Hi All,
It has begun. Blame my insanity, blame the clouds or maybe too much time on my hands, but I have started a project to build an upto 24" Newtonian astrocam on a GEM.
Part 1) Manufacture drives.
Here are images of the R.A. drive wheel blank. Dec should be finished by the weekend.
I take it you have access to all the good turning and machining gear or your able to get some of the key parts done as "foreign orders" by mates who do ???
What F/ ratio do you plan to make the Newtonian? I was planning a 10~12" F/2.85~F/3 system a while back for imaging, however I couldnt find a mirror maker willing to go under F/3.5. I've not made a mirror myself before, So I thought going for a 10~12 F/2.8~3 setup was overly ambitious... (not to mention collimation!!)
best of luck mate! I look forward to seeing progress.
I take it you have access to all the good turning and machining gear or your able to get some of the key parts done as "foreign orders" by mates who do ???
What's your time line look like ?
I have been deciding on a GEM or Fork, probably the fork.
I have the moral support of the blokes in the TAS Faculty at work, They are helpfull with advice and a bit of welding, other than that I'm on my pat malone.
Timline is open ended, that's the best thing.
their 2" 0.73x corrector is 873 EURO
their 3" 0.73x corrector is 1260 EURO
their 3" 0.95x corrector is 1020 EURO
their 4" 0.73x corrector is 1740 EURO
but in the all up cost of 24" equatorial newt , that would not be a minor cost component I'd say, but probably more than worth it if you plan on large format digital imaging.
Where's that "green eyed" smiley when you need it .... I wish I had the funds to embark on such an project.
Will you build the 24" as a Newt-Cassegrain type of convertable configuration ?
Last edited by Ian Robinson; 25-12-2008 at 06:27 PM.
Great project Jeff. Regarding the mount Id recommend a fork mount, as with the GEM you have to do meridial flips with long imaging runs. Thats a real pain in the bum, and takes up valuable imaging time getting the flip just right. Guide stars have to be re aquired and the frame has to be aligned with the previous ones.
The Keller correctors are great, and though expensive, result in a system thats still far cheaper than a RCOSS type scope and much faster photographically, opening the way for deep narrorband imaging, or just going very deep in LRGB in a reasonable amount of time.
From your very dark site (which makes Wiruna look light polluted by comparison), a fast corrected Newtonian with a fork mount could do 6+ hour uninterrupted runs on one area producing mega deep results.
For a big aperture reflector, Id look at active cooling for the primary mirror. to get the mirror temp as close as possible to ambient nighttime temps to get the best possible seeing. One fella in the Newcastle society was looking at a small refegerated airconditioner blowing cold air over the back of his 24 inch mirror to cool it down to nighttime temps before starting observations.
Cheers.
Scott
The Keller correctors are great, and though expensive, result in a system thats still far cheaper than a RCOSS type scope and much faster photographically, opening the way for deep narrorband imaging, or just going very deep in LRGB in a reasonable amount of time.
Quote:
Originally Posted by Satchmo
Alex , If you want a super-fast flat field scope you use a Phillip Keller flat field corrector which gives you F2.55 from an F3.5 mirror.
Netwolf mentioned these to me reciently, but I missed the website. I now have it and will difinately be looking into these for further down the project.
Jeff, Glad to see your steaming ahead on this. The gears look great so far. The motors and encoders originated from another forum member, Mark who is also planning a 10" corrected Newtonian. And I think he used the motors to drive a very large Fork mounted newtonian. So I think the universe is saying fork mount with a corrector.
Surprisingly when you work out the pricing with a locally made Mirror and a Keller corrector you will find the cost is far less than what you can buy it for from ASA in Europe. Even a 24" would cost less than there smaller apertures.
I have been deciding on a GEM or Fork, probably the fork.
I have the moral support of the blokes in the TAS Faculty at work, They are helpfull with advice and a bit of welding, other than that I'm on my pat malone.
Timline is open ended, that's the best thing.
Part 1) Manufacture drives. Still practicing hobbing teeth.
That sounds an impressive project. What are you using to hob the wormwheel? I used an M12 tap to cut the Wwheels for my 190:1 drives.
Further up the thread there is discussion on field flatteners... There is a bloke on the Gold Coast that built a 20" f3 (BVC blank), made the flattener from modified surplus optics and it's all controlled by a Bartels stepper drive. The guy is very successful at discovering asteroids (Over 400 I believe) and a comet - perihelion late last year.
The point is that it's all achievable I wish to give you every encouragement and I look forward to watching your progress.
That sounds an impressive project. What are you using to hob the wormwheel? I used an M12 tap to cut the Wwheels for my 190:1 drives.
I am cutting my own worms and tool from 1.5" bright steel and lapping them to the wheel. Practising on black bar.
I am looking at 10tpi threads that should give me 360 teeth on approx. 11" wheel. My confidence is growing with each worm I cut, and I have finally stopped breaking the threading tool (1.27mm) is painfull to regrind.
Thanks for the encouragement.
An example of a tool, strange shape due to image angle.
That sounds an impressive project. What are you using to hob the wormwheel? I used an M12 tap to cut the Wwheels for my 190:1 drives.
Further up the thread there is discussion on field flatteners... There is a bloke on the Gold Coast that built a 20" f3 (BVC blank), made the flattener from modified surplus optics and it's all controlled by a Bartels stepper drive. The guy is very successful at discovering asteroids (Over 400 I believe) and a comet - perihelion late last year.
The point is that it's all achievable I wish to give you every encouragement and I look forward to watching your progress.
What's your reasoning behind the choice of 190:1 wwheel pitch ?
My confidence is growing with each worm I cut, and I have finally stopped breaking the threading tool (1.27mm) is painfull to regrind.
It's a pain when that happens. bang-crunch-crunch .
I've seen an example of where a bloke made the hob and worm on the same shaft in the same setting, so that they were identical form. Then hardened the hob end and cut the wormwheel. Finally he cut off the hob end to leave the worm ready for lapping. I hope that makes sence.
What's your reasoning behind the choice of 190:1 wwheel pitch ?
Hi Ian, a Bartells stepper drive needs a ratio of A-LOT:1 somewhere between 600:1 to 2500:1 So a 190:1 + a 8:1 toothed belt primary drive gives something about right. The important thing is not to end up with 190 1/2:1
I've seen an example of where a bloke made the hob and worm on the same shaft in the same setting, so that they were identical form. Then hardened the hob end and cut the wormwheel. Finally he cut off the hob end to leave the worm ready for lapping. I hope that makes sence.
Yes, I am trying this method to make my gears. It makes perfect sense.
Quote:
Originally Posted by DaveGee
Hi Ian, a Bartells stepper drive needs a ratio of A-LOT:1 somewhere between 600:1 to 2500:1 So a 190:1 + a 8:1 toothed belt primary drive gives something about right. The important thing is not to end up with 190 1/2:1
I have a 25:1 gearbox to drive the worm, this should give me A-Lot(9000):1 reduction. I may look into a 150-180 tooth wheel.
Simple workshop below.
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I may look into a 150-180 tooth wheel.
