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Setting Circle Help


catman161
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Right, so I have taken the plunge and purchased a setting circle printed on heavy duty vinyl and a digital wixey with magnetic base.

As far as how I am going to see the setting circle I am barefaced copying Micks idea with the desk cable tidy but as my scope (and base) are smaller than this have gone for 50mm desk cable tidy. Plus I already own the drill adapter at that size to make the appropriate hole. Thanks Mick :)

So I am now awaiting the delivery of aforementioned items.

This has got me thinking is this all as straightforward as it sounds? Do I just stick the setting circle onto the base? I will obviously need to cut three holes for the, um I don't what they're called! But they allow the top part of base to rotate on the bottom base! I'm sure there's a better way of wording that but the drug combination I am on really has slowed me down mentally! So I will need to make x3 cut outs to allow for those.

Then is it as simple as sticking the setting circle down? Or is there a particular starting point along the diameter of the base where 0 degrees must be? The only reason I ask is because I read on another forum of a woman who was trying to do this mod and she stated that the numbers were "the wrong way around"? I don't see how this is possible with a circle?

I was also thinking the use of a setting circle and digital wixey is all well and good as long as the ground is level. So I feel another purchase needed will be levelling feet.

Any recommendations/links on a) the type of feet needed and B) how to attach the feet to the Dob base? I am assuming some sort of cross brace??

Any help/advice much appreciated :)

Felix

Edited by catman161
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Copycat :lol:

Felix as you say for this to really work the more level your base the more accurate it will be.

As you are not using a sliding pointer on your top board to determine where zero degrees is, you will need to make the degree circle able to move a little bit so you have some leeway while trying to find zero degrees.

My original dob had a sliding pointer and it's very easy to make as you can secure the degree circle to the ground board via those three teflon sliders.

But as you are using a cable tidy your degree circle will have to rotate and once polar aligned can be locked down so it does not move.

It's a bugger to have no tolerance while trying to find polaris, so much easier with a little leeway. The zero degree can be anywhere you want it to be, thats what makes the rotatable degree circle so good.

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Confused, does 0 degrees not have to point North, aka, Polaris, so you rotate the base (if you have stuck your setting circle to the bottom board) of your dob until 0 degrees points to Polaris, then you use the pointer that you will of fixed into the hole cut out of the top board so you know what degree you are at? Then as your top board and OTA rotate, you can see what degree you are at?

Or am I missing something?

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Thats correct but the zero can be anywhere on the board, as soon as you have Polaris in your eyepiece then you set zero degrees. The idea of the slider or rotatable degree circle is the ease of moving it to zero. If you have to physically move the ground board to achieve zero degrees it's a PITA to do that, much easier to move a slider.

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But as you are using a cable tidy your degree circle will have to rotate and once polar aligned can be locked down so it does not move.

Can I not just lift the base and rotate the bottom base until 0 degrees is pointing north (Polaris) then it is locked in that position when I place it on the ground? Then put OTA on slap the wixey on, zero it and get started? This I confusing me now! I am sure it will be made much clearer once I see someone do it in practice :)

Suffice it to say am I safe to stick the setting circle on the bottom base and drill the hole in top base and fit the cable tidy?

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Ahhhhhh, I see, never thought of that.

Back to the drawing board!

Sorry Felix for the thread hijack by the way....... :blush:

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Suffice it to say am I safe to stick the setting circle on the bottom base and drill the hole in top base and fit the cable tidy?

Depends if you want to either.......

a: pick the bottom board up every time you set up - then sticking it down is okay.

b: if you don't want a fixed setting circle then no, you cant stick it down, as like Mick says, if you get Polaris in your FOV, and zero degrees is right round the opposite side, then you are going to have to pick the whole thing up, turn it, get Polaris back again, no, not quite right, pick the board up again etc, with a movable setting circle, very easy.

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Also, if 0 is at the 12 o clock position, which way should the numbers go, should 5,10,15 etc be going up clockwise or counter clockwise, or does it not matter?

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OMG! I am getting too confused about this now!! I think the meds I am on are not helping!

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I couldn't just pick up my 16" dob base, it weighed a ton, hence a movable slider to give me +/- 50 degree tolerance.

Your 8" should be OK to pick up and get accurate polar alignment.

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I take your point Mick with a 16" monster Dob. So how are you going/how do you make a setting circle that is moveable? As in what surface can I stick this setting circle that I have ordered to?!

Sorry for all the questions I am sure I will get it at some point :) thanks for your advice so far

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What I'm going to do is this:

1. Print out a degree circle that allows the figures to be shown through the drilled cable tidy hole in the top board.

2. Cut it out so it's the shape of a two dimensional tyre, it has a outer and inner edge.

3. Cut out two pieces of 4mm perspex the same as apove and secure them together, so in other words you have sandwiched your degree circle between two sheets of perspex.

4. Place this on your ground board and place three little bearings 120° apart laying flat on the ground board with the edge of the bearing touching the inner circle of your perspex tyre shape.

5. Mark out centre of bearing and drill and secure to ground board.

6. Your degree circle will now be secure in two dimensions and be able to rotate around the bearings.

7 Attach some sort of handle cum bracket which is secured to the degree circle enabling you to move it anywhere you wish and once polar aligned you tighten the clamp on to the underside of your ground board.

I hope you understand this.

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That is absolute genius mick!

Thanks for explaining it to me. I just wasn't seeing it before.

Can I ask where you're sourcing the Perspex & bearings from?

I would very much like to be exactly what you called me above "a copycat" ;)

It's just such a good idea!

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It is a great idea and is so simple to use.

1. Plonk your scope down in any position

2. Level the base

3. Move your scope to the horizontal position and zero your wixey.

4. Centre Polaris into your FOV of your eyepiece.

5. Wixey should read your latitude.

6. Move your degree circle to zero degrees

7. Tighten your degree circle down.

8. Thats it.

Not sure about perspex, there's lots of places on E-bay, also bearings from e-bay, dead cheap only a few pound each.

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You're right Mick-great idea. Do you know if you have to use any specialist types of tools to cut Perspex?

Also I know this will make sound so dumb but what kind of bearings are required as I googled bearings and there are loads!

Oh yeah and levelling feet? Best types? How to attach etc?? Sorry I'm such a noob when it comes to diy!

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Cutting Perspex I presume with a normal hacksaw.

Bearings I would say your normal ball bearing encased in a race, don't need nothing fancy, not going at any great speed, only need them as a guide really, in fact just a bolt would do, but it wouldn't look as nice.

Levelling legs I would use three lengths of aluminium screwed to your ground board 120 degrees apart and a M10 hole drilled and taped into the end. I have seen M10 bolts with rubber cups on the end from e-bay. Buy three of these and screw them in, so just screw them in to raise scope and unscrew to lower.

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Ive just had a thought whats the size of the gap between your ground board and top board.

Mines 20mm so plenty of room for perspex and bearings.

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Ive just had a thought whats the size of the gap between your ground board and top board.

Mines 20mm so plenty of room for perspex and bearings.

No where near as much, I have a lazy Susan bearing in mine and I don't think the gap is even that! My gap (going from memory) is about 10mm.

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Well I've just measured the gap between my ground and top board and its only jus 4mm! That's the Perspex idea out the window :(

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Well I've just measured the gap between my ground and top board and its only jus 4mm! That's the Perspex idea out the window :(

Are you not running the lazy susan mod Felix, how are you coping without it?????

If you go for that mod, you could incorporate 2 lazy susan bearings, one built up a bit higher to carry the weight of the OTA and a bigger one (but not built up a lot) on the outside to carry the perspex setting circle.

Just a thought?

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No, no lazy Susan bearing for me presently. I do keep meaning to do it just never got around to it. I don't follow about the double lazy Susan bearing though??

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I would imagine one placed in the inner part of the board and one on the outer edge so to balance the scope in the horizontal plane.

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Well I've just measured the gap between my ground and top board and its only jus 4mm! That's the Perspex idea out the window :(

Not really as you can get 1mm or 2mm perspex.

What I would do in your case is secure it to the ground board and either move the base by hand until polar aligned as it's only an 8" so not to heavy or instead of the peephole just make slider pointer.

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Thanks Mick,

I will look into thin persex options but will most likely end up sticking to the ground board and moving base manualy. Right now to sort leveling feet. Thanks for your suggestion by the way mick :)

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