Mounting the fan

[iceman (Mike)]

Ok, i've seen Matt's thread, I've read previous threads by DP and seen Bird's site..

Just trying to pull it all together in my brain.

The easy solution is just to mount the fan on the back of the mirror cell, but obviously that's not ideal. My eventual goal is to go to active cooling, so I want to take the steps to get me there, without doing it all at once.

So, without including Peltier's into the design right now, what's the best way to attach my fan to the bum end of my scope?

Design factors:

1) Is one big (9cm) fan enough? Would I be better with 3 small fans (as bird has)?

2) These fans (or this fan) needs to be blowing onto the mirror

3) The mounting plate should be aluminium

4) The mounting plate should close in the end of the tube (ie: the size of it should be the outer diameter of the tube?)

5) Cut a hole in the mounting plate for the fan to blow through

6) How do I attach the fan to the mounting plate? Just using 4 long screws? (my fan didn't come with any mounting screws)

7) How do I attach the mounting plate to the scope or mirror cell?

8) It needs to be able to be removed easily, for when the mirror needs to come out for cleaning

9) Need to be able to reach the collimation screws, so I guess 3 holes need to be cut in it so I can reach the collimation screws. Will this affect the desire to "close in" the end of the tube?


For active cooling (later on), it appears I need a couple of peltiers, an insulating perspex sheet (or polystyrene), another aluminium plate, some heat sinks and some more fans. Is that about right?

Thanks for any advice, and remember a picture is worth a thousand words

[matt]

Mike

Have a look at (I think) Starkler's post "rough as guts dob fan".

He's used velcro to attach his to the rear of his tube.

I was lucky that my backing plate arrived already screwed to my mirror cell. So I use the same screws and holes to attach to my mirror cell.

As you can see in my mirror fan pic I cut 3 holes around the plate's rim so I can get at the collimation screws.

I alsi drilled holes for attaching the fan to the backing plate. The central hole (for the fan) was cut in a drill press using a circular metal cutter.

[davidpretorius]

Originally Posted by iceman

what's the best way to attach my fan to the bum end of my scope?

i make use of those three locking threads. So make sure disc is large enough to get to these threads and then cut out so you can still turn your collimation screws. Make sure the screws are not too long so that when you do attach the disc, you are not extending thu and "locking the mirror"

I will take some pictures and thread diameters today as i still crook with this damn gastro!