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Equipment Discussions >> ATM, Optics and DIY Forum

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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]
      #6024293 - 08/14/13 12:35 AM

(Says something inappropriate for a family-oriented forum...)

Now that gives me a sense of the scale.

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]
      #6024544 - 08/14/13 07:11 AM

Oregon Star Party 2013 Report
Back in December 2012 I had the rear opportunity to get a 1” by 20” quartz blank so I took the leap and got it. Now I had to build a telescope for it and get the mirror made so the work started. This report is in 2 parts starting with part 1 the build, part 2 first light at OSP.

After several days of haggling and trading I assembled my list of parts. My secondary mirror would be a quartz 3.5” by Mike Lockwood, the primary mirror would be a F4.5 done by Carl Zambuto optical, and the focuser would be a SIP system from Feather Touch and a Servo Controller II by Dan Gray. My goal was to have it completed for the Oregon Star Party Aug 7th 2013. I started with a drawing of what I wanted to create which changed several times during the build but stayed within the theme I was looking for. I wanted to make the OTA to be 40LBS with mirror, well that did not quite work out but at 69lbs with mirror focuser and all working parts it is still not too bad. As you look through the photos of the project from start to finish you will see that I used a honey comb fiber board for just about all the parts with some carbon fiber over balsa for key areas. The weight for one 4’ X 8’ by .25” is only 10lbs keeping things very light but strong. I found that the ALT bearings were harder to make and took me weeks and weeks to complete which was much longer than I expected. The mirror cell I must say turned out fantastic, 27 pt full flotation support with 180 degree cable support giving the mirror a very stable foundation to rest on. I was able to get the OTA completed but 3 days before the OSP I was still working on the drive system and base which I was able to patch a working system together at the last minute. I will need to complete this now that OSP is over.

Speaking of OSP how was first light? Well with all I had to do it turned out great, whether was not great on Thursday night and earlier when we arrived I found out that my telescope would not focus as my struts were to long so I packed it up for the night. Well around 3AM I stuck my head out and to my delight it was a very clear night so out came my back up telescope. Great views of M13, M31, Andromeda Galaxy, and many others. So the first night was not too bad after all. Friday I found a hack saw and some blocks with clamps (thank you Gary Kline) and was able to get my trusses shortened. Friday night and the sky were hazy to start but by 11:30PM were clearing up very nicely. I started off with some easy to find objects and was completely pleased at how much detail I could see. The 2 dust lanes in Andromeda were very clean and easy to see, The Ring nebula had a very nice shape and filled the eyepiece and M13 was just a stunning with my 9mm explore scientific + the Barlow. I felt like I was right there. Next stop contrast test, M101 pinwheel galaxy was well defined in the 20mm 100 degree EP. I was able to see each arm of the pinwheel with the central core and could not be more pleased about the optics. I enjoyed the rest of the night hopping from one area to another and everyone that stopped by was just as pleased as I was.






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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]
      #6024556 - 08/14/13 07:28 AM

Well gone!! If you have another quartz blank might wont to try grinding one. You would have Carls to compare It to .

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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: kfrederick]
      #6025310 - 08/14/13 02:48 PM

Hey Chris,



There's the money shot! How many people can do that with a 20" OTA?

Best,
Mark


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Kretieg
member


Reged: 03/21/13

Loc: Louisiana
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #6025416 - 08/14/13 03:48 PM

What wood or veneer are you using?

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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: Kretieg]
      #6025654 - 08/14/13 05:39 PM

 Bubinga Wood more information on page 2

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johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #6025897 - 08/14/13 08:09 PM

Awesome, fantastic job!

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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]
      #6035469 - 08/19/13 10:08 PM

Quote:

Hey Chris,



There's the money shot! How many people can do that with a 20" OTA?

Best,
Mark




Mark if that is the money shot where is the money? LOL
Wish you could have made it but there is always next year.


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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]
      #6035668 - 08/20/13 12:18 AM

It's a metaphor in this case, on second thought I'd call it:

CALLING DOWN THE LIGHTNING!



Best,
Mark

PS those pics of that 16" Sudiball mount on the walkabout have got me doing sketches for the structure I need for the 14.7" meniscus mirror now...


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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]
      #6046141 - 08/25/13 10:44 PM

Was asked this question in the OSP walkabout so thought I would post it hear as well.
So to answer your question on carbon fiber layup I have added a photo (see below) along with this link
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5755364/page...

As you can see I am using the carbon fiber for outside support, strength, and damage protection, it also looks good. The best way I have found to work this is to use a sheet of glass on a flat surface then a Teflon release sheet (black plastic looking stuff in the photo), layer of epoxy on the release sheet slow setting then the carbon fiber then another thin layer over the carbon fiber to make sure it is soaked in. When this is done squeegee off the excess epoxy to be used on what you want to bond to it (for me it was a fiber glass nomax core ¼” board sanded with 120 grit for good bonding). Next is 2 options 1 bag the whole thing and vacuum it down or 2 if you have a flat board and lots of weight to put on it this works as well. It is like making a sandwich with a time limit based on the epoxy set time. No room for mistakes as this stuff is not cheap. Now you let this sit for 24 to 48 hours and when you are done you now have a nice carbon fiber bond. To finish you sand with 120, then 220, then 300 grit and recoat with thin layer of epoxy in dust free room. This will give you a nice finish. Last step is to sand with 600 grit and give a final over coat with UV protecting urethane spray. Simple lol


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careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: The Making of my 20" telescope for a Carl Z mirror new [Re: ctcables]
      #6047187 - 08/26/13 03:15 PM

Great stuff! Thanks!

Where did you source your fiberglass Nomex panels from?

Making a polygonal UTA from prepared CF-honeycomb sheet using this cut-and-fold technique looks interesting:

http://www.acpsales.com/Cut-and-Fold.html

A variation on this would be to use those pre-scored end-grain balsa sheets, laminate it with CF, and then cut on the outside make them foldable. Applying a non-stick treatment to the pre-planned EGB joints would be needed so that they aren't glued together. After they are cut and bent, an patching compound would need to be troweled end (preferably also resin-based) and covered with CF tape.


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polaraligned
professor emeritus


Reged: 12/26/08

Re: The Making of my 20" telescope for a Carl Z mirror new [Re: careysub]
      #6047511 - 08/26/13 06:42 PM

The cut and fold technique has been used by the composite airplane builders for years. You can also pretty easily form a round tube by cutting a series of kerfs in the back of a single skinned panel. It will then roll into a nice tube. The inside then needs to get cloth covered.

CF certainly can enable the home builder to cut his weight to maybe 1/3 of that of a similarly stiff wooden structure. An advanced builder on a large scope can maybe achieve a weight of 1/5 that of a similar wood or metal scope. For advanced scopes the reduction of thermals and the nearly 'set and forget' focusing are huge. CF scopes even in tubes can perform superbly as demonstrated by the Dream Astrograph. There is a remote 16" Dream in AZ that discovered 6 comets in the last year. There is also a 24" scope (doing research) that used a lot of CF and is light enough to be mounted on a Paramount. This is in stark contrast to the metal monsters of days gone by. Plenty of 24" "professional" scopes are weighed by the ton...The 24" I referred to above is barely over 200# including mount!


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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: careysub]
      #6047772 - 08/26/13 09:38 PM

Quote:

Great stuff! Thanks!

Where did you source your fiberglass Nomex panels from?

Making a polygonal UTA from prepared CF-honeycomb sheet using this cut-and-fold technique looks interesting:

http://www.acpsales.com/Cut-and-Fold.html

A variation on this would be to use those pre-scored end-grain balsa sheets, laminate it with CF, and then cut on the outside make them foldable. Applying a non-stick treatment to the pre-planned EGB joints would be needed so that they aren't glued together. After they are cut and bent, an patching compound would need to be troweled end (preferably also resin-based) and covered with CF tape.




Yes this works great; I have used this folding system before. I find a 5 minute epoxy works great for this, if it is to thin it tends to not hold where you want it to stay. Set times are very important depending on what you want to glue together.


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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]
      #6187724 - 11/10/13 10:44 PM

Just added a 5 to 1 gear box to my 2 drive motors now I will get about 10,000,000 counts per rev. Need some clear sky's so I can see ISON.

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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]
      #6438588 - 03/30/14 10:33 PM

Just cleaned the mirror for the first time, very happy with how it turned out. Looking forward to some clear nights.

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