This invention relates to an instrument dial which will form the face of an instrument such as a speedometer in a motor vehicle. The dial will carry a set of indicia against which a pointer or other indicating device will move. The invention relates both to the instrument dial itself, and to a method for the construction of such a dial.

According to the invention there is provided a method of constructing an instrument dial characterised in that the dial indicia are first printed on a sheet of thermoformable plastics material, and the sheet is then formed to provide it with a planar surface and with detent portions extending out of the plane of the surface, the detent portions being adapted to clip onto the edges of a support structure which thus supports the thermoformable sheet.

The detent portions may be spaced around the perimeter of the surface, or may be in the form of a continuous lip around the whole edge of the surface.

The thermoformable sheet can be printed on either one or both sides prior to forming, and in preferred embodiments both sides are printed each with a number of layers in different colours.

The invention also provides an instrument dial characterised by a thermoformed face panel on which indicia have been printed and which is divided into translucent and opaque areas, and where the panel has a planar surface and detent portions around the perimeter of the surface and extending out of the plane of the surface to allow the panel to be clipped onto a support structure.

The sheet material itself should be translucent before anything is printed on it. A suitable material is transparent polycarbonate.

It is particularly convenient if the detent portions on the formed thermoformable sheet are arranged so that the sheets can form a stable stack with one another ready for assembly.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a support structure for use in a first embodiment of the invention;

Figure 2 is a plan view of a face panel for mounting on the support structure of Figure 1;

Figure 3 is a detail taken in the direction of the arrow III from Figure 2;

Figure 4 is a cross section on a larger scale, taken on the lines IV-IV from Figure 3;

Figure 5 is an outline sectional view showing a second form of support structure for use in the inventio ;

Figure 6 is a detail showing the edge condition in a second embodiment of the invention;

Figure 7 is a plan, view of a face panel for use with the support structure of Figure 5;

Figure 8 is a section through the face panel of Figure 7 on the line VIII-VIII; and

Figure 9 illustrates how two face panels stack with one another.

The support structure shown in Figure 1 has a surface 12 in which various mounting holes 14 and strengthening ribs 16 are formed. These features have no connection with the present invention and will not be further described.

Around the edge of the structure are four radially projecting lugs 18 mounted on resilient stalks 20. These lugs serve to hold a face panel 22 in position on the structure. A face panel 22 is shown in Figure 2 and has a continuous planar surface 24 with a central aperture 26 for the shaft of a speedometer pointer, a series of speed-indicating indicia 27 against which the pointer will move and additional apertures 28, 30 through which the figures of an odometer display can be viewed.

The face panel has a peripheral skirt 32 and edge formations 34 formed in the skirt. The edge formations are positioned so that they register with the lugs 18 on the support structure and are shown in more detail in Figures 3 and 4 where an aperture 36 can be seen in each of the formations.

In use, the face panel will be placed over the support structure. Because of the outward flare of the edge formations 34 and because of the inherent flexibility of the material of the dial, the face panel can simply be pressed onto the structure and the lugs 18 will enter the apertures 36 to hold the face panel in place.

Figures 5 to 9 relate to an alternative embodiment. Here the face panel 122 has a continuous peripheral skirt 132 of constant cross-sectional shape. Continuity of the skirt is not however essential, but in this embodiment the skirt, where it is present, will have a constant

cross—sectional shape. This shape is shown clearly in Figures 5 and 6. The edge region 118 of the support structure surface 112 also has a constant cross-section and the way in which the face panel is clipped onto the support is shown in Figure 6. Figure 8 illustrates how two (or more) face panels can be stacked on top of one another to form a stable stack so the the top face panel can be lifted off without disturbing the face panels below it. The face panels do not jam together.

The face panels 22, 122 are made from polycarbonate or other thermoformable sheet. The sheet is initially flat and transparent. It is then printed using a coverlay process to deposit on the sheet various differently treated areas. If the face panel is to be viewed only under reflected light, then there will be no requirement for translucent areas and the front surface only of the sheet need be coated with the required markings in the required colours. If the face panel is to be illuminated with transmitted light from light sources arranged behind the face panel, then some areas will need to be translucent, and these translucent layers, in their various colours will normally be laid down before the final opaque layer covering the parts of the face panel where no light is to be transmitted.

After the printing of the surface of the face panel, the sheet of printed material is formed to produce the edge skirt 32, 132. The material of the face panel is chosen so that thermo orming can take place at a relatively low temperature, and it is important that the printed part of the sheet should suffer no distortion and no other damage from the forming process.