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

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#51 ctcables

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Posted 06 April 2013 - 05:26 PM

Gator that indeed is one very nice looking telescope I am counting on the lightness of my mirror to make up for the extra weight anof my components. 40lbs is going to be very hard and that is not including the base.

#52 mark cowan

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Posted 06 April 2013 - 10:26 PM

Chris,

That looks OK to me. Just be careful not to crimp the wires with the through-holes on the secondary holder, you might want to radius those corners and only tighten it up once on any given set of strings - another reason to follow the design and use the flex plate and collimation screws for tweaks rather than messing with wire tension. I recommend using a jig to fix the secondary assembly in space before tightening down the wires (I updated my web site to say this a while ago) and also note the tension is not high at all - the spider gets its stability from the geometry, not from tension.

.008" might be on the light side for a 3.5" secondary but of course you can always change it as needed.

Best,
Mark

#53 gatorengineer

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Posted 07 April 2013 - 06:00 PM

Chris, You have a great project going... The mirror will cool superbly no question, and optically your rig will be amongst the best 20"ers in existance. No question.

Quartz mirrors actually increase the need for counterbalance. I have well over 40's of lead shot in the tail of my obsession (with its massive rocker rocker box) 2" plus thick mirror, steel mirror cell, etc). Its all about the balance, and moment arms a 31 nagler is a bugger to balance.....

Great project and cant wait to see the end product.

#54 ctcables

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Posted 07 April 2013 - 09:00 PM

Yep COG is a bugger for sure gator; because of my very large bearing (effective 36" R) my COG is out there around 18 inches from face of mirror. Also I am working on making the bearing into what some might call a 2 strut system but the cage of the mirror replaces the lower struts and the bearings form the mid box making my top struts around 40". May not be a small system but because most of it is hollow it is much stronger and lighter. Will post some new photos along with my less than 1lbs upper strut.

This strut folds into a triangle that is 2.5" OD by 47" long and is less than one pound. Will cut down to size when complete, this is also going to get covered in carbon fiber.

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Revised plans.
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Looks like the added sips and extra epoxy to make it look nice is going to push me over the 40lb mark and then some, High hopes for supper light are not gone just revised in that I do want it to look nice as well. Anyway if you want to change your guess on the weight you can. After this I will not be posting any more updates on the weight so from this point everyone has = information. I think with the info I have posted we should get very close to a finished tube weight.

#55 ctcables

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Posted 13 April 2013 - 08:40 PM

Well made some head way on the alt bearings, need to work on the carbon fiber lay up next.

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#56 ctcables

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Posted 16 April 2013 - 12:20 AM

Got started on the carbon fiber lay up. Lots of work left to do but it is going well.

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#57 ctcables

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Posted 21 April 2013 - 10:50 PM

Another week and a big part almost complete, this took lots and lots of time and checking but it looks to be turning out very well. So here are the photos.

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This is how it will sit, cross bracing not showing in this photo as I still need to make them which is next.
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inside of alt bearings showing the 4 cross bracing supports.
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#58 mark cowan

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Posted 22 April 2013 - 01:52 PM

Looking great Chris! :waytogo:

Best,
Mark

#59 ctcables

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Posted 23 April 2013 - 01:34 AM

Thanks Mark, Getting things ready for it. Just put an order in for a ES 20mm 100 and found a great deal on an Ethos 13mm. Not sure if I should sell the 10mm and 4mm radian because I am not sure how they will work out with the SIPS system. Anyway going to make the COG bottom heavy. I have lots of room with the alt bearing location to shift the weight up top or to the bottom. I am thinking it is better to be bottom heavy so when the big eyepiece goes in it is just right.

#60 ctcables

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Posted 01 May 2013 - 06:29 AM

getting things done but it seems like it is taking way longer than I expected. The bearings were not easy but they are turning out well.

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#61 gatorengineer

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Posted 01 May 2013 - 02:01 PM

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

Mark

#62 ctcables

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Posted 01 May 2013 - 09:06 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.

#63 gatorengineer

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Posted 03 May 2013 - 03:15 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...

#64 coinboy1

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Posted 03 May 2013 - 04:17 PM

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

#65 ctcables

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Posted 21 May 2013 - 10:21 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.

#66 ctcables

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Posted 25 May 2013 - 08:52 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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#67 ctcables

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Posted 28 May 2013 - 04:05 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 23.25” I hope this makes sense but if not let me know what I need to add for information.

Thank You

#68 ctcables

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Posted 29 May 2013 - 08:00 AM

Ok let’s 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.

#69 gatorengineer

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Posted 29 May 2013 - 10:34 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.

#70 mark cowan

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Posted 29 May 2013 - 02:42 PM

Ok let’s 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://starlightinst...rectors/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. :foreheadslap:

Best,
Mark

#71 ctcables

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Posted 29 May 2013 - 09:01 PM

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

#72 ctcables

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Posted 09 June 2013 - 08:49 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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#73 ctcables

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Posted 18 June 2013 - 06:46 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.

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#74 jtpowers

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Posted 18 June 2013 - 07:49 AM

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

#75 ctcables

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Posted 19 June 2013 - 08:36 PM

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

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