Intro and Aternative Mirror Screw Construction Idea

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Intro and Aternative Mirror Screw Construction Idea

Postby cuteorkill » Mon Mar 05, 2012 4:06 pm

I just joined the forum but have been interested in mechanical television for a very long time. For now the Mindsets kit will do, but eventually I'd like to construct other sets.

Perhaps others here have employed this idea. If so, it has also occurred to me that a sufficient mirror screw might be constructed more easily and cheaply.

Adhesive mylar on the edges of black styrene strips in the proper helical arrangement should be almost as good as polished metal. It would also be much lighter allowing a smaller motor and a less substantial mount.
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Re: Intro and Aternative Mirror Screw Construction Idea

Postby Harry Dalek » Mon Mar 05, 2012 9:10 pm

cuteorkill wrote:I just joined the forum but have been interested in mechanical television for a very long time. For now the Mindsets kit will do, but eventually I'd like to construct other sets.

Perhaps others here have employed this idea. If so, it has also occurred to me that a sufficient mirror screw might be constructed more easily and cheaply.

Adhesive mylar on the edges of black styrene strips in the proper helical arrangement should be almost as good as polished metal. It would also be much lighter allowing a smaller motor and a less substantial mount.



I like your ideas might be best to test them out via a experiment see how well they reflect a dot of light ...laser pen is a good tool.

If you have tried any of them out do post a picture i have not tried that stuff out so would be interested to see .
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alternative update

Postby cuteorkill » Mon Feb 18, 2013 3:32 pm

I has been almost a year since I've read or posted in this forum (other hobbies have taken precedence - you know how that goes). A better idea occurred than the adhesive mylar. Maybe laser cut acrylic mirror strips adhered to matte black plastic pieces would work using a service such as Ponoko. The precision is very high, which means it would also be possible for each piece to have alignment holes as well as part numbers etched discretely on the top of each piece. Besides the central hub, a single pin could fit through the holes for effortless assembly. The maximum length of any piece would be 15 inches. The thinnest mirror strip would be .118 inches. This could make a 7 inch tall 60-line mirror screw possible.
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Re: alternative update

Postby Harry Dalek » Mon Feb 18, 2013 5:27 pm

cuteorkill wrote:I has been almost a year since I've read or posted in this forum (other hobbies have taken precedence - you know how that goes). A better idea occurred than the adhesive mylar. Maybe laser cut acrylic mirror strips adhered to matte black plastic pieces would work using a service such as Ponoko. The precision is very high, which means it would also be possible for each piece to have alignment holes as well as part numbers etched discretely on the top of each piece. Besides the central hub, a single pin could fit through the holes for effortless assembly. The maximum length of any piece would be 15 inches. The thinnest mirror strip would be .118 inches. This could make a 7 inch tall 60-line mirror screw possible.


They would be pretty thin to work with.
When i made a staggered mirror drum its in away a cross between a mirror drum and mirror screw where as a mirror screw the mirrors are staggered on the thin mirror side on mine are staggered on the large flat and i found no need for a thin strip of mirrors just stagger the mirrors and you sort of get the same effect no need for a strip of light either just point a clear luxeon at it .

https://www.youtube.com/watch?v=2qPE9JeCg14

But your idea is what it is just saying theres lots of ways to do the same thing in NBTV i find it amazing there are so many ways to make a mechanical television some better some worse all have their good and bad points but really WOW.

It would be an interesting build i hope you go ahead with it i for one am interested.
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Postby Panrock » Mon Feb 18, 2013 5:41 pm

Hi! I'd be interested to learn more about this, including a diagram if possible. Can plastic be precisely laser cut without untoward molten edge effects? In particular, I'm curious how the 'single pin' indexing would work. Indexing really needs to be carried out near the circumference for sufficient precision and to minimise the effect of any 'slop'. I used + 50 micron clearance in my system.

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Postby cuteorkill » Tue Feb 19, 2013 11:15 am

Good point about the radius along which the alignment holes lie - single pin through all of them would be too small. The resolution and precision of the laser-cut acrylic is very fine but I do not know the exact limitations. The thicker the material, the greater the deviation from perpendicular the laser is from the cut, but .118 inch thick material should present no problem.

Two holes in each strip would be better. There would be no need to mount pins or other hardware in the holes. Instead, a pin could fit in place temporarily while two strips are adhered together. Alternately, the holes could be omitted entirely. A laser-cut alignment tool could be used to clamp the strips in place while the adhesive cures.

Also, laser-cut pieces could be an easy route to effortless angles in a mirror drum assembly. Fortunately the plastic pieces themselves are fairly cheap so it's a low expense to experiment.

<img src="http://doctorwhoscarf.com/drwho/mirrorscrew.jpg">
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Postby Panrock » Tue Feb 19, 2013 8:29 pm

From your figures you are assuming horizontal scanning and 4:3 aspect ratio... exactly as did I. The 0.118 inch thickness is as near as dammit 3mm... again the exact thickness of slat I have used with my 60-line rig. So you''ll end up with a display of the same size, but not weighing 40-50 lbs ! :lol: My slats are actually a bit wider than 4:3, to give a less critical viewing position at the correct aspect ratio.

I would put your indexing holes even further out and have a pair of them either side for more balanced locking. Any positional errors then may balance out too. In my case, I used sets-of-three holes. This permitted me to choose between 60 and 120 lines. In 60 line mode, the 1.5mm stainless steel slats were arranged in pairs to obtain the 3mm slat thickness.

I think your idea sounds promising. Another way to lighten a mirror screw was proposed by Karen Orton, who suggested using 'rods' instead of slats; ie. basically the reflecting surfaces on their own.

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