Baird's hole drilling

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Baird's hole drilling

Postby Viewmaster » Fri Jun 15, 2007 6:44 pm

In the 30 line Baird system, he increased the spacing of the first and last two rows of holes to get a wider picture.
To prevent black lines he must have also increased the diameter of these four rows of holes too.
I wonder if he drilled all the 30 rows of holes the same size then redrilled the four rows larger or changed the drill to a larger size whilst initially drilling all the holes?

Also, did Baird actually make all his many discs himself or get an engineering firm to do the work? If so, I wonder who the engineers were?

Now the above just shows what odd ball things go through this mind of mine! :lol:
Albert,
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Re: Baird's hole drilling

Postby Steve Anderson » Fri Jun 15, 2007 8:21 pm

Viewmaster wrote:Now the above just shows what odd ball things go through this mind of mine! :lol:
Albert,


Not oddball at all, but it is a bit of a quandry. What we don't know (or at least I don't know) what is the increase in spacing of the outer two lines each side compared to the rest. On the assumption that they were twice the spacing of the centre bunch, then the apature would have to be twice the area of the the centre ones to appear the same luminous intensity.

However, to keep the same resolution they would need to be the same vertical dimension as shown in the upper row of the attached sketch. But this would let through more light than needed, i.e. the total apature is greater than two circles on thier own.

Perhaps an ellipse was employed as shown in the second row, I've forgotten how to calculate the area of an ellipse...but I hope you get my drift.

Now how these were achieved, that's a different matter.

The simplest way would be to drill two holes exactly side-by-side.

Steve A.

Yes, I know, the line numbering is back-to-front, it's the concept that's important, just pretend you're looking at the rear of the disc.
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Postby AncientBrit » Fri Jun 15, 2007 10:27 pm

Have any such discs survived?
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Postby Viewmaster » Sat Jun 16, 2007 12:21 am

AncientBrit wrote:Have any such discs survived?


There's a Baird disc in the Hasting Museum, but it's 32 hole. It appears to be the disc used by Baird for his demonstration to the Royal Inst. in 1925.
This Baird disc was found in his Bexhill home when he died in 1946.
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Original Baird 32 hole disc.
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Re: Baird's hole drilling

Postby Viewmaster » Sat Jun 16, 2007 12:28 am

Steve Anderson wrote:However, to keep the same resolution they would need to be the same vertical dimension as shown in the upper row of the attached sketch. Now how these were achieved, that's a different matter.

The edge resolution is not as important as the centre part, where most of the picture interest would be composed. So, Baird may not have bothered too much with the edges and the brightness could also be allowed to fall off slightly there too.
For, how often do we notice what is going on at the edges of our TV screens?
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Re: Baird's hole drilling

Postby Steve Anderson » Sat Jun 16, 2007 2:04 pm

Viewmaster wrote:For, how often do we notice what is going on at the edges of our TV screens?
Albert.


Yes, very true, it's just the engineer within me...

I'm the same with lossy file/data compression (mpg and the like), it just goes against the grain.

For decades there was a lot of time, effort and money spent on developing accurate sound and picture systems (Hi-Fi). Now what do we do? Throw great chunks of the data away.

OK, 99.9% of the population don't notice it (including myself), but to an engineer it's abominable! (Getting down off soap-box again).

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Re: Baird's hole drilling

Postby Viewmaster » Sat Jun 16, 2007 6:24 pm

Steve Anderson wrote:For decades there was a lot of time, effort and money spent on developing accurate sound and picture systems (Hi-Fi). Now what do we do? Throw great chunks of the data away.
Steve A.


There's so much rubbish on TV/sound these days that as far as I'm concerened, you can throw all the data away! :lol:

As TV technical quality grows 32/405/625/HDTV so the program quality goes down. I cannot remember 32 (Man with a flower in his mouth etc) but I can remember 405 after WW2 and it was thoughtful, tasteful and interesting then. Now.....?
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Re: Baird's hole drilling

Postby Steve Anderson » Sat Jun 16, 2007 7:08 pm

Viewmaster wrote:There's so much rubbish on TV/sound these days that as far as I'm concerened, you can throw all the data away! :lol: Albert.


We have some 60-odd channels of TV here, plus the FM band is packed with radio stations (The government gets a pile of money every time they issue a licence). Is any of it worth bothering with? Generally no. There are occasional exceptions (Thank you Discovery, The History Channel and once in a while the Beeb), but they few and far between.

So those with at least a modicum of intellect have turned to the 'net, which is vast and you can be as selective as you wish. Whilst I'm typing this I'm listening to a US jazz radio station via the net, no commercials, no babbling DJs, few promos and mostly the music that I like.

The entertainment industry continues to complian about copying/piracy of their 'intellectual property', sorry, I find that oxymoronic.

Steve A.

I must dispose of that soap-box of mine!
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Re: Baird's hole drilling

Postby Viewmaster » Sat Jun 16, 2007 9:40 pm

Steve Anderson wrote:Steve A.
I must dispose of that soap-box of mine!


You could always varnish it and use it for the cabinet of a NBTV. :lol:
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Postby Andrew Davie » Mon Jun 18, 2007 11:03 pm

On the subject of Baird's disk holes, the inside cover of the CD 'The Dawn of Television Remembered' has a section of a restored picture of Baird's Double-8 apparatus. In the foreground of this picture is a disk? or mask perhaps, which shows very clearly rectangular holes in a disk, of approximate 2:1 dimension -- that is, the wider part is from scanline to scanline, and the narrow part in the vertical direction. These would, I think, be ideal for the best light and the best resolution -- better vertical resolution than square holes, better light than round/oval.
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Postby AncientBrit » Tue Jun 19, 2007 5:45 pm

I wonder what the mechanical capabilities were in the 20's for drilling small holes?

Could small NBTV sized rectangular holes be milled?

GL
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Postby Klaas Robers » Fri Jun 22, 2007 5:29 am

I remember that the discs for the Baird televisor were punched, not drilled. The precision was very good. The holes of the edge lines was rectangular. If someone want to know how this could be done, call or e-mail Denis Asseman. He punches his own discs for his replicae of disc monitors at home and the precision is good enough.

As far as I know the most left 3 lines and the most right 3 lines have a width of 1½ the width of the central lines. In the 30 lines video on Club-CD number 3 this is taken in account. So in fact the picture has a width of 33 lines of the central type. As the 30 line part is converted from the 32 line part this was quite easy..... There is a wide blanking around the sync pulses, giving an aspect ratio of about 2 : 3.
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Postby Telehor » Sat Jun 23, 2007 7:27 am

Indeed, the Baird discs are punched. I had the possibility to take the dimensions on a genuine Televisor disc. What a special item to have in your collection! see my page http://users.skynet.be/telehor/eng/bouw_3_televisor.htm
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The square holes are 0.7 x 0.7 mm and the rectangular 0.7 x 1 mm.
These rectangular holes need two punches: the first makes it 0.7 square and after advancing 0.3mm an other push.

It is a job that needs full concentration.

For my later replicae i used the laser method. The disc in the GE Octagon has holes of 0.3 x0.3 mm, only high precision laser machines can handle this.

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"Television To Day" volume 2
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