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My Azimuth Degree Circle Mod


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I'm going to show you how I designed and built my azimuth degree circle mod on my Skyliner 300P Auto Dobsonian.

I wanted to design it as neat as possible, so I had the thought of a cable desk tidy as the porthole onto a degree circle encased in perspex running on bearings to keep the circle concentric, also a tab and locking mechanism so it can be rotated to any position to make polar alignment dead easy.

I bought the cable tidy from e-bay for £3.75 click on the link to see it.



I drilled two small holes and superglued a length of 1.5mm diameter rod into the holes. This will act as a pointer when the degree circle is installed.


Cable tidy with cover on.


The first thing to do was mark the exact centre of where I want this cable tidy positioning. Then with a 76mm cutter installed in the drill I began cutting it out, this took some doing and I had to recharge the drill.


Hole is cut, note the handle was removed as this was in the way.


The hole turned out to be a very tight fit and I had to file it a touch bigger before the cable tidy would fit, but it is still a very tight fit. Note the plastic flange on the top, this is where I am going to install a red LED bulb, but not sure how to proceed without the wire showing.


With lid on, looking factory fitted.


Looks very professional. Thats it for now, next step designing the degree circle.

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Looking good mate.

After modding my dob base with a setting circle, one thing I would do differently would be to print test scales and test them in the dark to find the optimum line thickness as my scale is a little hard to see.

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  • 1 month later...

Now for part Two

My perspex tyres arrived today and wow aren't they lovely, they are precision cut and by the look of it polished as well.

I marked out the position of the cam rollers which will enable the degree circle to rotate uniformly around on the base.

I then drilled and screwed in 6mm wood inserts into the base.


Once done I screwed in the cam follower bearing and marked out 120° and done two more.


The next photo shows all three drilled and inserted with a cam follower bearing. The perspex has been placed over the top and turns freely.


Next photo is a close up of the circle and the opening to view the degree circle from.


Thats it for now, next part the degree circle itself.

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Looks fantastic Mick. Puts mine to shame. Who did you use to get your perspex tyres done?

I need to adjust mine anyway as I don't know if the wood expanded/shrank due to humidity in the air as there is a lot of play on the setting circle. It's unwanted movement so I need to take things apart and have a look.

Keep up the good work Mick. Are you going to make the setting circle yourself or do you have a company in mind?

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Your mods are gonna be the business Mick - looks very slick and professional and I bet it'll work like a dream - I'd do the same if I wasn't after something bigger lol. :)

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Well - Clive and Ron next to us at Kelling both had Lukehurst 18" and 20" dobs - couldn't believe the detail in the stuff I was looking at. Welllll... I've gotta have an ambition .... don't I ? lol

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Dunno about Naglers - but Andromeda in the 18" Lukehurst dob with a 35mm Panoptic is just like the images in magazines (only in b&w) - unbelievable :)

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  • 3 weeks later...

The next step was the Degree circle which I obtained by using Robert Willets program which cost me £10 but I can now use for as many degree circles as I want for one year.

It printed one out 580mm in diameter, it was a little to big ideally I wanted 570mm but I can do another one so it's not a problem.

I had it printed out a Staples for £3.


Next I placed the degree circle between the two sheets of perspex and drilled a small hole through both sheets.

Then I drilled the bottom one with a 5mm drill and taped the bottom sheet with a 6mm tap.

Then I drilled a 7mm hole in to top sheet and the perspex cracked twice, I could have cried but it wasn't to bad I could place the handle bracket accross both split sides and superglue them together and screw the handle to both sides of the perspex to bridge it.

So beware drilling perspex is a pain in the rear, you must be on slow speed.


You can see the split above the handle.

I then screwed the two sheets together and drilled two holes through the angled plate I found at work.


I placed the bracket between the sheets as it's only 1 mm thick and screwed it into place. I then screwed a knob into the front of the plate.

I'm going to paint the bracket black at some stage.


And final set up. I found there is no need to lock the degree circle down it's quite heavy and doesn't move unless accidently touched. It rotates very well, a little tight in two places but there is no lateral movement at all so will leave this as it is.


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Mick, do you know if they can laminate it?

The setting circle that is!

Edited by Daz Type-R
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