DIY Dobsonian Setting Circles

[burkedc95]

Hey guys, just wondering what deminsions I should use to create my own strip azimuth setting circle.

This is the model telescope I have: http://www.skywatcher.com/swtinc/product.php?id=51&class1=1&class2=106

I want one to go around the circumference of my base, not sitting on top.

The diameter of my base is 571.5mm or 21.5in

Thanks for the help in advance!

[Carbon]

I want one to go around the circumference of my base, not sitting on top.

As on the outer edge trim of the ground board like this?:

[burkedc95]

As on the outer edge trim of the ground board like this?:

Yes!

[Carbon]

That above was my temporary solution until I decided to modify the base with a cutout and all. It actually worked out really well.

I think the easiest way to do this is to do what I did. First, separate the ground board from the base.

Use light colored electrical vinyl tape and apply over the edge trim. Don't stretch the tape when applying as it can contract, shifting your degree markings. Better if you used tape that didn't stretch at all.

You'll get a truer 360 degree divisions by taking the ground board and dividing it into 4 quadrants using a large carpenter's square and subsequently dividing those down to single degree divisions. I used a large protractor for this. The degree lines and numbers were drawn freehand using a fine permanent marker.

[astronymonkey]

The strip you would need would be 1806mm long based on Pi (3.16) x Diameter. One degree would be just over 5mm of length.

Astronymonkey

[8kids]

The strip you would need would be 1806mm long based on Pi (3.16) x Diameter. One degree would be just over 5mm of length.

Astronymonkey

Pi = 3.16, I think not.............discuss

[Steve Ward]

3.14159265 would be a little closer , one of those things that stick from school , albeit 34 years ago ............

[Gina]

I still remember Pi as 3.14159 from school nearly 60 years ago Mind you, I do use Pi a fair bit

[Steve Ward]

Yet another damning indictment of the failing education system eh ,

Bring back the times tables and daily spelling tests I say...........

[Gina]

I wonder how many youngsters can do long division in their head

[Steve Ward]

Most can't even tie shoelaces let alone do maths ....

I'd better be careful , don't wanna be dissin' da yoof...........

[fwm891]

I wonder what the current record is for the number of decimal places for solving pi....

As the outer edge of your base is black you could use one of the fine typing correction pens directly on the edge giving you white markings. I would suggest you over coat these when fully dry with a water based varnish/lacquer to seal and prevent chipping

Edited July 13, 2012 by fwm891

[Steve Ward]

http://www.numberworld.org/misc_runs/pi-5t/details.html

[Carbon]

As the outer edge of your base is black you could use one of the fine typing correction pens directly on the edge giving you white markings. I would suggest you over coat these when fully dry with a water based varnish/lacquer to seal and prevent chipping

...or use a label maker to apply numerals directly on the edge trim...

[fwm891]

Thanks Steve, I guess 3.14159 will do fine for setting circles....

I know one guy who used a carpenters tape measure wrapped around the base of his dob. Then used a simple programmable hand calculator to work out what 'measurement' he needed to go to to find the next object. Did the same for the alt bearing making the dob a 'manual' goto...

[Carbon]

Or you can also use tiny labels like I did here to mark the degrees, except place them on the edge trim. There are a number of ways to do this.

[iamjulian]

Thanks for posting the photos Carbon. I got the calculator out last year and made up a set of eight strips on an A4 sheet, which I then had laminated. Double sided sticky tape only lasted about a day and then they were all hanging off. I like the electric tape idea, I also like the white pen directly onto the base edge idea, and cutting a window in the top board would work too. Decisions decisions.

[twinhexydan]

Hi guys ,

a very interesting thread you have here ----I made a digital azimuth circle like the one carbon showed but included the single figure markings to be more accurate ,which it was -- am wondering if anyone here knows of a way to make it more accurate by including a vernier scale type add on ??if thats possible at all.thanks.

curious Dan

[Carbon]

Well, I find that with a wide field eye piece I can place most objects within the field of view. I think what's more important than smaller increments of the degree circle is the absolute levelness of the base for consistent accuracy. I use a digital angle finder, place it on the base and spin the base 360 and adjust level. This is a bit more accurate method than using simple bubble levels for the base.

[twinhexydan]

Thanks carbon for that,

hadn,t considered that part of the equation too well, but your right , you got excellent logic , and very clear ideas --spinning a digital angle finder with the base is a real cracker and as accurate as they come ,

I do like mechanical success but I,m off to buy a digital angle finder now if only to take advantage of your appreciated idea --twill be more accurate than a ghost stick or a dumb judge ==,(spirit level) that,s for sure.

whohay! bagged another gem collector Dan

[AllanJ]

Have a look at Rob Willett's website, linear strip section. Not free, but inexpensive.

http://settingcircles.robertwillett.com:8000/index.php?cmd=linear_screen

Allan

[twinhexydan]

Hi allan ,

many thanks for that ,sounds very interesting ,will try myself .

vernier Dan

[Lee from ERA]

I added an adjustable setting circle to my Skywatcher 8" and I'm going to do the same this month to the 12" that has replaced it.  More detailed notes available in the attached.

Adding a setting circle to my Dobs.pdf

[Guest]

On 12/07/2012 at 16:44, burkedc95 said:

Yes!

Did you ever get this all worked out?  This is exactly what I want to do.

[jjohnson3803]

16 hours ago, Mike Q said:

Did you ever get this all worked out?  This is exactly what I want to do.

Since you're in the US, you might want to check Oregon Rule company.  They sell a variety of angle gauges, tapes, and such.  I use their 360* circle gauges for azimuth circles on my Twilight-1 and Skywatcher AZ5 mounts.  FWIW.