Starting at the beginning with Mirror Screws

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Re: Starting at the beginning with Mirror Screws

Postby albertMunich » Wed Aug 09, 2017 8:27 pm

I have started a new topic "Introducing front Projection" - thinking out loud about retro-reflective materials.Why does the light have to pass thru a Nipkow disk or drum scanner? Somewhere in my head I see the retro reflective process and some new or different kind of scanner based on it. I do not think this idea would be relevant on the mirror screw because the lamp has to be off-axis if I understood it - I still don't get it completely :evil:
How are things going? Can electro plating be done at home or is this too toxic or complex and would have to be farmed out? What would an electrically conductive coating be?
Harry as I said applying reflective strips of material might not be possible given the requirements for flatness and precision....the glue alone would probably throw things off.
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Re: Starting at the beginning with Mirror Screws

Postby albertMunich » Wed Aug 16, 2017 3:10 am

Hi,
I'd like to know if any of you have 3d printed a full mirror screw by now? How's it going?

Today I found this thing sitting in the beautiful French countryside...a king-size mirror screw? Mass viewing 30 s style?

windmill.jpg
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Not a large scale TV set but probably a misfired attempt to create a windmill----I never saw it make a single turn....though we had some strong winds today....
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Re: Starting at the beginning with Mirror Screws

Postby Panrock » Wed Aug 16, 2017 7:22 am

And runs from solar power too, I see.... :lol:

More seriously, whether my mirror screw would try to ascend - or descend - was a serious concern at the start of its development.

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Re: Starting at the beginning with Mirror Screws

Postby Robonz » Thu Sep 28, 2017 10:11 pm

In my opinion 3D printing is never going to have a mirror finish even with an acetone treatment. The coating method that is used to give a mirror finish on plastic parts is called vacuum metalisation but the surface needs to be dead flat before you start.

Being the optimist I think you could adhere some very thin acrylic mirror to the 3D printed parts. Andrew, if you give me the dimensions I will cut and send you 40 mirror strips that are 1mm thick rear surface mirrors so you can have a play. They have an adhesive backing too. Free of charge of course! Let me know if you want them.

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Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Fri Sep 29, 2017 1:16 am

Robonz wrote:In my opinion 3D printing is never going to have a mirror finish even with an acetone treatment. The coating method that is used to give a mirror finish on plastic parts is called vacuum metalisation but the surface needs to be dead flat before you start.

Being the optimist I think you could adhere some very thin acrylic mirror to the 3D printed parts. Andrew, if you give me the dimensions I will cut and send you 40 mirror strips that are 1mm thick rear surface mirrors so you can have a play. They have an adhesive backing too. Free of charge of course! Let me know if you want them.

Cheers
Keith


Hi Keith

I didn't ever intend/expect to coat a print and expect it to be a decent mirror-screw. The basic approach was to print the frame to get the dimensions right, and then apply mirrors. Thanks for the offfer - but I'm not actually making a mirror screw. I was just interested in the 3D printing side of things with regard to building a mirror-screw out of printed sub-components. So - not much use for the mirror strips you offer, at least at this stage - but thanks anyway :)

I might hit you up for a complete laser-cut televisor frame like your beautiful baby sometime, though! Quite jealous of how nice it is compared to mine. Perhaps you could let me know how much materials and postage might cost, if you're prepared to do it.

Cheers
A
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Re: Starting at the beginning with Mirror Screws

Postby Robonz » Fri Sep 29, 2017 11:06 am

Sure Andrew, glad to cut you up a set. I still need to finish the final design and adorn it. But yes, anything you want!
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Re: Starting at the beginning with Mirror Screws

Postby Harry Dalek » Mon Oct 02, 2017 8:37 pm

Just posting this up as i have never seen a mirror screw have a reflector used with it . :shock:
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Starting at the beginning with Mirror Screws

Postby ppppenguin » Tue Oct 03, 2017 1:14 am

albertMunich wrote:Not a large scale TV set but probably a misfired attempt to create a windmill----I never saw it make a single turn....though we had some strong winds today....


Rather off topic but vertical axis mills have never been a serious contender for power generation. They have obvious advantages of the generator being at ground level and not needing to be steered into the wind. Apparently the problems of the bottom bearing (which is under both thrust and sideways load) have never been resolved.

Steve (Panrock)'s mirror screw is a magnificent bit of engineering. i hope to see it one day. Why didn't mirror screws catch on for TV? Probably too much high precision engineering when compared to CRT based solutions which were improving all the time and more amenable to mass production.
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Re: Starting at the beginning with Mirror Screws

Postby Panrock » Tue Oct 03, 2017 10:14 am

Harry Dalek wrote:Just posting this up as i have never seen a mirror screw have a reflector used with it . :shock:

Thanks Harry. Now this is really weird, because one aims for a really unreflective dark environment around the screw to maximise contrast!

The .pdf made me chuckle when it talks about the danger of nitrobenzene exploding! (In an earlier project) I was worried about this when I gingerly first applied the full 1000 volts across the narrow gaps in my own Kerr cell and hid at the other end of the room. If it had exploded, at least I would have ended up smelling sweet... even if dead. I understand nitrobenzene was used in some perfumes in the 1930s! :mrgreen: Anyway, my Kerr cell was a disappointment. It never worked. Maybe it required even more volts?

ppppenguin wrote: Why didn't mirror screws catch on for TV? Probably too much high precision engineering when compared to CRT based solutions which were improving all the time and more amenable to mass production.

Also the little matter of the picture aspect ratio changing with viewing distance, with multiple pictures appearing side by side as you move in closer, wouldn't have made them very practical.

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Re: Starting at the beginning with Mirror Screws

Postby Harry Dalek » Tue Oct 03, 2017 5:22 pm

Hi Steve thinking about the reflector on the mirror screw only thing i can think of for the reason its there is perhaps a wider view angle ?
The light to the screw would be reflected to the sides as well so may give you side viewing as well , just speculating.

Yes only the Brave try and make a kerr cell so you are Brave ! I used to work at BHP and operated a plant that made benzene i don't know the difference to nitrobenzene but Benzene was bad enough ! one fellow at our plant had the bright idea to put it in he's car the result was he couldn't turn the car off ! :lol:

I like the ultra sonic cell idea and Faraday effect but this below is a new one to me ....i was thinking perhaps its an early liquid crystal diode but doesn't sound like it .
THE KAROLUS CELL is similar to the Kerr cell different liquid but.

ON the Kerr cell i am pretty sure needs the prisms either side of the cell and adjusted it looks similar to the Faraday effect device it used magnetic field this uses electrostatic charge to do the same thing but in that nasty liquid ,so your cell might of been working all along.
You can use the polarized sun or 3d glasses for the effect needed either side of the cell ...putting one in front of the other and turning them a touch you can see the effect of blocking and unblocking the light i have tried that in manual control ....the cell must do that turning of the light rays angle when its modulated............. with out the prisms or polarized glass you would see no difference to the light but with those either side and adjusted at an angle to each other and you applied voltage it should go dark or visa versa depending of the adjustments to the polarized glass angles.
http://www.tvhistory.tv/1935%20TV%20Tod ... rt%202.htm
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Re: Starting at the beginning with Mirror Screws

Postby Panrock » Wed Oct 04, 2017 1:45 am

Wow, some fascinating attachments there! Yes, I did lay on polarised light for my Kerr cell, with crossed polarising films on each side.

Another method of light modulation to try, Harry, might be the 'speaker' method. Use a small 3-inch speaker say, and glue on a cardboard strip sitting at right angles to the cone and bottom edge cut to mate with it. At the top edge there is a small V-shaped notch. This is set against a stationary edge (another piece of card) and bright DC light shone through the resulting tiny triangular hole. The moving speaker cone then modulates the light.

The higher the modulating frequency, the less the excursion of the cone that carries the same power. But to compensate, the less the excursion (if things are set properly) - the closer the hole is to the point of the 'V', so the more the modulating effect.

One problem I can see with this is that on bright scenes the pIcture definition would be worse. The picture gamma would be determined by the angle of the 'V'. In addition you could experiment by replacing the flat edge of the stationary card with a curve or even another 'V'. Or use two facing speakers and moving, meeting, V's to double the effect.

Just a half baked idea I've never got round to trying. Maybe you have?

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Re: Starting at the beginning with Mirror Screws

Postby Harry Dalek » Wed Oct 04, 2017 5:26 pm

Panrock wrote:Wow, some fascinating attachments there! Yes, I did lay on polarised light for my Kerr cell, with crossed polarising films on each side.


I did hope you missed the polarizing side of it but if you did try that i am not sure ,do you still have the build some where to show it could just be the plates to far apart or a problem with the liquid you used ....I noticed on the net there is a kit that uses a modern Kerr cell to show the effect adjusting the light of a laser .
http://www.indosawedu.com/kerr-effect.php

What a good how to do video ...yes more voltage you were right ! 10 to 30 kv we need a EHT circuit to modulate it pretty easy just a 555 timer running at 20 to 40 khz and modulate to pin 5 pin 3 to a power trany and a EHT coil ,,,if it were smaller version of this perhaps less voltage

youtu.be/ppDTs-dr_8w

youtu.be/8czz7FdFUNk

youtu.be/6Nc0lMsxEp8
very interesting other idea

youtu.be/XhU-nNiAgtI

There have been a bit of talk over the years on making a kerr cell and others it must be a hard nut to crack ....the early work on the Kerr sounds like they had problems as well see below .

Well finding the videos its very nice to see how these work The faraday one with the oil is safer ,perhaps with a larger coil voltage tests better Polarizing lens darker oil ? might work better .
The Kerr Cell is a bit of a worry as far as the liquid we were always told never spark any thing near Benzene ,the vapor and air mix would be alike a bomb ,in the past post PDF there were some alternative chemicals but none look as good as nitrobenzene ..never heard of a kerr cell exploding but makes you wonder .

Another method of light modulation to try, Harry, might be the 'speaker' method. Use a small 3-inch speaker say, and glue on a cardboard strip sitting at right angles to the cone and bottom edge cut to mate with it. At the top edge there is a small V-shaped notch. This is set against a stationary edge (another piece of card) and bright DC light shone through the resulting tiny triangular hole. The moving speaker cone then modulates the light.


Funny enough i was reading like the stuff i posted on methods of modulating light... they were not keen on the mechanical method saying it could not modulate the light fast enough ,in one of the old news letters there is a mirror drum modulated by an idea you just mentioned ..work best it would need a wide bandwidth .
So i agree it would work to some degree at least .

The higher the modulating frequency, the less the excursion of the cone that carries the same power. But to compensate, the less the excursion (if things are set properly) - the closer the hole is to the point of the 'V', so the more the modulating effect.


Perhaps Tweeters and transducers might work as well as with all mechanical ways higher the frequency the movement is tiny .

I was tossing up the idea once of using a liquid crystal diode but the amount of light it would have to block would be to much be unable to block the light enough .

One problem I can see with this is that on bright scenes the pIcture definition would be worse. The picture gamma would be determined by the angle of the 'V'. In addition you could experiment by replacing the flat edge of the stationary card with a curve or even another 'V'. Or use two facing speakers and moving, meeting, V's to double the effect.

Just a half baked idea I've never got round to trying. Maybe you have?

Steve O


Its an interesting idea to use mechanical modulation not a bad idea at all ,i have not tried it for modulation but scanning i have bit like the ideas below ,had no problem on the framing side of it but line scan not so good ,you sort of need a lot of light and distance to increase line size ...its a much better idea for a small mechanical camera size of the image does not matter that much for a camera .
Playing around with the PMT tube at the moment i didn't think it would be possible to use these with say a lens disk or mirror drum camera due to the increase in the amount of light but i know now all you have to do is reduce the operating voltage 200 to 400 volts no wonder the old television analysers worked with case open and PMT still operating with nature room lighting no damage.
It makes me wonder if you pointed a PMT at your mirror screw could you make a mirror screw camera ? would you need a slit mask as the reverse for a monitor ..the PMT would have to be run low but i think it could be done ....have not come across a mirror screw camera reading but you could have a first Steve .
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Re: Starting at the beginning with Mirror Screws

Postby Panrock » Thu Oct 05, 2017 12:17 am

Harry Dalek wrote:It makes me wonder if you pointed a PMT at your mirror screw could you make a mirror screw camera ? would you need a slit mask as the reverse for a monitor ..the PMT would have to be run low but i think it could be done ....have not come across a mirror screw camera reading but you could have a first Steve .

I don't think this would work with a bare mirror screw. Remember, when viewing, it doesn't create any real image (that could be reversed in principle by a camera) at all.... instead, just a series of virtual images depending on where the viewer stands.

However, if you modified a mirror screw to give a projected image on a screen, using a lens say, then I guess you could use it in reverse as a camera.

My opinions could be wrong. I may have made a mirror screw but I still don't really understand the optics in sufficient depth! Karen is much better in this regard.

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Re: Starting at the beginning with Mirror Screws

Postby McGee2021 » Thu Oct 05, 2017 1:19 pm

I seem to be getting the feeling that you want to make a kerr cell, but, then again, i did just have to skim over the last few post very quickly! Anyway, i found a list of extremely dangerous and pretty safe chemicals that have a high kerr constant. Might i suggest Anethole, a sweetener?

https://www.nist.gov/sites/default/file ... crd435.pdf
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Re: Starting at the beginning with Mirror Screws

Postby Robonz » Thu Oct 05, 2017 4:07 pm

I think you could make a good representation of a Kerr cell using some polarisers out of an old LCD monitor and a liquid crystal cell to go in-between the polarisers I guess the catch would be finding a simple 1 cell lcd, or you could hack a small LCD and just turn on all the pixels at once.

This video will have a lot of interesting hints

https://www.youtube.com/watch?v=_zoeeR3geTA

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