REGIONAL TECHNICIANS GROUP

Repairs - The Wimshurst Machine

Or 'The Curse of the Wimshurst Machine' as described by Austin Coulthard at a recent repairs and maintenance seminar.

The Wimshurst Machine can be very temperamental in its operation but as demonstrated by Austin Coulthard, provided some basic procedures are followed, good results can be obtained from this piece of equipment. The first check is to make sure that the apparatus is mechanically sound i.e. components are well secured, brushes and arms are not loose or floppy, and bearings are free running but not loose and wobbling. The arms must be set at right angles to one another in the 1 o' clock / 5 o' clock position when viewed from the front. The collector brush mountings should be parallel with the base and the collector brushes at right angles to the plates. The collector brushes are best teased out into a fan shape and positioned close to, but not touching the plates The belts need to be under equal tension and one of them crossed so that the plates counter-rotate. With the machine set up this way it should work when the handle is turned in one direction only, usually anti-clockwise, but if no spark occurs then try turning in the opposite direction..

If, after the above procedure, the machine still does not spark or the spark is weak, then a number of improvements can be made. To dismantle the unit, turn the collector brushes away from the plates (or remove the brushes if detachable) and remove the leyden jar assembly in one piece. Remove the belts, then loosen and remove the plate assembly. Lubricate the rotating shaft assembly and the lower bearings using a good quality mineral oil. Unscrew the nuts either side of the plates and remove the two charge brush arms. Clean the plates with a nylon scouring pad and warm, not hot, water - too much heat will buckle the plates permanently. Dry the plates thoroughly - placed in front of a fan is best, but again, not hot.

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The aluminium strips on the plate do not have to be in perfect condition for the machine to work well, but if too many are missing they can be manufactured from self-adhesive, aluminium body tape (used in panel beating.) An easy method is to stick a strip of the tape onto a plastic bag, cut the strip to the desired shape (which is not critical), then peel off the plastic and fix into place on the plate.

When re-assembling the machine, inspect the leyden jars carefully - if there are any cracks at all in the jars, then the machine will never work. Clean the underside of the jars and ensure a good electrical contact with the metal bases in which they sit (fix new aluminium foil to the base of the jar if necessary.) The rods inside the jar must be buried in the aluminium turnings in the jar (the turnings may have been dislodged if the jars have been inverted.)

Original belts were made from leather, and if this has become hard and dry, the leather can be softened using neatsfoot oil or a leather conditioner. Alternatively, replacement belts can be made from neoprene belting. Some practice will be needed to cut the belts to the correct length, remembering that one of the belts must be crossed so that the plates counter-rotate. This is best done by wrapping the belt around its intended path until it is a snug fit without stretching the neoprene, then cut the belt approximately 2mm shorter than the measured length which will give the small amount of tension required to drive the plates without slipping. To join the belt, heat the ends of the cut length over a gentle flame (lighted match or spirit burner) - when the plastic begins to melt, carefully align the ends, push gently together, then run under cold water to set. Before the joint has completely hardened, roll gently between finger and thumb to smooth out the ridge formed when joining. If the ridge is too pronounced, then the belt will tend to jump off the pulley when it turns. It is also possible to 'super glue' the ends of the belt together. The neoprene belting is available from (north of the river) "euro-seals" 178 Camboon Rd., Malaga, W.A. or (south of the river) "Ludowici & Son" 25 Glassford Road, Kewdale, W.A.

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Short lengths of de-soldering wick, or the braided copper sheath from co-axial cable can be used to replace missing or damaged brushes. The collector brushes should be teased out into a fan shape and the charging brushes left relatively tight. One idea for mounting the brushes is to insert a short length of the neoprene belting into the end of the copper braiding and fix this to the brush mounting.
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One way to determine whether the machine is likely to work or not and to determine which way to turn the handle, is to position the Wimshurst machine in front of a transistor radio which is tuned 'off station' (600 to 700 AM is suitable). The noise is very distinctive when the machine is being turned in the correct direction and is charging - the noise gets louder. If the machine is not charging then the noise heard on the radio will diminish. The machine does not have to be fully assembled for this test to work, thus providing a check for correct assembly when re-building the machine.

The Wimshurst machine used in the demonstration would not produce a spark before it was dismantled, irrespective of the direction in which it was turned. After following the above procedure, the machine produced a healthy spark of some 30mm or more (and it was raining that day too!)

Congratulations Aus. and thanks for a great demo.

***Any hints, tips or suggestions would be gratefully received - please contact Eric Payne at Belmont S.H.S. ***

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