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ZielkeNightsky
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Newton wire spider & holder, will it work
      #5591788 - 12/27/12 08:42 PM

Merry Christmas

Now my OO 10Ē mirror finally gave up, Iím in the process of build the final 10Ē Newton for my observatory. So a 10Ē F/6 Royce mirror is on the way and my dream scope will be build around this fine mirror.

Iíve thinking and reading a lot about wire and curved spiders and right now Iím hooked on a wire spider. Is it worth going for a wire spider compared to a curved spider. (I think a curved spider I think is somewhat easier to make an install)

Some ideas are from Mark Cowanís nice design and a couple are from Royceís secondary holder design.

Secondary holder:
As the renderings shows I use a hinge and therefore only the angel can be adjusted, no tilt/3 axes as we normally see. I canít fully figure out if it is enough with that together with the rotation of the secondary. Any thoughts?

A link to Royceís secondary spider/holder design

Iíve also used his suggestion with only one 1/2" square silicone in the centre to clue the secondary mirror and holder together. Iím going for a nice Antares secondary.

The secondary holder will be made in aluminium 4mm. thick, powder coated black.

Wire setup:
The wire is crossed in to dimensions. Will this be strong enough to keep if vibrating?
The tube is made of carbon with a 5mm. hard foam core, a total of 8mm. So it should be strong enough to hold the tension of the wire.

Comments are most welcome.











Edited by ZielkeNightsky (12/27/12 09:01 PM)


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glennnnnnn
sage


Reged: 10/20/09

Loc: San Diego, CA
Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5592030 - 12/28/12 12:27 AM Attachment (39 downloads)

Just as an added feature you could put a metal insert in the tube at each of the points of attachment. The wire or cable will have a lot of tension and might tend to cut into the tube unless there is a strong anchor. The small part I'm thinking of is known as a threaded insert. You might even be able to use the thread and have the ability to increase or decrease the tension for that segment, so you could more easily "tune it."
What you show in your drawings is a fine design!

EDIT: A tension on each wire can be adjusted by turning the bolt. This is a hollow bolt. I have seen these used in many different applications, but what comes to mind is some sort of bicycle part, like the tensioning for hand-brake cables. There's probably no shortage of bicycle parts in Denmark, or anywhere else in Europe which is bicycle friendly!

Edited by glennnnnnn (12/28/12 03:12 PM)


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mark cowan
Vendor (Veritas Optics)
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Reged: 06/03/05

Loc: salem, OR
Re: Newton wire spider & holder, will it work new [Re: glennnnnnn]
      #5592047 - 12/28/12 12:52 AM

Quote:

The wire is crossed in to dimensions. Will this be strong enough to keep if vibrating?




Hi, vibration shouldn't be a problem for any reasonable wire thickness. At least a couple people (that I know of) have built my spider design. The limits on wire diameter are going to be set more by how tightly you want it to hold collimation over the range of motion, and because the COG of the overall assembly gets close to where the support converges the moment arm is small which helps a lot.

I understand the hinge but I like my version better. Of course it doesn't rotate very far and requires more careful setup alignment for that reason. About which I'd have to ask, how often will you need to rotate the secondary and how far? If the hinge were a single pivot and there were two angle adjustments outboard on the front you'd be able to accommodate small amounts of rotation...

You've incorporated the essential elements for vibration stability and I'll be really interested to find out how well it works.

Best,
Mark


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ZielkeNightsky
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5592178 - 12/28/12 06:20 AM

Hi

Thanks for the comments.

Quote:

About which I'd have to ask, how often will you need to rotate the secondary and how far?
Best, Mark




Mark, you're right. I've been looking a lot on your design, but in the end I was to nervous about the initial setup in your design.


About the wires.
A metal insert (threaded) in the tube will, is in the design now.

How do you set up such a system? How do I find and set the correct tension of the wire?

What about the numbers of wires. It can be 4 in a "loop" or 8 one for each connection.



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KenScharf
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Reged: 12/16/12

Loc: South Fla
Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5592443 - 12/28/12 10:53 AM

I've seen wire spiders before, they work. One fellow used guitar parts to adjust the wire tension for centering the mirror.

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bremms
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Re: Newton wire spider & holder, will it work new [Re: KenScharf]
      #5592843 - 12/28/12 03:16 PM

Played with one years ago on my RV6, broke the tube with fender washers. Really needed a metal ring where the wires were attached. I took apart a Novak spider and wrapped the wire through the pins. Worked well until I tightened it up a little too much

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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5592904 - 12/28/12 03:58 PM

Quote:

I've been looking a lot on your design, but in the end I was to nervous about the initial setup in your design.




You just have to construct a simple jig to hold it in place while you attach the wires and tighten them minimally - since it works by opposing forces (for anti vibration) you don't need much tension at all. 8 or 4 wires it probably doesn't matter much, but it's easier if you lock down one end (of each of 4) on the tube and tighten the other (also on the tube). In my version the lockscrews on the assembly are essential once the position and tension is set...otherwise it will try to flip.

Best,
Mark


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Jeff Morgan
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5592932 - 12/28/12 04:17 PM

Interesting design. I was interested in doing this myself, but get-done-itis caused me to just order a standard 4 vane spider. But from what I learned from those that have built them, lots of wire tension is not required, but should actually be avoided.

I see Mark Cowan has already commented, so I'm sure you've seen his design. Another very interesting design was on one of the German sites - Reiner Vogel I believe. His design minimizes overhang distance by building the diagonal holder as two concentric tubes. The wire supports attach to the outer tube. The inner tube is held and collimated by six bolts, much like a finderscope. There was also a safety mechanism so that the inner tube/mirror could not slide free and fall.


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ZielkeNightsky
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Re: Newton wire spider & holder, will it work new [Re: Jeff Morgan]
      #5593051 - 12/28/12 06:02 PM

Thanks for the new comments.

I'll have look at Reiners work on his website.

So good support at the tube, a jig to get everything in place, some lock-screws, guitar parts for adjustment of tension.

I'll alter the design an upload it here.

So one last question before I go ahead with building it. Is it worth doing compared to the curved spider?


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mark cowan
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Reged: 06/03/05

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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5593063 - 12/28/12 06:08 PM

Ha ha ha ha ah ha ha ha. Seriously?

Best,
Mark


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ZielkeNightsky
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5593125 - 12/28/12 06:49 PM

Not really. Then it should have been the first question before spending time designing it.

Nevertheless, always nice if others confirm what I think is the right path to go

BTW: Here is the design I first was going after, pretty much your design Mark. For the reasons about rotation and adjustment of position I ended in the current design.





Edited by ZielkeNightsky (12/28/12 06:57 PM)


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mark cowan
Vendor (Veritas Optics)
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Reged: 06/03/05

Loc: salem, OR
Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5593266 - 12/28/12 08:13 PM

A curved spider works fine at doing what it does - replacing wider dispersion of smaller diffracted energy with closer dispersion of larger diffracted energy. I've never compared them directly, though. I do kind of like not having to make the vanes themselves for the wire spiders.

Best,
Mark


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ZielkeNightsky
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5593353 - 12/28/12 09:09 PM

Thanks for all the advice so far.

This sketch, I think is close to what I'll start building now.



And there is a plan B - buy a curved spider if I find it to difficult to make.

Edited by ZielkeNightsky (12/28/12 10:06 PM)


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NHRob
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5594200 - 12/29/12 11:32 AM

are the diffraction spikes from such a wire spider nearly invisible?
Are they significantly less intrusive than a thin, solid spider?


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ianm
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Loc: Kenwood, CA
Re: Newton wire spider & holder, will it work new [Re: NHRob]
      #5594295 - 12/29/12 12:18 PM

I built a wire spider for my 12.5 inch dob using Mack Cowan's design. It works beautifully and is not as hard to make as one might think. I never see any diffraction spikes. Click here

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allardster
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Reged: 07/01/11

Loc: Toronto, Ontario, Canada
Re: Newton wire spider & holder, will it work new [Re: ianm]
      #5594389 - 12/29/12 01:16 PM

Here is an interesting, recent thread comparing different secondary holders and their impact on diffraction:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4137547/page...

Both wirespiders and curved cone out very well.


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ZielkeNightsky
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Re: Newton wire spider & holder, will it work new [Re: allardster]
      #5599171 - 01/01/13 08:03 AM

Thanks for comments and links.

I've started building one now.


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NHRob
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5599292 - 01/01/13 09:56 AM

how about a curved wire spider ??


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careysub
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5601076 - 01/02/13 11:21 AM

Quote:

...

Secondary holder:
As the renderings shows I use a hinge and therefore only the angel can be adjusted, no tilt/3 axes as we normally see. I canít fully figure out if it is enough with that together with the rotation of the secondary. Any thoughts?
...





After seeing Royce's secondary holder design I was puzzling this out myself.

This is what I conclude.

The design has two axes of rotation adjustment - rotating around the center bolt, and adjusting the mirror angle tilt. These are axes are both perpendicular to the focuser sight line, vertically, and horizontally.

There is one additional missing degree of freedom - and that axis is the focuser sight line.

It is helpful to try this with a model - say a piece of corrugated cardboard stuck on a pencil at a 45 degree angle (the corrugations keep the card flat, the hex cross section of the pencil keeps it from turning on the pencil).

Look at the card from the side so that you see the 45 degree angle. Now spin the pencil 90 degrees (this is an extreme "adjustment" to make the change involved clear).

What you see is the card is still at 45 degree angle, but that angle is no longer inclined to the vertical, but to the horizontal. And if you made the card long like the elliptical secondary you will notice that the long axis is now pointed horizontally as well.

Now here is the thing. Look at the rotated card from the front (along the pencil axis). It is inclined to your point of view, and this can be fixed by rotation along the support bolt axis. The card is now flat to your view line, but not tilted at 45 degrees. Using the tilt angle adjustment fixes that.

The final problem that hasn't been fixed is that the mirror's long axis is no longer pointing up. If you can rotate the mirror in or with its mount to adjust its axis then this problem can be fixed.

But remember that in this design the spider is actually perfectly rigid along the focuser sight-line axis. It is impossible for new mis-alignment to arise here unless the hinge axis is actually inclined with respect to the optical axis in which case tilt adjustment will create a very small mirror ellipse axis rotation as well. This doesn't affect collimation though and with an appropriately sized secondary shouldn't create any issues. In a well made and installed spider assembly (we are not assuming perfection here, just no obvious manufacturing and assembly errors) this should not be a significant problem.


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: careysub]
      #5601234 - 01/02/13 01:08 PM

Yes. You only need to be able to make the last few tiny tweaks with the adjustments on the spider, the rest is taken out during installation with a jig.

Best,
Mark


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GlennLeDrew
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Re: Newton wire spider & holder, will it work new [Re: careysub]
      #5601292 - 01/02/13 01:50 PM

Is it *really* worth the effort to go with wire? Does a thinner material truly amount to a change in diffraction intensity of any note? I ask because even the finest roof prism, with its effectively micron-thin roof line produces an easily visible spike. If going from a 'thick' vane to a thinner wire did result in a sensible diminution, one would naively extrapolate and ascribe to to the *vastly* thinner prism edge a vanishingly small diffraction energy.

My thoughts go as follows. Within reasonable limits of practical vane thickness, their small obstruction areas relative to the unobstructed area of the objective is hardly ever greater than 2%. For example, a 10" with 0.05" thick vanes would have the vane obstruction at about 1.2% The secondary central obstruction whose relative diameter is 0.12 is considered as having a barely detectible impact. Such an obstruction has an area of 1.4% that of the aperture. And so even relatively stout vanes offer obstruction area only of this order. Because of the fact that even a 'wavelength-thin' vane already introduces readily visible diffraction, the damage is already done, and the difference between this and a 'thick' vane is really minimal.

The linked-to thread from a couple years back is all well and good. But the investigator missed an opportunity to do a *proper* comparison with his simulated vane/wire setup. And that is creating a version where one diametrical vane is the thicker and the other is the thinner. In such a way one had a *direct*, unbiased comparison where any difference seen will be real, and not reliant upon fallible memory. I am always leery in the extreme where a test relies upon taking the time to swap out the apparatus and then require for comparison one's memory of the previous appearance.

Has anyone made a text rig having differing obstructor widths? I know I should, just to see for myself.

I should add a final factor which puts me off from wire spiders. And that is that they require precise longitudinal alignment. If to the incoming light they present as not two exactly overlapping obstructors, their effective with is now larger. And even if of the most precise construction, for light coming from any distance off-axis, the wires no longer exactly overlap, presenting as thicker. At some point off axis, depending on wire thickness and their longitudinal separation, they will present as two obstructors, with a concomitant doubling of diffraction!

In the 'cross-braced' wire arrangement as proposed here, it's obvious that the wires cannot mask their counterparts, thus projecting as having greater width; the advantage of thinness so desperately sought is nullified at a stroke! And for each of the four wire pairs, at some small off-axis angle it will project as an 'X'-shaped obstructor, with portions of the 'vane' being doubled, which, again, doubles diffraction.

Where the wires project as separate obstructors, the diffraction will most definitely be worse than that of even a quite thick singleton; you can take that to the bank.

Truly, is all the bother really worth it?


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careysub
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5601600 - 01/02/13 05:06 PM

Quote:

Yes. You only need to be able to make the last few tiny tweaks with the adjustments on the spider, the rest is taken out during installation with a jig.

Best,
Mark




And I have a suggestion for a collimation tool or jig for tweaking the vertical axis rotation.

The problem with adjusting this is that unlike using a screw to adjust the mirror tilt, there is no mechanical reduction involved that converts a large motion into a small one. And if you are rotating the whole mirror assembly on the support bolt, then tightening the locking nut will tend to create torque that un-collimates what you have carefully adjusted.

The idea is to have a top plate (for example) on the mirror assembly with two holes drilled in it. Make a beam long enough to rest across the top of the UTA with two prongs that fit in the holes.

That's basically it.

You now have long arm to assist in precisely adjusting the mirror assembly rotation, and using the arm you can hold the assembly in place while tightening up a locking nut.


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bratislav
sage


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Re: Newton wire spider & holder, will it work new [Re: GlennLeDrew]
      #5601667 - 01/02/13 05:57 PM

Quote:

Is it *really* worth the effort to go with wire? Does a thinner material truly amount to a change in diffraction intensity of any note?




The main advantage of a wire spider is not that they are thinner. They have less mass. Not for the immediately obvious reason.

Let's remember where spider usually is - at top of the tube, or in an upper cage (e.g. large Dob). Both allow spider assembly to be exposed to large areas of the night sky, which in turn promotes a lot of radiative cooling. In such environment (typical night sky will be around 50 Kelvin or so), anything that is directly exposed will achieve equilibrium below ambient air (sometimes WELL below ambient air. That is why car is often covered in ice even if night temperatures stay well above freezing point).
Now, more mass keeps more (in this case negative) energy. That is, more massive spider will cool more surrounding air. This cooler layer will have different refractive index from the surrounding air, and that will in turn increase the effective spider profile, making it look thicker.
Wire spiders will have less of this 'effective' profile, and show less diffraction most of the time. It will be still there, no question about it, but it will be less noticeable.
Of course, as with anything else, our logarythmic senses make those advantages anything but subtle (as you pointed out, even thinnest obstruction is very obvious); nevertheless the effect, and the advantages, are real.


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GlennLeDrew
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Re: Newton wire spider & holder, will it work new [Re: bratislav]
      #5601703 - 01/02/13 06:19 PM

Then how about a lower emissivity coating on all metal components exposed to the sky? And lightweight tube extensions ('dewcaps').

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bratislav
sage


Reged: 09/07/06

Re: Newton wire spider & holder, will it work new [Re: GlennLeDrew]
      #5601773 - 01/02/13 07:15 PM

People have reported that insulation (e.g. cork) works well in metal tubes. But considering that there is usually a generous space inbetween the tube and a light path, it is probably not so important (as to remove this boundary layer - it can't be much more than a mm thick. It may be important for different reasons, as in reducing tube currents).
But spider is right in the middle of the tube, and anything that can make it look thinner must help.


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: GlennLeDrew]
      #5601884 - 01/02/13 08:20 PM

Quote:

Has anyone made a text rig having differing obstructor widths?




Yes. We should discuss wire spiders over a couple of beers sometime.

Best,
Mark


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careysub
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Re: Newton wire spider & holder, will it work new [Re: bratislav]
      #5602090 - 01/02/13 10:43 PM

Very interesting analysis.


I am familiar with all of the physics of all of these physical phenomenon, but this had never occurred to me.


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Dick Jacobson
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5602551 - 01/03/13 08:55 AM

Has anyone tried making a spider out of thin, tape-like material, for example videotape? The advantage would be ultra-thin profile along the optical axis. For example, you could use a long central bolt and four loops of tape. Each loop would make a 90-degree bend around the bolt. There would be one pair of loops at the top, oriented to make a "+" pattern. A few inches down would be a second pair of loops to keep the bolt parallel to the tube. Outside the tube, each end of the tape would be wrapped around a shaft which could be tightened as needed.

Personally, I agree with the previous post that questioned whether it is really worth all the effort to build an ultra-thin spider. But for purists who want to reduce diffraction to an absolute minimum, it would be interesting to see how well a tape spider could perform.


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careysub
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Re: Newton wire spider & holder, will it work new [Re: Dick Jacobson]
      #5603582 - 01/03/13 07:35 PM

Quote:

Has anyone tried making a spider out of thin, tape-like material, for example videotape?...




Looking up the specs on videotape, it is thin I grant you that: 1.5 mils for old, old tapes, to 0.5 mils for recent ones (0.0015" - 0.0005"). Maybe too thin.

It is made of PET, and is 1/2" wide for VHS family tapes. From PET tech data I calculate a tensile strength of no more than 2.7 lb for recent tapes, and 8 lb for old ones. I read about people with very thin tensioned spiders using something like 20 lb force to hold them rigid. And at a near breaking-strength load (as would be necessary unless doubled up a few of times) it would have something like a 2% stretch.

OTOH you can get very high modulus carbon fiber unidirectional tapes that are 0.006" (6 mils) thick in widths as narrow as 1/2". Using a minimal epoxy binder (otherwise the tape would start fuzzing) you would get a highly flexible tape with a tensile strength of 860 lb (1/2" wide).

Carbon fiber tow (thread) would seem to be a promising material for wire spiders, you would probably wipe it with resin and twist it before it sets to bind the fibers together. Unfortunately it is only available in spools used for weaving, and a spool is a lot more than you (or you and 99 other ATMers) would ever use for this purpose.


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: Dick Jacobson]
      #5603799 - 01/03/13 10:18 PM

Quote:

Personally, I agree with the previous post that questioned whether it is really worth all the effort to build an ultra-thin spider.




This is what I hear regularly, but rarely if ever from anybody who's actually built one, because they know it's not difficult at all. [EDIT: I'm only referring to a wire spider here, for good reason.]

And tensile strength is not an issue if the geometry is solved correctly. Which is why I did what I did. And they're CHEAP to build. Exotic materials are not required, though I did experiment with Vectran yarn (too fluffy, like all polyamarids).

Even Mel Bartels (though a latecomer to wire spiders) now raves about the ease of construction, durability, and performance. As well as how CHEAP THEY ARE TO BUILD. He used a spool of wire from Lowes...

I was hoping someone else would refute Glenn's argument, but since they're no takers I'll guess I'll have to do it - when I've got a little more time and tact on hand.

Best,
Mark


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Lightning
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5604034 - 01/04/13 03:12 AM

Beta Pictoris by Rolf Olsen

The extra contrast gained from the small diagonal and thin vanes are a good part of what let Rolf capture the protoplanetary disc of Beta Pict. I think that says it's worth it right there.

Cheers,
Cam


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ZielkeNightsky
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Re: Newton wire spider & holder, will it work new [Re: Lightning]
      #5604427 - 01/04/13 10:03 AM

Great posts.

I'm still working on the new spider, although I've made a few changes. I'm still convinced that there's a little performance gain with the thin spider wanes (wire). I haven't found a single ATM that's complaining over the performance. (Maybe I haven't looked hard enough?)



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NHRob
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5604449 - 01/04/13 10:15 AM

There has been some discussion in the other forum over cooling fans for the primary. It seems that if one used a rear tube fan, gently pushing air up the tube, this would help reduce the thermal layer on spider vanes, and reduce spider diffraction. Has anyone experimented with this?

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Ed Jones
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5604490 - 01/04/13 10:34 AM

I believe the wires will probably not be line up on top of each other and thus will double their small diffraction. I prefer scope with no spiders but when I do I think the best solution is a 3 vane spider with vanes as thin as your wires. I built one wire spider on a 6 inch and it never was as solid as a vane spider, but then it wasn't this design either. I have a 3 vane spider with .010 inch vanes and you don't see spikes except on the brightest stars.

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ZielkeNightsky
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Re: Newton wire spider & holder, will it work new [Re: Ed Jones]
      #5604620 - 01/04/13 11:42 AM

Good point with the line up on top of each other. Maybe it's better to not line them up, but instead increase the distance so I end up with 8 wires.

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GlennLeDrew
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Re: Newton wire spider & holder, will it work new [Re: ZielkeNightsky]
      #5605301 - 01/04/13 06:00 PM

In the 'vein' of try it your self and see...

I just performed a test, with a 60mm f/7 Carton refractor and 4mm long eye relief eyepiece (0.57mm exit pupil.) I placed a white LED flashlight down at the far end of my apartment building's hall. A piece of foil had numerous pinholes, producing 'stars' of at least Sirius brightness down to near invisibility.

At the front end of the shade/dew cap I taped two straight pieces of wire diametrically, and mutually perpendicular. The thicknesses are 0.47mm (0.0185") and 1.7mm (0.067"), the latter being 3.62X thicker than the other.

In the main, the *overall* brightness and extent of the diffraction spikes is fairly similar. The most outstanding difference is the frequency of the sinusoidal variation in intensity along the spikes (visible on only the brightest couple of 'stars'.) Not having first measured the wire thickness, my estimate had the thicker wire's spike varying some 3.5-4 times more rapidly (compare to the 3.6X thickness ratio.) So we see that this angular frequency apparently scales linearly with obstructor width, at least over a limited range.

The thicker wire's spike immediately beside the 'star' was certainly brighter than that produced by the thinner wire. But it dimmed more rapidly with distance, the first minimum in the sinusoidal variation occurring closer to the 'star.'

When I threw the image well out of focus, on those 'stars' sufficiently bright to show it the superimposed linear component of diffraction was certainly more prominent, too.

But the surprising thing I found is that for the dimmer 'stars' (for which spikes were too faint to see) it was most difficult to detect at all that there were obstructors present. Even while spinning the lens shade. The first and second diffraction rings surrounding the Airy disk appeared hardly altered from uniform circularity and azimuthal uniformity of intensity.

In this experiment, using a 60mm aperture, the 0.47mm wire presented an areal obstruction of 1%, and the 1.7mm wire, 3.6%.

My early conclusions are that over the range explored here, while the differences in the diffraction spikes differ much in detail, in the main they are not so different. Total extent and overall brightness are not obvious at first glance. The worst aspect of a thicker obstruction is the spike's higher brightness adjacent to the source.

Yes, a thinner vane is better, but things do not change so very greatly over any reasonable range, particularly in the Fresnel pattern of the image point. I should try a thinner wire yet to see if the trend continues linearly, or if the realm of diminishing returns is soon (or has been ) reached.

This was a quickly performed test using stuff ready to hand. I should drag out one of the 120mm refractors so that something closer to a Newt's aperture is used.


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: GlennLeDrew]
      #5605996 - 01/05/13 04:02 AM

That's a start.

You might want to look at http://home.digitalexp.com/~suiterhr/TM/Spiders.htm if you haven't. Try thinner wires and larger apertures. You can lay a thin wire at angles over any spidered dob and compare easily.

Best,
Mark


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careysub
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5606660 - 01/05/13 01:46 PM

The Suiter page gives some very good insights that I have not seen presented elsewhere (certainly not so clearly).

Note that in his final "apples-to-apples" comparison of the 1%, 2% and 4% vanes (thickness fraction of aperture) that the ratios are very close to the simple ratio of vane thickness.


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careysub
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5606707 - 01/05/13 02:10 PM

Quote:

... Exotic materials are not required, though I did experiment with Vectran yarn (too fluffy, like all polyamarids).




Most (probably all) fibrous filamentary materials (Vectran, Kevlar, CF, Spectra and fiberglass) would need to be wiped with resin to bond the fibers together to prevent eventual (or immediate) fuzzing. But it wouldn't take much.


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bratislav
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Re: Newton wire spider & holder, will it work new [Re: Ed Jones]
      #5607527 - 01/05/13 11:29 PM Attachment (13 downloads)

Quote:

I believe the wires will probably not be line up on top of each other and thus will double their small diffraction.




It is not that hard to make wires line up perfectly. This wire contraption needed rather basic tools (drill press and a router to cut big circles were most advanced).
And it is not wobbly either! (those are 2.5kg weights each - 11 lb in total)


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: careysub]
      #5607535 - 01/05/13 11:33 PM

Quote:

Quote:

... Exotic materials are not required, though I did experiment with Vectran yarn (too fluffy, like all polyamarids).




Most (probably all) fibrous filamentary materials (Vectran, Kevlar, CF, Spectra and fiberglass) would need to be wiped with resin to bond the fibers together to prevent eventual (or immediate) fuzzing. But it wouldn't take much.




I suppose you could do that. But the strength advantage is mostly by weight, not diameter, and even if you wind them tight you still get more thickness than thinner wires (SS) that can be plenty strong.

Best,
Mark

PS if anybody wants some Vectran yarn just ask - I've got a hundred yards or so.


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telfish
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5607882 - 01/06/13 08:17 AM

There is a spectra fishing line called Power Pro which has a waxed coating. The 50 lb strength is 0,014"

I have used it for fishing for years and it's plenty strong and does not fuzz. It's woven braid.Spectra lines have almost zero stretch.

The 20Lb which may be enough is 0.009"

http://www.powerpro.com/publish/content/global_fish/en/us/power_pro_v2/produc...

Terry


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careysub
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Re: Newton wire spider & holder, will it work new [Re: telfish]
      #5608181 - 01/06/13 11:56 AM

Quote:

There is a spectra fishing line called Power Pro which has a waxed coating. The 50 lb strength is 0,014"

I have used it for fishing for years and it's plenty strong and does not fuzz. It's woven braid.Spectra lines have almost zero stretch.

The 20Lb which may be enough is 0.009"

http://www.powerpro.com/publish/content/global_fish/en/us/power_pro_v2/produc...

Terry




Looks like Spectra line holds the edge in minimum diameter for a given strength, well above trolling leader wire, and somewhat above music (aka "piano") wire.

The Proline specs for the 0.009" line give it a strength of 470 KSI, music wire in this diameter range has a minimum strength of 400 KSI or so (this is extremely high for steel, essentially maraging steel). It is an edge, but not much of one.


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telfish
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Re: Newton wire spider & holder, will it work new [Re: careysub]
      #5608840 - 01/06/13 05:07 PM

Being a Guitarist and a Fisherman I can tell you that you are far more likely to get an unexpected failure in a guitar string that is under far less pressure than a power pro fishing line with a 40 lb fish on the end!

The high E sting or the high G string on a 12 string guitar is apt to break if it is over tightened or can cut itself if crossed over during winding.

No sure what would happen with a 40 Lb fish on the end of a G string!


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: telfish]
      #5609412 - 01/06/13 10:59 PM

I've broken many an E string as well. The tensions used in a properly designed spider (i.e. relies on geometry not tension for holding position) are far less than in that application. So if you're doing it right it's really a nonissue. Can't emphasize this enough, as people ALWAYS go to the "must have lots of tension in a wire spider" mindset.

Best,
Mark


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telfish
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5609712 - 01/07/13 07:55 AM

I am guessing the wire used in this application would need to be stainless. Guitar wire tends to rust.

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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: telfish]
      #5610117 - 01/07/13 12:20 PM

Not really a problem in application, but stainless is preferable.


Best,
Mark


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ianm
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5610608 - 01/07/13 05:32 PM

Quote:

Can't emphasize this enough, as people ALWAYS go to the "must have lots of tension in a wire spider" mindset.




Very true. I was surprised by how little tension was needed to make my spider rock solid. I used .01 in ss fishing wire and if I make another I'll use .005.

A lot of emphasis has been put on the size of diffraction spikes and while I enjoy that aspect weight was just as important. My scope is a single pole hybrid with one 3/4 inch square x 1/16 inch aluminum ring as UTA and had to be as light as possible. An aluminum holder/ss wire design is hard to beat.

Another positive is the wow factor. I've had a chance to show my scope to large groups and at first glance the wire spider seems like magic. From a few feet away the wires are invisible.


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: ianm]
      #5610640 - 01/07/13 06:02 PM

Hey, if you have info online I'd like to link it on the page I put up...

Best,
Mark


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ianm
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Re: Newton wire spider & holder, will it work new [Re: mark cowan]
      #5610785 - 01/07/13 07:30 PM

Hi Mark,

The only info I have on line is the post I made here last year. If you want to use some of those photos that would be fine. There is a link above on my first comment. Also, I could email you what photos I have of the spider. I really think more people should consider it. I'm in the early planning stage of an 8 in (haven't got a mirror yet) and would definitely use a wire spider on it.

Ian


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mark cowan
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Re: Newton wire spider & holder, will it work new [Re: ianm]
      #5610885 - 01/07/13 08:44 PM

Yeah, that's why I want to put up some more examples and links. Once people see it being built it helps them get their head around it, maybe. I'll put up anything you email me at <mc@raddobs.com> BTW.

Best,
Mark

PS I would have seen it at OSP but I had to skip that year.


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ZielkeNightsky
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Re: Newton wire spider &amp; holder, will it work new [Re: mark cowan]
      #5612380 - 01/08/13 05:36 PM

Hi all

I've been in my small workshop testing the design I'm currently going for.

I've tested a very strong thin fiber braided fishing lines, < 0.1mm - I thought, if it's good enough for salmon and sea trout, then maybe it's good enough for a telescope?

Seems to work just perfect, only securing the line firmly on the tension screws was a little tricky. No wobbling, vibrations and displacement, very stable indeed.

I used an old fly tying trick to create the plastic bed for the wire. The beds works very well. (Is "bed" the right name?)



And here it is floating in space


Mark was spot on with the tension, not much is needed and way below the breaking point of the line.

So I'll continue down this path. More to follow..

Thanks for all the advise.


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