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12.5" please help with planning the first build

Dob
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#1 Speo

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Posted 02 March 2021 - 02:54 PM

I have a 12.5 / f5 mirror that is supposed to be good quality and I would like to build a telescope for it.

 

I never built a telescope, but I saw many pictures and movies of building ATM telescopes, and I think I have the skills to do it.

 

Being my first build, I would like to choose a design that is easy to build. 

 

Also, once I choose a design, how do I get to calculate the dimensions of all the pieces? For example, how many mirror support points, what size and location for the mirror supports, size of the mirror box, size od the rocker box, size of the secondary cage...size of the secondary...

 

My instinct is to try something like this:

 

https://1abxf1rh6g01...-AM-620x712.png

 

Are there any plans for sale?

 

Any input is appreciated.


Edited by Speo, 02 March 2021 - 03:07 PM.


#2 oilmanmojo

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Posted 02 March 2021 - 11:12 PM

There probably are plans you can buy. However, there are a ton of build threads and blogs and i am sure if you look you will find one that you like that you can mimic. Many times these blogs actually get very specific on measurements, etc. My first telescope (built about 20 years ago) was based on an Astrosystems tailgate and an associated altitude bearing set. I am in the process of refurbishing that old telescope and am using a series of Utube video from a guy that worked or works for New Moon Telescopes which just happens to match my mirror size (16 in). Also there are the "bibles" from Kriege and Highe which give you plenty of details to build a quality scope. Finally there are kits (astrosystems is one) that you can customize for your project. Teeter, Astrosystems, and others sell specific components that you can also utilize

Good luck with moving this project along


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#3 Waynosworld

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Posted 03 March 2021 - 12:58 AM

Over a 3 month period I looked at a bunch of others builds, I was going for light weight(not the lightest) so it would be easier to transport, I did not try to make it all bundle up neatly like a suit case, I went for what I could build with stuff I had around my house, I also built a version out of wood to see what would work and what would not work, my scope doesn't look normal but it is less than 90 pounds and holds collimation and I wheel it around using the UTA as basically a handle.

 

007.JPG

 

010.JPG

 

It works pretty good for something built by a guy that didn't even know how to collimate a scope almost 5 months ago, this is not for everyone and I can say if you have a cat or cats or any other animals around that hang out in your yard where you will use a scope I suggest a traditional type truss dob that you can cover the mirror when it is outside acclimating to the outside temps.

 

I spent a lot of time making jigs and other such stuff to build this scope, the mirror is offset from the side bearings center so I could use less counter weights to balance it, I seen this in others builds, it works alright, I have an appointment to have a shroud made for it, I have only started using it in the last week.

 

If you have the tools to build your own scope I would build it, you learn a lot about telescopes when you build one yourself.


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#4 Speo

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Posted 03 March 2021 - 09:58 AM

Thank you guys.

 

@oilmanmojo - I looked at Teeter and Astrosystems web sites and got some ideas and also clarified a few things.

 

@Waynosworld - I found your build thread and I learned a lot from the very detailed pictures and explanations. I was planning to do exactly what you did: start the build with less than perfect materials to figure out things and then build a second version with better materials.

 

Thank you for your replies 


Edited by Speo, 03 March 2021 - 03:43 PM.

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#5 Chucky

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Posted 04 March 2021 - 09:05 AM

Great job and effort Wayne.  Wishing you much success using it.  Congratulations. 



#6 Pinbout

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Posted 04 March 2021 - 11:16 AM

boxes are boxes, but how you make the cell is important.

 

for a mirror that size, I prefer a moving plate cell...

 

that's a welded metal frame that supports the collimation bolts/ springs holding a plywood plate that contains the rocker bars and edge support.

 

the plate keeps the mirror more secure than a sling style cell.


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#7 Speo

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Posted 04 March 2021 - 10:42 PM

boxes are boxes, but how you make the cell is important.

 

for a mirror that size, I prefer a moving plate cell...

 

that's a welded metal frame that supports the collimation bolts/ springs holding a plywood plate that contains the rocker bars and edge support.

 

the plate keeps the mirror more secure than a sling style cell.

Same principle with this? 

 

https://3dwarehouse....rror-Cell?hl=en

 

I used a software called Plop to calculate the support points and the results were 6 triangle and 18 points.

 

I forgot to mention my mirror is only 1.5" thick , 2 plates of 3/4" tick glass fused. Is this style still OK for 1.5" with 18 support points?

 

Thank you.


Edited by Speo, 04 March 2021 - 11:09 PM.


#8 Pinbout

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Posted 04 March 2021 - 11:30 PM

Kind of

 

but here is a 12in frame that would be mounted to a welded H frame

 

but the collimation bolts and springs would face down

 

4CE10EDE-FAF6-4945-A40A-611B4C1AD98E.jpeg

 

 

like this

 

https://www.youtube....hqaMXFT&index=5


Edited by Pinbout, 04 March 2021 - 11:39 PM.

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#9 Pinbout

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Posted 05 March 2021 - 02:05 PM

for a 12" mirror

 

IMG_4041 (4).JPG


Edited by Pinbout, 05 March 2021 - 02:06 PM.

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#10 Speo

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Posted 05 March 2021 - 03:35 PM

It's settled then. I will try this. Thanks.



#11 cheapersleeper

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Posted 07 March 2021 - 06:37 PM

for a 12" mirror

 

attachicon.gifIMG_4041 (4).JPG

Best pic yet of the early Klingon influenced mirror cell.  Beats the heck out of all the rube goldberg stuff we made in the past.



#12 Speo

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Posted 25 March 2021 - 08:55 PM

Thanks Pinbout for the sketchup project, it made my life a lot easier. 

 

All pieces came back from the CNC,  I also got the 1" aluminum tubes and the star nut inserts (if needed).

 

 

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  • IMG_1447.JPG

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#13 Speo

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Posted 25 March 2021 - 08:58 PM

Another pic of the CNC cut plywood

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#14 Pinbout

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Posted 26 March 2021 - 12:13 AM

At f5 you’ll need to add some weight, but I prefer that than having kangaroo sized alt bearings 



#15 Speo

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Posted 30 March 2021 - 10:31 AM

for a 12" mirror

 

attachicon.gifIMG_4041 (4).JPG

I shopped around for the materials for the mirror cell and I can get 1.8 x 1" flat bar and 1" x 1" steel square pipe. Is this size OK?

 

A bunch of questions about the materials:

 

How thick are the aluminum bars holding the plastic support screws for the mirror?

How thick are the 6 plastic bolts supporting the mirror?

How thick are the collimation bolts?

How much of the mirror circumference has to be supported by the 4 bolts holding the mirror at the bottom? Are those plastic bolts as well?

How thick are the 3 bolts around the mirror - one at the top holding it to not flip and 2 at the bottom ?

 

Thank you.


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#16 bbasiaga

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Posted 30 March 2021 - 12:21 PM

Head on over to looptics.com and read his article about mirror cell supports.  It'll get you thinking and result in something similar to what you see pictured.  

 

The bolt sizes you can kind of choose - i use 3/8" on mine, though they probably don't need to be that big for support reasons on a 12" mirror.  Still, they are beefy and readily available.  5/16" would probably work.  1/4" seems too small to me but I don't have an engineering basis for that impression. 

 

The mirror cell support points are generally recommended to be .75-1" in diameter.  DO NOT USE BOLTS.  They need to be made of delrin or nylon.  You might find a nylon bolt you could use I suppose, but you'll need to flatten the head as they often have a nib from molding and/or some writing embossed on them.  The thickness of the head needs to make sure it clears any other hardware that is attached to the rocker arms, so the mirror is ONLY sitting on the support points. You can shim it up with washers between the support points and the pivoting bar if necessary.  

 

Whiffle supports as shown are discussed in the article above, but generally are 45 degrees apart .  The center of each whiffle is 45degrees off the vertical axis of the mirror, and the points are 45 apart from each other.  The upper left support is 67.5degrees off the bottom center of the mirror, and so is the one one the right, so the total coverage is somewhere around 135degrees.  

 

For aluminum thickness, on a 12.5" mirror this may be overkill, but I like to use .25" thick flat bar for the sides, and 1" square tube for the...tubes.  1/8" wall on the tubing, so it has some meat to drill/tap if you want to.    The pivot bars should be at least 0.5" thick, and 1" wide.  This gives enough meat to drill for the pivot hole and bolts to hold down the support points.  

 

 

Brian


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#17 VictorMG

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Posted 31 March 2021 - 03:47 PM

All you need is wood, bolts, t nuts, screw on metal plates, washers, formica, vinyl  or Teflon pads, caulk,  fiberglass from home depot, 1 inch wooden dowl rod,  and a sona tube, paint and stain, etc.  Ask for details if interested. Metal film cans work great for declination bearings and you need 9 inch ones. Check out my add, 16 inch Davidson Optronics Superplanetary scope, built it myself. Yours is easier,  as you can used a one piece sonatube. 


Edited by VictorMG, 31 March 2021 - 03:55 PM.



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