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How- Do you design your own printed circuit layouts? That being the case, you need a good light box. This one is cheap, easy on the eyes and easy to build. By LEO SIMPSON At SILICON CHIP we needed a good light box. We design our printed circuit boards using Bishop tapes so we needed a light box for that. And we needed a light box for checking our wiring and overlay diagrams and for marking up all the photographs for page layouts. When we came to look at commercially available light boxes though, there were few that met our requirements. There were plenty of large commercial units, intended for use in photocomposing rooms and so on 60 SILICON CHIP and some intended for doctors' and dentists' surgeries, but few that were reasonably compact and cool and comfortable to work on. None were cheap. Most, if not all, used frosted float glass as the working surface. We did not want these. Glass light boxes often break and therefore can be a real hazard to anyone working with them. Frosted glass is expensive and inconvenient to replace too, so that was another reason not to use it. Hence, we decided to design and build our own. We are presenting the details here for anyone who needs a similar unit and who is able to handle a saw and screwdriver. The total cost is less than $70, if you buy all new materials. Essentially, all that is required is a suitably shaped box, painted white inside and fitted with an 18 or 20 watt fluorescent light batten. On top is mounted a sheet of white translucent Perspex. And that is all there is to it. · We even saved ourselves the trouble of painting it by using white Melamine-coated particle board, 16mm thick. This was cut to size, screwed together and the job was half done. We spent more time shopping for the materials than actually putting it together. To make it easy to work on, particularly if you are taping up a printed board design, we made the box with a sloping top, angled at 15° to the horizontal. At the front , to build a light box the box tapers down to 38mm, so it is quite comfortable to work on. Tools required You can get by with the very minimum of tools for this project. In fact you could manage the whole job using hand tools. To make it easier though, you will need an electric drill and a circular saw, preferably with a tungsten-carbide tipped blade. The assembly process consists of cutting the Melamine-surfaced particle board to size, drilling the holes for the screws, power cord entry and ventilators and then simply screwing it together. Glueing the box together is not practical, since the Melamine surfaces won't take glue. The first task is cut the various pieces to size. We dimensioned the box to suit a standard 18 or 20 watt fluorescent batten (batten is the term used to describe the whole fitting, including the tube) with a few millimetres clearance at each end. Just to be sure though, measure your batten before you mark up the sheet for cutting it would be most frustrating to find you had made the box too small. The top edges of the front and back pieces of the box should be chamfered to match the 15° slope of the sides. This is easily achieved by setting the baseplate of the circular saw to the correct 15° setting. With care in your saw work, all the pieces should fit together squarely with little need for work with a plane or rasp. To ensure you achieve straight cuts, use a straight edge as a guide for your circular saw. The idea is to clamp a thin straight-edged length of timber to the particle board and use it as a guide for the saw. Don't forget to drill the various holes for the power cord and ventilation. We used kitchen cupboard vents which fit in a 28mm (actually 1-1/8 inch) hole. You will need a hole saw or a Speedibore (an auger 18W FLUORESCENT LIGHT BATTEN BOLTED TO REAR »F - - - - BOX WITH TWO 5mm DIA. x 35mm SCREWS AND NUTS. SPACE BATTEN FROM REAR OF BOX BY ONE NUT THICKNESS. HOLES A: 28mm DIA. TO ACCEPT CUPBOARD VENTILATORS 8: 10mm DIA. MAINS CORD ENTRY C: 6mm DIA. REAR 130x613 A i / --1 BASE 312x613 i 130 J CHAMFER TOP EDGES OF FRONT AND REAR TO SAME ANGLE AS SIDES (15'). ASSEMBLE BOX WITH 40mm COUNTERSUNK PARTICLE BOARD SCREWS. COVER SCREW HEADS WITH DRESS CAPS. MATERIAL: 16mm PARTICLE BOARD COATED WITH WHITE MELAMIME ON BOTH SIDES. COVER EXPOSED EDGES WITH IRON-ON EDGE STRIP. COVER TOP OF BOX WITH 360x645 PIECE OF WHITE TRANSLUCENT 5mm ACRYLIC SHEET. DIMENSIONS IN MILLIMETRES LIGHT BOX 4 rv 38 Fig.1: we made our light box from 16mm-thick Melamime-coated particle board. The dimensions shown suit a standard 20W fluorescent batten but we suggest that you check the length of your batten before marking the sheet for cutting. MARCH 1988 61 The fluorescent batten is fitted to the rear of the case to give an even spread of light. Kitchen cupboard vents are used to cover the ventilation holes. bit made for electric drills) to drill these holes. When drilling these holes, drill through until the bit just breaks through the surface and then finish the hole by drilling through from the other side. This stops you making a mess of the hole and possibly tearing the Melamine surface. Finish off the sawn surfaces with a rasp or sanding block before going to the next step, which is to make the rightangle butt joints to assemble the box. The various sections are then screwed together. We used Chipboard screws (Bg x 40mm, countersunk, made by W.A. Deutscher) which have a coarse thread for good holding power. Underneath each screw head we placed the countersunk plastic washer for a white Snap Cap (decorative screw caps made by Furnco ). Alternatively, you can use Furnco Directors, which are particle board screws which are supplied with their own decorative caps. Either way, there is no need to coutertsink the screw heads into the particle board. We used fourteen screws (and decorative caps) to assemble the box. To finish off all the exposed edges of the particle board, use an iron-on Melamine edging tape (Armaflex-GL) and then trim to fit using a sharp utility knife. Now fit four rubber feet to the underside of the box so that it does not scratch or move around on the table. The next step is to fit the Perspex top. Assuming that you have made the box to the same size as our drawing, the Perspex sheet should be 360 x 645mm. We used some 3mm thick sheet we had on hand but we suggest 4.5mm material as a better choice as it will be more rigid. You can get Perspex cut to size from glass suppliers or you can go to a specialist outlet such as Cadillac Plastics in Sydney. We attached the Perspex to be top of the box using four countersunk head self tappers, 20mm long. Drill and countersink the screw holes before you remove the protective paper coating from both sides of the Perspex. Having fitted the Perspex, remove it again so the fluorescent light fitting can be installed. Remove the tube and the top cover from the batten and place it in the box as shown. Mark the positions of the mounting holes at both ends and drill the box for 5mm diameter Close-up view of the batten wiring. The mains cord should be anchored with a clamp and its leads connected to the 3-way terminal block. 62 SILICON CHIP screws. Before securing the batten, fit the cord entry hole with a junction box grommet. Secure the fluorescent batten with two 5mm screws and nuts, with one nut used on each screw to space the batten away from the rear surface of the box. You may think that a more even spread of illumination could be obtained by moving the batten more towards the centre-line of the box but we found that it gives a hot bright strip across the middle which is unsatisfactory. Now connect a 3-core mains power cord fitted with a 3-pin plug. These battens are fitted internally with a 3-way insulated terminal block for this purpose. The centre terminal is connected to the earth wire. The cord should also be anchored with a clamp. Now the cover and tube can be fitted to the batten and power applied to test it. We didn't bother to fit a mains switch on the box, by the way, as it seemed superfluous. Now fit the snap vents. Of course you don't really have to fit these but the vent holes look a bit grotty without them. You could also fit a handle to each end, to make it easier to lift. And that completes the light box. Let there be light. ~ LIST OF MATERIALS 1 sheet of 1 6mm Melamine surfaced particle board 1 18-watt fluorescent batten, including tube 1 3-core power flex and 3-pin plug 1 4 40mm x 8 gauge Chipboard screws (or Furnco Directors) 1 4 Furnco white Snap Caps size 8/8 (not necessary if Furnco Directors are used) 4 20mm x 1 0 gauge countersunk head selftapping screws · 4 rubber feet 2 5mm 20mm long screws, with nuts and washers 5 kitchen cupboard vents 1 sheet of white 4.5mm or 6mm Perspex, 360 x 645mm Miscellaneous Iron-on Melamine edging tape (Armaflex G-L)