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The Making of my 20" telescope for a Carl Z mirror

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#101 mark cowan

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Posted 13 August 2013 - 11:35 PM

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

Now that gives me a sense of the scale. :waytogo:

Best,
Mark

#102 ctcables

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Posted 14 August 2013 - 06:11 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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#103 kfrederick

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Posted 14 August 2013 - 06:28 AM

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

#104 mark cowan

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Posted 14 August 2013 - 01:48 PM

Hey Chris,

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

Best,
Mark

#105 Kretieg

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Posted 14 August 2013 - 02:48 PM

What wood or veneer are you using?

#106 ctcables

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Posted 14 August 2013 - 04:39 PM

 Bubinga Wood more information on page 2

#107 johnnyha

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Posted 14 August 2013 - 07:09 PM

Awesome, fantastic job!

#108 ctcables

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Posted 19 August 2013 - 09:08 PM

Hey Chris,

Posted Image

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

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.

#109 mark cowan

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Posted 19 August 2013 - 11:18 PM

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

CALLING DOWN THE LIGHTNING!

:lol:

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... ;)

#110 ctcables

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Posted 25 August 2013 - 09:44 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.cloudynig...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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#111 careysub

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Posted 26 August 2013 - 02:15 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....t-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.

#112 polaraligned

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Posted 26 August 2013 - 05:42 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!

#113 ctcables

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Posted 26 August 2013 - 08:38 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....t-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.

#114 ctcables

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Posted 10 November 2013 - 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.

#115 ctcables

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Posted 30 March 2014 - 09:33 PM

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

#116 ctcables

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Posted 16 June 2014 - 12:35 AM

So been some time from last post, I have decided to change my base rotation setup, I now have a 22" bearing that I am mounting up, will provide photos when done. I hope this will give me a solid platform and still stay light. Old setup had some movment in it.

#117 ctcables

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Posted 20 July 2014 - 03:04 AM

altitude bearing is now driven by a 500 to 1 motor giving me 14,137.17 counts for 90 degrees. will be about the same for the rotate as well.

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#118 ctcables

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Posted 20 July 2014 - 03:10 AM

This is a photo of the belt drive rotate bearing. I have used a 26" Mt Bike wheel sandwiched between 1/8 inch plywood and a honey comb core. Mounted to the top of this is a table top server bearing 24” diameter, it makes for a very smooth rotate with a nonslip direct drive cogged belt. Now I need to get it dialed in and cleaned up.

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#119 ctcables

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Posted 17 August 2014 - 07:08 AM

So I have decided I started way to late to complet the finish work on my telescope to be complete for OSP but it will work better than last year with the new motors and mirror shroud.  I did find a cool way to mount it and I think it would work for many applications.  Using a small trailer tire tube is fantastic, anyway some day It will be all sanded down and finished with no blems.

Attached File  tube.jpg   123.66KB   1 downloads

Attached File  shroud.jpg   70.91KB   1 downloads



#120 ctcables

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Posted 25 August 2014 - 03:00 AM

Well second year for the 20” at OSP and the views were just outstanding.  There were some clouds at dusk but they cleared of and the sky was very nice.  Stayed out from dusk to done and was blown away by the Vail nebula, and Orion nebula.  So much detail I had never seen in my smaller telescope which saw very little use on this trip.  I was able to complete the binocular level 0 and level one in one night and had lots of fun doing it.  Still have a few things to tweak in with the tracking but the new base bearing works very well and the telescope is now very stable and no vibration at the eyepiece while moving it around looking for the had to find objects.  So other than some sanding and touch ups it is complete and will now see much more use in the years to come.

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Edited by ctcables, 25 August 2014 - 03:37 AM.







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