mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2158
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.
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They are espcially nice for imaging because there is no need epoxy the primary in place.
Say what???
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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: 227
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: 1272
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: 552
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: 552
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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