Adding vents to my OOUK 10" Dob

[Alan White]

I decided to vent my OOUK 10" Dob, others have done it on here before me in varying ways.
Having not stripped the scope before, I was quite frankly terrified to start.

Anyways, the before rear end image:


 

Clearly the 10mm single hole is not for ventilation and plays a part in factory assembly.

After many options on what hole size and where to go for it I was left with two options:

1. Copy someone else and have about 18 cm2 hole area.

2. Strike out with my own thoughts, played with a sketch in paint and
and have about 61 cm2 hole area.

After a few days of erring and uhhming I stripped the scope base and hit my first surprise,
inside it had a second alloy disc hidden within, it looks to act as a large washer for the primary cell
adjustment springs and slightly spreads the load.

So after much calculation and thought, well, two cups of Tea and a chat with an Astro buddy, thanks Ed.
I said stuff it, dump the disc, let's mark out some holes and get the Starret set out!

So here we have it with three 51mm dia holes and the feet now bolted on not with sticky tape as was,
the inner disc function I hope is replicated by 3 stainless penny washers fitted under the spring against the outer
alloy base of the scope.

My mirror now has some ventilation, something I was stunned to realise older OOUK scopes did not have at 10" or under.

I also cleaned the primary, probably for the first time ever by the dust and crudd on it.
Rather nice and clean now.

The pencil marks are my thoughts for additional
holes for a vent and a fourth hole in place of the
10mm one, perhaps with a fan.

Or do I go mad a fit three small fans for mirror cooling?

In another thread I ask about the secondary and how to
improve it, as it really is rubbish.

Stripping the scope made me realise how less than premium
the build quality is on this olde OOUK scope,
however the mirrors at 1/6 wave always make me happy.

I now have the fettle bug for my dob, watch for more in the coming months.

Your thoughts, encouragement and any, oh my, why did you do that fool type comments are all equally welcome.

This was a perfect light project for me to undertake, I am recovering I think, from Heart problems at Christmas and
it has proven quite therapeutic for me. 
Something to concentrate on rather than feeling rough.
So a win/win for me all round.

[Paz]

That looks like a promising upgrade, will be interested in your observations of its effect on cool down.

[John]

Very interesting to read about this and see your photos Alan.

Your OO 10 inch looks exactly like my old OO 10 inch Europa did. I had the same thoughts re: ventilation but never got around to drilling the back plate or getting rid of the internal plate.

I found that the scope cooled reasonably quickly so that pursuaded me away from DIY work which I probably would have messed up !

You have done a nice job on yours 

 

[NGC 1502]

 

Alan & myself are members of our local club and we both have similar OO 10” Dobs.  The pic of the OO cell in the first post that has multiple holes is my own. I think that Alan’s choice of 3 larger holes looks better.

I’ve had the 10” for about 8 years, at times there was a definite cooldown issue when there was just the single small vent hole, so the extra holes were added to help.  I’ve recently added a fan.  This was added to increase the airflow around the primary to reduce dewing of the primary.

Last October Alan & myself were at our club’s dark site and both us us suffered dewed primaries.  I’ve read posts that claims that solid tube primaries don’t dew up........our experience says otherwise, it was however a very damp night.

Of course Newtonian secondaries are much more prone to dewing, but at least a 12v dew gun can be pointed down the focuser.  Primary dewing is much more of a problem, I’m hoping that a fan will promote air flow and reduce dewing on those extra damp nights, as well as a quicker cooldown.

Ed.

 

 

[Stu]

Nice job both, seems like a sensible approach you've taken. Will be interesting to see whether it improves things.

I started a project which I never finished (what a surprise!) with an old SX250, and after a failed attempt to create larger vent holes in the base myself, I took it to a machine shop and they did a great job. Cost me an arm and a leg though so it's not a route I would recommend for the financially prudent! ??

You can see the results in this post.

 

[NGC 1502]

 

Stu, looking at that thread the ventilation looks excellently done, especially compared to how those older and much more basic OO cells were done with hardly any ventilation.

I’m not knocking OO, but I also recall the Europa models had a 6mm thick bar across the full diameter to support the secondary.

The current OO Newtonian primary cells are beautifully done, excellent ventilation, built in fan, 9 point mirror support even with the smaller sizes.   Those thick secondary supports are long gone, replaced with a proper 4 thin vanes.

Ed.

[Space Hopper]

2 hours ago, NGC 1502 said:

   Those thick secondary supports are long gone, replaced with a proper 4 thin vanes.

 

True, but theres still room for improvement there.

The vanes and secondary holder itself, isn't terribly well made.

[NGC 1502]

7 hours ago, Tubby Bear said:

True, but theres still room for improvement there.

The vanes and secondary holder itself, isn't terribly well made.

 

Yes, I agree about that.  I’ve done DIY modified spring loaded versions that make secondary alignment so easy.  

Also the way the secondary is untidily siliconed to the holder may work, but looks crude.  There are better ways to mount the secondary with it being held in a shell, without distorting it of course.  Looks nicer and more professional, and allays fears that some have about the secondary coming unstuck and dropping onto the primary.

None of this would be hard to do during production.

Ed.

 

[Peter Drew]

I've taken a slightly different approach with my home built 17" Dob backplate. I have 6 radial holes for ventilation but each hole has a rotating cover to blank the hole off once the mirror has cooled. The reason for this is to prevent air from the usually warmer ground rising through the tube causing the other irritating effect, tube currents.    ?

[John]

I found my OO Europa 10" F/4.8 worked well enough but I was glad that I did not pay much for it - the overall finish was quite crude in some areas. My later 12" SPX F/5.3 was a step up and I believe that the current VX series are much better in terms of quality. I think OO have slowly got the message that producing good quality mirrors is not enough - the mechanics, fit and finish of the rest of the scope needs to be good given the new prices that they charge.

At least improving them gives us something to think about when it's cloudy !

Most brands can stand some modifications in a few areas to be fair though.

 

 

 

[Alan White]

12 hours ago, Tubby Bear said:

True, but theres still room for improvement there.

The vanes and secondary holder itself, isn't terribly well made.

Please refer and input to my other thread on this Tubby Bear 

[Alan White]

5 hours ago, NGC 1502 said:

 

Yes, I agree about that.  I’ve done DIY modified spring loaded versions that make secondary alignment so easy.  

Also the way the secondary is untidily siliconed to the holder may work, but looks crude.  There are better ways to mount the secondary with it being held in a shell, without distorting it of course.  Looks nicer and more professional, and allays fears that some have about the secondary coming unstuck and dropping onto the primary.

None of this would be hard to do during production.

Ed.

 

I will talk with you about these options tonight at the club Ed if I may.

[Alan White]

I have to report back after one session since adding vents,

Scope cooled faster vented and was much more enjoyable than pre-vent vesrsion.

The cooldown was faster and deliberately had no precool before use, straight from house to car to observing and it cooled faster by a lot, just having an open airflow has made a significant change.

The best bit was I and astro club CPAC viewed Pallas with it last night, so doubly pleased.

[NGC 1502]

 

That’s great Alan.   I think that Dobs in general are good in so many ways, simple in concept, low hassle to set up or pack up, largest aperture per £ spent, most issues are a DIY fix.

Not knocking technology but one of our fellow members at our recent observing session gave up in frustration with his go-to.  

Technology is great when it works ( like now as I type this ) but when it doesn’t play ball...........?

Ed.

[Gina]

Quote

Technology is great when it works ( like now as I type this ) but when it doesn’t play ball...........?

Oh so true!!

[Alan White]

Latest update.

I observed at a darker site with a fellow SGL member NGC1502, Ed on Saturday.
The scope was taken from house, to car to observing location, no pre-cool.

It cooled well and very usable in less than 30 minutes from the car, very happy with that as
before it needed a good hour to settle.