Setting Circle of 10" dob

[209herschel]

Hi everyone,

I've found a couple of files online for setting circles that I can print but they're not quite the diameter of my base, which is 54cm. The files are pdfs and I'm unable to modify the file. Would any of you know how I might get a setting circle template to my exact specifications? In using setting circles, do you set zero degrees to north?

Thanks very much

[glend]

There : used to be a guy that woud make them up for you. Have you searched here? If not most print places could probably alter say a 12" file. Yes zero is north, but make sure its true north, you can get your local declination online.

[209herschel]

Thanks Glen. I'm going to search again because I saw a few entries where a guys was creating a file for someone else.

[Visionoz]

Please see here; http://www.iceinspace.com.au/forum/showthread.php?t=60946&highlight=setting+circles

HTH
Cheers
Bill

[byronpaul]

Herschel,

your after richardda1st ...... but he hasn't been on the forum for a few months.

If you scan through this thread, you might find what your after.

http://www.iceinspace.com.au/forum/showthread.php?t=60946

Paul

[skysurfer]

I have a setting circle in SVG format which you can modify with e.g. Inkscape.
Maybe this helps.

It contains PDFs as examples.

[209herschel]

Hi there, thanks so much for this. I really like the look of this setting circle. I'm heading out to Office Works tomorrow to see if I can get one printed and laminated on an A1 sheet.

When I open this file, it's showing six pages when I print. Is there any way to get one page output when I take it to Office Works? I'm sorry if this is very basic, unfortunately I really know nothing about this process.

Thanks again.

[209herschel]

Thanks to all of you for your help. I've got a few files I'll be taking to Office Works for printing.

My choice is either to print the file for the GSO 10", diameter 54. This would be good as it's my actual scope. If I go with this, I'd cut a notch in the top rotating part of the base so that I could see the setting circle from above.

Otherwise, I have another file of 46cm diameter. If I go with this, I'll go to Bunnings to get them to drill a 3cm or so diameter hole above the setting circle. This wouldn't be at the edge of the top part of the base - it'd be inset a bit. I think I prefer this finish as it seems neater.

The other things I've noticed is that some people seem to attach the setting circle to the top part - the rotating part - and fix a pointer to the bottom. This seems to avoid the need to cut a piece out of the top, rotating part of the base. Any thoughts on this difference?

One last question, how would you all recommend fixing the setting circle to the bottom part (non-rotating) part of the base? Double sided tape or should it be held in with a screw, perhaps counter sunk so it doesn't interfere with the movement of the rotating top?

Thanks again for all the help.

[byronpaul]

Herschel,

Others will chime in with their ideas but I would not attach the circle to the base. It should float!!!!!

The reason for this is that you just do a rough alignment when you set the scope up. Then upon finding a real target you adjust the azimuth circle by rotating it to match the correct object coordinate. As such. I allowed my base circle to have about 75mm of adjustment in either direction and then I just secure with Velcro. It works an absolute treat as does the Wixey for altitude.

Paul

[209herschel]

Thanks Paul, it's remarkable how little I understood about this! I've been reading that the circle needs to float. As you say, you align on an object you're certain of, and move the circle to match that azimuth, found on stellarium or something similar. Can I ask your opinion on this circle I found online:

http://www.instructables.com/id/Manual-Setting-Circle-for-Dobsonian-Telescope/?ALLSTEPS

The circle is about 2cm greater in diameter than the base, so it sticks out - you can just rotate it with your hand, matching the coordinate to a fixed marker.

Can you quickly explain what you do with the velcro? I didn't quite understand that part. Thanks again for your help.

[209herschel]

Hi Paul, sorry to ask another question. How do you see the setting circle? Have you cut a piece out of the top rotating piece or have you done something else? I'd be keen to hear what others have done. Thanks

[byronpaul]

Herschel,

I've attached some quick photos of my 12" Lightbridge base, which shows my cutout and the azimuth circle.

The cutout is approx. 9" long as I didn't want to have to get too close at night to see the reading.

The 3 photos with the Velcro show how the circle rotates about the axis bolt. I could spin it 360 deg if I want to as the Lightbridge has a Lazy Susan bearing (similar to what's shown in the link you provided). If you have Teflon bearings, you still centre it on the bolt, and just cut out sections to allow the circle to pass around the Teflon bearings.

I wouldn't have a circle that sits outside the base board. It will get knocked, look tatty very quickly, and also collect dirt and moisture that will go between your boards.

The circle does not have to come all the way out to the edge of the board, but the closer you get allows a smaller cutout to see it. I've seen different cutover styles and sizes. The best one to use is the one that suits your needs and is "easy" to do. As most base boards are just chipboard. Seal it up after cutting to minimise moisture penetration over time.

Good Luck.

[skysurfer]

I saw your answer, the SVG (Scalable Vector Graphics) can be resized in the Inkscape app (both Windows and Mac, freeware). The PDF has a fixed size which is 54cm diameter (for my Dob which is a 16") which is well beyond A4 that's why it are six pages (which I really printed out and aligned and pasted on a circular sheet of aluminum.

See here how I did it. http://skysurfer.eu/dobson.php

But you can resize it when you select to print it, just set the size to 46/54 times the size the printer popup shows.

I hope this helps.

[Allan_L]

I like your solution Paul. :thumbsup:
Obviously won't work for all setups, but very neat and clever adjustment.

When I had mine, the scale was affixed, but I had a few degrees of adjustment that I could move the pointer to improve accuracy once observing began.

Another thing I tried was to attach a scale to a slightly oversized levelling base. This didn't require cutting a slot in the mount, but it had its own weaknesses.

Regards
Allan

[209herschel]

Hi Paul, I think it's all starting to make sense. Am I right in saying that you use the velcro tag (the one that hangs off vertically) as a handle to move the circle around? Once you're happy with alignment, you then stick the velco down to the patch on the base, fixing the circle for the session? This looks brilliant - I've seen examples of hard cut outs as a handle and I always thought I'd end up walking into it a few times a night! One question I have is do you just move the velcro tag if the scope is moved to a position where the velcro tag is in the cutout area?

Can I quickly ask what your pointer is? Is it a nail, drilled and glued into the top rotating section?

I was also uncertain about the best place for the cutout/viewing area. Am I right that since the circle can be rotated, I can have the viewing cut out anywhere around the rotating base? So I thought it would be most convenient to have it close to under the eyepiece when in the focuser, just in front of my feet. So I could just look down and rotate to the desired coodinate.

Can I please summarise what I'm going to do tomorrow for a final comment that I haven't gotten something wrong:

1. I'll print and laminate the 54cm GSO circle that Richard made a while ago for the GSO 10", which is exactly what I have (thanks again Richard for this and the pm).

2. I'll cut a hole out of the middle of the circle for the lazy susan bearing bolt and place the circle under the lazy susan grey bearing (as in the link from before), allowing it to be rotated once the top platform is put on top of the lazy susan bearing.

3. I'll attach the velcro tag to the circle (did you use glue to attach the velcro tag and strip or maybe double sided tape?)

4. I'll measure a cutout area and head to Bunnings to have them cut it out. I'll then fix a pointer to the centre of the cutout arc, allowing it to pass across the circle as the scope rotates.

5. I'll get the Wixey for altitude. My yard slopes down but I can set the Wixey to zero when the OTA is level so my altitude will be independent of the base.

Thanks again for all the help. If you can see any problems, I'd appreciate any feedback before doing this.

Herschel.

[byronpaul]

Herschel,

good to see it's all starting to make sense.

The answers to your questions.
- My Velcro adjustment tab is located on the 0 or 360 deg position of the circle
- I start by placing the Velcro in the middle of the adjustment piece on the base
- I then put the base down and try to have my pointer directed due west (my set-up) which means my adjustment tab is due north
- I then align on a star I know the co-ordinates of and fine tune the Velcro adjustment to get it as close as possible to the correct azimuth setting.
- After practicing this a few times, I normally only need to rotate the circle a few degrees to correct it.
- If you add about 150mm of Velcro to the base as the adjustment, this would give you about 30 degrees of azimuth adjustment which is may more than you should need.
- If I relocate the scope, I start the alignment process again - which takes no more than 1 or 2 minutes. It's that easy once you get the hang of it.
- My pointer is a cooking skewer that I pinched from the kitchen draw. Cut and drilled into the base to securely attach it. Never been damaged yet and it's easy to replace if needed. It is fixed in position and I don't remove it.
- I would place the cutout section on the side of the scope you view objects, right beneath where you would be standing. If placed on the front or back, or other side, it would be difficult to use and you'll find you're walking around the scope all the time.

For your process, here's a couple of other comments.
- when you get it printed, go with the smallest size than fits the drawing. I'm not sure what size you'll need, but you may not have to go up to the A1 size - this just costs you less
- depending on the stiction of your azimuth bearing and weight of the scope on the lazy susan bearing, you may not be able to place the circle on top of or below the lazy susan as it might be too hard to rotate. If I recall what I did, I placed my circle perfectly on the base. Once located, I carefully added the hole for the centre bolt to ensure I was centred, then I scribed and cutover the lazy susan. So my circle rotates around the outside of my lazy susan.
- the Velcro I used for both pieces was 2 sided - easy !!!!
- everything else looks good.

The Wixeys are ingenious. Once I had mine levelled to zero, I stopped re-zeroing each set-up as I place it on exactly the same spot on the scope every time.

With the Azimuth Circle and Altitude Wixey in place, finding targets will by pretty damn easy. This set-up is not as good as say an Argo Navis in finding really faint fuzzies, but it's a significant leap above star hopping which I have just never gotten my head around.

I remember my first target with my set-up was Tarantula Nebula. I spent about 10 minutes the prior session trying to find it and eventually did. After installing my set-up, doing a few alignment checks on stars, I then went to Tarantula. I think I would have had a 24mm Panoptic in at the time (so about 64x magnification and 1.1 deg FOV) and hey presto there she was in the middle of my eyepiece :eyepop::eyepop::eyepop:

Take your time with the modifications, and all should be good.

Paul

[209herschel]

Hi Paul,

Once again, thanks for clearing a lot up. Final questions before I head into Office Works tomorrow:

1. Is the velcro tab stuck to the bottom of the setting circle at the zero/360 degree mark? That way if you rotate to 360 degrees, you won't see the tab?

2. Is your circle laminated? I'm going to print out 3 templates tomorrow and check them out on the base before I get the one I want laminated. The only problem is that Office Works will print the circle onto a rectangular page (eg A1), then laminate. They can't cut out the laminated circle. So I'll be doing that. Did you just do this yourself carefully with scissors? I can't think of a better way. Office Works recommended I cut out 5mm outside of the circle to ensure the laminate surface remains stuck together. Is there a better way to do this? I'm worried my cutting, the additional 5mm, etc might look clumsy.

3. How did you cut accurately around the lazy susan bearing? It's pretty wide. I could perhaps try a compass to draw the circle and cut as accurately as possible with scissors?

Thanks again Paul. The logic of this is becoming pretty clear now.

Herschel.

[byronpaul]

Hi Herschel,

Yes Velcro is stuck to bottom side of the circle. I fixed the loop part of the Velcro on the side of the base and the hairy part on the circle.

I progressively drilled the centre bolt hole from very small to the final size to get it as accurate as I could. Cleaned the hole up with utility knife.

I traced the lazy susan cut using the bearing itself as the template. I then pre-cut the lazy susan cutout with a utility knife leaving about 10mm to be cut, then I performed the actual cut with good scissors. The reason for doing it this may is I found scissors to be a more controlled cut than the utility knife as it must be circular.

Ideally you would have that 5mm on the very outside of the circle so the laminate sticks together well ..... but I couldn't be stuffed making 2 trips to officeworks to do mine. I got it printed and laminated in 1 visit and then just cutout it out when I got home. So far the laminate hasn't parted, and even if it did and got to a point that it was getting tatty, I would just redo it. I think it only cost about $20 to print and laminate so it's not that critical.

I would spend more time getting the cutover on the lazy susan as close to perfect as you can. This cut has more effect of the useability and accuracy of the circle. The very outside cut is purely aesthetics so that's up to you how accurate you want it.

Paul