Indexing head for Nipkow

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Indexing head for Nipkow

Postby Viewmaster » Sun Apr 15, 2007 9:19 pm

Just a thought.....
One problem with hole positioning on a Nipkow is the angular position.
(11 1/4 degree for 32 hole disc and 12 degree for 30 hole disc etc. ) Errors here leading to crooked horizontal lines in the monitor.
The most accurate way to get these angles is by use of an enginneers indexing head set up on a milling machine table. Most do not possess
such facilities.

BUT, say one had a large old clock movement and the hour hand axis was fixed to the centre of the Nipkow.

By moving the minute hand through 22.5 minutes each time then 32 hole spacing would be achieved. So minute movement would be...
0/22.5/45/7.5 past next hour/30/52.5 and so on.

For a 30 hole disc it would be every 24 minutes. For 60 holes 12 minutes
and so on.

One would have to be careful to keep the axis tight against the gearing to avoid backlash.

If no clock movement available, then a 12/1 set of 2 gears might suffice
using an large old clock face.
The above together with either a radial lead screw or vernier would achieve hole positioning.

As I said, just a thought. :) Maybe someone can suggest further improvements.
Albert.
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A timely idea.

Postby Stephen » Mon Apr 16, 2007 12:03 am

This is a great idea, Albert!
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Postby Viewmaster » Mon Apr 16, 2007 12:29 am

Further thoughts.....
The 'clock' would have to be bigger dia than the Nipkow else one wouldn't be able to see the minute graduations.


Assume that one could set each minute position within, say, about 1/8 of the distance between each minute.
(if one overshot the correct position, go back more than required and move forward again to prevent backlash error)

So, for a 32 hole disc this equals an accuracy per hole of 22.5 x 8 = 1/180th of the hole angle to the next hole.
(22.5 minutes 'clocking' from hole to hole)

Assume that the picture height in a 12 inch, 32 hole disc is just over 1 inch high. This gives an error of just over 1/180 inches vertically on the image....about 6 thou.
Now, is that good or bad for a Nipkow error? .....and we haven't yet tackled the radial spiral hole problem accuracy. :cry:

If bad then forget the whole idea. :lol:

Albert.
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Postby DrZarkov » Mon Apr 16, 2007 1:16 am

I wish I had this idea 20 years earlier. I'm not going to tell how I've made my first discs! :lol:
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Postby Viewmaster » Mon Apr 16, 2007 1:34 am

DrZarkov wrote:I wish I had this idea 20 years earlier. I'm not going to tell how I've made my first discs! :lol:


O go on! :lol:

My 'clock' idea is superceeded by your friends laser square cut disc for 10 euros!
.........Unless one wishes to take up the challenge and DIY Nipkow.

I wonder how accurate his holes are positioned ?
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Postby DrZarkov » Mon Apr 16, 2007 7:03 am

Well it depends! I would like experiment with other discs, like for the old german system with 30 horizontal lines, or with increasing the number of lines. For that it is the best way to use the "old fashoned" way. Even with a cardboard-disc for experiments you have to work exactly.
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Another idea.

Postby Viewmaster » Mon Apr 16, 2007 6:33 pm

If you wish to make your own Nipkows another idea is using Myford lathe change wheels. (or any other make you can get)

These are easily purchased for a few pounds.
If you have a lathe turn up a spindle for the gear to turn upon. Fix Nipkow to rotating gear.

Turn up a tapered screwed plug (and suitable housing ), to act as an indexing peg in the tapered gear tooth involute.

Use a 90 teeth gear for 30 hole Nipkows and index every 3 holes.

Use a 64 teeth and index every other hole for 32 Nipkow.

Use the biggest dia gear you can get with suitable tooth number combination. (Big dia leads to less error)

This is pretty accurate if the taper fits the gear involute walls well and is screwed down tight for each Nipkow hole.


Happy Nipkowing Dr. :D
Albert.
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Backlash

Postby Klaas Robers » Mon Apr 16, 2007 6:35 pm

A problem might be that a clock mechanism has quite some backlash. You can move the short hand while the gearing is having some play. This is on purpose, because play makes the mechanism run freely, needing very little energy.

A fellow Ham radio amateur here in my neighborhood, Mart Schouten made his discs (punched) with a lage wooden circle around which a bicycle chain was mounted, of exactly 32 x n chains. Bicycle chains are extermely exact in measures. He had a wedge that fitted in between the teeth to make a rotation of 1/32 of a full circle. This has no play.
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Re: Backlash

Postby Viewmaster » Mon Apr 16, 2007 6:44 pm

Klaas Robers wrote:A problem might be that a clock mechanism has quite some backlash. You can move the short hand while the gearing is having some play. This is on purpose, because play makes the mechanism run freely, needing very little energy.

A fellow Ham radio amateur here in my neighborhood, Mart Schouten made his discs (punched) with a lage wooden circle around which a bicycle chain was mounted, of exactly 32 x n chains. Bicycle chains are extermely exact in measures. He had a wedge that fitted in between the teeth to make a rotation of 1/32 of a full circle. This has no play.


Yes, I did mention about the backlash and keeping it tight. If overpositioning to go back and come forward again because of backlash.
The clock face is a ready made index, so thought it might be used.

I once made a 4 foot dia wooden disc with a motor bike chain fixed to outer cicumference for something else I was making. Similar layout to your friends idea.
It's worth looking around junk shops for anything that has equal divisions divisable by 32 too.
Albert.
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