A new 90-line Mirror Screw

[Panrock]

IMG_20210326_143144.jpg

I couldn't find any photos of the process of making a mirror propeller, but there is a photo of making a TV with a Nipkov disk based on drawings from 1937. Videos of the propeller in action are poor, but in real life everything is much better.
https://youtube.com/shorts/KoszVQuAT_8? ... UiCHI9DC6A

That really is very impressive! The fidelity is good.

It looks like Spike Milligan on the "screen"...

Steve O

PS. It's the first time I've heard it described as a Mirror 'Propeller', but it is apt. What is the Russian word you use?

[Dmitrij]

This is how Google corrected my text. We usually call it a screw.

[Dmitrij]

Once I sent a Leningrad-T2 TV to America and wrote that inside was dust from the times of communism. But in translation it turned out that inside was the ashes of communists. It turned out awkward. That's why I often apologize for my English.

[Panrock]

The polishing of the new slat edges is done... and hopefully sealed against long term oxidisation with furniture polish.

I'm using a permanent black marker pen to 'black' the opposite and end edges of each slat as I go. This has better adhesion than paint. With the stainless steel 120-line screw I used roofing mastic!

The new indexing method is proving a bit of a fiddle to do but seems to be working. It's good that it is being applied at both ends of each slat - each confirms the other. There's just one - critical - angular position where everything fits together.

Steve O

[Panrock]

Half way!

Slat 45 passes by. The stack looks exactly as it should at this point.

Sadly I missed the deadline for the Convention this year, on Saturday. How did it go?

Steve O

[Panrock]

Today the mirror screw was finally assembled. It all fits together correctly... I can't say I enjoyed the repetitive slog of preparing, polishing and fitting each of the 90 slats, but the precision of CAD based fabrication I find amazing. There's no 'play' in any of the "four-degree" index holes and 90 of them do really add up to an exact circuit of 360 degrees.

How did TeKaDe do it 90 years ago? Or did they just accept fuzzy pictures from high-line-count mirror screws?

If this doesn't work, I shall give up! I have a history of trying to push NBTV further than it really wants to go. Stay tuned.

Steve O

[Panrock]

I had it running yesterday, just on a test square wave for now. First indications are that the slat angles are much better, and it should be possible to pull in the remaining errors with Karen's correction unit (which definitely works on 90-lines!).

However, it looks like the quality of the picture may later be affected by shortcomings in the surface quality of the mirror-polished slat edge. This is not a problem with the reflectivity as such. It seems that granularity in the aluminium sets a limit to the ultimate underlying smoothness. Of course, my previous mirror screw was made of stainless steel. But this was much heavier and after all the metal had been removed required special balancing - a bit of a pig really.

I'll keep battling on.

Steve O