Setting Circle Mod For Dob Bases.

[Daz Type-R]

Just like my lazy susan bearing mod guide I did, I thought I would also knock together a guide for any dob user who wants to fit a setting circle to their dob base, just to aid in finding those faint fuzzes.

So first off a list of the things you will need.

1. While not actually part of the setting circle, if you intend to find those faint fuzzes then you need something to give you the ALT co-ordinates, for this you need a Wixey or similar angle gauge, these retail for approx £20 and can be picked up from Amazon, E-Bay etc. Just do a search fir wixey digital angle gauge.

2. This is a list of things you will need for the actual setting circle itself.....

A sheet of 3mm Ply wood or MDF.

A cable tidy (Approx 2" in diameter)

Some black wood paint (I suggest Matt black, as gloss could reflect some shine) and a paint brush

Sand paper

A drill

A drill bit the width of a paper clip

A hole cutter (2")

A paper clip (red or white)

Strong glue

A squirty bottle with a fine spray nozzle with some water and a tiny bit of washing up liquid in it

The actual setting circle itself which can be purchased from our very own member Mike (Perkil8r) by dropping him a PM. (for non-members reading this his website should be up and running soon, I will insert the web address here when he is ready).

Jigsaw or hand saw

Credit or debit card (not just to buy everything)

Now there are a number of ways in which you can attach the setting circle and it also depends on what other mods you have done (lazy susan bearing for example) and how much time and effort you want to spend.

The simple option would be to just stick the setting circle to the ground board and cut a hole in your top board but this means you would have to keep lifting your whole dob base and OTA just to get Polaris in the centre of your FOV and the setting circle to be at zero degrees.

I went for the more difficult option but also the option which gave greatest flexibility come set-up time.

So the picture below is my ground board with the lazy susan bearing and slide guides all ready attached.

Now, I need to fit my movable setting circle around the bearing and the slide guides, so to do this I have had to cut my setting circle with a hole in the middle (for the bearing) and holes just out side this to cater for the slide guides. To cut the hole in the centre I just removed the bearing and drew around it onto the setting circle then cut it out. To cater for the slide guides, I just measured how far they were from the centre hole and then decide how wide the hole needed to be, see picture below...

The width of the gap equates to 20 degrees on the setting circle, so come set-up time, I can get Polaris in the centre of the EP, then adjust the setting circle so it reads zero, with out having to keep lifting the dob base and OTA up.

Now the setting circle by itself is only thin vinyl so is very weak and flexible, so to give it some strength I am going to stick it to some 3mm ply wood. This wooden base will also have a handle, this is required as when the setting circle is sandwiched between the ground board and the top board, it will be very difficult to turn the setting circle.

The wooden base for my setting circle also needs to be the exact shape and size as the vinyl setting circle, so this was simple to achieve as you just place the vinyl setting circle onto the 3mm ply wood and draw round it and cut it out, see picture below (note the extra "lump" on the base, this is the handle, you can make this as large or as small as you like).

Next I just sanded it smooth, wiped it down with a damp cloth and then once dried, set about painting it.

And the finished look..

While this was drying, I set about measuring how wide the actual degrees were on the setting circle and where the viewing window on my top board would need to be (by "how wide", I mean how wide is the black boarder with numbers on, see below....)

I have not provided any measurements in this guide as the size of the ground board, setting circle and top board will all vary depending on the size of your OTA ( a 6" OTA will have a smaller dob base than a 16" OTA).

Now my setting circles degrees are 2" wide, hence why I have listed a 2" hole cutter on the list of requirements.

Once measured where the setting circle viewing window would need to be, I cut it out.

Now you need to stick the vinyl setting circle to the 3mm ply wooden base, to make this a lot easier, I peeled the backing sheet off the setting circle and then using the squirty bottle with water and a small amount of washing up liquid in, I sprayed the back (the side that is sticky) with the soapy water and then placed the vinyl onto the ply wood matching all the spaces etc. Sqirting the soapy water onto the vinyl makes it a lot easier to move into place, without the soapy water, the vinyl would just stick to the wood and you would end up in a mess. The vinyl may have air bubbles in it, so using a credit/debit card, gently push the air bubbles and any creases out.

It should now look something like this...

and placed on the ground board...

Now I advise that you leave this overnight somewhere warm and with a heavy ish weight on it. This will make sure it dries flat.

While that is drying, I set about making the marker that will fit into the viewing window and makes reading the Azimuth degrees a lot simpler.

So taking your cable tidy, draw a straight line on the top of both sides of the cable tidy and then extend the lines down the side, now on these lines and at equal height, drill a small hole so that the paper clip (once completely straightened out) will fit through, so that you have something like this....

I used a red paper clip but you could use white.

You could glue the paper clip in place but I held it in place by bending it and leaving it like this....

It is held in place once you insert it into your top board but before you do, place some strong glue on the lip of the cable tidy and then press firmly into place, wiping up any excess glue immediately. It should now look like this...

By now your setting circle should be flat, dry and ready to be put back in between your ground board and top board and bolted back together.

If you have measured everything correctly, it should now look like this.....

Hope this guide has been useful, if you have any questions or comments, please post them below.

[Eastridge]

Oh, that looks fantastic Daz. Thank you.

We did the lazy susan following your previous thread and are very happy. It's really helpful to have things step by step like this for those of us less confident DIY wise.

Quick question, probably foolish and I should be able to work it out myself if I had a logical brain - to use this accurately do you need the scope base to be perfectly level? We have a gently sloping garden and one of the attractions of the Dob was we could easily just plonk it anywhere as long as it was stable.

As I understand it setting circle and wixey is the ideal combination - does anyone know if adding a wixey changes the answer i.e. do you have to calibrate it each time or does it 'self level' or what?

Thanks again.

[Moonshane]

that's a fine mod and well explained.

you also need something to calculate the alt and az co-ordinates for your position and time as they are not fixed but change by the minute (where RA and Dec co-ordinates are always the same). many people use a laptop / PDA which for me is the main reason I have never considered setting circles. I hate using gadgets at the scope.

[JamesF]

That does look very neat. The "viewing window" looks particularly nice.

James

[devoncow]

Looks great, giving some thought to doing this and your 'lazy susan' mod to our 200p, but as it's new will probably use it as-is for a while, bookmarked both topics though for the future! Thank you for sharing

[Daz Type-R]

Oh, that looks fantastic Daz. Thank you.

We did the lazy susan following your previous thread and are very happy. It's really helpful to have things step by step like this for those of us less confident DIY wise.

Quick question, probably foolish and I should be able to work it out myself if I had a logical brain - to use this accurately do you need the scope base to be perfectly level? We have a gently sloping garden and one of the attractions of the Dob was we could easily just plonk it anywhere as long as it was stable.

As I understand it setting circle and wixey is the ideal combination - does anyone know if adding a wixey changes the answer i.e. do you have to calibrate it each time or does it 'self level' or what?

Thanks again.

Hi, really happy that you and other people are finding the guides usefull. I find that Sky Watcher and possible other makes of dob based scopes do not put enough design and planning into their build, granted, the 200P is really cheap for what you can see with it, but I do feel that some of the mods are essential to make the scope even useable!

To answer your question (and to give you something else to do) when using the setting circle you need your dob base to be very level, to get round this I bought 3 shed levelers from B&Q for £4.99 each and removed the rubber feet on the ground board and replaced them with these, you can just make them out on some of the pictures above. They screw up and down, so if your garden slopes or is uneven, just buy a spirit level and alter the adjustable feet until your dob base is level on all axis.

Found a link to them here .......

http://www.diy.com/nav/garden/sheds-storage/wooden-sheds/shed_bases/Shedmate-Adjustable-Shed-Base-System-Black-11027510

As for the wixey, the setting circle only gives you where an object is in azimuth, i.e, how far left and right something is, to get the dec (height) you need the wixey.

This wixey needs to be set to zero (level) and your OTA needs to be level, so all I do is get a spirit level on my OTA, once that is level, add the wixey and reset the wixey to zero.

Sorted.

Like someone mentioned above, you do need a laptop/pda or iphone for example to get the alt/az co-ordinates of any given object but i put a home made red screen over my iphone when viewing to not ruin my dark adaption.

The only other downside to this is, you also need to polor align your dob (who ever heard of polor aligning a dob, what is the world coming too???? - lol.)

By this, I mean you need to get your base level, you need to get your OTA level to set your wixey to zero, then once you have found Polaris and got that in the centre of your field of view, you need to set your setting circle to zero. Only after doing all this, can you use it to find objects.

Hope the above helps, any further questions, fire away.

[Daz Type-R]

Correction.....

On this line..... As for the wixey, the setting circle only gives you where an object is in azimuth, i.e, how far left and right something is, to get the dec (height) you need the wixey.

I meant to say ALT for the height not DEC - doh!!!

[Carbon]

Nice tutorial!

I installed instead an adjustable pointer to align the base, with over 30 degrees of adjustability.

If the view of Polaris is obstructed I use Saturn for instance, quickly note its current azimuth position on Sky Safari, and move my pointer accordingly. This of course is done after roughly orienting the base to north, then leveling the base with adjustable levelers.

[houston]

Hi guys. I put the setting circle on the top board of mount and attached a metal sheet under the bottom board. Then with a bent hair grip attached to a small magnet it can be moved around base 360° so no need to line up north, just put any object in field of view and move magnet with hairgrip pointer to its azimuth. Works every time as long as completely level and wixey calibrated right for altitude. Must say it dont look as professional as these photos. Job well done!

[Eastridge]

Thanks for the comprehensive reply Daz, tells me all I need to know. Just need to persuade hubby to add it to his list of jobs ( I help him but...)

[knobby]

Nice guide Daz, I use pretty much the same system myself and... I find stuff now its great.

Only thing I do differently is to not bother aligning north... Instead I center something recognizable... Moon / Saturn / Jupiter etc. And then set the scope marking to suit.

it also does definitely help to level the base for better accuracy.

[iam4208]

It would be good if other people would put up pictures of their alternate solutions.  I'm not very handy on the DIY front, so I'd have to consider something simpler (as a beginner, I do have real problems finding fuzzies, so I'm always looking for cheap ways to overcome this).

[houston]

Iam428, heres mine, no cutting required.

[michaeldurban]

Nicely done yes..

This will help a great deal in finding just about anything..

One tiny little mode I did was to make sure the setting circle rotates freely around

the LS bearing...so I couldn't add any friction pads..

The plus side is...I don't have to rotate the whole base to line it up..

I just plonk it down...find any star...rotate the setting circle to the correct Az. degrees

and voila!!

Dead on every time..

In any case...setting circles take away the frustration of not being able to find that 'fuzzy'

you've been hunting for...

Last night I think I did 20 messiers, some nebulae and a handful of galaxies...

All came in my FOV after my first alignment with the setting circle..and Wixey..

Just make sure your board is level..

maybe went a bit overboard but...I sank a granite slab into my back garden..

Ah..one more thing...make two -25mm deep- aperture rings...

I used them last night and it makes a nice difference, especially when you have

a fast scope and can't afford US$ 300,- eyepieces !

[happy-kat]

Looks very interesting, would this be over kill on a heritage 130p dob base?

[michaeldurban]

For any dob the golden rule is -when using setting circles- that the base

(or the ground) on which it sits is level...

So yes, rather than 'hoping' for a level surface it is best to use either a

leveling board (see my post: dob leveling board)..or make your own

level patch of ground.

leveling boards are very easy -and very cheap to make

[Daz Type-R]

Looks very interesting, would this be over kill on a heritage 130p dob base?

No, not really, I suppose, the smaller the appeture, the harder it will be to find the faint fuzzies, so I would say, it makes more sense to have one on a smaller scope.

[houston]

I have found some of the messiers under bad light pollution using setting circles and wixey which i would have missed for sure just scanning the skies. Well worth doing.

[happy-kat]

Thanks OK, I will need to consider how to adapt the concept as the bottom base on the heritage does not cover the circle pad of the top part I also want to understand how the relative rather than absolute concept works as that may for the mount better. More research I need to do.

[Mr TamiyaCowboy]

very cool. 

have you thought about a low powered red LED. and using a copper wire strip.

a small non-toriod coil joule thief and a small button battery. the combination would last a very long time

and could be added into a small recess on the dob base, in low light you could filp

the joule thief on and it would run the led from the low powered button cell.

[Daz Type-R]

very cool. 

have you thought about a low powered red LED. and using a copper wire strip.

a small non-toriod coil joule thief and a small button battery. the combination would last a very long time

and could be added into a small recess on the dob base, in low light you could filp

the joule thief on and it would run the led from the low powered button cell.

I did, but as I usually have a red light strapped to my head to read star charts etc, I just thought it would be something else to power.

[andyb505]

If anyone figures out how best to do this for a Heritage 130P I would be very interested

Andrew

[happy-kat]

have you thought about a low powered red LED. and using a copper wire strip.

a small non-toriod coil joule thief and a small button battery. the combination would last a very long time

and could be added into a small recess on the dob base, in low light you could filp

the joule thief on and it would run the led from the low powered button cell.

I already have some LEDs and button batteries, I got the LEDs checp on Ebay for a different project and I could paint one with nail polish.

I have so many projects on the simmer, this and the barn door and finish the OU course and ...