imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Less than a month after finishing my astrograph it’s time to start my next ATM adventure. I’m fairly excited about this new project as it will probably get more skytime in the coming months than my astrograph. Design and planning began several months ago, but first sawdust just took place last Thursday, October 15.
The concept for this project stemmed from two things:
1. Must…..build….another…..telescope…..
2. The desire to correct my imbalanced approach to amateur astronomy. For the past 2.5 years I’ve been intensely focused on imaging and down right neglectful of the simple pleasures of visual observing that got me hooked in the first place. I came to this realization several months ago, but since then I’ve had to detach myself from imaging for financial reasons. My astrophotography arsenal has been liquidated to start a comeback fund. In the meantime I hope to satisfy my project-oriented brain by working towards several of the AL Observing Clubs as well as returning to planetary imaging using this new truss-dob as the platform.
I had read most of the K&B manual when I started shopping for a primary mirror. Cost and transport limitations kept me in the 12” – 15” range, with the latter being a little ambitious. In May my want-ad on Astromart fetched a great deal on a Royce 12.5” f/6 conical. Several weeks later I completed a rough draft 3D model of the entire telescope, only to realize how difficult it might be to balance such a long OTA without additional counterweights on the mirror box. I got spooked and spent several weeks trying to swap my f/6 mirror for an f/5 in the same aperture. In hindsight I’m glad I wasn’t successful. Eventually I settled on the f/6 mirror again and beat my model into submission.
Here is a screenshot of the first draft, modeled in TurboCAD 14 Deluxe. This version shows specs for f/5 rather than f/6. Also shown are the original bearings I intended to make. The K&B manual was my bible for this project, so at this point the appearance is very Obsession-ish.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Shortly thereafter I went back to the f/6 arrangement and redesigned the bearings to raise the balance point. I like to think they are more attractive, but it’s purely a subjective opinion. The moon shape seemed appropriate.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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….and a few more changes still. If I could point at one model and call it the working beta, this would be it. This arrangement is the end result of some aggressive efforts to make the scope balance without adding counterweighs to the mirror box. I raised the balance point again, made the mirror box deeper to add more torque to the tailgate and primary mirror, and I was able to kill two birds with one final rebuild of the bearings. This scope will feature DSC, hence the upward scooping flare near the center of the altitude bearings. An encoder will attach there directly onto the axis of rotation. Lastly I removed some material from the bearings to avoid over-correcting in the weight department.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Nothing original or revolutionary here. I patterned the tailgate after recommendations made in the K&B manual.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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On materials and components:
- Baltic birch throughout (1/4”, ½”, and ¾” needed)
- Steel flatbar and square tube for the tailgate
- Moonlight truss tubes and ball-socket connectors
- Ebony Star and virgin Teflon pads for both bearings
- 2.14” secondary and straight 4-vane spider from Protostar
- Either a JMI Ev-n3 or a Moonlight CR2 focuser (still deciding)
- 12.5” f/6 Royce conical primary mirror
- Custom designed aluminum cell (flotation is unnecessary with the conical)
- Discovery DSC v3.66
- Stellarvue SV50S finder scope
- Probably a Telrad too
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Right now about 80% of the wooden parts are sitting in my garage waiting to be rough sanded. Last Thursday my CAD drawings were used to drive a CNC router. Some of the pieces came out very rough around the edges, but overall it went very well. The last few parts are being cut today and tomorrow.
I’ll post some photos of the CNC results in a couple of days, as well as a video of the router in action.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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PrestonE
Pooh-Bah
Reged: 04/29/05
Posts: 1170
Loc: Houston,Texas
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Hi Curt,
Nice looking design...
How do you like Turbocad 14...
We used 14 and then 16 Pro for the 20 inch RC build.
What CNC are you using and what software to control the CNC, Mach by any chance?
Best Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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JSeay86
super member
Reged: 04/26/09
Posts: 133
Loc: Norman, OK
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Great looking design. The bearing design on your beta version is really nice.
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Jared
Orion XX12 Dob
Ten Acre Observatory
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Thanks guys. Preston, so far I have been very happy with TurboCAD 14. At work I have access to autocad but I'm not a ninja with it like some of my coworkers. But through trial and error and reading the help menus I've become decent with TurboCAD. It is fast and capable for everything I'll ever want to model.
A very good and generous friend owns the CNC router that is cutting my parts. They use Wood Wop to drive it. The automation was a blessing and allowed me to design some parts that would have been impossible to do via my hand and power tools. Even so, I have a good amount of hands-on woodworking ahead of me. The corners in the finger joints have to be chiseled out and all of the parts need diligent sanding. I'm going to manually countersink many of the holes as well. Lots to do!
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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PrestonE
Pooh-Bah
Reged: 04/29/05
Posts: 1170
Loc: Houston,Texas
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Hi Curt, Why manually counter sink when you have the use of the CNC router?
Holes and countersinking are a snap with CNC and SO MUCH MORE accurate...
Have you seen my thread on the build of our 20 Inch RC?
If not, though it is a Long read...we did a lot of CNCing in aluminum on our CNC router.
Best Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Preston, yes I followed that thread for awhile and was somewhat inspired by it. If money were no object I would have opted for aluminum as well. The router that cut my parts can also to aluminum albeit much slower.
There are still some kinks being worked out of the CNC system at my friend's shop. My project was an excuse to debug. I have already imposed and I didn't want to tax them any further by requesting an additional layer of programming to countersink every hole. Several holes were countersunk though, particularly the pole seats in the UTA. I also had the hole for the azimuth nut countersunk, but the rest are merely cosmetic issues and non-critical. It would be nice to have the flat tapered head bolts sit flush with the wood throughout the telescope, so I'll probably do some quick touch ups on my own and countersink as necessary on my drill press.
Tonight I spent some time sanding and laminating. Each bearing is 1.25" thick (1 x 3/4" and 1 x 1/2"). The rocker sides are similar. Very soon I'll post more photos and a video of the CNC router.
Squaring out the rounded finger joint corners is really going to be a chore....
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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All parts came off the CNC router more or less exactly as expected. We only had two pieces that needed to be recut. One of them was the 1/2"-thick half of the right altitude bearing due to a single path being set to the inside of an arc rather than the outside. The result was three identical bearing pieces and one odd man out. The path was corrected and enough 1/2" material was left over to cut one more. The second redo was the light baffle due to the first piece moving as the bit rounded a corner, chewing it up.
All parts except for the lid to the mirror box are pictured. From top left to bottom right:
Rocker back
Ground board
Mirror box back
Mirror box front
Light baffle with gussets inset
UTA rings with box braces inset
Mirror box sides
Rocker side
Altitude bearings with focuser and finder boards inset
Rocker side
Rocker front
Rocker floor
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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One of the altitude bearings clamped and glued. These are 1.25" thick, consisting of one 3/4" piece laminated to a 1/2" piece. The side facing the mirror box has a 1/16" countersunk pole seat similar to what's cut into the facing sides of the UTA rings. I'm going to span the gap between the uppermost points on the altitude bearings with a strut for stability. They reach high enough away from the box that I felt it was worth it.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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So far I think it's coming together smoothly. I was dreading the thought of chiseling out the corners in the finger joints. After some discouraging first attempts on the scrap, I bought a set of corner chisels. These too disappointed as there just isn't enough material in those little joints for the tool to work well. Finally I slapped my forehead and pulled out my scroll saw. I took my time scribing some guidelines and the scroll saw made quick work of something like 100 finger joints across various pieces. Thank goodness I finally woke up on that one.
The rocker box and mirror box are both clamped and glued right now. With any luck I'll do the final sanding and maybe some staining this coming weekend.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Nice work!
Love the Klingon Bat'leth trunnions. Very handy if the horse comes after you...
A little inlay work and you could have a majQa' article of fear!
Best,
Mark
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Mark, thanks for the laugh. That's the funniest photo I've seen on these forums.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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The mirror box and rocker went together smoothly. Here's the box still clamped:
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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NHRob
Post Laureate
Reged: 08/27/04
Posts: 3152
Loc: New Hampshire
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Curt,
Awesome work! I'd love to have a CNC-driven woodworking setup. I've cancelled many an ATM project because of the amount of handwork involved.
Looks like that mirror I sold you will get a good home!
Can you post pics of your cell design?
Thanks,
rob
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Rob
**********************
Canon 12x36 IS binos
TEC-140: #433 on CGEM
Faworski orthos (7,10,16.7mm)
stuff ...
no free time ... lots of clouds !
" Life is what happens to you while you're busy making other plans" !!
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Rob, yes I'm happy to say the 12.5" f/6 conical is doing to be the heart and soul of this telescope. After running the numbers and seeing my torque deficit below the balance point I almost got spooked into using a different mirror (f/5 or faster), but I was able to rework everything and find a set of dimensions that 'should' balance with only a few pounds of CW added to the mirror box.
Sure I can post a drawing of the mirror cell later today. Because the tailgate already serves as the lower plate, this mirror cell only requires an upper plate and is less complicated than what I designed for the astrograph.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 665
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very nice work .
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