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Equipment Discussions >> Reflectors

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Pinbout
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Reged: 02/22/10

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Re: High End Components new [Re: davidpitre]
      #5775201 - 04/03/13 10:38 AM

Quote:

The 10" has 4 fixed points for bottom support. How is this a good idea?




it has 6 supports according to this drawing


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Jeff Morgan
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Re: High End Components new [Re: Daud]
      #5775227 - 04/03/13 10:55 AM

Quote:

What about cost and source for carbon fiber trusses ?




A google search will turn up many suppliers. I priced this out a couple of weeks ago. The bottom line is around 12x the cost of anodized aluminum.

On my scope it worked out to around $1500 to drop the center of gravity about 1-1/2".

Perhaps in a few more years additional production capability will come online to satisfy the demands of aerospace.


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Pinbout
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Re: High End Components new [Re: Jeff Morgan]
      #5775320 - 04/03/13 11:22 AM

dragon plate 1" x 72" braided cf tube $126

Moonlite 1" x72" anodized alum. $18

CF x7 more.


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davidpitre
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Re: High End Components new [Re: Pinbout]
      #5775509 - 04/03/13 12:56 PM

Quote:

Quote:

The 10" has 4 fixed points for bottom support. How is this a good idea?




it has 6 supports according to this drawing



It looks like you are right, but that doesn't seem any better if they are all fixed. Certainly they don't provide equal or uniform support. For most 10" mirrors I'd rather 3 fixed points than 6.


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gaz-in
scholastic sledgehammer
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Reged: 12/17/07

Re: High End Components [Re: davidpitre]
      #5775548 - 04/03/13 01:19 PM

at $45 this one looks interesting

19 MM OD by 48 inches CF Pole


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saemark30
Pooh-Bah


Reged: 02/21/12

Re: High End Components new [Re: gaz-in]
      #5776068 - 04/03/13 05:53 PM

Any source of tube clamps? I can't see anyone justifying paying $1200 for a CF tube.

What aren't there any pure dielectric coated diagonal mirrors for Newtonians? Coatings loose contrast even after cleaning.


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Pinbout
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Re: High End Components new [Re: saemark30]
      #5776123 - 04/03/13 06:16 PM

Quote:

Any source of tube clamps?




I make them...

http://www.youtube.com/watch?v=sVpjifuRRXE

I have since turned them around and added thumb screws.


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careysub
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Re: High End Components new [Re: saemark30]
      #5776148 - 04/03/13 06:33 PM

Quote:

...
Would it be practical to make one?




Yes and no.

It takes some experience working with CF and epoxy, it would be a poor choice for a first effort (rather like trying to make a large mirror by hand on your first go at mirror making).

If you want to try, my advice would be to use one of those HomeDepot Quiktubes as the inner part of tube (simplifying mold building and eliminating the problem of core mold removal) and trying it in fiberglass first as a practice run.

Carbon fiber fabric is not really terrifically expensive, Soller Composites has it at $2-$3 per square foot depending on weave and weight (fiberglass though runs only $0.50 to $0.75 per square foot).

Part of the reason for the high cost for carbon fiber tubes is that customers expect a perfect cosmetically unblemished bare carbon fiber surface for bragging rights. This means blemished tubes get scrapped, and you pay for them anyway when you buy the unblemished ones.

If you just want CF for its mechanical properties (light weight, stiffness, absence of thermal expansion) you can paint the end product (if blemished) and it will work the same. You can also get convincingly looking carbon fiber contact paper to cover your scope with to make it look like what it is, but in unblemished form.

Here are some good links showing techniques just posted on the ATM forum (Google Chrome automatically translates from Spanish):

http://canaryastro.webs.com/apps/photos/album?albumid=13105589
http://www.aagc.es/observatorio/modificacion-del-telescopio-orion-optics-14


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careysub
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Re: High End Components new [Re: Jeff Morgan]
      #5776178 - 04/03/13 06:52 PM

As Jeff indicates it is hard to make a case for using carbon fiber truss tubes - is not a compelling application for the material.

Part of the reason* is that though CF is stiffer than aluminum, you can't make tubes any thinner for structural integrity reasons, so you only get the 40% weight savings from the lower density but at an enormous price increase.

You really need to be weight sensitive or have deep pockets to justify it.

The cost is not so much the cost of materials as the high cost of the cosmetic expectations of the buyers and consequently the production costs. It is a vicious circle.

If someone came out with a plain rough-looking CF product like so much fiberglass tubing costs could be much lower.

*Another part of the reason is that one of biggest advantages of using CF, or any composite fabric, is that you can use it with a low density core material to get an enormous increase in the stiffness to weight ratio. Tube walls are solid and so get no such benefit.

Edited by careysub (04/03/13 08:04 PM)


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Pinbout
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Re: High End Components new [Re: saemark30]
      #5776494 - 04/03/13 09:10 PM

hey check out this old thread on making a CF tube.

if you can do a fiberglass tube you can do a CF tube.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3383451/page...


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careysub
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Loc: Rancho Cucamonga, CA
Re: High End Components new [Re: gaz-in]
      #5776538 - 04/03/13 09:33 PM

Quote:

at $45 this one looks interesting

19 MM OD by 48 inches CF Pole




Ah! If you notice one of my earlier posts on this thread, I commented that the high cost of many carbon fiber components was mostly due to purely cosmetic considerations, and if the same techniques used in fiberglass tube production were used, you would get a rough looking product but it would be considerably cheaper.

That is exactly what this is - it is pultruded CF tubing, and if you zoom in on the image you see that it does not look so sleek with the polished fabric surface. But it saves you substantial $$.

This would be good tubing for a true truss system - the thick walls give a lot of resistance to elongation for the diameter.

Cost/performance for this is around two to four times what you would pay for aluminum tubing of similar performance and generally similar dimensions. But you could come close to cutting the weight in half.


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gaz-in
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Reged: 12/17/07

Re: High End Components new [Re: careysub]
      #5777056 - 04/04/13 06:46 AM

Thes folks have a .75ID, .032WT by 70 incches for less than $50...

.75ID, .032 WT by 70 inch CF Tube for less than $50


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saemark30
Pooh-Bah


Reged: 02/21/12

Re: High End Components new [Re: gaz-in]
      #5777805 - 04/04/13 01:59 PM

Perhaps we can make a 12" tube from 12 sq ft of CF @3 x12 or $36 then add in cost of epoxy and put this over a cardboard tube and voila.

Is there something wrong with this idea?


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Pinbout
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Re: High End Components new [Re: saemark30]
      #5777860 - 04/04/13 02:25 PM

no, I'm doin' that for a 6inf8. but the good expoy is $$

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mtb54703
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Re: High End Components new [Re: saemark30]
      #5777882 - 04/04/13 02:45 PM Attachment (16 downloads)

Quote:

Any source of tube clamps? I can't see anyone justifying paying $1200 for a CF tube.





Check out DJ lighting clamps - $5-$6 each - I've used 1.5" variety on my next scope project - same type of clamp that is used on Webster telescopes.


3/4"

1"

1.5" or 2"

Edited by mtb54703 (04/04/13 02:47 PM)


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mtb54703
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Re: High End Components new [Re: mtb54703]
      #5777886 - 04/04/13 02:50 PM Attachment (19 downloads)

Example...

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careysub
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Loc: Rancho Cucamonga, CA
Re: High End Components new [Re: saemark30]
      #5777942 - 04/04/13 03:22 PM

Quote:

Perhaps we can make a 12" tube from 12 sq ft of CF @3 x12 or $36 then add in cost of epoxy and put this over a cardboard tube and voila.

Is there something wrong with this idea?




So the tube is 4 feet long, and 12" is diameter?

Actual costs might be $35 for a 36"x50"(standard width) piece of heavy weight (19.9 oz/square yard) of CF fabric, but you would need to undersize your tube slightly from 12" since 36"/Pi = 11.459" (unless they happen to cut you a little extra, typically they do but you can't count on it). This material is sold by the yard (some others are sold by the foot).

http://www.solarcomposites.com/composites/compositecarbon.html#12K

Sometimes they have remnant specials, check these out first:
http://www.sollercomposites.com/specialdeals.html

A good epoxy+hardener kit, enough for one layer of fabric, is available for $15.75 here:
http://www.uscomposites.com/epoxy.html


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davidpitre
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Re: High End Components new [Re: careysub]
      #5778024 - 04/04/13 04:07 PM

Mike.
Nice work there.


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JimMo
I'd Rather Do It Myself


Reged: 01/08/07

Loc: Under the SE Michigan lightdom...
Re: High End Components new [Re: mtb54703]
      #5780130 - 04/05/13 04:49 PM

Thanks for posting the link to the clamps. The 3/4" clamps are exactly what I've been looking for and cheap, too.

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JM La Galette
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Reged: 11/24/07

Loc: France
Re: High End Components new [Re: JimMo]
      #5809990 - 04/20/13 02:48 AM

Quote:

Perhaps we can make a 12" tube from 12 sq ft of CF @3 x12 or $36 then add in cost of epoxy and put this over a cardboard tube and voila.

Is there something wrong with this idea?




Like this?



JMarc


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