Re: [ATM] Carbon Fiber for Spider Vanes

["Rod Shea" <RodShea@comcast.net>]

In past postings, the ? of a fragile CF spider breaking has been raised.  I 
have been looking into this, and plan drop testing the whole sec assembly 
with a dummy secondary, to find out if the sec would break loose with rough 
handling.

Rod


----- Original Message ----- 
From: "Peter" <peter@kitgear.com>
To: "Dream - Telescopes & Accessories, Inc." <shane@dreamscopes.com>; 
<atm@atmlist.net>
Sent: Monday, April 04, 2005 3:24 PM
Subject: RE: [ATM] Carbon Fiber for Spider Vanes


> Shane,
>
> Thanks for the reply. Obviously I agree with most of what you have 
> written.
>
> I'm just dabbling a little in composites to reduce the weight and increase
> the performance of my next scope. Most of the composite parts I have made
> used fiberglass laminates so this was my first experience with CF.
>
> My intent has been to try something different and expose people in the ATM
> community to those new techniques. I was a bit unsure about the spider
> because there was so much past discussion on this subject with no real
> guidance one way or another. I will stick with CF for thin vanes with low
> thermal mass and I will report how if worked out. Material properties of 
> CF
> are exceptional for telescope work. My biggest concern is that my scope 
> may
> be too light and blow around. I am also considering pegging the ground 
> board
> to ensure the scope does not topple in the wind.
>
> I checked my postings and I did not say "carbon fiber" is "five times
> stronger than steel". You must have me confused with someone else.
>
> The greatest weakness which I see is as you say - the resin because if not
> processed in the correct manner the parts may soften in the heat of the 
> sun.
> I'm using aviation grade epoxy which can be high temperature post cured.
> Would you share with us how you attain extremely high temperature
> performance?
>
> You've peaked my curiosity.
>
>
> Peter
>
>
> -----Original Message-----
> From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf
> Of Dream - Telescopes & Accessories, Inc.
> Sent: Monday, April 04, 2005 10:55 AM
> To: atm@atmlist.net
> Subject: [ATM] Carbon Fiber for Spider Vanes
>
>
> Peter,
>
> A business colleague sent me your posting regarding carbon fiber.
>
> I am a composite's company that specializes in carbon fiber products for
> the astronomy and opto-mechanical industries.  The biggest issue with
> composite's, among a great many, is resin content.  The strength is in the
> fibers, not in the resin.  In order to maximize properties, low resin
> contents and also extremely low void content are vital.  Resin weighs much
> more than the fibers too so either not using as much resin to begin with 
> or
> somehow getting some resin back out of the composite lay up is of utmost
> importance.  Vacuum bagging and using traditional vacuum bagging 
> materials,
> like breather, is a very good way to reduce the resin content in the part.
>
> There are a tremendous amount of variables in composites that can affect
> their strength and stiffness.  In astronomy we are much more concerned 
> with
> stiffness than strength, in our opto-mechanical systems.  We're not
> building bridges but simply holding (relatively light) optics as stiff as
> possible, especially for imaging applications.
>
> Parts with high resin contents, voids (areas that weren't wet out 
> properly)
> and general inconsistencies of the wet out all make for a very poor
> part.  Such a part would be heavy, brittle and generally will have low
> properties (strength and stiffness).  If however the part is made in a
> fairly meticulous manner concentrating on fundamentals of lay up, the part
> (carbon fiber) can have greater stiffness than steel yet weigh
> less.  Remember that steel is stronger than aluminum so carbon fiber can 
> be
> far superior to aluminum.
>
> Again, there are so many variables in not only the lay up portion of 
> making
> a composite but also materials (dry goods, resins, prepregs, etc.) used
> that flatly stating "carbon fiber" is "five times stronger than steel" is
> simple ignorance.  If the part is engineered with certain types of carbon
> fiber & resins and it is laid up and processed correctly, it can have
> numbers exceeding the typically heard "fives times..."  BUT, parts not
> designed or made properly will not meet that statements claims.
>
> Here's an example that further illustrates my point.  A given part can be
> made by two different companies or even two different people within the
> same company.  Both parts are produced using the exact same carbon fiber
> dry goods, exact same resin, same equipment, same room, under the same
> temperature, humidity, etc..  One part is made in a sloppy manner and the
> other very meticulously.  The latter will exhibit not only lighter weight
> but higher properties.  It will also be extremely consistent.  The sloppy
> part is very heavy, very brittle (since many resins are brittle and this
> sloppy part is more resin than fiber).  Testing the sloppy part in one 
> area
> will yield wildly different results than another test sample from 
> somewhere
> else on the part.
>
> So the answer to your question is yes, it can be extremely beneficial to
> have spider vanes, or any other part of the telescope made from carbon
> fiber.  BUT, it won't be if the person making the part isn't meticulous 
> and
> pushing their techniques and QA on every single part.  Just the simple use
> of carbon fiber alone does not automatically give the product the ultimate
> properties it can attain.  There are many, many variables along the way
> that greatly affect performance.
>
> You can see a few things that my company has produced using carbon fiber
> below.  Just click on the home icon at the bottom of the page to get to
> photos of other carbon fiber products.
> http://www.dreamscopes.com/pages/projects-04/oven/26.htm
>
> The above mirror cell uses truss style members that will be almost
> identical to spider vanes I will be producing in the coming months.
>
> The (general) properties of carbon fiber is extremely beneficial for
> astronomy applications.  Carbon fiber does not like to hold heat.  My
> painter took a strand of carbon fiber from my shop and put a small butane
> torch to it.  He waited until it glowed orange/red hot, expecting it to
> burn up or at least fall into two pieces.  It did not.  He then took the
> torch away and waited 15 seconds before trying to touch the strand with 
> his
> bare fingers at the point where the flame had been.  He kept doing this
> heat up cycle until he was touching the strand approximately three seconds
> after the flame was off of it.  It cooled that fast.  Somewhat similar to
> the ceramic tiles on the Space Shuttle.
>
> Carbon fiber is, in general, the stiffest of the composite dry
> goods.  Stiffer than E-glass (common fiberglass), S-2 glass (a stronger
> version of E-glass), Kevlar, etc..  It is also very light.  The only other
> common material that is lighter is Kevlar.
>
> Carbon fiber also has a very low CTE (coefficient of thermal
> expansion).  In an opto mechanical system dissimilar CTE's in the 
> structure
> and glass will cause, among other things, focus shifts.  Carbon fiber can
> be highly engineered and thus gives the designer the ability to match the
> carbon fiber's CTE to the optics materials used.
>
> You can see that the material properties are very appealing: stiffer,
> stronger, lighter and doesn't hold heat.  These properties are so 
> appealing
> that two companies, that I've spoken with, have been in R&D to produce
> carbon fiber mirrors.  The US company has been in R&D for more than 10
> years and is working on the ULTRA project.  The other company is in the
> UK.  Besides ULTRA, the US company is under contract to produce a complete
> 1m telescope (mount, OTA, optics, etc..) that will weigh 80 lbs or less.
>
> Structural components are very feasible to produce, albeit expensive
> compared to metals and especially wooden products.  Producing an optical
> surface on composites is another story.  My company has done some
> preliminary R&D on this but other than seeing a reflection, additional 
> work
> would be needed to get the optical surface even remotely close my own
> optic's standards.
>
> I hope this helps answer your question...
>
> Sincerely,
> Shane Santi
> Dream - Telescopes & Accessories, Inc.
> http://www.dreamscopes.com
> 610 - 365 - 2833
>
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