GB2107017A - Dowel pin - Google Patents

Abstract

This is a dowel pin suitable for easy driving into members to be pinned together. There is a longitudinal bore (22) in the pin and there are external flanges (21) and internal projections (23) of helical form. The specification teaches how lengths of such dowel can be used as a writing implement, as a projectile, as a heat exchanger, in a lamp, in a paint- sprayer, in a simple jet-engine, as a drilling tool, as a structural component, or as a decorative device. <IMAGE>

Description

SPECIFICATION Dowel pin This invention relates to dowel pins, for example for connecting together two or more pieces of similar or dissimilar materials which will usually be of lesser hardness than that of the pin material unless one of the pieces is anchored to the pin by welding or cementing. It is an object of this invention to provide a design of pin enabling pins to be made economically and used efficiently and to resist withdrawal and resolve disconnection forces.

According to the present invention a dowel pin comprises a core having two or more protruding helical flanges of the core, the core having a longitudinal bore.

The invention is an improvement on the invention the subject matter of British Patent Specification No. 1233175 in which many of the advantages of a dowel pin are described.

Conventional dowel pins are solid as indeed is the core in the pin described in the above patent specification and the improvement forming the basis of the present invention is the longitudinal bore in the core which has striking advantages.

It is possible to insert by self-tapping a screw into the bore in the dowel and that is made easier if the bore has a number of internal projections which may also be of helical form corresponding to the flanges and indeed the dowel can be formed by twisting an extruded section with flanges and projections which extend parallel with the axis.

The self-tapping screw arrangement enables the dowel pin to be used with knobs secured for coat hangers, drawer pulls, feet for furniture legs and so on.

Such fittings need not constitute self-tapping screws but could be formed with cylindrical ends, possibly with spigot projections which can be simply pushed firmly into the bore in the core.

A bored dowel pin can be inserted below the surface of a wall or a piece of wood and then a plastic wood or other filler can be inserted in the bore and finished off flush with the surface, to give a good finish with a good anchorage.

Smooth cylindrical pins can be inserted within the longitudinal bore in the dowel pin which thus can act as a bush for forming a journal bearing, for example for hinges, or folding furniture, wheels on toys and so on.

It is also possible to insert a tension spring within the bore and connected to components on either side of the part containing the dowel pin to hold those components together.

The dowel pins may be used for forming rails on decorative security grilles and then if piano wire or the like is inserted freely within the central bore it will be difficult to cut through the dowel pin with a hacksaw. Again an insulated electric wire could be inserted in the bore in such a rail and that could be arranged to operate a burglar alarm if it was cut through.

Each such rail can be forced at its ends into spaced side rails - perhaps consisting of steel angles containing hardwood backing.

In a preferred form of the invention the longitudinal bore in the dowel pin is formed with a number of grooves which may be helical in the same way as the helical flanges and that makes it possible when a dowel pin is inserted into a closed ended hole for the end of the dowel pin to be split into a number of 'petals' to form a kind of rivet head at the end of the pin. If the grooves are helical as suggested above, all the petals will fold down with the same rotational hand. A conically headed pin could be slipped into the end of a dowel driven into a pilot hole with a closed end and that would also cause the end of the pin to split and to spread out and increase the anchorage.

in some applications, for example for use in hard masonry or in steel, or in their components, the dowel pin flanges can be cranked over near their tips.

The external arrangement will be somewhat similar to a multi-start screw thread except that the pitch of the flanges will be rather greater than that of conventional screw threads and the flange sections will be much more pronounced than the squat Vee of a conventional screw thread. Usually there will be a length of core apparent between adjacent flange sides and the flanges will have opposed sides which are spaced from each other and do not meet in an edge at the radially outer ends. There will be no head for taking bearing loads, which will be taken by the flanges.

The leading end of the pin flanges can be formed with one or more cutting edges which may act like a knife, or a chisel, or both, to assist in cutting a helical path for the flanges, and the other end of the pin can have a grip for a spanner shaped to engage on the ends of the flanges. In use it will normally be that a lead hole is drilled corresponding in size to the core of the pin. The path for the helical flanges can be formed in the process of inserting the pin by turning, or, in many cases, merely by driving the pin axially either by pneumatic or by ballistic means.

Individual pins can be cut from a continuous length of the material to suit particular requirements, and as it has no head it can readily be punched below the surface of the material into which it is inserted to any desired depth without disturbing the surface or requiring extra work in countersinking.

The dowel pin could, for example, be of steel or aluminium alloy or plastics material.

Another object of the invention is to use such a dowel like pin in a nubmer of applications other than applications where a dowel pin would normally be used.

There may be an end member fitted into the bore in the core at one or each end of the pin. For example, a writing implement could have a closure gap fitted into one end of the bore and a writing head or nib fitted into the other end. Again if the pin was to be used as the body or shaft of an arrow, then a point could be fitted into one end of the bore and a head having a slot for a bow string could be fitted into the other end.

The outer edges of the flanges or the inner edges of internal projections, or both, can be of enlarged form to provide a good heat exchange surface or a good bearing surface.

Thus, there may be a cylindrical member within the bore located by the inner ends of the projections, and that could be rotatable. If it is in the form of a tube, then the bore within that tube could be used for supplying a fluid along the pin, and where two fluids are to be mixed, for example, in a fuel burner or a paint spray, one fluid, for example, fuel, or paint, could be drawn along such a bore, while air for combustion or for atomising the paint could be drawn along the bore within the longitudinal bore but surrounding the inner tube.

The helical form of the projections can cause air to swirl as it passes along the longitudinal bore.

There may be a cylindrical tube surrounding the pin and it could perhaps be fixed to the edges of the flanges, or the flanged core could be arranged to rotate in such a cylindrical tube and there has also been a suggestion for using the pin with an internal tube in a fuel burning lamp or in a paint sprayer. It would also be possible to use such a device as a blow torch.

Another possibility is to have an internal body in the form of a cylindrical mesh filter which could collect condensate from wet gas flowing along the longitudinal bore to leave dried gas passing along outside the filter, and within the inner surface of the longitudinal bore.

The protruding helical flange will cause air passing along the outside surface of the pin to be given a swirling motion, which will be useful in a number of applications, for example for supplying air for combustion purposes.

Another possibility is the use of such a device as a part of a jet engine with combustion fuel ejected from the longitudinal bore into the space between the external flanges and the surrounding cylinder, so that the products of combustion acting on the helical flanges cause relative rotation between the cylinder and the flanged pin.

Again the pin with or without the surrounding sleeve could be used as the stem or shank of a drilling device so that the action of the helical flanges can be used to remove dust generated in the drilling process. The external sleeve could be used as a bore liner to be left in position after drilling has been completed.

The invention includes a method of making a fastening or a fixing including drilling a pilot hole corresponding to the diameter of the pin core and then inserting a pin in the pilot hole and causing the flanges to cut corresponding grooves as they are driven in and to turn at the same time.

The invention may be carried into practice in various ways, and one embodiment will now be described by way of example with reference to the accompanying drawings of which:~ FIGURE 1 is a cross-sectional view through a helical dowel pin which is of uniform cross-section throughout its length although it has a continuous uniform twist to give its external flanges a helical form; FIGURES 2 and 3 are similar views showing a variation of the pin of Figure 1 in use respectively in masonry or steel, and in timber; FIGURES 4, 5 and 6 are views corresponding to Figure 1 showing modifications of the dowel pin; FIGURE 7 is a diagrammatic elevation of a device which may have a cross section as shown in any of the Figures 1-6; and FIGURE 8 is an elevation of a fitting for an electric drill for driving a dowel pin in.

The section is basically of annular form 20 with an external diameter of 5.5 mm and a bore 22 with a diameter of 4.0 mm. Equally spaced around the outer diameter are six external flanges 21 terminating on the circumference of a pitch circle 8.00 mm in diameter. The flanges taper slightly with a width at the greatest diameter of 0.5 mm.

The outer ends form an edge between two bevels mutually inclined at 1200.

Opposite each external flange is an internal projecting 23 extending for 0.4 mm with a root width of 0.4 mm and an end width of 0.2 mm.

Equally spaced between each pair of internal projections is a groove 30 with a radius of 0.15 mm.

The dowel pin is formed by extrusion with the flanges extending parallel with the axis and then it is given a uniform twist so that the flanges, the internal projections, and the grooves, all take a helical form.

The dowel pin can be used in the conventional way to hold two timber members together by first forming a pilot hole in the two timber members equal to the external diameter of the annular core, namely 5.5 mm, and then driving the dowel in with a percussion tool or a press so that the flanges cut into the timber and the dowel pin is automatically turned in accordance with the helix angle.

The pin will also anchor well into masonry and into other hard material, and can be left projecting by any desired length, for example for supporting a suspended ceiling.

The dowel pin is a great improvement on the pin described in United Kingdom Specification No.

1233175, with its solid core because the hollow core reduces the amount of material necessary to give the pin great stiffness, while the internal bore enables self-tapping screws or rods or wire to be fitted into a dowel, as generally described above.

When driving into soft wood, it is possible for some of the wood displaced to be forced back out through the central bore. After insertion the bore can be filled with a filler.

The end of the dowel pin can be sharpened with a conical grinder for example, for ease in driving it into soft wood.

The internal projections are advantageous particularly if a self-tapping screw is to be threaded into the bore but they are not essential and in the simplest form of the invention, the shape of the bore is circular without either the internal projections or the grooves between them, which - as described above - assist in causing the inner end of the pin to split as it is driven in to provide a good anchorage. In the preferred form, there are no grooves but there are internal projections.

In a modification of the preferred general form of hollow dowel pin, the helical flanges are cranked over near their tips to the same hand as the helical flanges, as indicated at "X" in Figure 2, so that the overall radius of the pin section as extruded R, extends to the edge of the cranked over tip. A pilot hole drilled into steel or masonry or some other hard material has a radius R3 which is that of the inner corner of the cranked over tip and so is a little less than R.

As the dowel pin is driven into the pilot hole applied forces and reactions are set up as indicated by the arrows in Figure 2. The upper half of Figure 2 shows the forces set up when the pin is driven into masonry and the bottom half when the pin is driven into steel plates or tubes.

It will be seen that load is applied to the tips of the flanges eccentrically so that they will deflect elastically, and indeed may suffer permanent deformation if driven into hard steel. The stresses built up will apply outward frictional forces opposing direct withdrawal of the dowel pin, and if the pin is driven into hard masonry rather than into steel, the cranked over ends of the flanges will tend to cut shallow threads into the surface of the pilot hole giving a mechanical grip in addition to the frictional grip due to deformation.

There is an incidental advantage if the pin is driven into damp masonry or mortar with a high acid or alkali content because that will tend to corrode the pin surface to produce chemical products occupying more than the available space leading to a significant risk of cracks in the masonry. With the type of dowel pin shown in Figure 2, the deformation of the flange tips can accommodate the corrosion products without causing sufficient reaction to crack the masonry.

Corrosion at the outer surface of the core between the flanges can be accommodated in the available space between adjacent flanges.

If such a dowel pin is driven into a hardwood containing a dense knot, the ability of the flange tips to deflect is likely to enable them to ride past or through such an obstruction.

When a pin is driven into timber there is a natural tendency for the timber to split, and for that reason it is usual to avoid having screws and bolts and nails near the edges of timber members, but Figure 3 shows that if the dowel pin with the section of Figure 2 is used in timber, the action of the cranked-over flange tips as the pin is driven in tends to compress the timber, as shown by the arrows, where it would tend to split, and that will to a large extent overcome the difficulties described above with nails and screws.

The exposed end of a dowel pin with the section shown in Figure 2 may be heavily hammered after insertion so that the edges are turned over to form a petal-like head. Such a head is of particular use when joining thin members, and sheet members where there is not much depth for the flanges to bite into, and moreover the petal-like head may be considered to be decorative.

In general, the dowel pins shown in Figures 1 and 2 can be considered as multi-purpose fixings reducing the need to hold stocks of a variety of fasteners of different types and different sizes and lengths.

An external screw thread could be formed around the flanges 21, so that a nut, or nuts, can be fitted on the pin for fastening or for forming a substitute for a bolt.

Figure 1 shows in chain lines at 24 how the outer edges of the flanges 21 can be enlarged to provide an external surface which is fairly large, for example for heat conduction with the atmosphere, and which also has rounded edges so that the sharp edges of the simple flanges 21 are avoided.

A tubular member with a section as shown in Figure 1 and with or without the enlarged portions 24 can be used as a component of a heat exchanger, or a heater or cooler, with a fluid being passed through the longitudinal hole 22 with heat exchange to the surrounding air in contact with the outer surface of the tube 20 and the surfaces of the flanges 21, which air is arranged to swirl by virtue of the helical form of the flanges 21. The inner projections 23 assist in heat transfer between the fluid and the wall of the tubular member.

The pitch of the helix, the number of flanges, and the radial length of the flanges can all be designed in accordance with the heat transfer effect to be achieved.

Figure 4 shows how with the tubular pin of Figure 1 a closed ended cylindrical shell mesh filter 25 can be fitted in the bore just within the projections 23 to collect condensate from wet gas being passed along the tube, so that there is a freer flow of gas from which condensate has been extracted in the spaces 26 between adjacent projections 23 and outside the filter 25.

Figure 5 shows how an internal tube 27 can be fitted within the tips of the projections 23, and that could for example be used as a capillary tube forming a component of a ballpoint pen, and acting as an ink reservoir. The flanges 21 give the pen a good external fingergrip, and also at each end provide respectively a secure seating for a closure cap and a clip, and for a writing head or nib.

The projections 23 could be enlarged at the inner ends of their sections, as shown at 28, to provide a larger bearing surface for the outside of the tube 27.

The tube 27 could also be formed with one or more external flanges 29 (one only is shown in Figure 5) with a helical form conforming with that of the spaces 26 between adjacent projections 23, so that by relative twisting of the tubular pin 20 and the tube 27, the end of the pen can be projected and withdrawn into the tube 20.

Apart from the use as a propelling writing instrument as described above, such an arrangement in which the inner tube 27 has one or more external helical projections 29, can be used in any application where a rotary movement is to be translated into an axial movement, or viceversa. Rotation of either tube in relation to the other can produce axial movement of the other, and that is an arrangement in which a wheel could be mounted on one or other tube with means for providing a linear drive to the other. It is to be noted that in that application the inner tube 27 could be solid.

Grooves 31 in the inner surface of the tube 20 between the inner projections 23, can constitute lubricant channels in an application of that kind, or indeed the external projections 29 could perhaps be rounded off at their corners, or otherwise formed to leave space from the inner surface of the external tube 20 for lubricant. The size of such lubricating channels can be such as to promote capillary action in forcing lubricant along the channels.

The spaces 26 between the inner and outer tubes (the inner tube 27 could be solid) or even the space within the inner tube 27 could be used to supply liquid fuel to a lamp and act as a sort of non-combustible wick which will continue to burn even if the level of liquid fuel in the reservoir falls.

Where the member 27 is a tube, it can be arranged to supply liquid fuel of a different flash point from that conveyed by the capillary channels 26, so that the fuel with the lower flash point can be used for igniting the lamp, and then when ignition has started, the fuel of higher flash point can be preheated by conduction from the surfaces of the member 27. If for example the inner member 27 contains a small charge of lower flashpoint fluid for starting ignition, it can be closed off at the bottom while the outer tube 20 extends a greater distance to the reservoir for the main fuel.

Figure 6 shows how a tubular member with a cross section as shown in Figure 1 can be a fit in an outer tube 33 whether or not the tubular member 20 has an inner component, for example as shown at 25 in Figure 4, or at 27 in Figure 5, and this outer tube 33 gives rise to further possibilities.

Where a fuel is supplied along the bore 22, for example for a lamp as described with reference to Figure 5, then the helical flanges 21 within the outer tube 33 which can be open at one end, can cause air drawn in to support combustion at the end of the tube 20 to swirl and provide good mixing and efficient combustion at the flame.

Instead of air merely being drawn in through a short open-ended tube 33, air can be supplied under pressure along a surrounding tube 33 extending along the whole length of the tube 27.

Figure 7 shows how the tube with a section as shown in Figure 4 can be used with a lamp. The main fuel, e.g. paraffin could be supplied from a reservoir 41 along the central bore 22 and can burn in air drawn in through a surrounding sleeve 42. For pre-heating the tube 20, and hence the paraffin, a second - more-easily ignited - fuel, e.g. methylated spirit can be drawn along the spaces 35 between the tubes 20 and 33. As fuel is consumed it may be necessary to raise the reservoir 41 to maintain a steady flame. or capillary action in the bores may be sufficient.

In another possibility, the sleeve 42 is omitted and fuel and air are delivered along the passages 22 and 25.

Another possibility is to have radial bores, for example as indicated at 34 in Figure 6, through the wall of the tube 20 at a certain distance along its length, and then fuel passing along the bore 22 can pass radially through the bores 34 for combustion in the air space 35 within the tube 33 and outside the tube 20.

The products of combustion will be forced to escape axially, and the helical form of the flanges 21 can then cause rotation of the two components, and that can form the basis of a simple turbojet engine, for example for model aircraft. The tubes 20 and 33 will of course be designed for easy rotation in relation to each other.

Another application of the idea of forcing a fluid along one or other of the longitudinal bores, is that of a paint sprayer, according to which paint can be passed along a central bore while air is caused to flow along the bores bounded by the helical flanges 21 so that the swirling air can break up the paint into droplets, and provide a directed jet for directing the droplets of paint onto the surface to be panted.

A tube with a cross section as shown in Figure 6 could be used as the shaft of a drilling device with the flutes of the drill in communication with the spaces 35 between the helical flanges 21, and then as the shaft rotates the flanges 21 will lift out dust formed in the drilling operation. Compressed air could be delivered along the longitudinal bore 22 to assist in moving such dust. Such a rotating shaft 20 could be surrounded just outside the hole by a tube as shown at 33 in Figure 6 which could be held to direct the drilling process, although it is equally possible to have a rigid shaft with a section as shown at 20 rotated directly by an electric drill.

Indeed a tube such as 33 may be supplied around the rotating flanged tube 20. A tube such as 33 which is rotatable in relation to the longitudinal member 20 can be used to line a hole being drilled through a material liable to crumble, and left behind when the drilling operation is finished.

A rod or tube with an external section as shown in Figure 1, and possibly with a different number of flanges, can be used as the shaft of an arrow, dart, or javelin, so that the helical flanges cause the projectile to rotate in flight. It may be possible with such a projectile to avoid having feathers or fins at the rear for guiding it, or if fins are required, they could perhaps be mounted along the helical flanges.

One possibility is an arrow made from a tube with a section as shown in Figure 1, but which is twisted only along a part of the length, for example, at the rear, and that may enable fins or feathers to be dispensed with entirely.

In such a case the projectile could be arranged to be propelled through a bore of corresponding section in the bow or other propelling instrument, and then rotation will be imparted to the projectile as the helical flanges pass through that hole.

The tube with a section as in Figure 1 (or any of the other figures) could be large enough in crosssection to be useful as a structural member in scaffolding or as reinforcement in a composite column. A tube with the dimensions shown in Figure 1 could act as a connector in a toy construction kit. In any case, the helical flanges give a very simple way of connecting the ends of the tube to other components in an axial drive.

Short lengths of tube could be strung together on a cord as a decorative necklace, perhaps gilded at selected places. A single short length could act with a hair clip as a tie clip or the like.

Figure 8 shows a fitting for an electric percussion drill. A shaft 51 has one end for insertion in the drill chuck, while the other end has an eccentric cutting edge 52 at the diameter of the desired pilot hole for the dowel pin 53 which is fitted over the end of the fitting before drilling starts. A collar 54 is held on the shaft by a grub screw 55 and is reversible so that either a concave end 58 abuts the pin 53 for forming a rivet head, or a flat end 57 equal in diameter to the external diameter of the pin is able to countersink the pin below the surface it is being driven into. The pilot is drilled and the pin is driven into the pilot hole in one action of the percussion drill, which is then withdrawn with the shaft to leave the pin in position.

Claims (20)

1. A pin having a cross section which comprises a core (20) having two or more protruding helical flanges (21) running parallel with each other along the length of the core, the core having a longitudinal bore (22).

2. A pin as claimed in Claim 1 in which the bore has a number of internal projections (23).

3. A pin as claimed in Claim 2 in which the internal projections are of helical form.

4. A pin as claimed in any one of the preceding claims in which the outer edges of the flanges (24) or the inner edges of internal projections (28) are of enlarged form.

5. A pin as claimed in any of the preceding claims including an end member fitted or screwed into the bore in the core at one or each end of the pin.

6. A pin as claimed in any preceding claim including elongate helical grooves arranged around the surface of the bore.

7. A pin as claimed in any of the preceding claims including a cylindrical member within the bore and located by the inner edges of the internal projections.

8. A pin as claimed in Claim 6 in which the cylindrical member has external projections of helical form corresponding with the form of the internal projections on the pin section.

9. A pin as claimed in any of Claims 1-8 including a tube surrounding the helical flanges on the core.

10. A pin as claimed in Claim 9 in which the pin can rotate in the surrounding tube, or is fixed to the surrounding tube.

11. A writing instrument, the body of which comprises a pin as claimed in any of Claims 1-8.

12. A fuel burning lamp in which the body is constituted by a pin as claimed in any of Claims 1-10 and in which fuel is arranged to be supplied along the longitudinal bore.

13. A paint sprayer having a body as claimed in any of Claims 1-9.

14. A projectile having a shaft formed from a pin as claimed in any of Claims 1-8.

15. An engine having a body as claimed in any of Claims 1-8.

1 6. A fitting for an electric drill comprising a shaft with a cutting edge at a radius corresponding to that of the pin core, a section behind the cutting edge on which a length of pin as claimed in any of Claims 1-10 can be carried and a drive member on the shaft for causing the pin to be driven into a pilot hole as it is formed by the cutting edge.

17. A method of fastening in which a pilot hole is drilled in a member and then a pin as claimed in any of Claims 1-10 is driven into the pilot hole, the diameter of which corresponds with that of the core of the pin.

18. A method as claimed in Claim 17 in which the pin is carried on a drill tool so that it can follow the drill tool into the pilot bore as it is drilled.

19. A method as claimed in Claim 17 or Claim 18 including the preliminary step of cutting the pin from a length of material of constant cross section.

20. A dowel pin or a length of dowel pin material of constant cross section substantially as herein specifically described with reference to any of Figures 1,2,5 and 6 of the accompanying drawings.