RE: [ATM] Carbon Fiber for Spider Vanes

["Alan Scott" <alanne1956@hotmail.com>]

Peter,
  As a guess, the lighter you make the scope, the more you concentrate the 
mass in the mirror.  So, the CG should DROP.  As you have wind blow against 
the scope, this should make it MORE stable - I believe.  As a side 
statement, the scope that I have, which is pretty light, is VERY stable in a 
high wind.  Take a look at my lightweight scope.

  Also, as an alternative to CF for the spider vanes, try wire.  A wire 
spider works very, very well.  Once again, take a look at my lightweight 
scope (url below) for an example.

  I bet carbon would be fabulous to replace the wood commonly used in 
scopes, however.

Alan
http://www.xmission.com/~alanne/DS3Main.html
http://www.xmission.com/~alanne/Astronomy.html

>From: "Peter" <peter@kitgear.com>
>To: "Dream - Telescopes & Accessories, Inc." 
><shane@dreamscopes.com>,<atm@atmlist.net>
>Subject: RE: [ATM] Carbon Fiber for Spider Vanes
>Date: Mon, 4 Apr 2005 18:24:13 -0400
>
>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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