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Wimshurst Machine?

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Adam Munich

Thu Mar 31 2011, 09:30PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I was thinking of summer projects today and I remembered that I took apart a projection TV last month. Unlike most other TVs this one had a 4.5mm thick piece of acrylic (lexan maybe?) on the front.

So.. a wimshurst machine came to mind as the plastic is big enough for two 24 inch disks. How would one go about cutting such a disk out of this plastic though?

James

Thu Mar 31 2011, 10:48PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

If there's a plastics shop in your area, they can cut it on a CNC laser table. I've had parts made at TAP Plastics near me and it was pretty reasonable. Actually even the material is dirt cheap to buy.

To cut it yourself at home a jigsaw with a fine tooth blade can be used, but you might try to cobble together a hot wire cutter. Rough cut a square by scoring with a razor and snapping it off, then drill a hole in the center and screw it to something as a pivot so you can rotate it past the hot wire and get a nice clean circle. They make special drill bits to drill plastic without grabbing and cracking it, but you can file an old bit to do the same thing.

Antonio

Fri Apr 01 2011, 12:46AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Acrylic doesn't melt easily. A hot wire will probably not work. My preferred method to cut these disks is:
Mark the disks in the sheet.
Cut them out with a series of cuts with a small circular saw attached to a Dremel tool.
Drill the center with the same diameter of the axle to be used.
Fix the axle to a hole in a wood board so the disk can rotate on it. Put something between the disk and the board to avoid scratches. Fix the board to a table with a clamp.
Mount a grinding tool, as a Dremel with a cylindric cutting tool, in a vertical support so it touches the border of the disk.
Turn the disk slowly -against- the rotating tool, gradually changing the distance between the pin and the tool after each turn of the disk until all the border is uniform.
Never let the plastic get hot, or it will deform.

Nah

Fri Apr 01 2011, 07:34PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

I have some ready Wimshurst disks if you want them.

Paul

Adam Munich

Fri Apr 01 2011, 07:49PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I had a novel idea. Large sheets of copper clad are rather cheap, couldn't one make wimshurst wheels out of those the same way one makes PCBs? Just create a sector design on the computer, print it out and iron it on the board, then etch.

Nah

Fri Apr 01 2011, 09:29PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

I highly think that the high voltage will easily be able to arc through even the slighest imperfection in the trace. Also, I don't know how rugged those traces would be, there are some rather high currents in a Wimshurst Machine.

James

Fri Apr 01 2011, 09:41PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Nah wrote ...

I highly think that the high voltage will easily be able to arc through even the slighest imperfection in the trace. Also, I don't know how rugged those traces would be, there are some rather high currents in a Wimshurst Machine.

Whimshurst machines are electrostatic, the output is inherently very low current. The high current discharges come from the Leyden jars frequently connected to them. The machine itself is rather low tech and has been around for well over 100 years. I'm betting it won't be too hard to build one.

Antonio

Sat Apr 02 2011, 12:14AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

A Wimshurst machine made of fiberglass PC board would work. Cheaper PC board materials may be too conductive. Copper sectors may get easily stained. The currents in the disks are really very low, in the microampere range.
One of my best Wimshurst machines:

Adam Munich

Sat Apr 02 2011, 03:06AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Well I have some 12" by 9" copper clad, and I have some 3" by 4" copper clad. I'd like to make a small machine with 3" disks as proof of concept, and before I fire up autodesk do you have any tips on sector design? Number of sectors, shape of sectors etc.

As for copper getting stained, all you need is a quick wipe with HCL to clean it up. I could also try and get some liquid tin too.

Adam Munich

Sat Apr 02 2011, 11:50PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

No tips then?

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