical element 12 is rotatably supported by the guard 11 by means of rolling bearings 18 constrained to the inside surface of the guard 11 itself. The two rolling bearings 18 are positioned on opposite sides of the tubular element 12 and are separated by the helical gear wheel 16. The means 8 for translationally feeding the shaft 4 comprise a cylindrical tubular element 19 within which the shaft 4 is inserted and locked (Figures 2 and 3).

The tubular element 19 is externally threaded and is positioned inside an internally threaded bush 20 that is integral with the containing structure 3 on the side opposite the guard 11.

Thus, the means 8 for translationally feeding the shaft 4 are separate and distant from the means 7 for rotationally driving the shaft 4.

It should be stressed that the cylindrical threaded element 19 determines the pitch of the screw thread cut by the threading head 5, as will become more apparent below.

Advantageously, the cylindrical threaded element 19 can be substituted by other cylindrical tubular elements with external threading of different pitch, thus enabling the pitch of the thread to be cut to be changed as required.

Changing the element 19 (and the threaded bush 20) does not require any other operation on the machine 1, thus enabling quick and easy "changeover" to cutting a thread with a different pitch.

The threading head 5 comprises a rod shaped element 21 inserted transversally into the front end 6 of the shaft 4.

The rod shaped element 21 has a cutting end 22 which protrudes radially from the side of the shaft 4 and which is designed to cut the required thread on the inside walls of the hole (see Figure 2).

Restraining means 23 keep the threading head in the operating position

during the threading process.

In particular, the restraining means 23 comprise a clamping member 24 that can be applied to the part of the rod shaped element 21 that is inside the shaft 4. The clamping member 24 is activated by suitable activation means 25 that lock or release the rod shaped element 21 to or from the end 6 of the shaft 4.

More specifically, the activation means 25 comprise a rod 26 which, at a first, front end of it 27, is integral with the rod shaped element 21, and at a second end of it 28, opposite the first end 27, is integral with a revolving shaft 29 driven by a dedicated motor 30, said shaft 29 being screwably engaged to the end 28 of the rod 26.

The rod 26 is slidably inserted in the shaft 4.

The motor 30 screwably advances the rod 26 and with it also the rod shaped element 21 whose cutting end 22 thus tends to advance along an axis that coincides with the axis along which the shaft 4 extends. Given the connection between the two components 21 and 4, the rod shaped element 21 is inserted transversally into the shaft 4; the former, when subjected to forces that tend to move it translationally in this way, is thus locked with respect to the shaft 4.

The machine 1 also comprises a limit stop unit 31 that enables the workpiece 100 to be threaded for predetermined lengths.

In particular, the limit stop unit 31 comprises a telescopic cylinder 32 composed of a first part 33 that is fixed relative to the containing structure 3 and a mobile part 34 that is fixed relative to the shaft 4 (Figures 1 and 2).

The telescopic cylinder 32 thus becomes longer or shorter according to the translational movement of the shaft 4 relative to the containing structure 3. The mobile part 34 of the telescopic cylinder 32 is provided with position sensors (not illustrated since they are of well known type) capable of precisely detecting the displacement of the shaft 4 and therefore also of the threading head 5.

A central control unit 35 cooperates with the position sensors to stop shaft 4 feed when the required threading length is reached.

The central unit 35 (schematically illustrated in Figure 3) controls the electric motor 9 which, advantageously is a direct current motor, in such a way as to optimize the motor's rotation speed according to the thread to be cut.

In use, when the electric motor 9 is in operation, its output shaft 13 rotationally drives the cylindrical tubular element 12 which, as described above, causes the shaft 4 to rotate about its axis of extension.

At this point, the tubular threaded element 19 which fits into and engages

the shaft 4 starts rotating as one with the shaft 4.

The tubular element 19, as it screwably engages the bush 20 which is integral with the containing structure 3, advances translationally in a line that coincides with the line along which the shaft 4 extends, causing the shaft 4 to move translationally as one with it.

This is possible because the latter is free to move translationally thanks to the coupling between the protrusion 14 of the tubular element 12 and the groove 15 in the shaft 4.

Therefore, the threading head 5 is driven rotationally and translationally relative to the workpiece 100, thereby cutting a thread in the latter.

The use of a single motor to drive the threading head 5 both rotationally and translationally eliminates the need to re-synchronize the rotational and translational movements of the threading head 5, thus overcoming the disadvantages of prior art. Furthermore, the possibility of changing the tubular threaded element 19 and the bush 20 confers a high level of versatility because it means the machine 1 can be used to cut threads of any pitch.

The invention described can be modified and adapted in several ways without thereby departing from the scope of the inventive concept. Moreover, all the parts of the invention may be substituted by technically equivalent elements.