jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hi Preston, the picture above shows the piece of the spider that the vanes will attach to. There will be an ~1" hole bored through the center. A rod will go through this and the mirror will be attached to an arrangment on the end of this.
I can them move the rod up and down to achieve the correct spacing.
I haven't got a cad drawing with the mirror in the cell but I can answer the question  The walls of the cell will be machined a couple thousands of an inch larger diameter then the mirror.
This means if I have any movement it will be within these tolerances which I also believe is withing tolerences to keep good collimation in an RC.
This should provide little room for movement but also no stress imparted on the mirror with other pressure points.
Thanks,
Jason
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 840
Loc: Houston,Texas
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Hi Jason, My concern would be that the aluminum transfers heat so much faster then the glass, that the potential for the outer edge of the mirror to be cooling at a faster rate than the rest of the mirror and causing the figure of the mirror to change...perhaps badly.
You may want to think about doing some lightening/vent holes around the parimeter of the aluminum to mitigate this problem, but could wait and see if it's a problem...and if so do it later.
Just an observation, and it may be wrong.
Best Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hi Preston, you may be right, I dont know what impact it will have but I did plan to put some venting around the sides to help the airflow coming from behind the mirror. There will be fans on the backplate to keep it all circulating.
I have just been building some more patterns and I will post pictures later on.
Jason
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 840
Loc: Houston,Texas
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Great Jason...
Please keep the pictures and else coming...
Best Regards,
Preston 
--------------------
A few I enjoy,
and a few more in the works ;<)
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Right, just about finished the patterns, just need a quick sand around the holes in the backplate and then seal it.
They are 36mm thick (1.4") and some of that will come off as I get the surfaces flat on the lathe. Then I just need to machine all the edges to get it to look like a bought one
I will need to reduce the weight as well as it will be quite heavy once cast. I will probably just put a number of blind slots in some areas and call it quits, depending how I feel. As long as I am not close to taxing the paramount I won't be overly worried.
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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other angle.
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 840
Loc: Houston,Texas
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Hi Jason, I had not noticed the digital calipers in your wood shop...and I thought it was just me ;>)
Keep up the good work.
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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They are perhaps a little overkill for anything I do in wood but they do serve me pretty well for the metalwork
I have the pieces above modeled in solidworks. It tells me that the front piece is going to weigh 6.3 kg (or nearly 14 pounds).
A lot of weight will go after it is machined but it is nice to know how much it will cost as the foundry is $$/kg. in this case it will cost me $106 including labor, alloy and heattreatment to get it done. Still less then buying the alloy as plate by a good margin.
Jason
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 840
Loc: Houston,Texas
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Hi Jason.
You have got this down...
I only wish I could cast pieces rather than machine it from a solid...
We are getting closer...
Best Regards,
Preston 
--------------------
A few I enjoy,
and a few more in the works ;<)
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GuyFleming
member
Reged: 01/21/08
Posts: 23
Loc: Newcastle, Australia
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Coming along Jason. I am a way behind you, but now have access to a big CNC workshop, so I am working up a similar rear Al rear cage to you. Also finessing the primary collar/baffle arrangements. Are you going to integrate a field flattener?
cheers
guy
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hello Guy, I still have time to think about the field flattener.
I don't knw the cost that this will add, I think at least $500 USD to do something. I wish I had an idea of the performance improvement I could expect to get with one. Star instruments had given me that cost indication for one that would sit ~ the central hole.
As I am using an stl11000 I know it would make a difference, I wish I knew how much.
Luck guys with your CNC gear I am all knobs and handles
Jason
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 840
Loc: Houston,Texas
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Hi Guy, Mike Jones has designed 2 Field flattners for us so far. A 3 element that is as close to perfect correction as anyone could wish for, but it guestimated price was 10K+!!!US$
A second 2 element that had a flat field for the 11000 to the corners within 0.5% had not been put out for a quote but was guessed to be in the 4-8K region...still expensive...
Any single element FF will have lots of color and varying degrees of problems...
Ask Mike Jones to give a detailed reply if your really interested.
Best Regards,
Preston
ps...we have decided to get the scope up and running and then see just how bad the problem is and if we can live with the curved field or need the FF for the type of work we plan on doing
--------------------
A few I enjoy,
and a few more in the works ;<)
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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My intention has also been to get up and going and see the results.
Those prices are way out of my atm budget but to be fair I am sure you get more then I will ever need for my 'pretty pictures'
The fsq makes full use of the STL11000 and it may mean that I just need to crop the stl down to the size of an APS sensor, still not the end of the world
Jason
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 840
Loc: Houston,Texas
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Hi Jason, That's why we are waiting...still have the Paramount to purchase, property to site the scope, and all of the other things to get it robotic...
Flat field can wait for now...
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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Mike I. Jones
Pooh-Bah
Reged: 07/02/06
Posts: 1103
Loc: Fort Worth TX
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Hey Jason,
The price estimate I gave Preston is for a plug-and-play finished 2-element airspaced field corrector, null-tested for quality assurance, multi-layer broadband antireflection coated on all four surfaces, and mounted in a cell. That price could range anywhere from $2K to $4K or more, and will need to be sent out for quoting.
You and Preston both have wonderful machining equipment, and that price could come down by half. All either of you would need are the finished elements.
Post or PM me with all the mirror parameters. My files are all set up to do a design very quickly from those parameters. Let's see how good we can get the performance.
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and a new design you'll like.
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GuyFleming
member
Reged: 01/21/08
Posts: 23
Loc: Newcastle, Australia
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G'day,
I am looking at the 2 element 2.7" unmounted lens set Star Instruments suggest (as Jason mentions) - comes from the 10"RC astrograph kit costs about $500UUS. Certianly not in the league of a big custom made corrector for the 20. I am going to build it in from the start - but it will be in some sort of adjustable cell mount. I like the idea of castings - I made my own set of Al cast side bearings for my 20" dob - but I had a fair bit of trouble with the foundry. Castings certainly are the most cost effective route to go, providing the foundry is cooperative. I will only be getting the basic precision cuts and holes done with CNC in the 6061 5/8" plate to save $. The detailing I will do with my own small drill mill. I am out-sourcing threaded pipe/tube etc for the mirror cell barrel however - my machining skills are basic only.
guy
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hi Mike, thanks for your offer to help but given costs of the project without a corrector I am going to have to wait anyway.
It sure would be nice to see examples of a similar scope with a stl11000 to know what I would experience without correction. I honestly don't know what the difference would be as I have never had this size chip before.
Guy, I was lucky enought to find a guy about 5 minutes away that seems very capable. He does a lot of aircraft and marine work so he uses a good grade of alloy and its all heat treated for machinability afterwards. I think I am going to be happy when it all comes back
I know that this pic isnt so exciting but I am just finishing the pattern for the top ring which the spider will attach to. The two spokes coming out will be machined off, they are just there so that I have something to initially clamp with when I start things on the lathe.
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GuyFleming
member
Reged: 01/21/08
Posts: 23
Loc: Newcastle, Australia
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Hi Jason
I've seen a fair bit of the casting process elsewhere via a friend. You are fortunate to have such a facility close by. Not having 90 degree angles in the mould is another trick with sand castimg. I had 16"ODx14"OD rings milled at S&S machine (USA) using their cheap 5/8" disc scrap - found that link on the ATM site. The massive Van Slyke secondary focuser/spider I'm using needs a pretty rigid ring. I'm fairly close to having all of the components for the secondary cage. I have a cone shaped secondary baffle design, a bit like Prestons. It seems huge - about 185mm outer diameter, but hard to avoid with a 6" mirror.
cheers
guy
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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I haven't gt around to the baffling yet so I am not sure what it will look like yet.
I am interested to hear that yours is going to be 185mm.. You have the same optics set that I am using I think.. Thats about 35mm more its obstructing.. By the time its all finished I will have a mighty big 6" reflector
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GuyFleming
member
Reged: 01/21/08
Posts: 23
Loc: Newcastle, Australia
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Yes - same optics times two.
I think when the RC design ventures away from the more typical f8 or f9, plus a relatively small primary, the secondary size has to go up to keep a large well illuminated field (I don't claim to be an expert). The baffles have to be 'oversized' to prevent stray/off axis light etc. I guess the effective speed of the scope is reduced somewhat - I had 98% coatings done at Spectrum Coatings. I'll pass on a rough baffle diagram soon perhaps. Not a planetary scope - but I didn't want one of those. Makes the 16RC attractive - less obstruction - but my current budget didn't stretch so far. Meanwhile I'm imaging at F10 with my 12"SCT on the PME - the PME doesn't seem at all taxed.
guy
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