DIY: GSO Dob Fan Project

[iceman (Mike)]

Hi all

Scott Tannehill (Tannehill) has kindly written an article on how to build a GSO Dob Fan.

You can read the article on the IceInSpace Projects & Articles page, or directly by clicking on the link below:

GSO Dob Fan Project

Thanks to Scott for writing the article! If you'd like to submit an article or review for IceInSpace, please Contact Me.

[iceman (Mike)]

Article uploaded.

[doug mc]

A simpler way to seal off the mirror is to use canister caps . They look like shower caps and are available at kitchen section in supermarkets. I have a GSO 8 inch F6 tube assembly on an eq. mount and i fitted a 80 mm. box fan from Dick Smith. To increase air flow around the mirror I drilled a series of 10mm closely spaced holes between the collimation screws. Choosing the largest of the caps I cut a clearance hole for the fan , then I cut the elastic from a small cap and glued and taped it to the centre of the large one. With large cap around tube and the small cap around fan this seals off the tube nicely forcing the air around the mirror and up the the tube. The fan was driven by 8 AAA battery pack. Doug Mac.

[ballaratdragons (Ken)]

Originally Posted by doug mc

A simpler way to seal off the mirror is to use canister caps . They look like shower caps and are available at kitchen section in supermarkets. Doug Mac.

I use a shower cap idea from a pet shop. It is a plastic bird-seed catcher with elastic around the edge (just like a shower cap) but is a lot bigger than a shower cap. They come in a round shape for round bird cages
Mine was $5.

[Paddy (Patrick)]

I have finally gotten around to undertaking this excellent modification to my 12" GSO Newtonian. Rather than replace the fan, I left the original in place and just fixed the neoprine gusset over the back of the scope with velcro as Scott's article suggests, with a hole as an inlet for the fan. I also put the ring baffle on the inside of the OTA about 10 mm above the primary, as Scott describes.

AND WHAT A DIFFERENCE!

Firstly, there were no vibration issues with the standard GSO fan. There was a marked improvement in seeing. I was observing Jupiter still fairly low in the sky with good detail at 165x and even 300x - cloud belts and GSR clearly visible. When I turned the fan off, seeing deteriorated rapidly and I was looking at a pale blur. I was amazed. I also found that DSOs were also clearer. I also found that when the fan was on I could feel the movement of air out of the front of the scope. I am hoping that this will reduce dew formation on primary and secondary mirrors.

I thoroughly recommend this modification for these scopes and many thanks to Scott for a very readable and comprehensive account.

[AlexN]

Im in the process of making something like this for my 8" due to a very wet primary mid way through the night of my last star party... Im using a plastic bucket lid which will be held in to the recessed area of the mirror holder, there will be cut away sections for the collimation screws and it will be held on with velcro...

Being a bit of a computer nerd I have tons of spare fans around ranging in size from 80mm to 120mm.. I'll basically use trial and error finding the right fan to use, obviously starting at the 80mm range and working my way up to find the best trade off between CFM (cubic feet / minute) and vibration. most of the 120mm fans I have run fine directly connected to a 9v battery.. and are very silent..

I'll post pics later this week when its done.

Alex.

[Paddy (Patrick)]

I'll be very interested to hear how you go. Last night I got the scope out for some moon watching and was able to go straight to 600x without waiting for the mirror to cool and had excellent seeing throughout. I am a happy chap!

[Visionary (David)]

An excellent report and a pleasure too read.

[multiweb (Marc)]

Gotta make sure this thread doesn't get linked to the more recent "no cooling fan" thread. It would be like contact between matter and anti-matter and shred the IIS forums out of existence.