1 A Wimshurst Machine

A Wimshurst Machine The Wimshurst Machine consists of two varnished glass plates revolving in opposite directions. On the outside of each of these plates are cemented a number of tinfoil "sectors" arranged radially. Two conductors at right angles to each other extend obliquely across the plates, one at the back and the other at the front. These conductors each terminate in brushes of tinsel which electrically excite the "sectors" as the plates revolve. The electricity is collected by a set of "collectors" arranged as shown inFig. 42.

The Glass Plates are each eighteen inches in diameter. Purchase two panes of clear glass twenty inches square from a glass-dealer. The white glass is far preferable to the green glass and will make the best electric machine. The plates should be of the thickness known as "single light" and should be perfectly free from wavy places, bubbles, or other imperfections.The work is first laid out using a piece of stiff paper twenty inches square as a pattern. Describe a circle four inches in diameter. Using the same centre, draw other circles, making them respectively eight, sixteen, and eighteen inches in diameter. Then mark sixteen radial lines, from the centre, making them equal distances apart, as shown inFig. 33. Lay one of the glass panels over the pattern and cut out a glass circle eighteen inches in diameter, or perhaps you may be able to get a glazier to do the cutting for you and so save considerable trouble and possible breakage. Two such plates should be made.

The sectors are cut from heavy flat tinfoil according to the pattern shown inFig. 35. They should be made one inch and one-half wide at the wide end and three-quarters of an inch at the other end. They are each four inches long. Thirty-two such sectors are required. The easiest way to make them is to cut out a pattern from heavy cardboard to serve as a guide. Clean and dry both the glass plates very carefully and then give them each two thin coats of white shellac. After they have dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper. Then place a weight in the centre of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all sectors are in place the plates will appear like that shown inFig. 35.

The Bosses will have to be turned out at a wood-working mill or some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommo- date a round leather belt. A hole should be made in each boss about half-way through the small end. These holes should be bushed with a piece brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit." As shown inFig. 36.

The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the foil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle. Then apply some bichromate glue to the flat surface of one of the bosses and place the latter in the centre of the plate in line with the smallest circle. Place a weight on the boss to hold it down firmly against the plate and leave it overnight, or for ten or twelve hours, until thoroughly dry.The glue is prepared by placing some good quality glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enough glacial acetic acid to cover the glue. Heat the mixture until it is reduced to a liquid, stirring it until it is perfectly smooth. Add a teaspoonful of powdered bichromate of potash to the glue. The glue must now be kept in the dark, for sunlight will "set" the glue so that it becomes insoluble.The Frame of the machine is composed of two strips twenty five inches long, three inches wide, and an inch and one-half in thickness, and two cross-pieces of the same thickness and fifteen inches wide. Notches are cut at both sides of the base to admit the feet of the uprights. The Uprights are seventeen inches long, three inches wide, and one and one-half inches thick. The notch at the foot is cut the same width as the thickness of the long members of the frame, and is arranged so that when fitted in place the foot of the upright will rest on the table in line with the bottom of the cross-pieces. As shown inFig. 37.

The Driving-wheels are turned out of wood on a lathe. They are seven inches in diameter and seven-eighths of an inch thick. A groove should be turned in the edge to carry a small round leather belt. The wheels are mounted on a wooden axle made from a round curtain-pole. They are glued to the axle and arranged so that the grooves will fall directly underneath the pulleys turned in the bosses. The ends of the axle pass through the uprights, five inches above the bottom.As shown inFig. 39.

The front end of the axle is fitted with a crank and a handle. The plates are mounted on short iron axles passing through the top of the upright into the brass bushings. One end of each of the axles is filed flat where it passes through the wood upright, so that it may be held firmly by a set-screw and prevented from revolving. Fasten a small fibre washer to the centre of one glass disk so that it will separate the plates and prevent them from touching when revolving.The Collectors, quadrant rods, etc., are mounted on glass rods one inch in diameter. The bottoms of the rods fit in holes "(H H)" bored in the cross-pieces of the base (Fig. 37). The upper ends are each fitted with a brass ball two inches in diameter. The balls are mounted on the rods by soldering a piece of brass tubing to each ball and slipping it over the rod. The rods should be of the proper length to bring the centre of the balls on a line with the centre of the plates. (Fig. 41).

Make two forks, as shown inFig. 42., out of brass rod, three- sixteenths of an inch in diameter, and solder brass balls at the ends. The forks are eleven inches long. A number of small holes must be bored in the "prongs," and pins made by cutting ordinary dressmakers' pins in half and soldering them in place. These pins, mounted on the forks, form the combs, or collectors. Bore a horizontal hole through each of the brass balls on the tops of the glass rods and pass the shanks of the forks through and solder them in place. One of the shanks may be provided with a discharge ball at the end, as shown by "D B" in The other is provided with a hard rubber handle made from a piece of rod. Bore a three-eighths of an inch hole directly in the top of each brass ball to receive the quadrant rods forming the spark gap.The quadrant rods extend over the top of the plates and are three- eighths of an inch in diameter. They are loose in the tops of the balls so that they may be moved about or removed entirely. A small brass ball three-quarters of an inch in diameter should be soldered to the top of one of the quadrant rods, and a similar ball two inches in diameter to the other.Fig. 41.

Two large brass balls, two inches in diameter, are fitted over the ends of the axles, which project through the uprights. Bore a one quarter-inch hole through each ball at right angles to the axle and slip a one-quarter-inch brass rod through and solder it fast.Fig. 43.

The ends of the rods should be tipped with a bunch of tinsel or fine copper wires and be curved so that the brushes will just touch the sectors on the disks when the latter are revolved. These are the neutralisers, and are arranged in the approximate positions shown inFig. 44.

The driving-wheels are connected to the bosses by means of small round leather belts. The belt at the rear of the machine is crossed in order to make the plates revolve in opposite directions. If the machine has been properly built it is now ready for operation. It may be necessary to charge the machine the first time that it is used, by touching several of the sectors with the charged cover of an electrophorus. Then if the handle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine in the form of bright blue sparks.2

Two contra rotating disks with foil sections

At the centre middle horizontal position two brushes positioned at front and two at rear to collect and transfer a charge to storage Leyden jars and then hold it or discharge it through a spark gap when sufficient charge has been collected from spinning disks.

A common line connection is shared by two of the other brushes C and D to equal the charge on the both sector plates under these brushes at the same time .

The same happens on disk two but with a common line connection at a 90 degree angle to the front common line connection. E F

Power from position A is fed to the inside metal plate of the Leyden jar and from position B to the other storage capacitor.

There also a common line connection to the outer metal plates of both Leyden jars.

Construction tipsObtain two old gramophone records approx 30 cm in diameter (smaller ones can be used or a different material could be used.)

Mark each record into 36 equal segments by drawing lines across the diameter in ten degree segments.

Mark two circles on each record about one inch from the outer edge.

the inner circle is dependant on the foil size segments you use and then use these for guides for placement of the metal plates.

Most designs for this machine suggest using al foil but I found by getting some linotype used aluminium plates and it is

easy to cut with scizzors and you probably get some used sheets from a printer for about 60 cents each and two sheets

are all you need. I find also it lasts a lot longer than normal al foil..

The cut aluminium foil must be able to fit into one of the drawn segments on the disk and can be glued into place by any good contact adhesive.

The sectors I used were approx 8cm in length with one end 1cm wide tapering out to 2.6cm with all corners rounded

you will need eighteen for each record a total of 36 cut sections.

Place one in sector leave the next one blank and then repeat

Glue these metal leaves into position and let them set for a couple of weeks or longer depending on your climate.

Make sure all aluminium leaves are flat and no metal sectors plates are sticking up

Later a couple layers of varnish around the plates and onto the record surface will also be needed as well.

On the back of one disk also attach a fibre washer to stop the records for touching one another when in construction and working position.

You will also need to make and glue pulleys to centre of each disk

When the unit is put together these records will be mounted on two separate shafts and be placed back to back

with metal sections place on the outside.

Making your PulleysI have heard people have used cotton reels but I prefer to make them out of perspex disks cut with a normal

home drill attachment that cuts holes from 3/4inch to about 2 1/2 inch in diameter.

The drill feed screw should be no more than 1/4 inch and the bored hole can later be drilled out to 5/16 of an inch

(this will fit in on the threaded shaft mounted on the perspex supports)

Cut four large diameter disk and two smaller ones and glue them together using a nut and bolt in the drill hole

to hold the three pieces together to form a pulley.

You may need to smooth off the rough edges on the small disks thus created before glueing together.

I used a lathe but you may get away with using the perspex disk mounted on a drill chuck with a 1/4 inch bolt and sandpapered ( be careful not injure yourself by doing this )

The drive PulleysYou will also need to make two more set of pulleys for your drive wheel section

If you intend to hand drive this you will need to make these pulleys of a larger diameter

to insure a higher gear ratio to enable the records to rotate at higher speed than hand cranking.

something like ration 3:1 or 2:1 is possible.

When these are mounted one pulley must be fixed in position by tightening nuts around both sides of pulley on threaded shaft

( 5/16 threaded shaft is okay 1/4 is too thin and bends)

The second drive pulley needs to be able to rotate freely.

Connect drive belt as below with drive wheels at right angles to the disks

(These belt driving design for this set up had me puzzled for months and I using an inefficient cross belt in my

set up before someone sent me this idea.)

Making the brushesyou will need to make eight collecting brushes for this unit

Centre BrushesThese will be mounted at positions A and B on perspex mounting at the centre diameter edges mid point horizontal to each disk and they will also be a common position on the rear disk

Diametrical Connections

Basic wiring connectionsA further two common connected brushes are needed at position C and D (C may need to set higher and D lower than those shown on the drawing.( blue line)

Brushes E and F shown in white on the drawing are the from the back of the drawing and will need to mounted

at a position of 90 degrees to that of C and D on the front.(white line)

some people have used foil to make the sliding contacts with the foil on the disk for their brushes but I find that

ordinary small springs mounted on small bolts via the thread make excellent brushes I then can bolt and tighten

them into position using nuts to adjust their positions relative to metal sections on the records.

Basic Leyden jar construction

I find this simple to construct using the same linotype aluminium as used for the leaves on the disks.

I always had trouble with the wrapping foil as sold in the shops and find the above easier to handle.

I used normal preserving jars of about 17 cm in height and 8cm in diameter. but any thick glass type

with straight edges may do also.

Cut the metal so that it will go around the outside of the jar and overlap slightly and leave one inch gap at top and bottom

with glass exposed at each end.

Wrap the aluminium around the outside of jar and hold in position with tightly wound insulating tape and then apply some

contact adhesive and let it flow between the metal and the glass.

Apply some self adhesive clear plastic sheeting and cover both the metal and the glass.

For the inside of the jar cut metal the same height but smaller than outside length and form into cylinder using another glass jar of the same diameter and then slip inside of the Jar.

It may pay to have an electrical insulated wire connection to the metal before you do this however.

Your Leyden Capacitor jar is now completed.

You will need to make another one of similar dimension try to keep all the measurements the same.

3

The Wimshurst Electrostatic MachineYears ago (1973-1975) I built a first series of electrostatic machines. With this I learned a lot about electricity, and I still think that all people interested in electricity or electronics shall try these machines to get a real feel of the subject. At least, high voltage static electricity is something that you can see and feel.The best machine I could build at that time was a Wimshurst machine. I learned about it in old physics books [1], and it was not difficult to build one that was immediately successful. Following are instructions on how to build a machine similar to mine. Take also a look at the several pictures and plans of Wimshurst machines in other areas of thesite, some much better than this one.The Wimshurst machine was invented by James Wimshurst, in England, and first described in 1883. Similar structures, although sectorless, were previously studied, in Germany, byHoltz and Poggendorff, by 1869 [p45][p47], andMusaeus, by 1871 [p47][27][p93]. A sectored machine of rather poor performance was described by Holtz in 1876 [29][p94]. This machine eventually become the most popular electrostatic machine, due to its relatively reliable operation and simple construction.To build one what you need is: Two plastic disks, with about 31 cm of diameter (It is possible to use exactly two old LP disks, but the result is rather ugly). I used two acrylic disks, about 2 mm thick, with 20 cm of diameter This is rather small, but big enough to allow the observation of all the important electrostatic phenomena, without taking too much space. If you want some power, make disks with more than 30 cm. The spark length that can be obtained is about 1/3 of the diameter of the disks.Mount in the middle of the disks wood cylinders, to be used as "bosses" to turn the disks, with precise holes to pass a steel axle in the center. Make grooves around the cylinders to be used as pulleys where the cords that will move the disks will pass. I actually used more elaborated bosses, turned in a lathe, with flat faces to be glued to the disks in one side and small pulleys at the other side. Metal or a plastic as nylon can also be used for the bosses. Mount the assembly in a wood support composed of a base and two upright supports, in a way that allows the disks to rotate in opposite directions, maintaining a separation of 1-2 mm, never touching. The distance can be proportionally larger with larger disks. The construction must be solid and well balanced. I fixed the bosses to the disks with glue, adjusting the disk positions while the glue was drying. Larger machines require screws to fix the disks to the bosses. I like to use three flat-head screws with a flexible washer between the disks and the bosses, so the pressure of the screws can be adjusted to make the disks run true. Ball bearings between the bosses and the axle are a good idea. I used some cardboard washers soaked with paraffin to adjust the spacing between the disks. It's important to select the plates for the disks with very uniform thickness, or they will vibrate when turning fast. If this happens, it's possible to glue small lead blocks to the edges of the disks, at the lighter sides. Not a perfect solution, but works.Mount in the same support two pulleys, larger than the boss pulleys, in an axle moved by a crank. This axle can pass a few cm below the disks, mounted on adequate bearings. For this small machine, I just made holes in the upright supports and inserted a layer of brass foil between the axle and the wood. In other machines I used brass, bronze, or Nylon for the bearings. Ball bearings are the best solution. Pass cords from these pulleys to the boss pulleys. Turning the crank shall make the disks turn in opposite directions at several turns per second. Cross one of the cords to make one of the disks turn in the opposite direction. I used rubber cords of the type used in tape recorders to connect the pulleys to the disks. Large "O" rings make good cords too, but that don't last much. Round leather cords are the classical material, but sewing machine cords are too thick for a machine of this size. An exellent material are polyurethane cords that can be joined by melting. When joining the cord that will be crossed, make two loops on it. In this way the cord ends with a half twist, and operates better. For the other cord, make just one loop.Make a set of aluminum sectors from thin aluminum foil. The sectors shall be perfectly flat stripes a few centimeters long, with one side larger that the other, and with rounded corners. A minimum width of about 1 cm is adequate. These sectors are to be glued to the plastic disks, at the external face. forming a symmetrical pattern around each disk. The number of sectors shall be even, so there are always two exactly opposite. More sectors is better than few, with the usual number being between 16 and 40 (I used 18). The output current of the machine is proportional to the area covered by the sectors. The maximum spark length that the machine can generate can be estimated as the sum of sector spacings along a third (for the neutralizers at 60 degrees) of a disk. A distance between sectors similar to their average width is adequate (they have the outer side larger than the inner side to keep this fixed distance along their length). Wider sectors result in more current, but in smaller sparks. The distance from the sectors to the disk bosses also limits the maximum voltage. Originally, I used kitchen aluminum foil for the sectors. To glue the sectors to the disks, I used common paper glue, soluble in alcohol, fixing tightly the strips to the disks, with help of a piece of cardboard, leaving no bubbles. The excess of glue I removed carefully after it dried with alcohol, leaving the disks perfectly clean. It is important to do not leave any sharp corner in these sectors. The thicker foil used in discardable food containers (a pizza pan is ideal) is a good material for sectors, and is more resistant to wear. In this case a stronger glue is required. A "contact" glue based in synthetic rubber is adequate, and results in a clean disk that can be used almost immediately. A very convenient possibility is to make sectors using adhesive aluminum tape, of the type sold as "metal repair tape". Look for a type that has a backing foil, that simplifies the operation of marking and cutting out the sectors. To make the sectors, make first a hard cardboard template, a bit smaller than the desired sectors, use it to mark the metal, running a pencil around it (hence the smaller size). Cut the sectors carefully with scissors. To apply the sectors with precision, it's enough to make pencil marks on the disks, or to draw a template that is kept under transparent disks.Adapt to the upright supports two solid wires having at the extremes very thin flexible metallic brushes (I used just one thin wire as brush) that touch the disk sectors at opposite sides of each disk, at adjustable 45-60 degrees angles with the horizontal and at crossed positions. These "neutralizer bars" shall short-circuit two opposite sectors when they pass under their brushes. Thin silver foil strips is the ideal material for the brushes. The thin nickel-chrome wire from a high-value wire-wound resistor can also be used, thin enough to not scratch the disks or the sectors. The brushes can be fixed to the neutralizer bars with a section of plastic wire insulation, can be inserted in holes at the ends of the bars, or some other form that allows simple replacement of broken brush wires. The neutralizer bars are fixed to metallic rings, fixed to the upright supports of the machine by screws through their centers at the outer sides of the upright supports, or better, directly in the same axle of the disks, at the inner sides of the supports. As the centers of the neutralizer bars are neutral, it is not important if they are electrically connected to the structure of the machine or insulated from it.The basic Wimshurst machine is now ready. In a dry day, with the disks very clean, turning the crank shall rapidly charge the disks to a very high voltage, what you can easily recognize by the noise of small sparks between the sectors, the ozone smell, the electric field pulling the hair of your hands, and the effort you must apply to the crank to keep the disks turning. In humid weather, a hair dryer can be used to dry the machine and make it work. Some carnauba wax in the disks helps to make them highly insulating and nonhygroscopic.To complete the machine, build the charge collectors. The disks become charged at opposite polarities at two quadrants, and at identical polarities at the two others. Adjust the position of the neutralizing bars to position the quadrants where both disks have identical polarities at the two sides of the machine. In the correct position, the disks pass first under a charge collector, and then under the closest neutralizer brush (easy to verify, as nothing will be collected if you arrange the neutralizing bars in the wrong position). The collectors can be two thick solid wires with U forms with sharp points directed at the disk sectors (not touching them, of course) fixed to them. The charge collectors are connected to a spark gap that is the machine output, and the assemblies are mounted in long insulator supports. The insulation of the charge collector and terminal assemblies is of fundamental importance. The insulators must be as long as possible and made of material with extremely high electrical resistivity, as acrylic plastic. Wood or similar materials act as total short circuits, and are not suitable for this purpose. The assemblies must also be kept away from any other part of the machine structure. I mounted the collectors and spark gap in a acrylic bar fixed to the machine support, with some screws to allow adjustments in the position of the collectors. Be careful to do not allow the collectors to touch the disks. This is the most common problem with these machines, and may cause extensive damage to the disks. It's recommended to make the collector points with flexible thin wire, so they can't scratch the disks. Do not leave any sharp point or corner in the assembly, with the exception of the charge collector points, or charge will be lost to the air. I made the spark gap and collector assembly with brass wires 3 mm thick, connected through aluminum balls. Screws cut at the end of bars with loops at the other end fix the spark gap bars at the chosen angle. The spark gap was made with two aluminum balls with 1 cm diameter, turned in a lathe. The diameter of the terminal balls shall be consistent with the size of the machine. Too small spheres result in weak short sparks and just corona if the terminals are separated beyond a certain distance. Too large spheres result in short, strong sparks and nothing if the balls are too separated, due to insufficient voltage. A good rule is that the diameter of the terminal spheres shall be of about 1/15 of the diameter of the disks.Frontview of the machine.Backview.The spark gaps produce a practically continuous faint spark, a few cm long in my machine, while the disks are turning. To get stronger sparks, I added two Leyden jar capacitors, one to each side of the spark gap. I made them using cylindric plastic boxes, with aluminum foil strips glued inside and outside, with a margin of a few cm to the opening of the box for insulation. To the outer side of each box I fixed a wire with a terminal, and passed another through the lid, making contact with steel wool inside the box, that makes contact with the inner foil. This wire is terminated in a closed loop, or a ball (no points), and has a form of a hook that can be used to hang the capacitor in the spark gap structure. One capacitor is used at each machine terminal, with the outer plates interconnected by a wire. This assembly results in intense sparks at each few turns of the disks. Note that the capacitors are in series, and a pulsed output is available over a load placed between them, at each spark. It is also possible to use just one Leyden jar, or to put them in parallel, what doubles or quadruples the energy ot each spark. But the voltage attained can be not so high because the losses are higher due to the smaller insulation. An improvement was to add small steel balls glued to the spark gap balls, separated by small plastic tube insulators. They generate more intense electric fields, and little sparks between the small balls and the main terminals trigger long sparks across the terminals. This works better with the positive terminal inclinated in the direction of the negative terminal. The maximum spark length increased from 2 cm to 5 cm.