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Old 4th Jul 2022, 8:34 am   #21
McMurdo
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Default Re: Wimshurst machines.

A wimshurst machine was restored on 'The Repair Shop' a while back.

There are a few photos of early xray machines using wimshurst-style generators but they had to be the size of a wardrobe to get any useful effect.
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Old 4th Jul 2022, 8:34 am   #22
Malcolm G6ANZ
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Default Re: Wimshurst machines.

These very high voltages can be used to create 'litchenburg' figures. http://www.capturedlightning.com/fra...htenbergs.html
As seen in my avatar.

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Old 4th Jul 2022, 12:46 pm   #23
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Default Re: Wimshurst machines.

I missed that one! Unless I can find it on iPlayer, I'll wait for it to come round a second or third time.
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Old 4th Jul 2022, 1:09 pm   #24
Graham G3ZVT
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Default Re: Wimshurst machines.

As schoolboys, a friend and I made a Wimshurst machine using counter-rotating 12 inch 78 RPM records.

Recently, someone mentioned that it couldn't have worked because shellac records were loaded with carbon.
I can attest it did work! I think the reason was we prepared the surface before applying the tinfoil segments, I remember having to obtain a tin of dope thinners, but I can't remember much else, except that we made a condenser from scratch with alternate layers of tinfoil and paper shapes meticulously cut out with scissors.

We must have followed an article in a book or magazine.
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Old 4th Jul 2022, 1:48 pm   #25
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Default Re: Wimshurst machines.

In the late 1970's there was an article in the French popular science magazine "Science et Vie" showing you how to make a Wimshurst machine using two vinyl LPs. (We used to get some foreign language journals circulated at work .)

In one of the 1904 Model Engineer articles, one contributor had made his capacitors from beer bottles filled with lead shot and with tinfoil wrapped around the outside

Last edited by emeritus; 4th Jul 2022 at 1:53 pm. Reason: typos, diy capacitor note added
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Old 4th Jul 2022, 2:26 pm   #26
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Default Re: Wimshurst machines.

Quote:
Originally Posted by Dave Moll View Post
If you're referring to my machine, it also needs a repair or replacement of the front drive belt.
(Urethane round-section belting is available on ebay in various thickness - it joins by sliding the free ends off the two sides of a red-hot knife held in a vice, and pushing them together for 10 secs or so. I've had some success with it, though it is a little 'stretchy').
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Old 4th Jul 2022, 4:28 pm   #27
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Default Re: Wimshurst machines.

Thanks, Mark, for the tip about replacement belting. I shall check that out. Getting the discs spinning correctly will make a good start, then it's a matter of fettling the discs and brushes.

Quote:
Originally Posted by McMurdo View Post
A wimshurst machine was restored on 'The Repair Shop' a while back.
I've found it: Series 8, episode 14.

It wasn't just a Wimshurst machine, but apparently built by James Wimshurst himself and brought in by his great great grandson - and what a machine, with twelve discs rather than the usual two.
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Old 4th Jul 2022, 4:59 pm   #28
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Default Re: Wimshurst machines.

At our school in the late 60's our physics teacher, known as Bumble, was demonstrating the Wimshurst machine by charging himself up, while standing on an acrylic sheet. The idea being, if you were insulated from earth and no current flowed you wouldn't feel a shock. A chap called Dumelow came in late (habitual), and Bumble threw his keys, on a long chain, to him 'Dumelow, get us some paper from the stationary cupboard'. Dumelow caught them and had quite a shock! The teacher was expecting it. A good demonstration, and to avoid H&S remonstrations I must say should not be attempted today.
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Old 5th Jul 2022, 9:10 am   #29
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Default Re: Wimshurst machines.

Quote:
Originally Posted by rambo1152 View Post
As schoolboys, a friend and I made a Wimshurst machine using counter-rotating 12 inch 78 RPM records.

Recently, someone mentioned that it couldn't have worked because shellac records were loaded with carbon.
I can attest it did work! I think the reason was we prepared the surface before applying the tinfoil segments, I remember having to obtain a tin of dope thinners, but I can't remember much else, except that we made a condenser from scratch with alternate layers of tinfoil and paper shapes meticulously cut out with scissors.

We must have followed an article in a book or magazine.
My first attempt at a wimshuurst machine used 12" 78 rpm records and I could never get it to work. ( 12" vinyl LP would have, but in 1954 were very expensive )
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Old 5th Jul 2022, 11:09 am   #30
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Default Re: Wimshurst machines.

I got some urethane belting from RS a few years ago. I melt the ends by pressing againt the barrel of my Henley Solon soldering iron and quickly press the joint into a Vee block to ensure alignment. Trimming with a sharp scalpel blade is usually required to get a smooth join. Also good for large O ring gaskets.
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Old 5th Jul 2022, 9:12 pm   #31
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Default Re: Wimshurst machines.

Quote:
Originally Posted by Dave Moll View Post
For comparison, here is a Wimshurst machine (unfortunately non-functional) I bought at RetroTech in May.
I've got one the same as the one you've got there, other than mine is obviously older and has a metal framework mounted on a wooden base. They still work quite well with one or two of the segments missing and are great fun to play around with. Mine has one original leather belt and one made of a length of 'old school' elastic, stretched around the pulleys and tied in a knot. It's in storage at the moment, but I think it may be time to dig it out again for a bit of 'sparking' amusement. Yours looks like it's got 'made-up' Leyden jars - perhaps the original ones got removed for 'safety'. I've got a big bank of Leyden jars with mine and going back a few decades we were messing about trying to charge the extra Leyden jars. I wasn't turning the handle, but the person that was got the shock of his life when a spark jumped around the insulated winding handle from the metal crank part to his hand. That put us off trying to do that stunt again and we never worked out quite why it happened, but it seems we managed to 'unbalance' it somehow, so best to only connect the jars in parallel with the ones that are already fitted if you're going to try giving it more capacity. Obviously, paralleling large Leyden jars can be very dangerous anyway...so don't do it at home folks!
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Old 7th Jul 2022, 6:26 pm   #32
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Default Re: Wimshurst machines.

I think a practical use of these devices was for spray painting and powder coating.

I remember a guy in the year above me at school making a few variations.
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Old 7th Jul 2022, 6:52 pm   #33
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Default Re: Wimshurst machines.

Knowing how hot it's going to get in the next few days I decided to go up into the loft late last night, where it's been in storage for the last few years and brought it down. I'd had it wrapped in a bin liner to protect it from the worst of the loft dust and today I unwrapped it to see how it had survived the sharp temperature changes of that environment. It wasn't quite as I'd remembered as in the knotted elastic belt that had worked for so many years must have eventually failed and I'd replaced it with a knotted string version at some time in the recent past.

I've just been playing with it and it immediately worked with some large sparks being produced, but that was very short lived when the remaining original leather belt finally failed. So out came the string again to replace that belt, then the other string belt was slipping to the extent that it wasn't turning its disc, so that had to be re-tensioned, and it also lost yet another segment from the inside disc.

After all that it now works pretty well with some large sparks jumping between the 'balls', despite now having eight missing segments from the inside disc/rotor, with at least a couple more looking ready to let go. I'll have to look into cutting some out of foil and sticking them on, also I think I may have some of the old type knicker elastic that made a good replacement belt originally - that's if it hasn't gone rotten by now after being stored in the back of a drawer for decades.

So all in all a success. String works quite well for belt replacement if it's strung 'reasonably' tight, although not too tight, obviously it's not going to last long term without a bit of re-tensioning every now and again.
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Old 7th Jul 2022, 9:22 pm   #34
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Default Re: Wimshurst machines.

Having had mixed results with the rather stretchy urethane stuff as I mentioned upthread (though in this low-torque context I think it would work well) - I note that 'leather belting sewing machine' is a search string which brings up a lot of reasonably-priced hits on ebay. I might give this a go and compare with the plastic stuff.
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Old 7th Jul 2022, 10:51 pm   #35
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Default Re: Wimshurst machines.

Well I've learned something. I always thought it was a Windhurst machine

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Old 8th Jul 2022, 5:17 pm   #36
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Default Re: Wimshurst machines.

Home made lightening!

A room full of the smell of ozone!

The gap was just under 2 inches. It's capable of wider, but needs more time to build up a charge and the time between the sparks was too long to try to capture it in a photo. It'll probably be a lot more efficient if I replace those missing segments. I'll need to think about what I'm going to glue them on with that's not going to attack the plastic surface of the discs - whatever that is, probably some sort of Perspex. I believe the machine probably dates from 1959/60.

I did try to conjure up Frankenstein's monster last night, but I was unsuccessful. Perhaps once I get those segments replaced, some non-slipping belts fitted and a few more Leyden jars hooked up, the 'monster' may finally appear
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Old 8th Jul 2022, 6:46 pm   #37
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Default Re: Wimshurst machines.

Brilliant - even without any recapping!

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Old 8th Jul 2022, 7:02 pm   #38
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Default Re: Wimshurst machines.

We had Wimshurst machine at school in a case in the physics lab. We never saw it in action although we did have a demo of the Van de Graaf generator. The radio club had a preview of it in one of the prep rooms where we were impressed by the spark. The technician then said watch this and connected a Leyden jar across the spark gap and moved the spark gap balls about a foot apart. We were told to stand back and he turned the handle for ages then an almighty big spark jumped the gap. Very impressive.

We were also told the best way to draw a spark. Don't use the tip of your finger to draw the spark, use one of the joints in your finger as there are fewer nerves there and you don't feel the shock as much!

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Old 9th Jul 2022, 10:05 am   #39
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Default Re: Wimshurst machines.

In the 1970s, as a teenager, I had a summer job with Phillip Harris Limited, who made school science apparatus. I worked in their light engineering factory, which was huge fun, also I got to play with some of the kit in their demonstration labs.

I made parts for Van De Graaf generators, but was told they had stopped making Wimshurst machines because they were capable of delivering too much current and thus considered too dangerous for 'modern' school physics labs.

The Chicago Museum of Science and Industry used to display the remains of a really large (but broken) Wimshurst machine, I think, with four discs of about four foot diameter. I believe it came from a university medical research centre (but it's a few decades since I visited, so I may have mis-remembered). The museum's catalogue doesn't seem to be on-line, and its web site is frustrating, so I can't find a reference.

I think I found a picture though:
https://avoision.com/portnoy/images/.../MSIday_12.jpg
The dark brown hub on the main shaft closest to the camera was part of the assembly for the second pair of discs - when I saw it there was still broken glass round that part!

The Science Museum in London has Wimshurst's original machine. There is a note on the Wikipedia page that the early machines were connected to Leyden jars to improve the voltage stability, and used for x-ray experimentation.

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Old 9th Jul 2022, 5:25 pm   #40
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Default Re: Wimshurst machines.

I must have been misinformed in the 1970s -- PH still sell them, apparently, complete with Leyden jars
https://www.philipharris.co.uk/produ...chine/b8a48215
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