Indicator Dials

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Constructors are recommended to read all of these instructions first before commencing work.

With the current move away from mechanical tuning capacitors and the down turn in home construction it is becoming increasingly difficult to obtain these items from electronic or surplus suppliers. However, all is not lost as it is possible to make your own with some secondary double glazing material and a small number of tools. You will need the following items:

• Plastic (Perspex etc) sheet of 1/10 to 1/8 inch (2.5 - 3mm) thickness
• Power drill in a stand (or a small lathe)
• Threaded rod of 1/4 inch or 6mm diameter depending on the hole diameter required.
• Sharp wood chisel
• Model makers scalpel with a new blade
• Protective face mask or goggles
• Adequate hand protection
• Work bench and a drill stand or method of securely mounting the power drill
• Tool guide

Mark out your dial outline and centre hole on the plastic sheet (with the protective covering left in place and using a Biro pen) and cut out slightly oversize using a fret saw, hack saw or similar. Be careful with this task as the material is brittle and the saw can easily jam with a risk of splitting the plastic. Remove the protective covering and file off the rough edges but do not worry about getting the outside edge absolutely smooth at this time. Drill the centre hole with a small pilot and then to the threaded rod size using sharp drills and not to much pressure as the plastic will quickly melt.

Mount the drill in the drill stand. Mount the rough cut dial onto the threaded rod between two large flat washers and surrounding nuts, tighten the nuts carefully and mount one end of the threaded rod in the drill chuck. Mount a tool guide (I use a model makers vice) securely onto the table of the drill stand. You are now going to carry out a similar process to using a wood turners lathe.

Put on the protective goggles and hand protection, turn on the drill, rest the firmly held chisel on the tool guide at right angles to the edge of the plastic disk and slowly and gently move the chisel towards the disk. You will find that the edge of the disk is blurred but continue until you hear the tip of the chisel start cutting the rough edges of the plastic disk. Be patient - do not rush or the plastic will catch on the chisel blade and shatter. The chisel will gradually cut away the rough edge of the disk which will become smoother and the sound will also become smoother. Regularly stop the drill and check the work for finish and size - it is easy to remove too much material and is better to be on the safe side. Note - if the initial edge is very rough you can use a file first to smooth it down before using the chisel.

Eventually the edge of the disk will become fairly smooth and regular but may not be perfect. To finish the edge use the scalpel blade instead of the chisel to cut away tiny amounts of plastic - you only need to rest the blade gently at right angles to the disk with the scalpel resting on the tool guide for stability. Regularly stop the drill and examine the edge for finish and size.

I suggest that you experiment with a scrap piece of plastic first to learn and practice the techniques - the finished results will be well worth the effort. If required, carefully drill the centre hole to the final size. The finished dial may be marked using Letraset or Edding dry transfer letters and a suitable retaining spray or varnish - check that the varnish does not dissolve the letters or they may blur during drying. If your front panel is fairly dark in colour then white letters look good otherwise black will be fine.

Health and Safety Issues:

Make sure that the OFF switch for your power drill is within reach and other members of your household know what you are doing in case of an accident.

Do not do this work without adequate face and hand protection.

Do not point the chisel or scalpel blades against the direction of rotation or the blade may catch on the material and cause it to shatter. The blade should be at right angles to the plastic disk or pointing slightly in the same direction as the rotation.

Do not try to hold the chisel or scalpel without using a tool guide or rest.

Do not try to measure the work with the drill running - it is very dangerous and you risk severe injury.

Do not leave the chuck key in the chuck and turn on the drill.

Do not use a threaded rod that is significantly smaller than the diameter of the hole in the centre of the disk - you can always increase the hole size afterwards.

Do not over-tighten the retaining nuts or the plastic may shatter. Fibre or similar slightly flexible washers will spread the strain.