My Dob DEGREE CIRCLE Modification

[Doc]

This is my Degree Circle Modification.

The base measures 800mm, so I had a degree circle printed out on A0 paper at 795mm in diameter.

I then cut out some 3mm hardboard at 795mm as well and glued the circle to it.

I then coated both sides in sticky back plastic to waterproof it.

I then screwed through the teflon spacers and secured the degree circle to the dob ground board.

I then placed the bearing and plates on top of this.

I then had to make up some sort of indicator so I cut a piece of flat metal and drilled two holes in the ends and mounted this to the upper board with some bolts, spacers and inserts.

The indicator is made up of two cabinet magnets superglued together and a hole drilled in the middle to accomodate the indicator. I then painted the indicator red and the metal plate black.

The magnet now sits on top of the plate at the desired position.

[kniclander]

Doc, I take my hat off to you - that looks fantastic - thanks for posting the pics. Well done.

Let us knowhow it works.

[irishbloke]

That is a great job Mick. Did you manage to get the edge of the upper board sealed again. My wife works in a kitchen manufacturing place and they glue laminates onto boards with a hot glue. If you need it done somewhere like that might be able to help.

I'll be interested as to how it works for you.

I take it the point of the needle on the metal strips with magnets is so you can move it to make fine adjustments with alignments.

[Doc]

Well the sky is pants but there's enough stars out to test it and it worked perfectly.

Polar aligned and moved pointer to zero degrees and everything I put into the laptop to get the Az reading was there in the FOV or very close. Tried numerous stars, Saturn and M13.

I stripped the plastic rim off the offcut and restuck it using contact cement. Seems OK.

And the magnet and pointer is moved up and down the metal strip for aligning purposes.

[lawrie]

I added an azimuth scale without resorting to any "surgery" on the dob.

The website StarTrak home page provides suitable scales. The ground board scale is marked out by hand but the altitude is determined by an electronic inclinometer such as the Wixey.

With my Skywatcher dob. I removed the black PVC strip around ground board edge, cleaned and sanded the edge, filled it with Polyfilla, sanded smooth and gave it two coats of white matt-finish oil paint to give a good surface on which to mark the degrees. The scale is marked out using a paper quandrant template made from a print-out from the startrak website.

A diameter line was marked on the board with a second one at right-angles to the first to give four quadrants. A 90deg. template from Startrak was printed out large enough to fill a quadrant with overlaps and then trimmed to size. The paper template was temporarily taped in a marked quadrant and using a permanent black marker pen to make the points and numerals indelible, the ten degree points were numbered with smaller 5 degree marks and points at each degree. The template was moved into the next quadrant and the process continued for the full 360 degrees. It only took a few minutes but be careful to mark the scale clockwise as viewed from above. The rocker board edge just has a small white paper strip with a black line stuck directly at the front.

To resore it to its original state I have merely to replace the black PVC strip and remove the paper marker. Simple as that. It works a treat!

Lawrie

[Doc]

I've looked at your site before Lawrie full of interesting articles.

Your dob modification sounds very good indeed.

I am also using the wixey for altitude readings.

[philsail1]

Your scales modification do seem to be a very useful addition for your Dob Mick. In fact, I think anyone would say that they are THE most useful and workable addition anyone could add to make finding stuff much easier.

One would think that manufacturers would commercially make these either as standard additions sold with a new Dobsonian, or as "optional" extras.

Regards,

philsail1

[albedo0.39]

Yet another great mod from you Mick... Yet another must do for my (2 week old) LB. Where do you dream them up from ?

[lawrie]

Mick,

Your azimuth scale modification looks fine. Mine was a cheap and cheerful method. Yours is rather more elegant. Very nice.

(But how did we manage without them?)

Lawrie

[The Warthog]

I think this idea will eventually work its way into the commercial dobs. After all, it is in the original dobsonian spirit of simplicity. Great job!

[AndyBooth]

Just found this post, great idea !

[Sunwind]

this is pretty neat, but i'm suprised that you can't purchase modifications like this which you can easily apply to the dob so you don't have to make your own, it seems very simple aswell as ..well, essential!

I have a small question though, how do you align the scope to the correct azimuth, do you use a compass to find north and just point the azimuth which would be north over to it and go from there or what?

[kniclander]

you can just line up on polaris which (in alt/az terms) will always be 0 deg az (ie due north). not absolutely accurate but good enough?

I think:icon_scratch:

(mine's a WIP cos my wixey keeps freezing )

[Doc]

Dan's right you just line up 0° in azimuth by pointing to the North Star. It's sactually 0.52° but it very close annyway. Then with your Wixey you set that to zero and when it's pointing to the North Star should read 52.4° in my case.

[albedo0.39]

Gotta say - seeing how easy that system work at the SSP-1, It was brilliant !