jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hello Guy, good luck with your project!
I sourced my tubes from www.carbon-tube.com I couldn't believe that they were a 30 minute drive from me in Auckland. They make them to order and I paid ~30 NZD for each 800mm length. The Aussie dollar is similar to ours but it will be a little cheaper for you. I paid a little more for the nicer finish.
Thanks,
Jason
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JanM
professor emeritus
Reged: 03/07/05
Posts: 626
Loc: Sheffield UK
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Thanks for the infomation jason, that lathe looked pretty powerful. All i have is a mini desktop so when i go ahead with my project i'll have to get a lot of the parts made by a freind who has a larger machine.
Again looknig forward to seeing your project progress. It all looks to be going well so far.
Jan
Jan
--------------------
- AP 130 EDF
- Trifid-2 SA-6303E-C2, SXV-M7
- AP 900 GTO3
- Observatory Progress - Just the roof left
Website - http://www.pbase.com/janmclare/
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hi Jan, I understand. I had lathe lust as well as telescope lust.
My 16" lathe was an upgrade from an emco compact 5 so I also know about the table top ones. Lucky for me I can now do the bigger components.
Thanks,
Jason
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GuyFleming
member
Reged: 01/21/08
Posts: 23
Loc: Newcastle, Australia
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G'day Jason - thanks for the CF info. A supplier in Sydney wanted over double that for similar tube. I am also about to buy a small hobby mill (probably a Sieg X3). For a long time I survived on access to a friends mill and lathes in Sydney. Now I live in Newcastle. FYI - I used the ATM site links to source cheap Al-discs from S&S Machine (USA) - they have a variety of Mic6 Al-cast plate disc offcuts for sale. I used their 5/8" discs for milling of the secondary 16" rings. I am using other disc stock for the primary cell assembly. My current design uses a reinforced marine ply box at the rear end to carry the Al primary cell/rear plate assembly and the truss assembly. I think I will be milling similar truss tube connectors to yours.
I note that RCOS appear to use honeycomb-CNC milled Aluminium for the rear mirror assembly behind their truss assemblies - do you know if RCOS does use aluminum for these parts, out of interest??
thanks, Guy
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hello Guy, I hope the carbon tubes work out for you.
I believe that the part of the RCOS you are talking about is aluminium. I have seen close ups and it looks from pictures to be anodised machined aluminium.
I think they state that its all carbon/aluminium/stainless with an educated guess that this piece is not stainless.
Thanks,
Jason
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GuyFleming
member
Reged: 01/21/08
Posts: 23
Loc: Newcastle, Australia
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Aluminium... good. Also just wondering if you are going to have the primary baffle 'mated' to the cell or to the rear plate? My friend tells me Star Instruments have completed the optics and have sent it for coating. Have you used your PME yet? I am running an old 12" Meade SCT on it for now until the RC is finished. A joy to use the pme.
cheers, guy
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ezpcb
Vendor (Nova Instrument)
Reged: 06/07/06
Posts: 295
Loc: China
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Nice job!I'm going to make my 10" RC. The constructure is almost similar to yours
Mike
--------------------
make your astronomical parts online,
50% discount for astronomy amateurs
www.machinepier.com
Please write "cloudy nights" in comment
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 799
Loc: Houston,Texas
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Hi Jason,
I'd seen this thread around Christmas and then I became quite busy.
And yes, the RC optics back plate and center plate are CNC mill lightened aluminum.
We are building a 20" RC with Star's Standard taper backed Zurdur blank. All of the tube ends and mounting bits and pieces are finished. The balls are Invar and the inserts into the Carbon tubes are 6061 aluminum.
When you cut your carbon tubes, be careful to coat the exposed carbon fiber with a thin layer of epoxy...as carbon fiber/aluminum and moisture makes a great battery...and you loose aluminum!!! When cutting the carbon tube us a non toothed blade.
Our secondary structure will be all carbon made via VARTM or vacuum assisted resin transfer molding. That's where all of the conponents are layed up dry, the vacuum bag placed over everything, tested, fixed if leaking, and then vacuum pulled and resin infeed lines opened...much less nerve racking than wet layups, and considerablly lighter.
One thing to ask Paul at Star Instruments, as this is a differant optical design spec in the tolerance for mirror spacing...RC's have VERY Tight spacing and alingment specs and should not be focussed with the secondary...IMHO
I know it's done, but it's not the correct way to go...just ask Mike Jones. Why build a premimum scope only to mess up the quality by not adhearing to the tolerances...
I'll not hijack you thread by posting any pictures, but later on will start another for our build.
Our secondary is 7 inches in diameter and I plan on mounting it to a carbon triangle structure that is then mounted to a carbon fiber tube 4 inches diameter by 9 inches long. The mirror will then mount to the carbon triangle with silicone blobes. Then Carbon/Arimid spider vains will attach off axis of the 4 inch tube.. It's important to counter balance the secondary to lessen any vibrations.
Anyway, enough for now...Nice job so far.
Best Regards,
Preston
ps...The devils in the details...9 months of making CAD drawings and hundreds of revisions...
--------------------
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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Hello Guy, I am using my paramount at the moment. I have two WO scopes on it. A 110flt for imaging and a 90mm for a guidescope.
I sold my only cass, a 9.25 celestron. I wish I hadn't as the focal length would be really nice until the RC is finished. Catch 22 though as it helped pay for the RC optics 
The only problem I am having is with autoguiding, it seems to be hit and miss if it works or not, I am not sure where the problem is but I will play around with it.
Not sure if I will mount the baffle to the cell or to the rear plate. I understand that it should at least be independently adjustable from the optical axis.
Heres quick pic of the WO's on the paramount. Theres enough mount for them
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hi Preston, thanks for your advice. I know that I would and I am sure others would like to see something about your project.
Yes, the carbon will react with the aluminium. I will probably anodise the connectors. I have 5 gallons of 99% sulphuric sitting in a corner and have been meaning to use a little bit of it!
I am going to do my focus at the back not with the secondary. As I am not manufacturing I don't have to worry about making it easy for many customers. I will set up the secondary with the correct spacing and use a focuser at the back with an extension if required.
Thanks,
Jason
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 799
Loc: Houston,Texas
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Hi Jason,
Your welcome. I'll start a thread shortly. I've resisted starting in the past, as the number of hours spent making the tube connectors and parts thus far has been extreme...like hundreds and hundreds...
Again, I know that commercial manufacturers anodize thier aluminum, however I've been told by those in the know that anodizing acts like a mirror for IR and thus, we will not have any anodizing on anything in or near the optical path...
Our RC will be totally robotic in a robotic observatory and for CCD work only...no visual at all...
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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G'day Jason & Preston.....
Good reminder about the reactive carbon-Aluminium - I will keep it in mind. Many scopes look small on the Paramount. Looking forward to reading about the 20"RC project. I should've emphasised that my RC secondary focuser will end up relatively stationary much of the time. I am also aware that the primary-secondary distance needs to be kept ideally at a specific optical spacing. The Star Instruments 12.5" f6.6 set doesn't allow for a lot of back focus. As the OTA is intended purely for imaging I will be custom machining adapters at the rear to 'bolt on' the camera rig close to focus. The secondary focuser is primariliy to use the robofocus temperature compensation and to get the mirror spacing right. The VSI Robofocus mechanism gives a claimed 0.000021" per step - real fine. Perhaps I may switch to using a short focuser of some sort at the rear end - but this will be dependent on the useable back focus I end up with. I have stuck with the 12"SCT for now on the Paramount to get a decent polar alignment with a similar focal length instrument - I am just hoping my mirror lock prevents significant mirror shift. So far, with a TCFS focuser, I have not had obvious flexure problems with the SCT at f5.
cheers, guy
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hello Guy, yes the secondary focuser has an advantage with the short backfocus.
From what I have read if you start off with the secondary at the correct distance and make sure your camera is in focus by using an extension tube of the right length (obviously it wont be bang on) then the little amount the secondary moves shouldn't impact the image to any extent. I certainly can't complain about the rcos instruments which do this.
I want to put a filter wheel and rotator on my scope. They all take up back focus and this may have me reevaluating a secondary focuser if required..
Thanks,
Jason
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GuyFleming
member
Reged: 01/21/08
Posts: 23
Loc: Newcastle, Australia
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Yes Jason,
Focusing is not an easy question nor is it without some compromise. I am also going to put my existing ST8XME/CFW10 behind the scope and would like to add a motorised rotator - so room for a conventional rear low profile crayford focuser is not easy. Might even try an A0-8 as well? I have to wait until the primary cell assembly is completed. Although the VSI secondary spider/focus assembly I'm using is super strong, weight balanced and able to easily carry/move its payload within tiny tolerances, I'd expect it has quite a bit of thermal intertia. Local seeing effects may well swamp such heat effects however. When I have an OTA completed I might experiment with the A-P 0.75x reducer in the rear assembly. Star Instruments indicated that a custom reducer for the f6.6 optics may become available - not sure when.
I recently converted a Vixen VC200L optical set into a truss tube OTA. This VC rig peforms very well and gave me the confidence to home-build this 12" RC. Plus I built a successful 20" Obsession-clone dob a few years ago using local commercial optics. Just need the local weather to improve now.
thanks
Guy
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 799
Loc: Houston,Texas
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Hi Guy,
I believe that Star is working with Mike Jones for the reducer/corrector.
Mike has designed a 3 element field flattner for our 20"RC, but the sticker shock...has caused us to wait until the scope in finished and on the Paramount for our final desicion.
I'm sure we will have it made eventually as the scope will be used for research and we will want the field flat on the 11000 chip.
Have you looked at the thin FLI focuser? We will be using that and thier filter wheel.
The main reason for our going with Carbon Fiber for the secondary holder and structure, was Mike Jone concern of the thermal inertia...he though even going with Invar would cause massive issues.
He's even got me to make the secondary baffold with carbom fiber.
If you need a program to calculate the primary and secondary baffold lenghts, he has a great one that he offers for free...cannot remember where it is but I have a copy if your interested.
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: 1093
Loc: Fort Worth TX
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The 3-element corrector design I did for Preston's team that sticker-shocked 'em was a high-end version that gives an absolutely zero-distortion field, with maximum star image displacements on the order of 0.7 micron at the edge of a 2" diameter FOV at any wavelength from 0.38um to 1.00um. This extremely low distortion eliminates the need for distortion correction when making mosaic pictures or doing astrometry.
The 2-element corrector I designed is much cheaper and still gives good imagery, but the distortion is around 0.5%. We need to review the impacts to Preston's telescope program of this small distortion and the ways to accurately compensate for it in the imagery. The 2-element lens is definitely cheaper!
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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Benach
member
Reged: 01/24/08
Posts: 28
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Quote:
When you cut your carbon tubes, be careful to coat the exposed carbon fiber with a thin layer of epoxy...as carbon fiber/aluminum and moisture makes a great battery...and you loose aluminum!!! When cutting the carbon tube us a non toothed blade.
Anoter reminder: wear a very good mouthcap over your mouth and nose since tiny carbon fibres can be highly carcinogenic! Especially when cutting large pieces, it is as carcinegenic as asbestos.
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 799
Loc: Houston,Texas
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I'm sorry but this is not true in any way what so ever, other than a dust and irratant hazard.
Kindly review the MSDS data below and refrain from posting incorrect information.
MSDS data from SPI as follows:
Material Safety Data Sheet
SPI #11431-AB, 11431-BA, 11433-AB, 11433-BA, 11435-AB, 11435-BA, 11436-BA, and 11436-AB Carbon Fiber and Carbon Thread.
--------------------------------------------------------------------------------
Chinese
Section 1: Identification
Date Effective...... October 24, 2005
(most recent revision)
Chemical family..... Graphite/Carbon
Emergencies
Contacting CHEMTREC:
24 Hour Emergency Use Only #'s......
Worldwide phone: 1-(703)-527-3887
Worldwide FAX: 1-(703)-741-6090
Toll-free phone: 1-(800)-424-9300 USA only
Product or Trade Name.... Graphite (commonly called "carbon") fiber
Emergency Overview:
Contains no ingredients now known to be hazardous by OSHA.
The normal cutting of the fiber, either with scissors or razor blade
is suspected of generating small amounts of possibly respirable fibers.
We believe that such fiber cutting should be done in a ventilated hood
facility.
--------------------------------------------------------------------------------
Section 2 Composition
Name CAS # Approximate Weight %
Graphite 7782-42-5 >99.99%
No hazardous components as defined by OSHA.
313 Listed Chemicals
If none are listed here, there are no 313 chemicals present above
threshold values.
NFPA (Scale 0-4):
Not known
--------------------------------------------------------------------------------
Section 3: Hazard Identification
Potential Health Effects:
Eye: Dust may cause eye irritation
Skin Contact: Dust may cause skin irritation.
Skin Absorption: Not expected to be a major route of entry.
Ingestion: Not known
Inhalation: Small graphite fibers or dust are suspected as being possible
inhalation hazards.
Chronic effects: A review of the literature does not show obvious long
term hazard.
Carcinogenicty: No component known to be present in this product and is
at > 0.1% is presently listed as a carcinogen by IARC
or OSHA unless other wise noted.
Routes of exposure: Inhalation
Permissible exposure:
15 MCCPF OSHA TWA, 10 mg/m3 ACGIH TWA (Total Dust)
CIRCLA Hazard Ratings:
Toxicity: 1 Ingnitgability: 0 Reactivity: 0 Persistence: 3
Toxicological Information:
Graphite causes benign pneumoconiosis (graphitosis). Symptoms of
pneumoconiosis from graphite exposure are dypsnea, coughing, black sputum,
bronchitis, ventricular hypertropy and impairment of pulmonary function.
X-rays will show progressive nodulation of the lungs. The theshold limit
value was set in conformity with the limit for free crystalline silica,
which may be present in graphite.
Best Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
Edited by PrestonE (01/31/08 06:07 PM)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 799
Loc: Houston,Texas
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Hi Mike,
Thanks for putting up the data on the corrector you so kindly designed for our team.
Things are progressing and we hope to have the scope ready to trial in April, if I don't get tied up in a company turn around project. If you don't hear from me for a while, that's what will have happened. Time period about 6-9 months.
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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G'day Preston.
Thanks for the helpful info. The FLI focuser is definitely under consideration. Upgrading to larger chip cmaera is some way off. Any help with baffle design is greatly appreciated. A software based calculation done by a local optician gave what seemed to be an enormous diameter primary baffle. Yet the RCOS 'budget' OTA apparently using the same 12.5" f6.6 optics has quite compact baffles. Hence my wondering about this. So access to a copy of that software you mention would be great. I'm always pretty careful with dust - routing/sanding dust from marine plywood ain't good for your lungs either.
cheers
guy
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