How do I improve an OOUK secondary holder?

[Alan White]

I am fed up with the rubbish secondary holder on my OOUK 10" dob.
The damned thing does my head in when ever I adjust it,
which at the minute is a number of times as I am playing with the scope!

As soon as you make any minor adjustment the darned thing turns about and flops around.
My old SW150p had a better made unit in it!

Has anyone 'improved' the existing arrangement or should I just buy something better and stalk mounted?

I know this is the DIY thread, thought it the most likely location for ideas.
Thanks in advance.

Edited April 7, 2019 by Alan White

[fozzybear]

I fitted a stainless steel washer against the back of the secondary mount as the screws dug into the aluminium support for the secondary on my 150pds (skywatcher) also I did blue tip the 3 adjustment screws on  the washer and used a shallow countersunk bit as guides for the 3 adjustment bolts on the stainless washer that way nothing moves apart from the secondary mount and no twist

Andy

[Alan White]

Thanks for the input Andy.

The OOUK already has a stainless washer fitted by the previous owner/s but it still turns sadly.
 

[fozzybear]

Alan,

I thought your picture had an added washer but was not sure albeit a tiny one correct? half the size of the secondary holder? if you can get hold of a drill press then use a countersunk bit all the same depth lightly sink the three guides for the bobs knobs then no twist, you might need to sand the back of secondary holder to remove any burrs on the back of the holder so it is flat

[fozzybear]

11 minutes ago, Alan White said:

Thanks for the input Andy.

The OOUK already has a stainless washer fitted by the previous owner/s but it still turns sadly.
 

what turns the secondary? when you do what align sec to primary

 

Edited April 7, 2019 by fozzybear

[John]

I put a couple of washers made from a plastic milk carton between the collimation screw tips and the rear surface of the secondary holder on my 12" Orion Optics optical tube. That seems to have improved the functionality of the collimation adjustement quite a bit to the extent that it virtually never needs adjusting now.

This modification is explained here:

http://jaysastronomyobservingblog.blogspot.com/2010/09/milk-jug-washers-for-secondary.html

[Alan White]

20 hours ago, fozzybear said:

What turns the secondary? when you do what align sec to primary

As soon as I make any adjustment the whole secondary moves in a turning motion.
I will make have a go at countersinking a washer or the milk carton fix.

The SW ones just seem far simpler, yet more robust somehow.


 

[fozzybear]

Alan,

If you can then maybe a Teflon or ptfe sheet one/two if you can get hold of it Teflon sheet that is , Never seen the milk carton Mod

https://www.amazon.co.uk/Sheet-PTFE-white-Plate-Teflon/dp/B00MR1AJK6/ref=sr_1_10?keywords=ptfe+sheet&qid=1554745538&s=gateway&sr=8-10

[fozzybear]

21 minutes ago, Alan White said:

As soon as I make any adjustment the whole secondary moves in a turning motion.
I will make have a go at countersinking a washer or the milk carton fix.

The SW ones just seem far simpler, yet more robust somehow.


 

My SW 150pds same problem the 3 collimation screws dig into the back of the sec mirror mount as it is ali

[John]

5 minutes ago, fozzybear said:

... Never seen the milk carton Mod

 

It works well

The cost is £0, assuming you can lay your hands on a used plastic milk carton.

[fozzybear]

3 minutes ago, John said:

It works well

The cost is £0, assuming you can lay your hands on a used plastic milk carton.

only prob trying to get a large milk carton in plastic ours over here are 1 litre max so round..... Not like the uk 2 litre or even larger I do remember.

[John]

3 minutes ago, fozzybear said:

only prob trying to get a large milk carton in plastic ours over here are 1 litre max so round..... Not like the uk 2 litre or even larger I do remember.

The washers that I cut are about 50mm in diameter.

[fozzybear]

1 minute ago, John said:

The washers that I cut are about 50mm in diameter.

you have flat sided bottles so maybe a good try for Alan

[fozzybear]

For me got my boss to get some ptfe sheet at work 

[NGC 1502]

 

All good ideas above.  One thing that could be tried is to file the ends of the 3 collimation screws into a more rounded profile.  That means that the ends of 3 the screws that contact the secondary holder or washer have less area in contact.

With a larger contact area there’s more rotational effect on the secondary holder when a screw is turned than when the end profile is smaller.

I share the frustration that these issues can cause.  It’s a matter of trial & error to find what works, or doesn’t of course.

Hope you sort it.

Ed.

[fozzybear]

This astro hobby is always modify this modify that, Don't get me started got a desk full of Arduino stuff esp8266 and wrong model... Duh need v1 smaller footprint... and on the suppliers website no mention of which version all down to a chip on the board so frustrating...

Andy 

[Alan White]

To bring my own thread back to life one more line of thought.
The Secondary holder is  big lump of cast alloy and does not allow for a neat installation of a heater.
Or does it?

The stalks on all other secondaries are of a smaller diameter that I have seen.
Has anyone adapted the OOUK big lump of alloy to a smaller one to fit a secondary heater?

Photo again of what I have:

On my SW Newts the same f5 ratio, the holder was smaller and to be honest I felt worked better.

Insert other media

Edited July 31, 2019 by Alan White

[Alan White]

Has no one removed the large oouk secondary ally lump and refitted the mirror to a better arrangement?

I has seen some very nice secondary fittings in images online, but not fitted to a scope like my one,

someone surely has done this on SGL?

[Scooot]

Hi Alan, I haven’t refitted my secondary but I did manage to make and fit a dew heater which works ok. I’ve just found the thread about it. Bare in mind I’m useless at DIY, DIW expert (do it wonky) is how my wife would describe me  I can’t tell from your pics whether it’s possible with yours.

 

 

[Alan White]

Thank you @Scooot, much appreciated Richard.

Although our scopes are similar spect my stalk is the  same dimension as the mirror, but made me wonder about what material it is made from?

if the stalk is wood, I could get it reduced down in diameter.