GB1599743A - Mounting bush - Google Patents

Description

(54) MOUNTING BUSH (71) We, LUCAS INDUSTRIES LIMITED, a British Company, of Great King Street, Birmipgham B19 2XF, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a mounting bush that is intended for use in mounting circuit assemblies, such as printed circuit boards, on supports such as casings.

It is known, in using such a printed circuit board, to mount various components such as resistors, capacitors, or potentiometers on one face of the board, the other face of the board carrying conductors which serve to connect together in a desired circuit the components mounted on said one face of the board. Said components may include members (such as for example rotatable shafts) which have to be operated from that side of the board adjacent to said other face thereof (and therefore have to extend through the board) but on the other hand it is also desirable to be able to dip said other face carrying said conductors in a bath of molten metal (such as solder) in order to join together said conductors and wires which pass through the board to said components. In order therefore to avoid the necessity of covering said component members which have to extend through the board whilst said other face is being dipped and then subsequently uncovering the members (which covering and uncovering operations are of course time-consuming and expensive to carry out) it is desirable to provide bush means which serve to locate said component members, which also provide mountings for mounting the circuit assembly on a casing ot other support, and which can easily be assembled to the circuit board after the afore-mentioned dipping operation has been completed.

One known arrangement of bush means which possesses the above-mentioned characteristics is described in British Patent 1,377,012. In this prior arrangement however the bush means comprises two parts namely an inner bush and an outer bush which have to be assembled together and to the circuit board. The provision of these two parts and the subsequent assembly operation are relatively costly and moreover friction is relied upon to prevent rotation of the outer and inner bushes and keep them in place on the circuit so that it is possible that said bushes may, in certain circumstances, turn and become detached from the board.

The object of the present invention is to provide an improved construction of bush which avoids the above-mentioned disadvantages.

In accordance with the present invention, there is provided a bush for use in mounting a circuit assembly, such as a printed circuit board, on a support, said bush having at one end a base portion from which extends in an axial direction a reduced cross-section cylindrical portion having an external screw thread. In receiving a securing nut, said base portion having outwardly extending flange means and outer resilient and generally axially extending latch portions which are integral with said bush and which have free ends that can be displaced radially inwardly to permit them to pass through an aperture in the circuit assembly whereafter said outer latch portions will then spring outwardly so that outwardly projecting lips on said outer latch portions will then engage one face of the assembly whilst said flange means engage the opposite face of the assembly, said bush also having inner resilient and generally axially extending latch portions which are integral with the bush so as to form part of the bore thereof, said inner latch portions having free ends with inwardly projecting lips which are adapted to be engaged in an annular groove formed in a shaft or other member which in use will extend through said bore of the bush, such inter-engagement of said inwardly projecting lips and said annular groove being achieved by effecting relative axial movement of the bush and shaft or other member until the free ends of said inner latch portions spring into said annular groove.

The invention will now be more particularly described with reference to the accompanying drawings wherein.

Figure 1 is an end view of one example of a bush constructed in accordance with the invention, Figure 2 is a sectional view taken on the line 2-2 of Figure 1, but showing also part of a circuit board after the bush has been assembled to such board, Figure 3 is a sectional view taken on the line 3-3 of Figure 1, but showing in addition to part of said circuit board, a shaft which can be assembled to the bush and which is adapted for example to operate a variable capacitor mounted on one side of the board, Figure 4 is a side view of the bush, looking in the direction of arrow 'A' of Figure 1, and showing also a part of the circuit board, and Figure 5 is a plan view, on a reduced scale, of a hole in the circuit board in which the bush is received in use.

Referring now to the drawings, there is shown therein a bush generally indicated by reference numeral 10 which is formed as a one-piece moulding in a synthetic resin material. Said bush includes a base portion 11 from which extends in an axial direction a reduced generally cylindrical portion 12 having an external screw thread 13 which is adapted to receive a securing nut (not shown) the bush is also formed with an axially extending bore 14.

The base portion 11 of said bush is provided with an outwardly extending flange 15, said flange being formed with a pair of opposed notches 16 through which project in a generally axial direction a pair of outer latch portions 17 and 18. The bush 10 is formed of a material which is slightly resilient and a narrow gap is formed in the integral moulding between the inner surface of each outer latch portion and the adjacent part of the base portion 11 of the bush so that each outer latch portion is capable of being displaced inwardly by a distance generally equal to the width of such gap. Furthermore the outer or free end of each outer latch portion 17 or 18 is formed with a lip 19 or 20, the outer peripheral surface of each free end being chamfered to a generally frusto-conical configuration. The bush 10 can therefore be pushed into a hole of the shape shown in Figure 5 formed in a circuit assembly shown as a printed circuit board generally indicated by reference numeral 21.

The hole is generally circular but has two diametrically opposed arcuate cut-outs 211 into which the ends of the outer latch portions 17 and 18 respectively are inserted, the outer latch portions 17 and 18 being forced inwardly as the aforesaid frustoconical surfaces engage the edges of the cut-outs 211. The outer end of said base portion 11 is then pushed through the hole until one side of said flange 15 engages the adjacent surface of the circuit board 21 at which time said outer ends of the latch portion 17 and 18 will spring outwardly again beneath the opposite surface of the circuit board so that said lips 19 and 20 form latches which will secure the bush against axial movement on the circuit board.

Moreover, by virtue of the non-circular shape of the hole in the circuit board and the complementary shape of the outer latch portions 17 and 18, of the bush is also held against rotation relative to the circuit board.

Two other integrally formed latch portions namely inner latch portions 22 and 23 are also formed in the moulding of the bush and said inner latch portions are diametrically opposed to each other and form a part of the aforesaid bore 14 of the bush. Moreover said latch portions 22 and 23 are disposed on a diameter of the cross-section of the bush which is at right angles to the diameter of the cross-section on which the outer latch portions 17 and 18 are disposed. Said inner latch portions 22 and 23 are also resilient and can be flexed outwardly by virtue of gaps formed between their outer surfaces and the adjacent parts of the base portion 11. Thus a shaft or spindle generally indicated in Figure 3 by reference numeral 24 can be pushed into the bore 14 of the bush from the top as shown in Figure 3 until inwardly directed lips 25 or 26 formed on the free ends of said latch portions 22 and 23 engage an annular groove 27 formed on said shaft 24. Such inter-engagement between the inner latch portion 22 and 23 and the shaft 24 will permit said shaft to be rotated (one end of said shaft projecting to one side of said board 21 and having a dial or knob whereas the other end of said shaft will engage a component such as a variable capacitor disposed on the other side of said board 21) whilst at the same time of course detachment of the shaft from the bush in an axial direction will be prevented.

Thus the bush and shaft may very easily be assembled to the board 21, the outer latch portions 17 and 18 then preventing detachment of the bush from the board wilst the inner latch portions 22 and 23 prevent detachment of the shaft from the bush.

WHAT WE CLAIM IS: 1. A bush for use in mounting a circuit assembly, such as a printed circuit board, on a support, said bush having at one end a base portion from which extends in an axial direction a reduced cross-section cylindrical portion having an external screw thread for

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. bush and shaft or other member until the free ends of said inner latch portions spring into said annular groove. The invention will now be more particularly described with reference to the accompanying drawings wherein. Figure 1 is an end view of one example of a bush constructed in accordance with the invention, Figure 2 is a sectional view taken on the line 2-2 of Figure 1, but showing also part of a circuit board after the bush has been assembled to such board, Figure 3 is a sectional view taken on the line 3-3 of Figure 1, but showing in addition to part of said circuit board, a shaft which can be assembled to the bush and which is adapted for example to operate a variable capacitor mounted on one side of the board, Figure 4 is a side view of the bush, looking in the direction of arrow 'A' of Figure 1, and showing also a part of the circuit board, and Figure 5 is a plan view, on a reduced scale, of a hole in the circuit board in which the bush is received in use. Referring now to the drawings, there is shown therein a bush generally indicated by reference numeral 10 which is formed as a one-piece moulding in a synthetic resin material. Said bush includes a base portion 11 from which extends in an axial direction a reduced generally cylindrical portion 12 having an external screw thread 13 which is adapted to receive a securing nut (not shown) the bush is also formed with an axially extending bore 14. The base portion 11 of said bush is provided with an outwardly extending flange 15, said flange being formed with a pair of opposed notches 16 through which project in a generally axial direction a pair of outer latch portions 17 and 18. The bush 10 is formed of a material which is slightly resilient and a narrow gap is formed in the integral moulding between the inner surface of each outer latch portion and the adjacent part of the base portion 11 of the bush so that each outer latch portion is capable of being displaced inwardly by a distance generally equal to the width of such gap. Furthermore the outer or free end of each outer latch portion 17 or 18 is formed with a lip 19 or 20, the outer peripheral surface of each free end being chamfered to a generally frusto-conical configuration. The bush 10 can therefore be pushed into a hole of the shape shown in Figure 5 formed in a circuit assembly shown as a printed circuit board generally indicated by reference numeral 21. The hole is generally circular but has two diametrically opposed arcuate cut-outs 211 into which the ends of the outer latch portions 17 and 18 respectively are inserted, the outer latch portions 17 and 18 being forced inwardly as the aforesaid frustoconical surfaces engage the edges of the cut-outs 211. The outer end of said base portion 11 is then pushed through the hole until one side of said flange 15 engages the adjacent surface of the circuit board 21 at which time said outer ends of the latch portion 17 and 18 will spring outwardly again beneath the opposite surface of the circuit board so that said lips 19 and 20 form latches which will secure the bush against axial movement on the circuit board. Moreover, by virtue of the non-circular shape of the hole in the circuit board and the complementary shape of the outer latch portions 17 and 18, of the bush is also held against rotation relative to the circuit board. Two other integrally formed latch portions namely inner latch portions 22 and 23 are also formed in the moulding of the bush and said inner latch portions are diametrically opposed to each other and form a part of the aforesaid bore 14 of the bush. Moreover said latch portions 22 and 23 are disposed on a diameter of the cross-section of the bush which is at right angles to the diameter of the cross-section on which the outer latch portions 17 and 18 are disposed. Said inner latch portions 22 and 23 are also resilient and can be flexed outwardly by virtue of gaps formed between their outer surfaces and the adjacent parts of the base portion 11. Thus a shaft or spindle generally indicated in Figure 3 by reference numeral 24 can be pushed into the bore 14 of the bush from the top as shown in Figure 3 until inwardly directed lips 25 or 26 formed on the free ends of said latch portions 22 and 23 engage an annular groove 27 formed on said shaft 24. Such inter-engagement between the inner latch portion 22 and 23 and the shaft 24 will permit said shaft to be rotated (one end of said shaft projecting to one side of said board 21 and having a dial or knob whereas the other end of said shaft will engage a component such as a variable capacitor disposed on the other side of said board 21) whilst at the same time of course detachment of the shaft from the bush in an axial direction will be prevented. Thus the bush and shaft may very easily be assembled to the board 21, the outer latch portions 17 and 18 then preventing detachment of the bush from the board wilst the inner latch portions 22 and 23 prevent detachment of the shaft from the bush. WHAT WE CLAIM IS:

1. A bush for use in mounting a circuit assembly, such as a printed circuit board, on a support, said bush having at one end a base portion from which extends in an axial direction a reduced cross-section cylindrical portion having an external screw thread for

receiving a securing nut, said base portion having outwardly extending flange means and outer resilient and generally axially extending latch portions which are integral with said bush and which have free ends that can be displaced radially inwardly to permit them to pass through an aperture in the circuit assembly whereafter said outer latch portions will then spring outwardly so that outwardly projecting lips on said outer latch portions will then engage one face of the assembly whilst said flange means engage the opposite face of the assembly, said bush also having inner resilient and generally axially extending latch portions which are integral with the bush so as to form part of the bore thereof, said inner latch portions having free ends with inwardly projecting lips which are adapted to be engaged in an annular groove formed in a shaft or other member which in use will extend through said bore of the bush, such inter-engagement of said inwardly projecting lips and said annular groove being achieved by effecting relative axial movement of the bush and shaft or other member until the free ends of said inner latch portions spring into said annular groove.

2. A bush as claimed in Claim 1 wherein there are two outer latch portions which are diametrically opposed with respect to each other and two inner latch portions which are also diametrically opposed with respect to each other, said outer latch portions being disposed on a diameter of the cross-section of the bush which extends at right angles to the diameter of the cross-section of the bush on which said inner latch portions are disposed.

3. A bush as claimed in either of the preceding claims wherein said bush is moulded from a synthetic resin material.

4. A bush as claimed in any one of the preceding claims wherein said outer latch portions extend respectively through notches formed in said flange means.

5. A bush for use in mounting a circuit assembly, such as a printed circuit board, on a support, said bush being substantially as hereinbefore described with reference to and as shown in the accompanying drawings.