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

An offset wire spider design

  • Please log in to reply
109 replies to this topic

#1 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 19 January 2015 - 06:47 AM

By request, attached are some close up shots and the design plans for my offset wire spider. The telescope is a 16" f4.5 with an 88mm secondary and I rebuilt my spider as part of an UTA rebuild to lose weight. I'm not sure that anything I've done here is terribly original, but I'm pleased with the overall result - the spider is rigid and doesn't suffer from vibration - and I thank the many contributors on this and other sites that have provided many of the ideas I have implemented together successfully here.

 

gallery_217007_4746_88360.jpg

 

Key features include:-

 

1. low profile UTA, total height 162mm. I occasionally pack my telescope into the boot of an ordinary sedan. The photo below is my original (heavier) UTA but the rebuild (above) is dimensionally identical.

 

gallery_217007_4746_59539.jpg

 

2. Guitar strings and lockable guitar machine heads make installation and adjustment quick and easy, and permit collimation. Below are two views...

 

gallery_217007_4746_16563.jpg

 

gallery_217007_4746_7931.jpg

 

The spider uses 8 x #2 guitar string wires tensioned with lockable guitar machine heads. This technique made construction very simple; I found it easier to build a wire spider than a normal vane spider. I didn't even use a jig; I simply placed the central support upside down on the table and the UTA around it (upside down) and threaded each wire from the center out through each head loosely, locked the heads, cut the wires and began to tension. When it was roughly right, fit the laser and fine tune. So there is no reason to be intimidated by wire spiders being too fiddly or difficult.

 

3. wire vane fixture points offset from center to edge providing stable geometry preventing rotation (yaw). See discussion of this important feature in these threads here and here...
4. spider fixing plate offset behind mirror to minimise overall height of structure and by extension minimise UTA

5. wires are crossed vertically to maximise stability

gallery_217007_4746_52021.jpg

 

5. secondary is designed offset to optimise beam while maintaining parallel vanes to minimise diffraction.

 

Below is an image of the pdf file attached for anyone who wants to build their own. If you print it on A1 paper it will be drawn to scale full size. Attached File  16inch-newTER.pdf   142.11KB   306 downloads

 

gallery_217007_4746_282741.png

 


  • Daniel Mounsey, scott50, starman345 and 3 others like this

#2 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 19 January 2015 - 07:43 AM

nice drawing.

 

just from my experience, when making something that uses only two collimation screws, I could never use two screws that were in a parallel line [both on the base of a triangle]. typically in a kinematic cell the common corner [ the 90° corner] is the stationary screw [or ball].

 

same with my primary mirror cell, I could only use the middle bolt and one side, I could never just use both sides and not touch the middle bolt.

 

now your making me re-think my 12" travel dob spider! Darn you Oberon! :lol:



#3 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 19 January 2015 - 07:55 AM

I adjust my trusses for collimation. Both mirrors. Much quicker and much easier in every way, and greatly simplifies mirror support. But that's another story for another thread another day.

For normal telescopes with fixed tubes or trusses, the guitar machine heads on the wire spider may be used to collimate the secondary. This also makes support for the secondary much simpler and sturdier.

 

Of course, if I wanted an adjustment facility on the secondary support all would I need to do is place rubber washers between the mirror plate and the support block and I would have a three screw adjustment. I started out that way (before I built either the wire spider or the adjustable trusses) but it was so redundant I removed it.



#4 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 19 January 2015 - 08:04 AM

 

I adjust my trusses for collimation. Both mirrors.

 

I've heard about people like you.... :lol:

 

thanks for clarification on collimation.



#5 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 19 January 2015 - 08:08 PM

I copied this from the new ES dob design. they're angled plate is a little different.

 

gallery_106859_3508_139075.jpg



#6 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 19 January 2015 - 08:17 PM

I like it. That looks like an excellent design for spider vanes.

 

I would add a timber element between the glass and the metal to prevent stress on the mirror.



#7 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 19 January 2015 - 08:52 PM

And I would also prefer one one fixed perhaps ball shaped point that the other two adjustments rotated the mirror around, kinematic cell like. I don't trust springs and loose screws on their own to be reliable. You only need two screws. 


Edited by Oberon, 19 January 2015 - 08:55 PM.


#8 jtsenghas

jtsenghas

    Gemini

  • *****
  • Posts: 3257
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio --Bloomdale

Posted 19 January 2015 - 09:13 PM

I like that concept for adjustment. I am considering doing something like that with some scraps of carbon fiber composite plaques 2.5 mm thick that are left over from some R & D experiments at work. This material is light and has similar thermal expansion characteristics to glass. The CLTE is only slightly higher.


Edited by jtsenghas, 19 January 2015 - 09:15 PM.


#9 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 19 January 2015 - 10:46 PM

 

And I would also prefer one one fixed perhaps ball shaped point that the other two adjustments rotated the mirror around, kinematic cell like.

 

 

on my ultra light scopes the primary cell works well with only two screws, the third doesn't really need to be a ball, just don't touch it.

 

20140217_114746.jpg

 

 

this is a 2.7" 2ndry total height is 3.38" but I just eyeballed the mirror thickness.

 

look ma, no glue... :p

 

ke 2ndry holder.jpg


Edited by Pinbout, 19 January 2015 - 11:32 PM.

  • Pierre Lemay and bobruben like this

#10 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 19 January 2015 - 11:32 PM

Nice drawings yourself! What are you using?

What I find interesting about this offset spider method is that it is not only geometrically and structurally superior, but simpler and cheaper to make (and make well) than centered vanes. It requires no machined or cast alloy components, just flat metal. I don't understand why they aren't more prolific commercially.

btw Pinbout, collimation can be simplified ever further on your design; you only need one adjustment screw for the vertical axis. Horizontal rotation can be achieved by adjusting tension on the vanes themselves. This would permit a stiffer secondary support whereby the mirror plate would flex with respect to the vane plate only on one axis, leading to the possibility of using a single piece of metal plate bent on a thinned section to a V shape (one side supporting the mirror, the other attached to the vanes) with the spring loaded adjustment screw opening and closing the width of the V. This would eliminate any chance of flop.

 

Taking this further, you could also offset the vanes to the back of the mirror (so as the permit deeper stiffer vanes) as I did in both my spiders, and use a flat knurled disk rather than a knob to make your adjustments, and so keep the adjustment knob within the mirror shadow.


Edited by Oberon, 20 January 2015 - 05:37 AM.


#11 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 20 January 2015 - 12:06 AM

Check the scales. 725g. This is why I removed my steel and aluminium spider and went to wire.

gallery_217007_4746_28428.jpg

...and here is the 10kG counterweight I removed from my cell after my UTA rebuild (which involved more than just changing the spider)

gallery_217007_4746_71491.jpg



#12 Chriske

Chriske

    Kijkerbouw Urania

  • *****
  • Posts: 3113
  • Joined: 15 Aug 2004
  • Loc: Boechout, Belgium

Posted 20 January 2015 - 02:26 AM

I have yet another way of adjusting the secondary mirror. Should I post it here also or start another thread..?


  • michaeldurban likes this

#13 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 20 January 2015 - 02:32 AM

Post it here please...



#14 Chriske

Chriske

    Kijkerbouw Urania

  • *****
  • Posts: 3113
  • Joined: 15 Aug 2004
  • Loc: Boechout, Belgium

Posted 20 January 2015 - 04:32 AM

This is our own system to collimate secondary mirrors. All course members use it. Hundreds have been made.

In our opinion it's a far easier system compared to the 'classic 3+1 bolt + spring' version.

 

This picture is taken about 25+ years during course.

curvedspider.jpg

 

 

This explains it all. One spider is removed to make it clear.

spider3.jpg

 

Black screws to attach the vanes to the secondary holder, red set screws to position/collimate the mirror in its holder.

The setscrews closest to the mirror are fastened first. But before you do that the secondary mirror is positioned exactly in front of the focuser in both directions, rotating that mirror in it's holder and also adjust it in height. You also correct for secondary offset at the same time. At this point you never try to collimate the optical axis..!

After that is all done you start collimating the mirrors optical axis using only the other 3 setscrews.

 

spider4.jpg

 

 

These are the spiders made nowadays, same collimation system, covered by it's owner to protect the secondary mirror.

spider6.JPG



#15 Oberon

Oberon

    Vanguard

  • -----
  • topic starter
  • Posts: 2242
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 20 January 2015 - 05:27 AM

Thank you for sharing another method Chriske. I can see how it works, I can see it would be simple enough to build, but I can't see how it is a far easier system to use?

 

1. it requires a tool (an Allen key), and there is no space for a knob (at least not on a smaller mirror).

 

2. it might typically require at least 6 insertions of the tool into a grub screw (in the dark?) to loosen/adjust/tighten, and probably more for an inexperienced user.

 

Obviously I am guessing here...what do you find yourself doing?



#16 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 20 January 2015 - 06:10 AM

 

This explains it all.

 

yeah it does, your a mad man, you know crazy... :lol:

 

in a good way.


Edited by Pinbout, 20 January 2015 - 06:11 AM.


#17 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 20 January 2015 - 09:43 AM

 

you only need one adjustment screw for the vertical axis.

 

I know Royce would do that on his 2ndry's. I like to simplify but I don't like to limit the available movement.

 

http://rfroyce.com/u...holder coll.htm


Edited by Pinbout, 20 January 2015 - 09:47 AM.


#18 Chriske

Chriske

    Kijkerbouw Urania

  • *****
  • Posts: 3113
  • Joined: 15 Aug 2004
  • Loc: Boechout, Belgium

Posted 20 January 2015 - 02:54 PM

Thank you for sharing another method Chriske. I can see how it works, I can see it would be simple enough to build, but I can't see how it is a far easier system to use?

 

1. it requires a tool (an Allen key), and there is no space for a knob (at least not on a smaller mirror).

 

2. it might typically require at least 6 insertions of the tool into a grub screw (in the dark?) to loosen/adjust/tighten, and probably more for an inexperienced user.

 

Obviously I am guessing here...what do you find yourself doing?

Hi Oberon,

 

I think for most collimation systems(secondary) some tool is required, be it an Allen key or a screwdriver. And I never collimate a secondary mirror in the dark. Collimating a secondary mirror you need to see the primary's perimeter.



#19 dag55

dag55

    Viking 1

  • *****
  • Posts: 639
  • Joined: 13 Apr 2011
  • Loc: Hamburg, IL. U.S.

Posted 20 January 2015 - 05:04 PM

Thanks for the designs Oberon and Chriske,  I really like the wire spider design and am going to incorporate it in my current build project. I like the almost none existent  diffraction spikes that the wire spider design affords, and have always thought the wire spider is an elegant design.

Dane



#20 dag55

dag55

    Viking 1

  • *****
  • Posts: 639
  • Joined: 13 Apr 2011
  • Loc: Hamburg, IL. U.S.

Posted 20 January 2015 - 05:20 PM

Very good looking build, Oberon, I like the none traditional color of your build, the wood stain and UCA red tint set the OTA off nicely.

Dane


  • Oberon likes this

#21 Pierre Lemay

Pierre Lemay

    Apollo

  • *****
  • Posts: 1100
  • Joined: 30 Jan 2008
  • Loc: Montréal, Canada

Posted 20 January 2015 - 05:54 PM

this is a 2.7" 2ndry total height is 3.38" but I just eyeballed the mirror thickness.

 

look ma, no glue... :p

 

attachicon.gifke 2ndry holder.jpg

 

Danny, that is a very nice and simple diagonal support. I like how close the CG of the diagonal is to the attachement point of the vanes. I also like Oberon's offset wire support which also shares this short CG to spider attachement point distance.  

 

I don't like the diagonal support for the 4 inch diagonal on my own 20 inch:

 

DSC01914.JPG

 

It's overly complicated. It evolved from an initial design which, for all kinds of reasons started out as a good idea but ended up a strange compromise. It's not that heavy (the support and vanes weigh about 0.7 pounds) but with a simple design like your's I could probably reduce that significantly. My adjustment knobs are not as accessible as they should and I dont like the way the diagonal support "hangs" from the vanes.  I haven't detected excessive vibration but having it "within" the vanes instead, just like your design and Oberon's can only help. One feature I want to keep, however, is using the vanes as conductors for the diagonal dew heater. With proper insulation I think your design would allow that. I've been searching for a replacement and the design you show is pretty much what I am looking for. Thanks for posting. I will give it a try.



#22 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 20 January 2015 - 06:37 PM

 

however, is using the vanes as conductors for the diagonal dew heater.

 

I just use copper foil tape instead of making the entire vane live.

 

http://www.mcmaster....il-tape/=vjyews



#23 Jeff Morgan

Jeff Morgan

    Cosmos

  • *****
  • Posts: 9331
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 21 January 2015 - 11:15 AM

This explains it all. One spider is removed to make it clear.

spider3.jpg

 

Black screws to attach the vanes to the secondary holder, red set screws to position/collimate the mirror in its holder.

The setscrews closest to the mirror are fastened first. But before you do that the secondary mirror is positioned exactly in front of the focuser in both directions, rotating that mirror in it's holder and also adjust it in height. You also correct for secondary offset at the same time. At this point you never try to collimate the optical axis..!

After that is all done you start collimating the mirrors optical axis using only the other 3 setscrews.

 

spider4.jpg

 

 

I'm really liking this design. It will give me a lot to think about this morning.

 

A couple of things I might change:

 

1) For a three vane system, I would use a section of hexagonal bar stock and drill out the middle. Might be a bit easier than cutting the flats into the outer collar.

 

2) I would incorporate some type of wire loop safety connecting the center bolt to the outer collar so that if an upper and lower set/collimation screw came loose the secondary mirror could not fall free and turn your Newtonian into a Cassegrain.

 

I'm also wondering if a nylon swivel bearing could be incorporated to replace the lower collimation screws, something like McMaster-Carr part number 1071K12. In this arrangement, the safety device could be a simple cotter pin in the central bolt.



#24 dan_h

dan_h

    Mercury-Atlas

  • *****
  • Posts: 2545
  • Joined: 10 Dec 2007

Posted 22 January 2015 - 11:13 AM

 

Thank you for sharing another method Chriske. I can see how it works, I can see it would be simple enough to build, but I can't see how it is a far easier system to use?

 

1. it requires a tool (an Allen key), and there is no space for a knob (at least not on a smaller mirror).

 

2. it might typically require at least 6 insertions of the tool into a grub screw (in the dark?) to loosen/adjust/tighten, and probably more for an inexperienced user.

 

Obviously I am guessing here...what do you find yourself doing?

Hi Oberon,

 

I think for most collimation systems(secondary) some tool is required, be it an Allen key or a screwdriver. And I never collimate a secondary mirror in the dark. Collimating a secondary mirror you need to see the primary's perimeter.

 

 

I'm really liking this secondary holder. I suspect it will hold collimation much better than a poorly balanced, spring loaded system.   I also like the idea of using a hollow centre shaft and putting batteries in there for a secondary heater.  It should be able to handle as much as 1 watt for 5-6 hours. That would be good.

 

dan



#25 Pinbout

Pinbout

    Hubble

  • *****
  • Posts: 19719
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 22 January 2015 - 02:32 PM

 

 

Thank you for sharing another method Chriske. I can see how it works, I can see it would be simple enough to build, but I can't see how it is a far easier system to use?

 

1. it requires a tool (an Allen key), and there is no space for a knob (at least not on a smaller mirror).

 

2. it might typically require at least 6 insertions of the tool into a grub screw (in the dark?) to loosen/adjust/tighten, and probably more for an inexperienced user.

 

Obviously I am guessing here...what do you find yourself doing?

Hi Oberon,

 

I think for most collimation systems(secondary) some tool is required, be it an Allen key or a screwdriver. And I never collimate a secondary mirror in the dark. Collimating a secondary mirror you need to see the primary's perimeter.

 

 

I'm really liking this secondary holder. I suspect it will hold collimation much better than a poorly balanced, spring loaded system.   I also like the idea of using a hollow centre shaft and putting batteries in there for a secondary heater.  It should be able to handle as much as 1 watt for 5-6 hours. That would be good.

 

dan

 

 

this one out. it has a similar method to chriske's but on a wire support and uses thumbscrews

 

http://www.astrotref...Fangspiegel.jpg




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