Re: ATM A few silly questions

[mike coslo <mjc5@psu.edu>]

Hi Simon
Simon Fourstar wrote:

>  On the new design. I am thinking about using a two vain spider design. I
> am wondering about the positioning of the veins? Which should I go with, 90
> degree or 120 degree? Are there any advantages to one or the other? Or is
> it 6 of one half a dozen of the other?

	On the spider I made for my 2 truss tube scope, I used a  two vane
spider. It works well at a 90 degree angle.

	However, unless I needed to use the two vanes (which you do for a two
tube truss) a more traditional 3 or 4 vane spider can be a good choice.
This is because the two vane spider must be substantially more robust
than the others, due to the need for all the weight to be supported by
the two vanes, instead of supporting the ewight on the tube or upper
cage. The practical result is that the vanes are thicker.


>  Also I want to build the focuser, I have a full tool shop to play in. I
> might as well use it. I am wondering what makes a low profile focuser, low
> profile? I have read about a few of the advantages, but haven't been able
> to find a clear definition of just what it is?

	Low profile is a combination of the Main Mirror to Secondary mirror
size relationship, and the focuser location in relation to the other two items.

	Say you had a 12 inch mirror. If you decided to use a 2 inch secondary
mirror, you would need to look at a low profile focuser. This is because
the focuser needs to get closer to the secondary to view the entirety of
the secondary. The drawtube of the focuser then slides a bit farther
into the tube. If you were to use say a 3 inch secondary, the focuser
would not have to be so close to view the entire surface of the
secondary. Your design could then allow for more distance from the
mirror before the image comes into focus.

>  And, do any of you have any ideas/suggestions. On a solid stock material
> that I can turn on the lathe, for the altitude bearings? Teflon? I am
> reaching here, some type of plastic or similar material? If so do you know
> where to get it?

	Teflon works well, you probably don't need to turn it on a lathe
though. If you use Ebony star or aluminum for the large bearing surface,
flat strips of teflon can be formed for the other surface, as long as
they aren't too thick. I just used a sharp knife to cut mine, and
attached it with a couple countersunk screws.

	- Mike -