Re: [ATM] wire spiders

["Treur, Harro" <harro.treur@waternet.nl>]

Hello Jan,

In my  12,5 inch, the wires have a small angle. 
In fact, it amazes me how small the angle can be without the spider moving
away or vibrating.

In my first design, it was possible to change the vertical distance between
the wires. This way I was able to place the secondary on the desired
position. I experimented with several angles. I found that an angle of only
8 degrees is sufficient. My secondary is quite large (63 mm) and therefore
not very lightweight. But the tension in the wires must be quite high. 

I realise that in a 20 inch, the weight of the secondary is somewhat more
and that the wires are longer (The length of my wires is about 150mm. In a
20inch this will be 220mm). But I am convinced that an angles of 35 degrees
is way too much. I think that 15 degrees is more than enough for your
20inch-telescope.

If you hesitate, I advise that you experiment with different angles.

Good luck
Harro Treur

PS: Jan, how is the grinding going?? 



> -----Oorspronkelijk bericht-----
> Van: Jan van Gastel [mailto:jhm.vangastel@wanadoo.nl]
> Verzonden: woensdag 28 juni 2006 9:33
> Aan: atm@atmlist.net
> Onderwerp: [ATM] wire spiders
> 
> 
> I have been searching for information on the internet about
> the angle between the wires of a wire spider. I found some 
> postings, including one of Mel Bartels and one of Nils Olof 
> Carlin, telling there has to be 'some' angle, but not how 
> large that should be. Nils Olof, pointing to bike wheels 
> suggests, if I understand him well, that the angle doesn't 
> need to be large.
> 
> I want to use Mel's crossing system on the trilateral 20
> incher I am building at the moment. When I make the central 
> hub and the side bars 150 mm
> (6") long, the angle between wires at the crossing point will 
> be about 35 degrees, the angle between hub (or side bars) and 
> wires about 27 degrees.
> 
> Is this the way to go, or should the angle still be larger?
> Or is this overkill and is a smaller angle also OK?
> 
> 
> Jan
> http://home.wanadoo.nl/jhm.vangastel/Astronomy/
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 

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