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: 3157
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: 666
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very nice work .
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NHRob
Post Laureate
Reged: 08/27/04
Posts: 3157
Loc: New Hampshire
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will you have cooling fans?
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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Achernar
Postmaster
Reged: 02/25/06
Posts: 5026
Loc: Mobile, Alabama, USA
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They do look like Klingon Bat'Leths indeed, handy if he gets accosted by Klingons.........  Great design work by the way Imhotep, I would have done anything to get my hands on a CNC router. I'm building my telescope with a table saw, router, arc-welder, biscuit jointer and drill press, and it won't be nearly as nice looking as yours.
Taras
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15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
Two curious cats
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Here is what I'm thinking for the mirror cell:
Bottom view:
The holes are for weight savings as well as allowing air flow to and around the conical mirror. Thoughts on this are welcome as I've not invested any engineering into the placement, number, or size of these holes. That sort of thing is beyond my knowledge. All I have done is go with what feels adequate and safe too.
That is 0.25" aluminum on the upper plate by the way.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (10/28/09 04:52 PM)
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
will you have cooling fans?
Rob
I'm interested in opinions on this as well. Up at Chiefland I see guys with box fans aimed into the backsides of their 16" and 22" truss-dobs. They run the fans for a couple of hours leading up to sunset, then off and on as the night progresses. I was going to do the same thing for awhile and see how it goes. Royce's conicals cool more quickly than their full-thickness counterparts 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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Quote:
They do look like Klingon Bat'Leths indeed, handy if he gets accosted by Klingons......... Great design work by the way Imhotep, I would have done anything to get my hands on a CNC router. I'm building my telescope with a table saw, router, arc-welder, biscuit jointer and drill press, and it won't be nearly as nice looking as yours.
Taras
I was planning on doing everything myself until the CNC opportunity arose. From that point forward I added some features that I probably wouldn't have attempted otherwise, such as the finger joints and the shape of the altitude bearings. The finger joints had a suprise for me though. The inside corners had fillets which I had to cut out on my scroll saw. Fortunately it wasn't bad at all, but before the scroll saw idea dawned on me I was really dreading the hours of chiseling.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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A couple of friends and I have recently invested in a CNC machine as well. We run Alibre Design for CAD, and use Mach 3 to run the machine. I cut the mirror box and some other misc parts for mine so far. I will be doing the bearings and rocker box as well on the machine. I'd already done the upper cage so it was too late for those. CNC machining rocks.
There are programs out there for CNC's that can cut the finger joints for you. You need a mortising bit to make the square cut, but it can do them to match if you set up your wood in the proper jig. I'm not sure it would have been less work/less time than you spent doing them by hand. I love the finger joints on my Telekit, but I saved the effort on my current project and went with biscuit joints.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
Lust for something Larger than that
Past Lovelies:
Oberwerk 20x100 binocs
Meade AR5
Meade LX10 8" SCT
All sold to a good home
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NHRob
Post Laureate
Reged: 08/27/04
Posts: 3157
Loc: New Hampshire
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Curt,
Looks good. I would not bother having holes in the portion of the plate which the mirror sits on. It would be better to have as much of the mirror in contact with the plate as possible, to conduct heat away. Otherwise the holes will allow the air (fan) to flow and hit the back of the mirror. I actually made a neat cell plate for that very mirror before I sold it to you. I had rotating spherical joints bonded in the plate for the collimation bolts. I also drilled some holes but it was pretty ad-hoc ... no analysis involved.
Here's a pic.
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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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Achernar
Postmaster
Reged: 02/25/06
Posts: 5026
Loc: Mobile, Alabama, USA
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A scroll or coping saw is what I would have resorted to for removing the fillets. I have made dovetail joints with a router jig, but haven't tried finger joints yet because that requires either a lot of skill to cut by hand or a jig. There are jigs however that allow the use of your table saw to make finder joints. I see you dispensed with the bar and triangle flotation system. I simply followed the Kriege plan for mine, but it was quite a but of drilling, sawing and shaping to make the flotation system's parts. I welded the tailgate myself as well with a 230-volt MIG/Fluxcore welding machine using fluxcore wire that works just like the stick welding electrodes.
Taras
--------------------
15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
Two curious cats
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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bbasiaga, the CNC machine that cut my parts was driven by Wood Wop. Actually it was a mess leading up to the actual cutting. All of the hours I spent preparing individual CAD files for each part were for naut. The technician had to redraw much of it in Rhino and then program the pathways into Wood Wop.
There is a way for this machine to cut square joints but it involved too much setup. As you say, not much time would have been saved. The work must be layed up on a much thicker layer of MDF which creates problem for the vacuum, but without that thicker layer there's risk of running the bit into the platten.
Anyway, I think I got the best of both worlds in the end.
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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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Rob, that's a really good point. I'll delete/move some holes to allow an unbroken area of aluminum for the conical's footprint to rest upon.
Cool cell plate! Is that 0.5" thick aluminum? I'm thinking my 0.25" is plenty thick for an 11-lb mirror. Did you go with the thicker stuff to add ballast?
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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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Taras, I only diverted from a flotation cell because it's imcompatible with a Royce conical primary. Are you familiar with these mirrors?
I wish I could have welded my own tailgate like you did. Instead I bought the steel pieces for about $22 and then drove them to a local welder who did the rest for an additional $20. Not bad right? Well the welding job wasn't the best. My side rails are a tad bent inward at the top so I don't have a perfectly square tailgate. I'm actually downplaying the awefulness of the job he did. It's just terrible, but I think I can center the tailgate with some strategically placed washers.
Well I just glued the light baffle onto the mirror box. Tomorrow my to-do list includes installing the gussets, drilling mounting holes into the tailgate, installing the rocker floor, prepping the ground board and attaching the feet, and lastly cutting some struts for the UTA.
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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: 3157
Loc: New Hampshire
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Yes, it was 1/2" thick ... way overkill. I just got a good price on a 1/2" thick aluminum round plate and hand cut it to shape. I think 1/4 - 3/8" thick would be fine and have less thermal mass.
Quote:
Rob, that's a really good point. I'll delete/move some holes to allow an unbroken area of aluminum for the conical's footprint to rest upon.
Cool cell plate! Is that 0.5" thick aluminum? I'm thinking my 0.25" is plenty thick for an 11-lb mirror. Did you go with the thicker stuff to add ballast?
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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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Achernar
Postmaster
Reged: 02/25/06
Posts: 5026
Loc: Mobile, Alabama, USA
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I've heard of them, and without a flat back they wouldn't be compatible with the sort of tailgate and flotation system I made. I imagine you'll have to curve the plate to conform to the back of the mirror. When I made the tailgate, I built a jig first that I took great care to ensure was absolutely square. I then carefully measured, cut, drilled and tacked welded all five parts in the jig. After that, I removed the tailgate and welded one side of each tube at a time, because the extreme heat from welding causes metal to warp. So by welding a little on one side, then the other, you can control warping and avoid the risk of an out of square tailgate. It sounds like the welder who made your tailgate didn't use a jig when he welded it. Even so, my tailgate turned out 1/8th of an inch smaller than planned, so I used two 1/16th thick strips of aluminum as shims to center it in the mirror box and prevent the sides of the mirror box from bowing when the bolts are tightened. If you can make the gate fit in the box properly with shims, I would leave it be, if not, build a jig and have another one welded. If you go that route, position all the rungs in the positions and orientations they need to be in the jig. Then you can have a welder tack it together first in the jig before welding.
Taras
--------------------
15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
Two curious cats
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NHRob
Post Laureate
Reged: 08/27/04
Posts: 3157
Loc: New Hampshire
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The Royce conicals do have a flat back. They are "truncated cones". The flat section is smaller than the full diameter.
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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Quote:
I imagine you'll have to curve the plate to conform to the back of the mirror.
A picture is worth 1000 words. Here's what a conical looks like when mounted:
The point of the cone is cut off and there's a flat footprint with a threaded insert cast into the mirror itself. This one is my 8" f/5 and has a 3/8-16 threaded insert, but the 12.5" uses a 1/2-13 I believe.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (10/29/09 10:24 AM)
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Achernar
Postmaster
Reged: 02/25/06
Posts: 5026
Loc: Mobile, Alabama, USA
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Interesting design. I gather cool down times are shortened and the mirror remains well supported in it's cell with this design.
Taras
--------------------
15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
Two curious cats
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Correct on both accounts from what I understand. They are espcially nice for imaging because there is no need epoxy the primary in place. The mounting bolt is rock solid, very easy to install, and there's no diffraction spikes from the absent mirror clips. I'm using one for my truss-dob because an opportunity presented itself to buy Rob's, and also because I've been so pleased with my 8" conical.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (10/29/09 11:17 AM)
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Following Rob's observation that I probably need full coverage of the conical footprint, here is a revised concept for the mirror cell.
The Royce 12.5" conical has a footprint measuring 4.2" in diameter. I've placed three 1.0" holes and six 0.75" holes to aid airflow but it's probably a non-issue since so much of the mirror will be visible around the slanted sides of the upper plate.
Now here's a question probably deserving of its own thread -- this cell is very simple and I can probably hack it out using my own tools rather than dropping another $100 for water jetting services. Can a hole saw handle 0.25"-thick aluminum if I take it slow and lubricate? I don't care if I have to throw the saw out when I'm done because I can probably by both sizes for less than $20.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Achernar
Postmaster
Reged: 02/25/06
Posts: 5026
Loc: Mobile, Alabama, USA
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Using some sort of cutting oil wouldn't hurt, because hot aluminum acts like chewing gum and can clog blades, bits and hole saws. Use a hole saw with coarse teeth, fine tooth hole saws would gum up with aluminum. I have cut discs out of 1/4-inch aluminum flat stock with an hole saw on my drill press. Be ready for a lot of noise and clamp the metal to the drill press table firmly before starting the motor. Run the press at a low speed while you drill out the holes. You can also drill aluminum with twist drills, and you can get bits up to one inch in diameter. Smaller holes can be easily drilled dry, without oil. However, you need a larger machine that can operate at low RPM's to use them, and they're expensive too. You'll also have to drill a pilot hole first and I would use a hammer and center punch to mark exactly where your holes are to be drilled. That way when the bit starts into the metal, it can't wander. Without a dimple made by a punch, the bit will wander even on a drill press. Whichever method you choose, use eye protection because lots of bits of aluminum will be sent flying during the drilling operation. If you really want a precisely made part, I would create a design for a metal shop to cut it out with a plasma cutting machine.
Taras
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15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
Two curious cats
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Taras, thanks for the experienced advice. Earlier this year I had the upper and lower plates for my astrograph mirror cell cut at a local shop on their water jet machine. The reason I couldn't go with plasma is because some of my holes, specifically those that would later be threaded for the collimation bolts, were not feasible with a plasma cutter. They do a bad job of that specific thing but the rest of the outlines would have worked. It stinks because water jetting is twice the cost.
In this case I think I'll be fine with my drill press. I learned about dimpling my starting point the hard way  Now I always center punch before drilling metal. I actually do have a 1.0625 drill bit that I've used to bore out steel counterweights. It is duller than new but it is probably still ok for aluminum.
Also I have an X-Y milling vise for my press that has been awesome for precisely positioning my work under the bit.
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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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Quote:
and there's no diffraction spikes from the absent mirror clips.
Clips, if they extend slightly onto the mirror face rather than just contacting the bevel as they should, don't create spikes. They change the entrance pupil a bit, but the effect is very minimal.
Quote:
They are espcially nice for imaging because there is no need epoxy the primary in place.
Say what???
Quote:
Can a hole saw handle 0.25"-thick aluminum if I take it slow and lubricate?
Easy if you're using a drill press, lubrication optional. Bi-metal saws will not care at all. You can even do this with Forstner bits with lubrication and slow speed if you want a clean cut. Always wear eye protection.
Best,
Mark
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polaraligned
sage
Reged: 12/26/08
Posts: 229
Loc: P. R. of New Jersey
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Quote:
Can a hole saw handle 0.25"-thick aluminum if I take it slow and lubricate?
Use WD-40 as a cutting lubricant if you do not have another alum specific cutting fluid available. Problem with aluminum is that it likes to gum up and clog the teeth of cutting tools.
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Thanks again for the confirmation and warnings about cutting aluminum. I am just about ready to get it done. I'll come back to the mirror cell a bit later.
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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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I've installed the light baffle and interior gussets onto the mirror box. It along with the rocker are now finished and ready for final sanding before varnishing.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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lightfever
Pooh-Bah
Reged: 09/27/04
Posts: 1279
Loc: Macomb Michigan
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Mineral spirits will also work as a lubricant on aluminum.
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Mark
Tasco 15-TE 76mm
Sky Watcher 80mm ED
AT-111 Triplet
XT8i (with Woden re-figured mirror)
Discovery 12.5" f/5 Premium DHQ (PDHQ Split-tube Dobsonian)
12.5" f/6.3 Dob (Underconstruction)
Celestron CG-5GT EQ Mount
Celestron C4 EQ Mount
"Life is not about waiting for the storm to pass, but learning to dance in the rain" unknown
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Color choices usually hang me up for weeks. I had the hardest time deciding what color to paint my astrograph tube and then finally it hit me. The same thing goes for this project. I was torn between a "steam punk" look with dark walnut stain and brass hardware. My test samples show that dark stain on baltic birch is a huge risk. It is just too spongy and I don't have time to seal these parts and do it right. Plus, I've been thinking about this color/hardware scheme for so long that it's lost appeal.
In the meantime I've gradually fallen in love with the natural appearance of this beautiful wood. It is the nicest plywood I've ever worked with. I'm going to leave everything natural with the exception of the light baffle. Awhile back the it occurred to me to paint the baffle black. It seemed odd to paint the interior of the light box flat black and yet leave a semi-shiny light-colored baffle sitting there on top. I've never seen one done this way though. It's just an idea at this point.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 568
Loc: Riverview, FL, USA
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Curt,
First, I want to congratulate you on producing a fine well crafted Truss-Dob formatted telescope. Along with your Astrograph, they both show your technical abilities and convey your personal standards of utilizing superior components and knowledgeable architectural design practices. 
With that being said, don't cloud your great work with color concerns. As you mentioned, a natural finish that shows off the beauty of the wood grain (for which you appear to relish) would suffice tremendously. Should you decide to apply stain to give the wood grain some added character, just apply it with a brush and wipe the access off the woods surface with a soft cloth. This will prevent the high absorbency characteristics of Baltic Birch from taking up too much of the stain. I would perform tests on scrap pieces before applying it to your instrument. Hope this information helps if you decide to go the staining route. As I made note in my PM via Yahoo, I personally like a cherry stain, but it may be a bit to feminine for your taste. Walnut stain would work very well too in conjunction with the brass hardware.
I like your thoughts on considering painting the exterior surface of the baffle flat black (if my determination from what you wrote serves me right). I see it this way; if you decide to install a shroud around the truss tube system, you are in essence creating a tube enclosure. Now, think of it this way; would you want to have reflective surfaces inside of a permanently closed tube setup? Most certainly not. So, I subscribe to flocking the exterior or front of the baffle to aid in increasing contrast, even if it is only by a minute degree. Just my two cents on the subject. 
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Thanks Mel. I am leaning towards painting the light baffle black. My spar varnish is semi-gloss but I don't think it will be an issue for reflection with a shroud in place.
I like so many different stains it's hard to choose. But in general I tend to be on either end of the spectrum - either fairly dark or very natural. In this case natural has won me over.
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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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This week has been a little chaotic as I've dealt with a surprise or two, but persistence prevails.
With most of the woodworking finished I had shifted my attention onto the mirror cell. My budget for this project is maxed out at this point so I've had to think twice about my plans to have the upper plate water-jetted. Instead I've gone with a low-tech approach to fabricating it. I realized the cell for this scope is actually simpler than my astrograph's and therefore should be doable in my home shop.
A 1:1 printout was used to transfer the template from CAD onto the aluminum stock. Lines were digitized soley for the purpose of marking hole centers. The larger holes are for weight reduction and air flow, neither of which are even critical for this particular telescope because so much of the conical mirror's underside will be exposed to air flow already, and I actually need some extra weight below the balance point.
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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 outline was cut on a table saw. I drilled three additional holes to bolt the aluminum to a sacrificial piece of plywood that was ripped to be the same width as the template (measured from broad side to narrow side). The hardest part of setup was finding a fence that was thnner than the plywood jig so the metal could pass over it on the non-cutting side. Man what a funky contraption...
This made the whole process very easy. I ripped the metal along both sides of the plywood, then rotated the metal 60º (or one hole over) and repeated the cuts.
Edited by imhotep (11/06/09 09:31 AM)
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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The holes for mounting the conical primary and collimation bolts were an easy job on my drill press.
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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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Enter the nasty surpise, stage left.
It turns out my tailgate, which was made several months ago by a local welder, is WAY out of whack. Two of the cell plate's collimation holes miss their rung on the tailgate by 1/8". It's my fault for not checking this sooner.
Bob Ross would call this a happy mistake because it gave me an excuse to start fresh on a very important part of the scope. The original tailgate was a product of me not taking my time. I bought the steel and drove it to a welder before looking it over carefully and grinding off the burrs. Garbage in, garbage out. Plus, I gave the welder a simple drawing with dimensions, but I should have provided a carefully built jig.
This time I'll take no chances. A new set of steel was $13 at my local supplier.
Last night I slapped this jig together with some scrap wood.
Just for piece of mind I'm going with a more established welder this time. I literally handed the jig to him this morning with the metal already seated. It should be ready by lunch time.
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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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I just finished up a three-hour sanding fest. Tomorrow all remaining pieces, both assembled and unassembled, will go to a spray booth for finishing. Those pieces will come back to me on Tuesday.
In the meantime I am finishing up the tailgate and mirror cell. All that's left is drilling holes and painting both flat black. I was tempted to anodize the cell as I did with the astrograph. In this case the entire cell plate is hidden behind the primary mirror so reflection would be a non-issue. But in the interest of saving $80 I decided on flat black.
I've also got to cut the truss tube, install threaded inserts in the struts, attach the ball-joints to each truss tube, and get the struts ready to receive the spider.
More photos to come tomorrow!
On Tuesday night the scope will be fully assembled for the first time. Then it's off to Chiefland for FSP!
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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 tailgate and mirror cell fought me for awhile but I finally won the battle. Here's the finished product:
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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 rest of this project happened very fast. I barely had time to get the telescope functional before going to FSP so I've been derelict in posting updates and photos.
On 11/12 I took it up to Chiefland for what turned into the very first clear night they've had since FSP began. First light took place at about 7:30 right before clouds rolled in. I was happy with the views of Jupiter, especially considering the rough collimation and atmospheric issues. About and hour later the clouds left completely and the night became exceptional. I had to leave but I'm going back this evening for a mor substantial observing session.
 
Since coming back from FSP for a brief absense I've had time to spot the primary (no joke, I couldn't get it done before leaving the first time!), added an ADM counterweight set to the rear of the mirror box (photos later), and installed some teflon blocks to the inside walls of the rocker. The latter will fix some shifting issues.
I'm headed back to FSP in a couple of hours where I'll get a few more shots of the additional accessories added. Next week the Kydex goes into the UTA and a shroud will get made.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 568
Loc: Riverview, FL, USA
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Curt,
I just returned home from a trip to New Orleans and checked CN for updates on your 12.5" only to find you have performed First Light with it. I enjoyed reading your report and seeing the photos. Words can not express the degree of craftsmanship you put into this instrument. Congratulations!!! I hope to see it person soon. Its natural finish and architectural design is outstanding! I hope it performs to your liking. I see that you applied flat black paint to the front to rocker box face... Great decision! 
As you know, I have been working slowly to get my 127mm f/9.4 refractor completed. I plan to have the instrument ready for First Light the early part of December. I recently finished painting the plates for the tripod with Rustoleum Hammered finish spray paint before I went to NOLA. They turned out fantastic. Next, I will be painting the center legs with clear satin finish spar vanish. The construction of the accessory tray will follow.
I look forward to having both of our scopes standing together under perfect seeing conditions in the near future.
Mel
--------------------
Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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