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Equipment Discussions >> ATM, Optics and DIY Forum

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gatorengineer
Carpal Tunnel
*****

Reged: 02/28/05

Loc: Hellertown, PA
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5834600 - 05/01/13 03:01 PM

Chris, looking good what diameter alt bearings are you using? Thanks

Mark


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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: gatorengineer]
      #5835318 - 05/01/13 10:06 PM

36 inch. Alt will have a 6 to 8 inch from the bottom of the mirror cell to the bottom of the alt bearing putting the cog 21 to 22 from the mirror face.

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gatorengineer
Carpal Tunnel
*****

Reged: 02/28/05

Loc: Hellertown, PA
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5838682 - 05/03/13 04:15 PM

are you eccentrically mounting the mirror box on the bearings? That will get you a little more to COG, look at what Spica eyes does, hard to explain...

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coinboy1
sage
*****

Reged: 05/03/11

Loc: Tulsa, OK
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: gatorengineer]
      #5838769 - 05/03/13 05:17 PM

Great telescope. 41.3lbs is my guess. Good luck and cant wait to see the updates!

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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: coinboy1]
      #5877144 - 05/21/13 11:21 PM

Just got my carbon fiber trus tubes in to day, thay look very nice. I will post a photo later this week. It is looking to be in the 52 to 56lbs range for the ota depending on if I add finder and heater system. Not much done over the last 2 weeks as other things have taken up my time but will get back on it next week and start posting more photos. So the people in the 50+ lbs range are still in the running. Last update from Carl was the mirror was 70% complete and was lookiing good so we will see as it must pass his 5 tests.

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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5884706 - 05/25/13 09:52 PM

This is a photo of the rocker mounted up to the mirror cage, still making the cross braces and will add the liner to the mirror cage after mounting hardware is added. The second photo is of the new carbon fiber struts that will attache the secondary cage to the rocker, will be 8 struts.




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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5888347 - 05/28/13 05:05 AM

Ok need some help as this part is critical and just want someone to check my work. Using Newt for the web I have a 20.03 inch mirror at F4.5 using a 3.5 inch secondary. Inside ring is 22" and outside or (to focuser mount) is 23.25Diam or 11.684" from center of secondary to face of focuser mount. Newt shows 76.955 from face to secondary then the 11.684 to focuser. So my question is with a 1.5" feather touch with built in SIPS is this still the same? Dose my point of focus change with SIPS? If someone can confirm this for me that would be great, do not want to cut struts unless I am positive of the distance from mirror to secondary then secondary to where the focuser mounts. The outer diameter is fixed at 23.25Ē I hope this makes sense but if not let me know what I need to add for information.

Thank You


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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5890357 - 05/29/13 09:00 AM

Ok letís do something more simple, dose the SIPS change the focus point? Will I need to add or minus distance from secondary by adding the SIPS? Or am I correct in assuming the SIPS just moves it out so everything will come to focus as if the SIPS was not installed. Never had a paricor before or SIPS so I just do not know. Hope fethertouch sends info on this part if I get no answers here.

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gatorengineer
Carpal Tunnel
*****

Reged: 02/28/05

Loc: Hellertown, PA
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5890562 - 05/29/13 11:34 AM

suggest that you just cut your truss poles long and trim them in as needed. There is a thread here on Fast Mikes Dob in which Mike Lockwood gave a marked up photo of a SIPS and the focal location. Hope this helps, thread was in the last month.

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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5890903 - 05/29/13 03:42 PM

Quote:

Ok letís do something more simple, dose the SIPS change the focus point? Will I need to add or minus distance from secondary by adding the SIPS? Or am I correct in assuming the SIPS just moves it out so everything will come to focus as if the SIPS was not installed. Never had a paricor before or SIPS so I just do not know. Hope fethertouch sends info on this part if I get no answers here.




Yes, it changes it. Study that photo, it explains the geometry, it shows the original focal plane and the new one as well.

http://starlightinstruments.com/store/image/cache/data/coma%20correctors/SIPS...

In any case I wouldn't cut those struts shorter until you've installed the mirror and confirmed the focal plane of the entire OTA. You know, just to be sure.

Best,
Mark


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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: mark cowan]
      #5891437 - 05/29/13 10:01 PM

Thanks for the information and the photo, just what I needed. I do appreciate your help with this.

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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5912117 - 06/09/13 09:49 PM

Well I did not think the alt bearings were going to take so long, I think I over did it, lol. They are very strong and I think will work very well. I have completed the SS inlay for the drive motor contact along with putting in all the filler strips so the main part is done. I now need to laminate the wood then sand and recoat to clean it all up. Anyway hear is a photo, next steep drill mounting holes and make mirror cell which I have decided to go with a 27 point cell.





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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5926942 - 06/18/13 07:46 AM

I am now starting to make the parts for the 27pt cell. I have Aluminum laminated to the honeycomb which makes it very light flat and stiff this is then attached to the solid aluminum triangle which is attached to a pivot ball joint connected to a Titanium valve which is supported by a brass valve guide. This makes a very strong accurate stiff anchor point while keeping every one of the 27 points floating. See photos.









Edited by ctcables (06/18/13 07:58 AM)


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jtpowers
more clever in the first place
*****

Reged: 11/03/05

Loc: Cambridge, MA
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5927040 - 06/18/13 08:49 AM

Very inspiring project! I'll weigh in at 44.8lbs.

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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: jtpowers]
      #5930109 - 06/19/13 09:36 PM

One more steep in the right direction. Custom Blue one of a kind.



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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5930149 - 06/19/13 09:59 PM



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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: mark cowan]
      #5935419 - 06/22/13 09:49 PM

Mirror cell looking good, 27pt. There will be larg vent holes and a spot for small center fan if needed, with 1 inch thick quartz mirror I should not have much problems with mirror cool down.



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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5958202 - 07/06/13 09:48 PM

Well been some time from my last update, Looks like I over did the alt bearings. They are very strong but weigh much more than I wanted. I know now that 5 lbs could have been saved on each one by using AL instead of stainless steel. So looks like the completed OTA weight is going to be. 69Lbs this includes mirror 22lbs, mirror cell 5lbs, ALT bearings 22lbs struts 3lbs, secondary cage with focuser and mirror 6lbs and primary cage 5lbs. So even cutting the alt bearings down looks like the best I could do would have been around 61 lbs and if I left it without any wood lamination this would have saved another 10 lbs as the epoxy turns out to be heavy as well. Anyway this way it looks much better and is very strong.








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ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5958209 - 07/06/13 09:55 PM

Looks like the clear winner is Gatorengineer at 70lbs great job. PM me as to location you want me to send your new blank to. I will post more photos as I get the mirror and rocker box completed.

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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #5958225 - 07/06/13 10:12 PM



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