Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

34" F2.89 Large Fork Mount BHMO Project Build

  • Please log in to reply
294 replies to this topic

#76 polaraligned

polaraligned

    Viking 1

  • *****
  • Posts: 924
  • Joined: 26 Dec 2008

Posted 12 January 2017 - 08:17 AM

 

Range is 1.79 -05 to 1.49 -06 on the plop analysis. Only slightly better with the 54pt and the 27pt had a odd pattern with about the same readings.

Nice.  I guess the quartz makes a bit of a difference as it has a higher Young's modulus.  I am used to seeing mirrors over 28" with a 27 point support, so I was just curious how the 18 point did in PLOP.  You have a heck of a great optic there. 


  • ctcables likes this

#77 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 15 January 2017 - 06:17 PM

Checking the flatness of the cell, It is fairly good with a low of 2.27" to a high of 2.037 inches. Will need to add some shim stock of 30 thousands or 1mm to one support to make it just right. The sheet I am using is less than 2lbs and all points are in very flat contact. What I need to make a slight adjustment is the tilt, would be fine the way it is but might as well make it dead on.

Attached Thumbnails

  • messuer2.jpg
  • mesuring1.jpg


#78 mark cowan

mark cowan

    Vendor (Veritas Optics)

  • *****
  • Vendors
  • Posts: 9,713
  • Joined: 03 Jun 2005
  • Loc: salem, OR

Posted 15 January 2017 - 10:05 PM

It's an exciting project.   :bounce:



#79 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 20 January 2017 - 06:58 AM

The awaited day has arrived, the 34" mirror was delivered today and inspected. After the long trip across the country there it is no damage and the coating looks great. It is now all boxed up and weighting for me to finish the telescope.

Attached Thumbnails

  • mirror1.jpg
  • mirror2.jpg
  • mirror3.jpg
  • mirror4.jpg

  • PrestonE, brave_ulysses, Ravenous and 5 others like this

#80 PPO

PPO

    Vendor - PrecisionPro Optics

  • *****
  • Vendors
  • Posts: 782
  • Joined: 10 Feb 2012
  • Loc: Big Island, Hawaii and Owens Valley, CA.

Posted 20 January 2017 - 12:39 PM

A strong man indeed! I'd be unable to budge that thing out of its box ;)



#81 Mike Lockwood

Mike Lockwood

    Vendor, Lockwood Custom Optics

  • *****
  • Vendors
  • Posts: 1,894
  • Joined: 01 Oct 2007
  • Loc: Usually in my optical shop

Posted 20 January 2017 - 12:43 PM

That crate is a beast - it weighed quite a bit on its own, more than the mirror, I believe.  This is not necessarily a bad thing.

 

However, the crate came with the glass, and there was no reason to build a new (and lighter) crate just to ship it twice.  I cleaned it out and put all new foam inside.

 

Keep that lid clean and on the mirror, and take care when lifting it - either use two people or a mechanical aid.  It's not that hard to lift one side up and then lift the other side up and get it on top of the crate, but lifting it entirely is another story.

 

As usual, try not to touch the coating for a few months as it hardens up and becomes more durable.  I would wait until later to put on the center spot.


  • ctcables likes this

#82 garret

garret

    Surveyor 1

  • *****
  • Posts: 1,656
  • Joined: 26 Jul 2009
  • Loc: Netherlands

Posted 20 January 2017 - 02:48 PM

 

As usual, try not to touch the coating for a few months as it hardens up and becomes more durable.

Like concrete, aluminum alloy, wine...

 

I didn't know this fact, is this aging of what?

 

Garret

 


  • brave_ulysses likes this

#83 mark cowan

mark cowan

    Vendor (Veritas Optics)

  • *****
  • Vendors
  • Posts: 9,713
  • Joined: 03 Jun 2005
  • Loc: salem, OR

Posted 20 January 2017 - 04:21 PM

The coating oxidizes gradually with time and gets harder - especially if there is no overcoat, but that seems unlikely in this case.



#84 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 20 January 2017 - 06:24 PM

Only came out for inspection,  it was covered and boxed back up within minutes. Also note gloves for handling.  I do have a question is it OK to store the mirror in the creat on the side? This would give me much more working room.



#85 Mike Lockwood

Mike Lockwood

    Vendor, Lockwood Custom Optics

  • *****
  • Vendors
  • Posts: 1,894
  • Joined: 01 Oct 2007
  • Loc: Usually in my optical shop

Posted 21 January 2017 - 12:16 AM

As long as the lid is secure and all the packing is put back in, that should be fine.

 

Looking forward to seeing the OTA come together.  I'll get to the flat as soon as I can, though I'd like to get my new giant Fizeau put together to aid in that work.


  • ctcables likes this

#86 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 25 January 2017 - 06:25 PM

Link to cell compression test. https://www.facebook...65817040442047/

 

Rough compression testing the cell. There was some concerns about cell flex so I wanted to get a idea of what this cell would do. I am happy with the results. After several tests with 255lbs cell compression ranged from 10 thousands to 29 thousands. With the mirror weight of 139lbs  compression should be about half of measured and because the mirror will never be fully unloaded unless tipped at 90 degrees I should be looking at a even compression for most of the range between 1 to 3 thousands in real use.  This is a photo of what .0295 looks like.

Attached Thumbnails

  • compresshion.jpg

  • jtsenghas likes this

#87 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,304
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 25 January 2017 - 07:40 PM

Excellent! Deformation under gravity loading and its effect on focus and the locations of the edge supports should be negligible!

 

:whee: 



#88 polaraligned

polaraligned

    Viking 1

  • *****
  • Posts: 924
  • Joined: 26 Dec 2008

Posted 26 January 2017 - 08:38 AM

Chris,

For visual use, as you know, you only need to be able to hold collimation at all altitudes- and it is going to be tight at f/2.9.  My understanding is that you are only going to be using this visually anyway, so you are good.  

 

For photographic use, you would not be happy with this deflection at all.  At f/2.9, your depth of focus is down to 0.00027".  Half that number is the distance on each side of critical focus.  Yikes!  As you change from near zenith to say 30 degrees above horizon, you will move way out of focus, as the force the cell sees from the mirror will be cut in half.  There are a number of things that would have improved the stiffness of this cell vastly, but I digress, astrophotography is not your intended use.  Enjoy your build.   I look forward to seeing this scope in action.  :)   


  • Corky80124 likes this

#89 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 26 January 2017 - 03:38 PM

Chris,

For visual use, as you know, you only need to be able to hold collimation at all altitudes- and it is going to be tight at f/2.9.  My understanding is that you are only going to be using this visually anyway, so you are good.  

 

For photographic use, you would not be happy with this deflection at all.  At f/2.9, your depth of focus is down to 0.00027".  Half that number is the distance on each side of critical focus.  Yikes!  As you change from near zenith to say 30 degrees above horizon, you will move way out of focus, as the force the cell sees from the mirror will be cut in half.  There are a number of things that would have improved the stiffness of this cell vastly, but I digress, astrophotography is not your intended use.  Enjoy your build.   I look forward to seeing this scope in action.  :)   

No this is not a $250K project but after the testing I have done with loaded and unloaded cell the amount of travel for photos not lasting more than several hours the change would be in the ranges you are talking about. If I do use it for photos at some point I think it would be just fine for anything I would ever do with it. Like you stated it is for outreach and visual.


  • Mike Lockwood likes this

#90 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 1,855
  • Joined: 09 Aug 2016
  • Loc: Lynnwood, WA, USA

Posted 27 January 2017 - 07:36 PM

Also if you have straight deflection changing focus, the easy fix for that is to moto-focus and servo that off of the altitude. I don't think I would worry about it, there are like 30 other things to go worry about. :)



#91 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 28 January 2017 - 04:10 AM

Inside of base, little bit at a time. Link to vid and photos below. https://www.facebook...67035020320249/

Attached Thumbnails

  • inside 1.jpg
  • inside 2.jpg


#92 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 29 January 2017 - 04:11 PM

Some more work done on the direct drive motors. Lots of work left to do but progress.

Attached Thumbnails

  • coils1.jpg
  • coils3.jpg
  • coils4.jpg
  • coils5.jpg
  • coils6.jpg

  • PrestonE, brave_ulysses, Lightning and 1 other like this

#93 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 06 February 2017 - 02:03 AM

So I was able to get some work done on the side supports, the photos are of a mockup to see how it will work. The Tube was bent by hand not with the new bender as seen in vid ( see link) so the real parts will not have all the dents.  I will slot the back so the aluminum blocks can be adjusted for up down and tilt.  This will give me the fine adjustment so the contact points will be dead on.  There is almost no flex in the 9 inches (length to be determined yet with molding, help welcome as I want to get it right assuming 35 inch diameter Circumference = 109.955743 / 12 = 9.163") by 5/8” SS tubing.  So when all points are dialed in I should be solid and hold the mirror center at any angle.  Now I just need machine the parts for 6 of them and will countersink the block so the bolts do not stick out, do not want them to touch the mirror as it is going to be tight.

 

Link to bending of tubing

 

https://www.facebook...72116846478733/

 

Link to nice calculator

http://www.rkm.com.a...cle-sphere.html

Attached Thumbnails

  • side1.jpg
  • side4.jpg
  • side3.jpg
  • side2.jpg
  • side5.jpg

Edited by ctcables, 06 February 2017 - 09:53 PM.


#94 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 11 February 2017 - 12:20 AM

Ok some  more work done, tubing cut along with pivot pin blocks. time to make a jig for drilling center hole and block holes.

 

 

Link to tube and side support vid.

 

https://www.facebook...73821682974916/

Attached Thumbnails

  • side1.jpg
  • side2.jpg
  • side3.jpg

  • RAC likes this

#95 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,304
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 11 February 2017 - 11:34 AM

Looking good! It appears you have the bending process nicely tuned in!

 

Out of curiosity, have you settled on a name for this beast?  Big scopes need names.  In keeping with the theme of the "Black Hole Mobile Observatory" you could call it "The Event Horizon". Please give it a good name that means something to you. Few manage amateur construction in this class.

 

That reminds me, I never did hear if our moderator Greg "Shaft" Shaffer took me up on my suggestion to call his huge refractor "The Light Shaft"...



#96 Mike Lockwood

Mike Lockwood

    Vendor, Lockwood Custom Optics

  • *****
  • Vendors
  • Posts: 1,894
  • Joined: 01 Oct 2007
  • Loc: Usually in my optical shop

Posted 11 February 2017 - 02:05 PM

The edge supports look really nice.

 

Consider that there is going to be some flexure in the angle material that the bracket is made from.  You should measure the deflection with 30-50 lbs hanging from the bracket.

 

You also need to have a mechnism (if you don't already, I can't see it) to adjust the position of the edge supports quite precisely.


  • ctcables likes this

#97 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,304
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 11 February 2017 - 02:20 PM

You also need to have a mechnism (if you don't already, I can't see it) to adjust the position of the edge supports quite precisely.

Yes, I can imagine a careful one-time adjustment to get all the rollers in the same plane parallel to the back of the mirror after initial collimation may be required, but see no reason that couldn't be done by fine- tuning heights with shim stock under those supports. One of them may need no shim and the rest very thin ones. Increments can be right down to aluminum foil thicknesses. 

 

Since the three collimation knobs will move everything back and forth slightly, the overall mirror height could be tweaked to get that height tuned to the COG plane. That is, provided those supports are first tuned for height to a collimated scope.

 

To split hairs, that last adjustment for height could be done in the middle of the force range at 30 degrees altitude, but for the cell deflection Chris recently reported, I wouldn't be too concerned. 



#98 Mike Lockwood

Mike Lockwood

    Vendor, Lockwood Custom Optics

  • *****
  • Vendors
  • Posts: 1,894
  • Joined: 01 Oct 2007
  • Loc: Usually in my optical shop

Posted 11 February 2017 - 03:04 PM

Yes, shims will work, but I wanted to ask Chris what his plan was so that it would be shown on this thread.  It's important that people understand.

 

The collimation knobs will *not* move everything back and forth slightly because this is a moving frame cell - everything that touches the mirror is attached to one frame and thus moves with the mirror when collimation was adjusted.  This is the best way to implement a mirror cell, in my experience.

 

So, only the initial adjustment of height is required.


  • ctcables and jtsenghas like this

#99 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,304
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 11 February 2017 - 03:51 PM

The collimation knobs will *not* move everything back and forth slightly because this is a moving frame cell - everything that touches the mirror is attached to one frame and thus moves with the mirror when collimation was adjusted.

Good!

 

I appreciate the correction and clarification. I've always preferred moving cells for that very reason and my own smaller builds are done that way.  I mistakenly thought Chris' collimation knobs only adjusted back supports, as is often the case with larger dobs. A little easier to build, but not as good for the very reasons you mention.

 

Thank you, Mr. Lockwood. 


  • ctcables likes this

#100 ctcables

ctcables

    Viking 1

  • *****
  • topic starter
  • Posts: 572
  • Joined: 14 Nov 2006
  • Loc: Oregon

Posted 12 February 2017 - 01:52 AM

Mike my plan is to use set screws on the bottom block to adjust pitch and yaw so it will be a push pull system that can make a fine adjustment to the roller contact point to the mirror. Will provide photos when done but think it will work very well.


  • jtsenghas likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics