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J.T.'s ring style azimuth setting circles

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#1 jtsenghas

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Posted 04 August 2020 - 12:12 PM

I am writing this thread to share a scalable pdf file of an azimuth circle I drew five years ago, and to offer some tips on using it. Several of you have used this with reportedly good results. I've even printed and mounted a mini one for an alt-az refractor for a CN member as a trade for a finder. 

 

The key to this design is that it is a ring that straddles azimuth pads and can be spun at setup to agree with the azimuth coordinates of a known object.  Because the values increase in a clockwise direction this is designed to be stationary in use with a pointer that moves with the scope.  That is my preference, as it keeps the readings directly below the focuser of my dob.

 

The original one has stood up extremely well to five years of use. It was first laminated, then adhered to Baltic Birch plywood, then routered outside and inside, and then sealed with clear spray paint to avoid moisture penetration into the edges. I'll show these steps in detail in subsequent posts. 

 

First of all, here is the file itself. 

Attached File  setting circle2.pdf   162.83KB   58 downloads

 

Printed at 100% size the outside diameter is 20 inches and the circle of the degree scale is at a 9 inch radius. 

 

This is what it looks like on the folding base of my folding 10" dob.

 

20200804_124729_compress7.jpg

 

On this scope the setting circle HAD to be a ring rather than a disk due to the structure of the base.  Those shower door rollers in the above photo bear on the edge of a 12 inch hole in my rocker box.  I've learned, however, that this style works very well on traditional dobs and minimizes the rework involved as compared to full disk setting circles. 

 

To show how this looks printed at 80% size and mounted on a more traditional dob, here it is on a 6" Orion Starblast tabletop dob I reworked with and for a club member this spring. 

 

20200514_224100_compress4_compress67.jpg

 

Please bear with me for a while. I'll post numerous photos with steps detailed over seven or eight posts or so, hopefully within a single day. 

 


Edited by jtsenghas, 04 August 2020 - 03:21 PM.

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#2 Tenacious

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Posted 04 August 2020 - 12:55 PM

That is excellent!  Nice job.



#3 jtsenghas

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Posted 04 August 2020 - 02:05 PM

First, some history: 

 

There is a long-running thread in the Equipment Forum on making azimuth setting circles for dobs in particular, but really any alt-az scope.  I do mean LOOOONG- running.  The now moderator Carol (csa/montana) started it in May 2006. As of this writing the most recent post on it was in August 2019.  It was this very thread that got me interested in trying something like this, particularly for those faint DSOs for which nearby stars to hop from are scarce. I've contributed to that thread the last few years and pages, and have already shared my above file there. That thread can be found here

 

Combined with a decent inclinometer, or angle gauge, A dob can become a remarkably accurate push-to instrument.  Magnetic compasses have at best resolution and accuracy of a few degrees and are susceptible to the influence of nearby ferrous objects. Large analog scales such as mine are very easy to read to a very small fraction of a degree.  As I'll show in this thread, I've even added a vernier scale for reading to the nearest tenth of a degree. I can vouch for the fact that this does get me aiming within a few tenths of a degree, provided the scope base is carefully leveled and there is minimal slop in the mount. 

 

Later in this thread I'll get into details and tips for use, along with my recommendation on a specific digital angle gauge for precise altitude aiming without much impact on night vision. 

 

These azimuth circles fall into two basic types, clockwise or counterclockwise, depending on whether one desires a moving pointer and stationary scale, or vice versa. Azimuth angles count clockwise with north at zero degrees and east at ninety degrees. 

 

Jonathan Pogson's (Oberon on CN) azimuth circle on his 16" scope Merope is an example of a counterclockwise circle. This circle, handsomely printed by a professional sign maker on an aluminum composite sign material must have cost more than a few Australian dollars. His circle is mounted to the top of the circular "rocker box " and turns with the scope.  A pointer detail is another piece of the same material with a slit in it that wraps around from the scope base.  Pointers needn't be pointy things. Jonathan has said he is happy with the pointer remaining stationary and towards his observing table and turning his scope from there. Since the scale increases in a counterclockwise direction and turns, numbers increase as he turns his scope clockwise. 

 

I, however, prefer a clockwise scale with a moving pointer, particularly because I tend to use the very Android smartphone I'm writing with now with Sky Safari (in red night mode) for data.  When I look down from the eyepiece of the Tardiscope from my observing chair I needn't even stoop to read my inclinometer or azimuth angle with a dim red flashlight:

 

Screenshot_20200804-145843_Gallery_compress45.jpg

 

With the advent of smart phones and tablets and apps such as my favorite, Sky Safari, these low tech analog circles are even easier to use. All it takes is current azimuth coordinates (for one's location and time) to set the scale to match. 

 

That Degree Circle thread shows numerous ways people have found to fine tune a setup to a known object.  Put simply, either the pointer or circle must be moveable.  Trying to move a scope a fraction of a degree could be an exercise in futility, or at least frustration.   It appears the most common technique used in that thread is to roughy aim the scope and then tweak the pointer itself, either on a pivot or magnetic mount. Steel strapping is one possible mount for a pointer with a magnetic base. 

 

I wouldn't recommend that anyone try to read that entire 14 year thread, especially because of the recent advances in technology and angle gauges.  The last four or five pages should suffice and you may well find different examples that would work better for you than my offerings.  I'm not the only one to post drawings to share, either.


Edited by jtsenghas, 04 August 2020 - 05:35 PM.


#4 jtsenghas

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Posted 04 August 2020 - 03:02 PM

Personal design preferences:

 

As I mentioned above, I was constrained to requiring a ring type circle by my scope design.

 

I had several choices to make on the circle itself, which I drew in AutoCad. Should it be black on white or white on black? What font type and size should I use? How do I want the numbers to be oriented? How thick should the actual lines be? Thinner may suggest greater accuracy, but thin lines in low light are hard to see. 

 

I performed a number of experiments to help with these decisions.  It was a no-brainer for me that I wanted the numbers oriented to be read from outside the circle with their bottoms facing outward. I was surprised to learn, however, that very wide lines were a lot easier to read in low light.  Thin ones vanished unless I stooped down with a red flashlight. This makes sense because our night vision rod photoreceptors have less resolution due to their summing effects than our cones, but the effect was more dramatic than I had expected. 

 

I found I could read black numbers and lines on a white background better than white on black, particularly at a distance. 

 

An Ariel Bold Font looked best to me among the options I had in AutoCad and was the easiest for me to discern among the digits 3, 6, 8 and 9.

 

I decided to make every ten degrees in as large a font size as possible, and every five degrees between them smaller to remind me which way I was counting.  I also used slightly different line widths and lengths for individual degrees, every five degrees, and every ten degrees. 

 

I tried using half degree tick marks but found this no easier to read precisely. Interpolating within a degree was easy even to a quarter of a degree with the large spacing.  At my 9 inch radius for the scale each degree is 0.157" apart.  That's nearly 4 millimeters, or about halfway between 1/8" and 3/16" per degree. 

 

In the end I chose to add a vernier scale with a pointer the same width as a single degree line. Vernier scales appeal to my geekier traditional side.  I love that the next decimal place can be read from counting which line at 90% spacing matches any other line. 

 

20200804_154216.jpg

 

In the above photo the bearing is 240.7 degrees, since the seventh line from the pointer lines up with another degree mark. By making the vernier lines the same width this became easy to gauge. I'll describe that vernier mechanism later, but frankly, it's easy enough to see that the bearing is about 240 3/4 without the vernier scale. My obsessive compulsiveness must be showing, as Russ (Roscoe) said when I first posted these photos. 

 

I also wanted this circle to be reasonably cost effective, too.  Professional sign makers quoted me prices to put this on aluminum composite materials that made me pause.  Perhaps if I had been making many nesting circles and objects from one sign I would have reconsidered.  I was impressed with the low costs people had come up with on the degree circles thread, though, and wanted to go a simpler route. 

 

In the end I settled on printing on paper, and laminating.  That lamination could be adhered to good thin plywood and routered afterwards. My method of sealing it AFTER TRIMMING has stood the test of time and dew.  There has been no significant warping either.  Details are forthcoming. 


Edited by jtsenghas, 05 August 2020 - 08:36 AM.

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#5 Mike G.

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Posted 04 August 2020 - 03:37 PM

vernier scales are so old school, I love it! reminds me of when I carried a slide rule in high school (calculators were available, but insanely expensive)



#6 jtsenghas

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Posted 04 August 2020 - 06:57 PM

Setting this up on an Orion dob:

 

To show the process of setting up such a circle, I'd like to show the 6" Orion Starblast rework done just a few months ago. 

 

Jon, the owner of that scope,  provided my drawing to a local printer in northwest Ohio and had them print it at 80% scale and laminate it. This made the outside of the disk 16", which was just under the diameter of the rocker box base.  He found that the largest size this vendor could laminate was 24" wide by any length (within reason) because both the printer and laminating machine worked with rolls of material.  When I did mine five years ago the Staples store I used in the same city I had the same constraints, so printing at 100% scale was close to the limit. 

 

We adhered the laminated print to the plywood with DAP Weldwood contact cement. This is the stuff you paint both surfaces with in a well ventilated space and wait at least ten minutes for it to become only tacky to the touch. 

 

You have to be careful to place the sheet properly the first time because this stuff really GRABS as it glues to itself. I'm pretty sure the laminated drawing would crease and distort if you tried to pull it up and reposition it as you work. 

 

I provided 1/4" Baltic Birch plywood for the job as a trade for some cherry lumber. The local lumberyards and big box stores don't have anything of adequate quality for this work.  I got this material at the Woodcraft store in Toledo. They sell Baltic Birch plywood in numerous sizes and thicknesses, but sometimes you have to special order what you need.  There is no shipping charge if you pick it up at the store. I've done this on a few occasions for astronomy projects. 

 

One trick for positioning the laminate is the same as many use on countertops with this adhesive.  In this method you put several parallel wooden dowels on the substrate and then place the laminate across them. You then pull out the dowels one at a time working from one end to the other to avoid having any ripples. It's best if you don't set yourself up to require precise placement when you do this.  For laminated countertops this means allowing for a modest overhang on all edges for subsequent trimming. For this project it meant not placing the circle too close to any edges. 

 

20200514_190108_compress49.jpg

 

We didn't have to adhere the entire surface, just the region that fell between the inside and outside diameters of the ring, plus a safety margin. I didn't have a good roller on hand for promoting a good bond, but rather used a roller skate with plastic wheels.  This must be the fourth time I've done this that way and the result is a good really smooth bond. 

 

The next step is routering, and this can be done immediately.  I use a homemade router circle jig that uses a 1/4" dowel pin pivot.  I find that such a large pin allows for really round circles with matching start and end points. Small pivots from nails or such are more likely to tilt or bend or pull slightly out of position.  If you don't have a circle jig you can screw your router to a piece of plywood and make two holes in it for your two radii. I find a 1/4" pin is also a handy choice because it is easy to add 1/8" from distance from the near side of the pin  to either the near or far side of the router bit. 

 

I strongly recommend using a down-cutting spiral bit to avoid making fuzzy edges.  Such a tool makes the cut as crisp as if cut with a sharp knife. 

 

We carefully drilled the center hole with a brad point drill bit and set the router depth to just over half the plywood thickness and cut from both sides. 

 

20200514_193734_compress42.jpg

 

In the above photo I'm making the third of four passes.  The outside diameter was done from both sides and this is the first pass on the inside diameter. 

 

Note that the diameters needn't be precisely set, but you must have an exact center that is concentric with the circles.  The edge of the inside circle bears against the ring locators in use. 

 

When you make the last cut on the inside you must take care that the ring doesn't shift as you complete the cut. Remember, that cut is a locating surface.  I clamped both ring and center section down with a holdfast on a block on my bench just before cutting the last inch.  I could have simply taped everything down with two sided tape for the final cut, or have had a companion hold the ring and center down at the end of the final cut. 

 

20200516_200315_compress90_compress24.jpg


Edited by jtsenghas, 05 August 2020 - 05:58 AM.


#7 jtsenghas

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Posted 04 August 2020 - 07:39 PM

I had to move the azimuth pads about an inch closer to the Azimuth pivot bolt on this scope than they were originally for the ring to fit. I chose to keep the inside diameter of the ring more than four inches smaller than the outside diameter to help with stiffness against warping or sag over time. 

 

After we disassembled the base I chose to simply remove and discard (hoard) the 1/4" pads that had been stapled to the base.  I had some spare thicker disks of Teflon with a step cut into them left over from this very operation on my own scope from choosing to change dimensions midstream on that one.

 

20200514_224955_compress26.jpg

 

I chose to place these about a millimeter further out from the azimuth bolt than the ring would fit over initially, and then pared them down in place with a very sharp chisel to marks made with a circle compass that had pivoted on the azimuth bolt center. The side of the step is the locator.  The depth of the step is slightly more than ring material thickness. Jon did have to get a slightly longer 6 mm bolt for his azimuth axis to accommodate the slightly increased gap between the rocker box and base. 

 

Note that the ring must be mounted extremely concentric with the azimuth axis.  One needn't be as precise as I was here to get that level of accuracy, though.  The original 1/4" thick pads could have been drilled  and countersunk one or two millimeters off center and then screwed down to a couple of fender washers at least 1/2" larger in diameter.  The ring could then be set onto the exposed portion of the washers and the pads screwed down turned at approximately right angles to the radii. If the three pads were then rotated until the ring was both a slip fit and concentric all of this could be adjusted. Final measurements and tweaks could be done with the actual pointer to be attached to the rocker box later. 

 

Note that if you do move azimuth pads more than an inch or so, you might need to move the feet beneath the ground board to suit to avoid springiness during high power tracking.  On this little tabletop dob that was a non-issue.


Edited by jtsenghas, 04 August 2020 - 11:16 PM.


#8 jtsenghas

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Posted 04 August 2020 - 08:51 PM

There are several decisions that can be made regarding setting circle size depending on one's priorities and willingness to rework a scope.  

 

On my folding scope I can choose whether or not to include my circle when I stack my scope together and I'm not concerned that it sticks out.  I chose its size based purely on where a practically mounted pointer would sit. 

 

Jon wanted his circle to stay entirely beneath his rocker box and not to increase its size at all.  He also had the advantage of a willing helper who was confident about laying out and cutting a mouse hole for the pointer and installing some plastic edge trim to seal it. 

 

20200514_224458_compress13.jpg

 

Note that we could have simply cut a straight chord from the edge of that disk for the same effect. I've seen that option used in the Degree Circle thread mentioned and linked to previously.

 

That's me in the above photo. I made a 2 1/4" hole with a Forstner bit with a backup board to avoid tearout. I then laid out radial lines alongside that hole and scored them with an X-Acto knife. I then cut out the waste with a tenon saw. The edge trim I had on hand is sold with Melamine shelving at my local Menards store.  It was left over from a stretch dob base I made a few years ago for an 8" Orion dob. This was trimmed flush with a plane blade used as a bevel up chisel. 

 

Regardless of how a base might be trimmed, it is particularly important that raw wood or particle board in particular be adequately sealed against moisture. If one didn't have plastic edge trim as I did, the voids in the particle board could be filled with wood filler or, better yet, two part epoxy filler and then primed and painted. 

 

Particle board tends to swell with moisture and flatness of the disk could be compromised if it isn't sealed. 


Edited by jtsenghas, 04 August 2020 - 09:05 PM.


#9 jtsenghas

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Posted 04 August 2020 - 09:30 PM

Scaling it down:

 

Well, I've been posting intermittently on this since lunch time today, and must call it a day. 

 

Tonight I'll close by showing how this pattern can be scaled down. 

 

A couple of years ago I printed and laminated this at 40% size for a refractor in Florida and released it as a 45 rpm single album: 

 

20200516_195123_compress14.jpg

 


Edited by jtsenghas, 05 August 2020 - 07:21 AM.

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#10 RobertMaples

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Posted 04 August 2020 - 11:16 PM

This is a timely thread for me, I planning on redoing the base for my scope and was also considering a setting circle where I could adjust the circle itself instead of the pointer but haven't figured out exactly how  will implement it.  This will give me some things to think about, and that pdf will be a real time saver.

 

I'd also like to see more about that "Tardiscope"!



#11 jtsenghas

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Posted 05 August 2020 - 07:20 AM

...I'd also like to see more about that "Tardiscope"!

I still haven't put together a comprehensive thread on this build, though there are smatterings of it throughout this forum since 2015.  It was well received that year at Stellafane and picked up a few awards there.

 

It's gone through some incremental upgrades since then that have required an interior counterweight plate to be added. 

 

You can see it being packed up after the Cherry Springs Star party in 2018 here. Dave Mitsky posted a few photos of it later in that thread including one of the setting circle. 

 

I introduced that scope back in 2015 here. There's more information several posts further down that page. 

 

The image in my avatar was from it June 2015 at first light when it was functional but not flocked or painted and atop a temporary base. I've considered changing it, but as more of a woodworker than Dr. Who fan I may leave it as is.  Perhaps I should make the avatar a gif of it fading and reappearing in its present form. 

 

That build was fun whimsy.  It performs remarkably well but isn't my ultimate scope.  I've got three mirrors, two of them larger,  and two partially complete builds that I've GOT to get back to. 

 

Since I've just shown the mini version of my setting circle, I might as well show what I've done on a maxi version next... 


Edited by jtsenghas, 05 August 2020 - 08:23 AM.


#12 jtsenghas

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Posted 05 August 2020 - 07:50 AM

Scaling it up:

 

I'm going to put a bigger version of this circle in my 12.5" dob that has been languishing at least 90% complete for more than a year. The Cherry Springs Star Party that didn't happen was supposed to be my motivator to get it done this spring. 

 

Since laminating is limited to 24" wide at most printing facilities, I modified my drawing to be about 50% larger for a ring that should be an optional item at setup of the 12.5" scope. 

 

20200517_194321_compress74.jpg

 

I made two segments of just over 180 degrees each. I intend to cut them out oversized, overlap them precisely, and then slice through both layers between two of the degree tick marks. Those two pieces will then be adhered and routered like the previous ones.  I'll just have to make a larger, perhaps temporary, circle jig. 

 

I have a nice piece of 3/8" Baltic Birch for this one and will make the underside thinner for about half the ring width. The scope for this one has an adequate gap for fitting it in when desired:

 

Screenshot_20190707-211648_Gallery_compress69.jpg

 

 


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#13 jtsenghas

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Posted 05 August 2020 - 08:19 AM

That 12.5" scope is loosely based on Jonathan's (Oberon's) Merope, which is a 16" F 4.5". The build thread for it can be found here

 

The ring shaped rocker box is chamfered on the lower edge to help with circle readability. It will be able to be assembled and disassembled by stacking since the azimuth pivot is in fact a roller I made to a tight fit to a hole made with a Forstner bit. 

 

Screenshot_20200805-091329_Gallery_compress48.jpg

 

That roller was from my junk drawer and was salvaged from a conveyor system.  It had a slightly convex outside diameter as shown here, but I turned it cylindrical on my wood lathe. I may make an insert for it in the underside of the rocker assembly so that the hole doesn't wear significantly for long term pointing precision.  (Oops, my OCD is showing again...)

 

Screenshot_20200805-091353_Gallery_compress85.jpg

 

Anyway, I like the idea of these circles being optional for use.  When I get lost in the skies at a dark site they are handy.   When I'm showing eye candy like M13 or M8 at outreach events I'd rather not have such a circle sticking out where the general public might accidentally damage it. Transporting the scope in my car trunk should be easier if that ring is placed on the trunk floor first before the smaller diameter items. 

 

 



#14 jtsenghas

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Posted 05 August 2020 - 12:15 PM

Finishing up the circle on the 6" dob:

 

I have just a few more notes on finishing up this project on the Orion 6" tabletop dob.

 

First of all, in terms of layout, this scope has a single arm altitude bearing like its 4.5" counterpart. The side of the scope opposite the arm offers a lot more real estate for placing the indicator for the circle.  

 

Fortunately, these scopes are very flexible for right side or left side focuser positions, and whether they are used from the side with the arm or the opposite side.  The tube can be rolled around or reversed, though the latter change does require the zenith position stop to be moved. 

 

Jon prefers to observe with his right eye with the focuser on the left as seen from behind the scope.  When it is aimed south the focuser is on the east side. That's the way the scope came, but with arm and its eyepiece rack on the same side. 

 

We removed the two screws from the stop bracket on the base of the rocker while it was apart and drilled two small holes to move it to its opposite position.  We then took out the tube and installed it in the clamp reversed. 

 

The resulting layout looked like this. 

 

Resized_20200516_202028(1).jpg

 

If you look closely you can see the original holes opposite the stop, which is now on the left. It's of little consequence that the altitude tension knob and eyepiece tray now fall on the opposite side.  For such a little scope both are an easy reach, regardless. 

 

Before we reassembled the scope we had to seal the edges and underside of the ring. You have to be careful not to use anything that may bleed into the paper edges of the sliced laminate. We chose to place the ring face down on top of a few riser blocks and gave it several light coats on all edges and the bare plywood surface with a fast drying clear coat paint.

 

20200725_175210_compress65.jpg

 

We made each coat light to avoid soak-in to the paper and to avoid sags. I wanted to be sure that we didn't give one side of the plywood an opportunity to soak up moisture.  In the past I've seen plywood painted on one side warp convex on the unpainted side during times of high humidity and wanted to avoid this. 

 

This is the same technique and paint I used on my 20" ring of the same thickness five years ago.  Despite major dew and a few "moist" days at Cherry Springs State Park it has remained very nicely flat. 

 

I sealed the hole we carved for the indicator with contact cement and shelf edge banding.  This stuff is made several millimeters wider than such particle board is thick so that it can be trimmed flush. I like to do this work with a "wicked pissa' sharp" plane blade held flush to each surface bevel up.  Sideways stroking motions do quite nicely. 

 

20200805_120555_compress85.jpg

 

Note that the "mousehole" we cut had to stay outside of the inside diameter of the ring and outside of the azimuth pads for appearance and function. 

 

For the indicator I chucked a piece of 1/8" brass in a drill motor and spun it against coarse and then fine sandpaper for a curved blunt tip, much like that of a knitting needle. I imagine a knitting needle would do well also. I was going to paint it black for contrast, but Jon liked the brass color, so I also polished it with green rouge on my leather strop using the drill motor. 

 

I drilled by eye the hole for the indicator at an upwards angle of about 20 degrees and epoxied the pointer into place. After final assembly I bent it down a few millimeters to avoid, or at least minimize parallax.  It nearly touches the disk. 

 

That was pretty much it for this scope.  Jon did have to buy a 6 mm bolt that was 10 mm longer than the original azimuth bolt to accommodate the increase in height of about 1/4" from the taller azimuth pads.  We could have simply counterbored the hole for the bolt head and washer beneath the groundboard, though, at minimal loss of strength. 

 

 


Edited by jtsenghas, 05 August 2020 - 06:11 PM.


#15 jtsenghas

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Posted 05 August 2020 - 01:15 PM

The floating vernier scale on the Tardiscope:

 

On my scope I got a little OCD about putting the Vernier scale against the ring to minimize parallax, particularly if the ring warps a wee bit. 

 

Screenshot_20200805-134839_Gallery_compress4.jpg

 

I mounted the laminated vernier scale to a block between two inset blocks of Teflon that ride on the ring.  This block in turn is a slip fit in a wooden bracket that is pinned to the rocker box. That vernier block has two brass pins at its ends that ride in slots for height. Any slight variation in the relative height of the rocker box and ring is accommodated as the Teflon blocks glide across the ring. 

 

The bracket itself locks onto the rocker box with a right angled inside corner and an angled brass locating pin. It sits tightly against the rocker box though it can be lifted right off.

 

This floating block does have slop of a few hundredths of a degree, though.  It repeats really well if I consistently make my final tweak of the scope in a clockwise direction. If I need to turn counterclockwise I deliberately overshoot at least a few degrees and then come back. I do the same for setup targets. The hysteresis in the entire scope is incredibly small. It would be fair to say that it repeats within a tenth of a degree or so and is accurate within a few tenths provided it is leveled well. I'll get into setup and usage shortly. 

 

On my 12.5" dob under construction I'm experimenting with methods to tighten things up further on the mount.  I'm tempted to have the vernier scale just pivot on a hinge and close safely upwards against a magnet when not in use.  This way I won't even have to remember where I put it.  My memory is long for a lot of things, but all my life I've been prone to misplacing things I put down. It comes from thinking more than paying attention. At least soon I can start blaming that on age...

 

Hopefully you'll see the details in that 12.5" hexapod build thread soon



#16 jtsenghas

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Posted 05 August 2020 - 02:50 PM

Adding digital angle gauges (inclinometers):

 

There are a wide variety of digital tools out there for accurately reading altitude angles and many now have repeatability and resolution of 0.1 degrees, and accuracy within 0.2 degrees. 

 

I like the term inclinometer for such devices that are sensitive to gravity, to avoid confusing them with digital protractors.  Digital protractors could work too, provided you set them to a reference object, but inclinometers have a few distinct advantages and help to minimize setup and read errors.

 

I prefer devices that have silver and black unlit LCD displays.  Since I'm reading my azimuth circle with a dim red flashlight it's easy to read such a display with the same. The batteries in an LCD display tend to last almost forever due to their low current draw and they don't have bright illuminated displays to rob night vision. 

 

The original Wixey gauges had bright green displays, the absolute worst color for night vision for DSO observing.  In the Degree Circle thread some people have put red film over such devices, and that helps considerably if that's what you have. 

 

These original Wixey devices also had only one scale for level and some couldn't even be zeroed. You'll see on the Degree Circle thread some members mounted these on hinges with screws for tweaking level. 

 

What I have and love is a newer model, Wixey WR365. A link that works at the time of this writing for these is here. Current prices shipped appear to be $36 to $46 USD. The link is to one of the more expensive sources, but I expect that link will work longer than most. 

 

An image of it is here: 

 

Screenshot_20200805-174922_eBay.jpg

 

I like the fact that there is a fixed level scale on these and one that can be zeroed anywhere.  It retains its setting if it times out from inactivity, so a single poke of the ON/ZERO button brings it back up at any altitude angle. 

 

The display can be tilted up for better readability, which I REALLY LIKE. I like to mount my Wixey on a steel plate on the top of my semicircular altitude bearing,  which is angled about 45 degrees to my optical tube.  This way it is tilted only 45 degrees left and right as the scope is pointed from zenith ro the horizon. 

 

Here again is the view looking down from my eyepiece. 

 

20170417_161631_compress88.jpg

 

For setup, I first use the device on the bottom of my rocker box and use the fixed scale to level the three adjustable feet on the folding base.  I then put the gauge on the altitude bearing and aim the scope close to the horizon so that the fixed scale shows 45 degrees. I zero the other scale at that point to be rough aligned with the scale I use. At this point the scope is roughly leveled and the altitude gauge is very close. 

 

To fine tune level of the scope, I press the scope firmly down to make sure the feet have settled firmly, and adjust the leveling feet to give the same altitude reading (close to zero) in every compass direction. I point the scope over one foot, perhaps the north one, and adjust that foot so that I get the same reading when I point north or south. I then point east and west and adjust the other two feet EQUAL AND OPPOSITE AMOUNTS until I get the same reading east and west.  Finally, I repeat the north and south checks to verify them, or to fine tune. By adjusting east and west feet equal and opposite amounts the north and south leveling is maintained. 

 

To fine tune the altitude gauge, I use the current coordinates of Polaris if possible, though if I'm quick, any astronomical object would do. With a high power eyepiece I defocus so that the target nearly fills the field of view.  This helps with centering. I zero the gauge when the target is centered.  Note that Polaris varies nearly 0.7 degrees above and below your latitude angle, so use current coordinates from a good star app. I like Sky Safari. 

 

Now aim the scope to the horizon until you see the current altitude of your previously chosen target displayed in the opposite direction.  The Wixey WR365 doesn't show plus and minus but does indicate with pictures left and right. If Polaris was at 41.5 degrees when I zeroed on it, then I rezero with the scope pointed level and reading 41.5 degrees the other way. 

 

Altitude is now set, even if the gauge is tilted to any angle with respect to the scope. 

 

Setting azimuth is even easier.  I like to choose a low object east or west since such objects are barely drifting in azimuth during this process, but again, anything will do if you are quick. 

 

Point at a known object, defocusing again to help with centering, and simply spin the setting circle until it agrees with azimuth coordinates on an app. For precision and repeatability I aim at the object with a clockwise motion of the scope. 

 

If you use Sky Safari and choose to center the object on your screen, the top of the screen will display up to the second coordinates. If you zoom in you'll get coordinates in degrees, minutes, and seconds.  IF YOU PAN OUT YOU'LL GET DECIMAL DEGREES.  This feature helps with matching both the circle and inclinometer, which are read in decimal degrees. 

 

PIECE A' CAKE!

 


Edited by jtsenghas, 05 August 2020 - 06:36 PM.


#17 jtsenghas

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Posted 05 August 2020 - 02:57 PM

Questions, comments? 

 

Well, that's about all I wanted to present.  You'll learn tips and tricks with practice.  If the scope isn't perfectly leveled, azimuth will be a little off  especially at angles to your tilt axis.  Altitude should always be within a couple of tenths of a degree, though.  If you  choose to rough level only,  you may want to set altitude first to your desired target and then sweep a little left and right to find it. 

 

That business of Sky Safari showing decimal degrees rather than degrees, minutes, and seconds of the center of the display when you pan out moderately can save you some mental arithmetic when pointing your scope too.

 

With care you'll be finding objects with high powered eyepieces! 


Edited by jtsenghas, 05 August 2020 - 07:05 PM.


#18 tommm

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Posted 05 August 2020 - 10:59 PM

Very nice! Have you used the system enough to say how close you usually get to a target object when you slew the scope to its coordinates? Are objects generally in the fov of say an ep with 1 deg true fov, 1/2 deg?



#19 jtsenghas

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Posted 06 August 2020 - 06:10 AM

Are objects generally in the fov of say an ep with 1 deg true fov, 1/2 deg?

They are easily within 1/2 degree FOV. That's why I confidently claimed accuracy within a few tenths. 

 

On my 10" dob with a Paracorr 2 (which boosts the focal length 15%) my 8.8 mm ES82 eyepiece yields 159 power and just over half a degree.

 

Objects are always in the FOV on the first attempt (within 1/4 degree) unless I have an assignable cause like a scope foot settling further into soft ground, etc.

 

Even if the scope hasn't been perfectly leveled, I always see my target with an 11mm or 18 mm eyepiece of that series, usually nicely centered. 

 

That trick of sweeping slightly left right always finds my objects if my setup isn't perfect, but I've at least set altitude precisely on my Wixey.

 

I've done repeatability tests on Polaris, which fortunately moves negligibly in a session.  Even when I spin my scope 360 degrees and dip it down and up, I can set the two angles and see it nearly perfectly centered. 


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#20 jtsenghas

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Posted 06 August 2020 - 06:23 AM

The biggest source of variation, and it isn't much, is slop between my OTA and rocker box.  When I gingerly  turn my scope from the rocker box only, and it isn't a significant stoop on this closed tube scope, I get the best results. 

 

I'm working on a good spring loaded roller to keep my nearer altitude trunnion against the side Teflon thrust pads, but at minimal friction, on my 12.5" to improve azimuth repeatability on that scope further. 



#21 jtsenghas

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Posted 06 August 2020 - 09:50 AM

Additional information on cost and some construction tips:

 

I realized I haven't yet discussed cost of making these rings, except to comment that having them professionally printed on aluminum composite sign materials is a bit pricey.

 

I just made phone calls to the only two printing and laminating services within 20 miles of home and made cost inquiries. I was pleased to learn that the closest one has a laminator with a 27" wide roll and offers to print up to 26" wide.  The man I spoke to conceded they could do nearly that 27" if the edges needn't be well sealed, which they don't for these circles. 

 

Laminating such a drawing would be in the range of $12 to $16 at present, though likely more in more urban areas. Printing would be another $3 to $4 in black and white if a print weren't provided.

 

The current price at Woodcraft for a 6mm (nearly 1/4") by 24" x 30" piece of Baltic Birch plywood is $10.99. There is no shipping fee if you can get to a Woodcraft store. For anything larger I'd go a bit thicker. 

 

A three ounce bottle of DAP Weldwood contact cement costs about $3.

 

If you, or a willing friend have the tools, this means that at current 2020 prices, a disk up to 24" could be made for less than $30.

 

Note that you could push the size a little on 24" wide plywood if you choose to trim the outside diameter of my drawing closer to the printed numbers and place your pointer at a radius of up to about 11 1/4".

 

This should fit most commercial dobs, especially if you are willing to move the azimuth pads inward a little. Just note, the feet of the scope should be under or very nearly under the azimuth pads for stability for high power tracking.  Note that pads would have to be moved a lot for scope stability to be compromised and that moving the pads inward slightly reduces the torque required to spin the scope.  This may be a good thing. 

 

For the DIYer of modest skills, the idea of having the three guides for the inside of the ring adjustable appeals to me. They needn't be the azimuth pads themselves, though care must be made to raise or thicken those pads at least a few millimeters more than the ring thickness to avoid it getting scuffed or bumped.  Having adjustment on the ring location and clearance would mean that the ONLY critical construction dimension is the location of the hole for the circle cutting jig. If that's carefully drilled to the print everything else should be fine. 

 

I like the idea of screwing three small disks to the groundboard with an off- centered flathead screw and turning them like camshaft for ring adjustment. After assembly the actual pointer used could be spun to check how well the ring is centered and subsequent tweaks could be made. 

 

As for reworking the groundboard, a large through hole that doesn't break the edge could be made, as long as the scale is visible.  One could even cut a ring of PVC pipe with a length of the groundboard thickness and bore (or bore and sand) and epoxy that into place for a clean looking waterproof rework. 


Edited by jtsenghas, 06 August 2020 - 09:55 AM.


#22 John Fitzgerald

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Posted 06 August 2020 - 10:13 AM

Last winter, I made a 25 inch azimuth circle for the new Baltic birch base I built for my 12 inch solid tube Dob.  It had to be hot laminated in two pieces.  I fitted those together on the base and stuck down to the ground board preliminarily with double sided tape.  Then, I fastened the teflon pads over it with countersunk screws. A V-shaped notch in the bottom board of the rocker box is the indicator.  I use a magnetic digital inclinometer on the top of the steel tube.  This has worked very well so far.  I can easily get objects into the center half of the finder field using only these crude setting circles and Sky Safari 6 plus.

 

I used the azimuth circle printing link that has been on CN for many years.


Edited by John Fitzgerald, 06 August 2020 - 10:13 AM.

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#23 jtsenghas

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Posted 06 August 2020 - 10:42 AM

...I fitted those together on the base and stuck down to the ground board preliminarily with double sided tape.  Then, I fastened the teflon pads over it with countersunk screws...

Nice!   There are some advantages to each method and attaching rigidly to a groundboard does keep construction simple and thin.   

 

I'm curious, though. If the circle is rigidly attached to your groundboard and your indicator is a notch, how do you fine tune alignment? Do you bump your whole scope?  I wouldn't mind doing that for a tabletop dob, but I imagine this would be tough to nail exactly with a 12" solid tube dob.



#24 jtsenghas

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Posted 06 August 2020 - 10:55 AM

....I used the azimuth circle printing link that has been on CN for many years.

Could you share that link in this thread? I believe I know which one you are referring to if it was among those in that Degree Circles thread in the Equipment Forum.  Others may find it better for their specific needs than mine.

 

It also could be used in my ring style if that's what one wanted. 

 

I'm not so vain as to presume that my offering is the best for everyone, but I did put a lot of thought into it for my preferences. 


Edited by jtsenghas, 06 August 2020 - 10:58 AM.


#25 John Fitzgerald

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Posted 06 August 2020 - 11:14 AM

Here's the link:

 

https://www.cloudyni...etting-circles/

 

I copied the printable file to a flash drive and took it to Kinkos.  They plotted it on their Hewlett-Packard E size plotter, then laminated it.  It was around $22, I think.

 

The 12 inch Dob sits in indexed holes in a heavier base on smooth, almost polished, concrete.   The zero point of the circle is fixed on what I always set as the north point of the base.  That gets it close. I slide the base a bit until it's aligned with the azimuth of a selected star in the south, between 20 and 45 degrees high.  It works well, and takes less time than aligning a DSC.  The base can be left in place in the rolloff.


Edited by John Fitzgerald, 06 August 2020 - 11:17 AM.

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