Starting at the beginning with Mirror Screws

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Re: Starting at the beginning with Mirror Screws

Postby Harry Dalek » Sun Aug 06, 2017 11:52 pm

These things don't have to be big they made them small as this 1930's French mirror screw these days as speaking 3d printers nice size to print the slats .
viewtopic.php?f=1&t=1380&p=11101&hilit=small+mirror+screw#p11101
Apart from the problem of using different materials there are other ways of doing it i suppose such as Karen i think i recall used wire in a transparent drum can't recall if it was a mirror screw but if not could be Great idea .
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 McGee2021 » Mon Aug 07, 2017 6:58 am

Andrew, if you could supply me with some .stl models for a mirror screw, Baird standard, i will start printing them ASAP. My print bed is about 10 x 9 inches. I was looking into chrome plating, and came up with a theoretical process on how you could chrome plate 3d parts. First, you would have to print the part of course, and assemble it. Sandblast it with extremely fine powder to get rid of the ridges on the print, and coat the whole thing in conductive paint. After that, electroplate it with copper, then nickel, and finally, electroplate it with chrome. Of course, i have not tried this yet, and it will be a while before i get my sand blaster up and running again. I have not used for five years now. I believe its from the correct period, the 30's!
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Re: Starting at the beginning with Mirror Screws

Postby Klaas Robers » Mon Aug 07, 2017 7:11 am

And then keep in mind that the final result should be that the front surface of the slats should have the optical flatness of a mirror, all over its length, not ony small parts. Steve can tell you more about this. After the scew is assembled, or even worse, manufactured as a whole, you have no chance any more to correct the optical flatness.
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Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Mon Aug 07, 2017 10:47 am

McGee2021 wrote:Andrew, if you could supply me with some .stl models for a mirror screw, Baird standard, i will start printing them ASAP. My print bed is about 10 x 9 inches. I was looking into chrome plating, and came up with a theoretical process on how you could chrome plate 3d parts. First, you would have to print the part of course, and assemble it. Sandblast it with extremely fine powder to get rid of the ridges on the print, and coat the whole thing in conductive paint. After that, electroplate it with copper, then nickel, and finally, electroplate it with chrome. Of course, i have not tried this yet, and it will be a while before i get my sand blaster up and running again. I have not used for five years now. I believe its from the correct period, the 30's!


Will do. Let me get the spacers designed too, just in case.
Wouldn't another way of flattening be to just put the whole block on a hot surface and melt it flat? PLA melts around 190C and ABS around 220C
With ABS you could use a solvent like acetone instead of heat.
To prevent parts adhering you could put (say) strips of paper between. Just some ideas!
There are a few online notes about plating plastic. Vapour deposition is another way.
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Re: Starting at the beginning with Mirror Screws

Postby McGee2021 » Mon Aug 07, 2017 11:44 am

Andrew Davie wrote:Will do. Let me get the spacers designed too, just in case.
Wouldn't another way of flattening be to just put the whole block on a hot surface and melt it flat? PLA melts around 190C and ABS around 220C
With ABS you could use a solvent like acetone instead of heat.
To prevent parts adhering you could put (say) strips of paper between. Just some ideas!
There are a few online notes about plating plastic. Vapour deposition is another way.


I have a couple of ways of doing it, they all involve my heated print bed. Either A: Print the parts on their sides, and get the nozzle close enough to the bed, so they will be as smooth as the glass, or B: print them correctly, and since PLA's glassing temp is in the 60 - 70 degree range, press them onto the bed for a bit. I think 190C would be total over-kill in my experience.
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Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Mon Aug 07, 2017 2:37 pm

McGee2021 wrote:Andrew, if you could supply me with some .stl models for a mirror screw, Baird standard, i will start printing them ASAP. My print bed is about 10 x 9 inches


Here (attached, slat9_9mm.stl and slat9_10mm.stl) are single slat STL files. One has a 9mm radius internal shaft hole, the other 10mm - so you can choose which to use. The design is such that a slat can be assembled 'flat' for polishing, and in a spiral for display. So there are two sets of holes/indents. Both of these slats are setup as 9" wide, Baird format (30 lines, 7:3 vertical format). Of course you just choose one of them and print 30 copies. I haven't had a chance to complete a print print/test here, but hopefully they're OK.

Screen Shot 2017-08-07 at 1.32.37 PM.png


Screen Shot 2017-08-07 at 1.31.52 PM.png


Screen Shot 2017-08-07 at 1.31.21 PM.png
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Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Mon Aug 07, 2017 3:02 pm

Whoops - I think this is wrong. Baird format is 7:3 vertical with 30 vertical scanlines. This model is 7:3 with 30 HORIZONTAL scalines.
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Re: Starting at the beginning with Mirror Screws

Postby Panrock » Mon Aug 07, 2017 3:04 pm

To illustrate what I mentioned earlier, here is the slat indexing arrangement I used. Note how the pins and holes are on the outside perimeter of the slats. This minimises the angular error caused by positioning tolerances of the pins and holes.

Steve O
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Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Mon Aug 07, 2017 3:06 pm

Here's a horizontal-format Baird standard slat. Hopefully! 7:3 ratio, 30 scanlines, 10mm shaft hole. 9" wide.

Screen Shot 2017-08-07 at 2.03.42 PM.png
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Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Mon Aug 07, 2017 3:23 pm

Here's my first prototype print of three slats...

IMG_20170807_141431.jpg


IMG_20170807_141925.jpg


They fit together but the pin/hole is really tight, and I should change the design to allow the pin to be a tad smaller than the hole, to cater for this. Will do. When I put it together I snapped off one pin on the lowest slat, but just before I did that I checked the edge alignment to see if the outer edges came together at a point on both sides of the "circle", which they did. I was very pleased with the rotational alignment shown in this simple test-assembly. I think it might be feasible to do a whole unit with this design (with the suggested modifications). The picture shows a bit of a visible gap between outer edges of slats - this is because the slats aren't exactly together - the pin issue making them slightly vertically displaced. Will fix.
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Re: Starting at the beginning with Mirror Screws

Postby Andrew Davie » Mon Aug 07, 2017 3:29 pm

Panrock wrote:To illustrate what I mentioned earlier, here is the slat indexing arrangement I used. Note how the pins and holes are on the outside perimeter of the slats. This minimises the angular error caused by positioning tolerances of the pins and holes.


Thanks - good design! I'll adopt this somehow in my next revision.
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Re: Starting at the beginning with Mirror Screws

Postby albertMunich » Mon Aug 07, 2017 8:51 pm

Incredible! You did it ! Damn it- my 3d printers are 800 kms away. Do you think it would be necessary to keep the "optical" sides of the slats in touch with the glass printing bed to keep them flat? Or will the flatness be ok for plating?

FYI: Found the original BRAMI VISIOLA patent- Harry this French Televisor from the 30s is a great find because it shows that a mirror screw does not have to be humungous in size. Simple motor, phonic wheel for sync and a led line lamp. A small handy 30 line demonstrator -thats what it would be without the need for a 50 cm diameter Nipkow. And the screw would be of a printable size.

In the Brami disc they kept the slats as a pack, polished the edges while the slats were kept in a jig and then they used the stepped edges for alignment with another special jig. Have a look at the drawings...perhaps the stepped edges could be made in such a way that the alignment is almost automatic.?
Once the thing is aligned the slats can be fused together. I think by the time I get home you'll have a 3d printed mirror screw!



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Re: Starting at the beginning with Mirror Screws

Postby albertMunich » Mon Aug 07, 2017 9:25 pm

Auto aligning slats? No pin...what do you think?

Bild 07.08.17 um 12.19.jpg


Bild 07.08.17 um 12.20.jpg


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Re: Starting at the beginning with Mirror Screws

Postby Panrock » Mon Aug 07, 2017 9:54 pm

Hi Albert,

A very elegant idea. This angles in this method would clearly be determined by the shape of the slats. For any but the lowest line counts they would end up very thin. See my diagram further up to get a feel for the angles. The reduced area of overlap though would lead to greater flimsiness and 'bendiness' in the complete stack. I noticed this effect even in mine, with lots of overlap.

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Re: Starting at the beginning with Mirror Screws

Postby McGee2021 » Tue Aug 08, 2017 12:30 am

I've started printing the slats, I have 11 so far. They've come out suprisingly well.
0807170928-1.jpg


Unfortunately, i tried to print at to high detail, and did not have enough solid top AND bottom layers. They'll serve their purpose, but they come with imperfections. I took out the handle on my bathtub, which was conveniently a circular acrylic tube. Now for the lighting part...
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