Starklers rough as guts dob fan

[Starkler (Geoff)]

Yes folks another one of Starklers rough as guts ATM productions

Since there has been a bit of discussion lately about cooling fans for dobsonians, I thought I should post a few pics of how I approached the issue.

Ingredients:

1x80mm computer psu fan, a plywood disk, a few inches of velcro strip and a few feet of foam weather sealing strip.

The weather strip serves as a gasket and also to isolate mechanical vibrations from the fan from transmitting to the scope.

[Dave47tuc (David)]

Looks neat. Hope it does the job for you

[janoskiss (Steve H)]

That's almost the same as mine (but mine's even rougher). I even used the weather strip too.

I turn the fan on after bringing the scope inside. That stops dew forming from the sudden temperature increase. BUT the fan collects a lot of dust too. So I need to fit a dust filter of some sort. Maybe just a bit of tissue sandwiched between sheets of flyscreen.

[acropolite (Phil)]

Nice work Geoff. Regarding dust filters, it would be relatively easy to adapt a dust mask screw on filter.

[davidpretorius]

very nice!!

[Starkler (Geoff)]

Originally Posted by janoskiss

Maybe just a bit of tissue sandwiched between sheets of flyscreen.

An idea worthy of the rough as guts tag
But I dont think tissue will allow much airflow through it . Try chopping up one of your good lady's stockings perhaps and stretching that over the outside of the fan

[iceman (Mike)]

Ok i'm getting a picture in my head now. This looks good.

Where is the weather strip in those photos?

Attaching the mounting plate to the back of the cell looks easy now, just velcro!

How far do your collimation screws protrude out? Can you still get at them by hand, or do you need to use a screwdriver now?

PS: Is dust really that much of an issue to take action to avoid it?

[janoskiss (Steve H)]

Originally Posted by iceman

PS: Is dust really that much of an issue to take action to avoid it?

And insects. I have several mozzies and other small flying insects on my mirror, and a lot of dust, but I am sick of cleaning it all the time...

[ving (David)]

i get dust and i dont even have a fan... maybe the fan and dust arent related?

also i have a 8" GSO and of course i could adapt this except for one thing... the huge metal disc that covers the entire back of the mirror! would i have to cut this up to get any positive efect or do the air currents actuall travel up the sides and around the front?

[iceman (Mike)]

Ving, you could do what rmcpb (rob) did..

http://www.iceinspace.com.au/forum/s...ead.php?t=8753

Use the plate, cut a hole in it for the fan, and away you go!

[ving (David)]

while i have taken the rear essembly off i have yet to take it appart... maybe i shoud
thnx for the linky mike

[matt]

Cut the plate. Turn it into something useful. See my thread in DIY.

[vespine]

Thing to keep in mind is that filter goes on sucking side of the fan.

[Starkler (Geoff)]

Originally Posted by iceman

Where is the weather strip in those photos?

Mike if you look at the first photo , you can see the weather strip running around the edge of the back of the scope, just inside the collimation screws.

Attaching the mounting plate to the back of the cell looks easy now, just velcro!
How far do your collimation screws protrude out? Can you still get at them by hand, or do you need to use a screwdriver now?

PS: Is dust really that much of an issue to take action to avoid it?

I collimate before attaching the fan disk. Velcro makes it easy to fit and remove. I need a thicker heavier duty velcro as the thin stuff I have only just grabs working against the force needed to compress the weather strip.

Dust hasnt been an issue for me as I observe from grassy areas mostly.

[matt]

Originally Posted by Starkler

Dust hasnt been an issue for me as I observe from grassy areas mostly.

Same here Geoff

[Tamtarn]

Hi Geoff

Thought I would add to your thread and post a pic of our Dob Fan.
Specs for the mounting plate were taken from your original pics, thank you very much.
The fan is 120mm computer type with three speed switch, giving speeds of 1200 : 1600 and 2000 rpm on high. I use it with a 12 volt power adaptor.

The 12" Dob came with a 70mm fan fitted as standard which was used for cool down periods before and after viewing.

In heavy dew conditions I would run the fan non stop while viewing in order to stop the secondary mirror from fogging over, the only problem with this was that when using med to high power ep's there was a shimmering effect through the ep. With the new fan running on low speed (1200 rpm ) our mirrors stay clear and there is no distortion though the ep.
Having the other speeds on the fan has also helped in the temperature adjustment when we move the Dob back indoors.

Thanks again for sharing you ideas it's been a great help



Small 3 speed switch mounted on right hand side


David