(Viewed 12,408 times)

[Kalvis]

I was wondering if any of you amateur telescope makers (ATM-ers) have
1. Experience in building a dobsonian mount for a newtonian reflector
2. Found inexpensive or free PocketPC or phone software with alt/az coordinate functionality
3. Built or came upon a nice portable and easily stowable observing chair.
I’ll describe what I have to work with, what I’ve done so far, and where I could use some additional pointers.

Background
My optical tube assembly (OTA) is the Orion 6 inch f/8 newtonian (so called “LT” for long tube) reflector. It was graciously sold to me last December by Chicago Astronomer (CA) Bill whose CA forum name is atomant. With the rings that accompanied the tube I was able to successfully mount the reflector onto my SkyView equatorial (EQ) mount and take in some awesome views of Saturn. However, the relatively tall height of my EQ mount even with the legs fully retracted places the eyepiece (EP) high off the ground. Often it is necessary to stand and even lean over when observing. The deeper I get into this hobby the more I realize that to really observe an object, soak it in and see its finer points you need to look at it for a longer time and not just a quick 3 second glance. For this reason accessibility to the eyepiece and a comfortable seated observing position have crept to the top of my list.

Dob altitude bearings
I don’t really like the cave man version of basic John Dobson’s tube box members.aol.com/sfsidewalk/sectionc.htm It’s too bulky and doesn’t allow for the tube to be easily rotated (for EP accessibility) or moved axially to adjust balance as needed. This is why I also want to avoid attaching permanent altitude wheels a.k.a. side bearings to the OTA such as can be seen in this otherwise very nice design guide: www.skyvalleyscopes.com/wood.htm Instead I very much like the idea of attaching such wheels / side bearings to my OTA by utilizing the mounting rings. I’m talking about the same rings that came along with the OTA and were used for attachment to my EQ mount. An off-the-shelf large diameter bearing which I’ve seen used in some ATM designs is the ole toilet floor flange. I just bought a pair of PlumBest 4” PVC Plumb Fit Closet Flanges at Lowe’s for $3.76 apiece. It took only two pairs of screws and a few minutes to attach both of these to opposite sides of my rings. Hey, it’s already starting to look like a dob!

Dob rocker box
I’m not going to use any real fancy design for this, just something plain. Perhaps inclining the vertical walls inward at the top might make it a little more stable and add to the aesthetic appeal, but I haven’t yet decided. My only real questions here are:
1. Should I use the traditional approach of cutting a notch at the top of the side boards and affixing a couple of Teflon pads spaced 90 degrees apart (45 in front of and 45 behind vertical)? An alternative approach I’ve seen is to cut out a quarter of a circle and line it with a strip of outdoor carpeting. What are the pros and cons?
2. What thickness of plywood is adequate? To keep the weight down I know to steer clear of particle board, but what should I use: half inch? three quarters? full-inch?

Dob ground board base and azimuth bearing
I really like the approach used by Berislav Bracun: www.pondi.hr/~beri/cald.htm I think that I want the leveling feet feature, but am unsure of how to convert wood clamps to this type of application. Also, he uses a polished steel plate on top of 3 roller bearings with a center Teflon guide bearing sandwiched in the middle. I love it, but I don’t think I can do it. Any suggestions on doing it simpler but maintaining the functionality? Furniture glides and Ebony Star laminate apparently work well since they are so popular for ATM dobs, but this roller bearing and steel place combo claims to be better. Thoughts?

Dreaming about adding a poor man’s digital Push-N-Go
Some crazy dob owners who want the functionality of a computerized finder install incredibly expensive digital setting circles and a handheld controller with LED readouts. This will easily drain your wallet by $500+. You could also buy the less expensive version from Orion know as the Intelliscope which comes preinstalled on their higher end dobs. Nevertheless, it still adds $230 to the price of their basic $260 SkyQuest XT6 Classic. Both Chicago Astronomer Joe and I admire the McGuiver approach where doing things with pencil, paper, magnets and paper clips (with a little bit of freeware/shareware) can give you something almost as good, sometimes even better, but definitely more satisfying. That’s why I like how Berislav Bracun used the StarTrak position tracking and setting circle template freeware www.startrak.co.uk The SetCirc.exe program is simple and easy to use. I’ve already printed out the scales I plan on using. However, I don’t have a Psion hand held anymore (mine busted years ago) so I will have to find inexpensive software for my PDA (running PocketPC) or for my cell phone. I’m intrigued by the Pocket Star software: www.nomadelectronics.com/PocketPC/PocketStars/PocketStarsIntro.htm. Anyone out there tried it and liked it? As an even cheaper version I would like to try out the freeware Orionic v1.2 www.dasys.cz/kamzi/ but the website seems not to be functional. I’ll search around on the Web to see if I can find it elsewhere. In any case, this type of software would require me only to input my lat/long coordinates and have the correct time of day running. The output should be an amazingly accurate pair of alt/az coordinates for any deep space object (DSO) in the database. With a my envisioned dob set-up it could be as simple as point-and shoot -- that is after a quick initialization. What d’ya think?

Observing chair
Being sick of standing, crouching, kneeling and bending over I want to get myself a nice observing chair. Yes, I know that Apogee sells a nice one for $70 www.apogeeinc.com/product.asp?itemid=77, but once again, I’m cheap and looking for something better. I love this TeleVue pneumatic stool www.focuscamera.com/prods/835835114.asp , but it can’t be worth $220! My thoughts are to find a used adjustable height drum throne (that’s what rock-n-roll drummers call their swivel stools) for under $50. Another thought I had was to take a height adjustable lumber support stand and convert it into an adjustable stool. It would still fold up and store easily taking up very little space. These cost only $15 at HomeDepot. All I would need to do is replace the roller bearing on top with some semi-comfortable sitting platform. Anybody ever tried it? Is this a stupid approach?

If any of you have gotten to the bottom of this message and have some helpful hints or experience to offer I would much appreciate it.

Thanks,

Kalvis

[Chicago Astronomer - Astro Joe]

Kalvis,

Both Chicago Astronomer Joe and I admire the McGuiver approach

Lol...let's dive on in...

(I found that many of the links were not viable and cleaned them up - no extra charge... )

1 - "The relatively tall height of my EQ mount even with the legs fully retracted places the eyepiece (EP) high off the ground".

*

[*Image of proper mount replaced]

I recall Bill's reflector, and can relate to the eyepiece out of comfortable reach on my own scope, especially when pointing near zenith.

Can't you rotate the tube in it's rings to angle the focuser tube more toward you? Also, it will whack it a bit off balance, but you could also slide it down some in the brackets? Sometimes I slide it almost to the focuser in order to reach the eyepiece for the public. A counter weight can be utilized to temporarily rebalance the tube...(heavy magnet, velcro exercise weight etc...)

I prefer to keep desired objects for serious observation about 10 degrees from zenith. Yes, the best sky is straight up, but EQ's are notorious for fighting the user straight up with OTA/tripod bump, inaccessible eyepiece reach and the tendency to hug the whole damned thing to view.

And I'm in agreement that one must be comfortable for an extended viewing session, and any effort in this area will enhance all other aspects of a session.

2 - Dob altitude bearings

I would like to see the set up you did with the toilet flanges. Attaching them to the rings is a great idea, as now you could rotate the OTA to any comfortable position - all Dobs should be like this, and not just the expensive rotating focus collar option. I have read where some have used milk bottle washers as rubbing surfaces instead of teflon for the Alt axis.

3 - Dob rocker box

You want solid stability, and anything thinner than 3/8th I think would be questionable. I would use gorilla glue as an adhesive as well as mechanical attachers. But here's an idea that I have not seen before, but just maybe be useful. PVC pipe is very strong yet lightweight. I wonder if one could build vertical support stands from them...with the horizontal piece slightly depressed in the middle where the toilet flanges would rest upon...?

4 - Dob ground board base and azimuth bearing

For a quick base support, one could use a large Lazy Susan for left/right movement. And the use of leveler feet can easily be incorporated onto material that the Susan would rest upon. Or the base of a spinning stool could be used, just remove the padding.

This guy's set-up is sweet that you linked to. I also like that we both have finder scopes made from binocular parts and homemade eyepieces!... ;D If he lived here in Chicago, we would hang out together. The movable weight is great, as is the whole scope.

5 - Dreaming about adding a poor man’s digital Push-N-Go

I haven't used one of these, but I understand if set up properly, it will assist in finder those DSO's and fuzzies. But alignment and leveling is critical. I personally would do without, and use the funds in other aspects of the mount. One could always incorporate it later on after all the bugs are eliminated. If one uses a Rigel star finder, you can obtain for free, celestial maps with the concentric circles overlayed for easy targeting. The Rigel should be on every scope, and stay away from the Telrad, as it's too heavy and will throw off the balance.

(See my review on the Rigel: astronomer.proboards23.com/index.cgi?board=Equipment&action=display&thread=1110828464 )

6 - Observing chair


I have used quite a variety of observing chairs, and liked them all. From the elaborate ladder-like friction chair to milk crates. Have you visited the Observing chair yahoo group? This is all they chat about. Here's the link:

groups.yahoo.com/group/telescope_observing_chair/?yguid=36640652

The $15.00 chair project is well worth exploring, as no chair is worth $200.00...regardless if it's covered in velvet, hydraulic and with a mini fridge.

I have been comfortable in using a ladder, one that was 4/5 feet high. I can comfortably rest my entire weight on the ladder, leaning into it while staying at the eyepiece for an extended amount of time. I can still reach the slo-mo controls and didn't cost my anything.

I am certainly no expert on Dob mount contruction, but the McGuiver in me can see the possibilities. Bounce more ideas and plans, and let's get your OTA mounted soon. Post some pics of your project so we can get a better idea.

[Kalvis]

Joe, I appreciate your thoughts and suggestions. In response here are some additional comments:

Eyepiece height and off-balance conditions
I have tried rotating the tube after loosening the rings. Unfortunately access to the eyepiece sometimes remains elusive. I've also tried the trick of sliding the OTA down to lower the height. As Joe notes, depending on how far you slide it down, the balance can become quite off-kilter. This affects my mount and causes the declination axis to begin to slip, no matter how much I tighten it. I've also got this (unfounded?) fear of bending my the metal tube of my OTA.

Altitude bearing
I'll try to get a digital picture of my toilet flange/OTA mounting ring subassembly and post it here.

Rocker box
Thanks for the construction tips. I think I'll be sticking with wood -- it's better than metal or PVC in attenuating vibrations. Another drawback of constructing from PVC pipe is that although it is strong, I don't think it is sufficiently stiff, i.e. the modulus is too low. That is where plywood really shines.

Az bearing & leveling
The lazy susan bearing is a great idea. I completely forgot that I bought a decent 12" one about a year ago at a hardware outlet store for only $5. I will probably just add some adjustable tension feature near the middle. Something like lag bolt/wing nut combo sandwiching a plastic guide bearing. I'm still a little puzzled about exactly how to install leveler feet.

Digital push-n-go
At dark sky sites I would gladly use my Rigel QuickFinder and/or mounted green laser pointer along with a nice set of celestial maps. However, living under (as Joe calls it) the Great Chicago Nebula, some important locating stars are often hidden from naked eye view which is equivalent to what can be seen with these otherwise very nifty unity finders. Installing these circles on my mount is really a no cost option. It is far easier to do it up front during construction instead of a retro fit afterward. Plus, software prices range from $0 for freeware such as Orionic to only $20 for Pocket Stars which is still a modest investment for this potential added functionality.

Observing chair
I'll check out the yahoo group site devoted to observing chairs. It's probably chock-full of gems.

Over-and-out,

Kalvis

[rnabholz]

I have some information on a manual push to dob setting circle system and an easy to build observing stool at my site at:

www.indytel.com/~rnabholz


Let me know if you have any questions

Rod

[Kalvis]

Rob:

Thank you for the link to your sight. I recall having previously linked to your Binocular Chair plans from a posting on Cloudy Nights. However, only today did I realize the wealth of additional project pictures and notes on your website. I admire the large amount of forethought, simplicity, multi-functionality and frugality evident in your work. Your article on manual dob setting circles answers a great number of questions that I didn't even know I had. It's also an efficient use research time when I can learn from the mistakes and insights of others. I'll let you know how it goes...

Kalvis

[rnabholz]

Kalvis,

Thanks for the kind words, I am glad you found the site useful. I have had a lot of fun making and using all of the projects there.

Once again, please let me know if you have any questions about any of them.

Good Luck

Rod Nabholz
Home Built Astronomy Projects
www.indytel.com/~rnabholz

[Chicago Astronomer - Astro Joe]

Rod,

Thank you for your experience in assisting Kalvis in his Dob project. I often wanted to dismount my 4.5" off of the German EQ and place it in a fork mount. I really dont need the attributes that a GEM offers, and the ease of a simple alt/az is just fine.

The 60mm project for your kids can be adapted to a larger OTA and perhaps the way to go.

Nice site and post more often...

[beri]

Hello everyone,
I am very surprised to see my old Dob here, and I am very glad that you like it

[Chicago Astronomer - Astro Joe]

Beri,

How nice to have you stop by and register as a member of the Chicago Astronomer family.

Please do tell us about your old Dob, which I think is quite impressive.

I have a 8" sewerpipe Dob that I aquired, and have some ideas for it from your project.

More on that in a short while.

[beri]

Thanks for the welcome Joe

Actually, the first scope I put the manual setting circles was my (very) old white commercial Dob...


azimuth


altitude

Despite costing practically nothing, they worked very well.
Then I built the scope you mention above, and sold it to finance a larger, 12" Dob, which is completely homemade, including the mirror. Also, again with setting circles.


A description of this scope can be found here
www.scopemaking.net/300/300.htm
I had this scope for 3 years, but unfortunately, consequences of an old back injury are catching up on me...
Using a telescope is becoming more and more difficult, observing sessions became shorter and shorter...
I hoped I could resolve the problem by building an observing chair

www.scopemaking.net/chair/observingchair.htm
but it helped just a little
I sold the 12" Dob just a week ago, because I realized I can't use a ordinary telescope for more than an hour.
My next project will be a motorized binocular chair with two 10" Newtonian tubes mounted on it. The tubes are already on the way, and I also found a dark location where I can keep the chair completely assembled.... just need to roll it out.
Packing and transporting it is not an option any more.
This is a long shot project, it will probably take me more than a year to get this done....

[Kalvis]

Beri,

I am glad that you have found the Chicago Astronomer website. The only link I had to your previous website became invalid about a year ago. It is excellent finally to make your acquaintance! Both you and Rob Nabholz (http://www.indytel.com/~rnabholz) have designed and built some simply beautiful equipment and my hat goes off to you. The fotos and descriptions in your websites are very nicely done as well. I expect that both of you would earn medals at Stellafane.

Kalvis