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  #11  
Old 03-24-2009, 02:04 PM
jasperlv jasperlv is offline
 
Join Date: Aug 2007
Location: utah
Posts: 49
Default simplified glass layups

the real advantage of BID (bidirectional) is the strength in both X and Y directions. whereas the UNI (unidirectional) has all of the glass fibers running in one direction the strength component is 1.0 in the X direction and ~0.0 in the Y direction. with the BID fibers running at 45 degrees to both the X and Y directions the strength component is 1.414 (sqrt 2) in both directions. the minimum strength component in any direction is 1.0. maximum advantage is obtained laying the fibers at 45 deg angle to your anticipated stress. (i know the math is greatly simplified and assumes equil wt glas; for illustrative purposes only)

glass is really much easier to work with than many builder comments would lead you to believe.

here's my technique:
get yourself a piece of 6 mil clear visqueen (polyethylene vapor barrier) from home depot. lay it out on the item you want to cover with glass. draw your shape with a sharpie on the visqueen. cut to approximate shape. lay the pattern on a piece of glass fabric and use your sharpie to draw pattern shape on the glass with 1" excess all the way around. cut glass fabric to sharpie line.

cut 2 more pieces of visqueen (a rectangle is fine) 4-5 inches larger in each direction than your pattern. center the glass on one piece of the visqueen. you are going to make a plastic-glass-plastic sandwich. mix your epoxy very well (3 min constant stirring) and pour over the glass. lay plastic sandwich top over the glass and use stiff plastic kitchen spatula or wooden tongue depressor or even the sharpie to move epoxy around. continue moving epoxy around till all the glass is transparent. any dry glass will be readily apparent. you may need to mix another batch of epoxy.

use this approximation;
glass = 9oz/yard at a ratio of ~1.5
so make 16 oz (2 cups) of epoxy/yard^2 of glass.
some excess is ok and will likely be blotted up. penalty is the plane is 2 oz overweight.

after all glass has been wetted. lift off the visqueen sandwich top and lay down 1 layer of paper towels over the glass. put sandwich plastic top back down over the paper towels and apply some pressure all over to blot excess epoxy. you just got your 2 extra oz back.

take your original pattern and lay it over the sandwich. trace pattern outline with sharpie. use scissors and cut to pattern line. lift off top visqueen and towels, invert glass onto your mold in proper position. slowly peel back the 2nd piece of visqueen.

you can do 2 or even 3 layers of BID simultaneously with same process. use proportionally more epoxy for more layers. three layer glass layup like Dan has shown can be done start to finish in 20 minutes. not a drop of epoxy on you or on the shop floor. well, i sometimes wear a pair of latex gloves and tap the glass into the corners with my fingers. however, a 69 cent 1" fiber paint brush dipped in epoxy can be used for same purpose. after glass is in place on your mold use a paper towel to lightly blot up excess epoxy pools.

cutting and moving around dry glass is difficult to maintain in the desired shape. lift a BID corner and a circle becomes a football. this process prevents that problem as well as distortion from applying epoxy to the glass.
]
the quantity of frayed edges goes to near zero doing layups this way. notice the frayed edges in Dan's 2nd foto. endemic problem with glass BID. cut glass 1" larger than the pattern and don't mess with the stragglers, just cut 'em off. all those frayed edges are discarded.

for a superior surface buy some 100% nylon from fabric store and lay over the glass/epoxy while it cures. nylon wicks epoxy to the surface leaving a smooth finish. oversize the nylon (roll ends at fabric store often sell for $1/yd) so no edges are in the layup. if the layup is so big you need an edge then use the factory hem. any cut fabric edges in the epoxy will leave fibers embedded in the epoxy. fibers aren't structurally weakening but they'll drive you crazy wishing you had done differently. after 24 hrs grab a corner of the nylon and pull it off. more days might mean more pulling!!

you'll fill the garbage can with lots of expendibles. polyethylene vapor barrier is ~$57/10x100 ft roll. that's a nickel/ft2. but, you're gonna buy a roll anyway to build your paint booth. a dozen paper towels and $5 scissors/month of layups. seems like a lot of stuff.. but doesn't really amount to much.
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  #12  
Old 03-24-2009, 02:59 PM
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n8zg n8zg is offline
 
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Location: 18FD - Baker, FL
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Default

Quote:
Originally Posted by DanH View Post
BTW, both Spruce and Wicks are terrible about identifying weaves.
Thayercraft ( www.thayercraft.com ), on the other hand, is a goldmine of glass.
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  #13  
Old 03-24-2009, 05:17 PM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Smile And for more...

Quote:
Originally Posted by DanH View Post
.......
There are many different weave patterns available in BID fabrics.

Plain weave is one over, one under, one over, one under.

Twill weave is usually two over, two under, two over, etc. It can also be one over, two under.

Crowfoot is usually considered to be one over, three under, one over, etc. It is also known as 4-harness.

8-harness is seven over, one under, seven over, etc.

.......

BTW, both Spruce and Wicks are terrible about identifying weaves.
.....purchasing confusion, Aircraft Spruce calls their 7781 cloth "crowfoot" on their web site.....

http://www.aircraftspruce.com/catalog/cmpages/7781.php

But the picture does look like 7 over, one under.

Dan - thanks for the weave explanation.

It's nice to know I've been using the best one for curved surfaces....

I want the East coast folks to keep using Wicks, so I can use the original Aircraft Spruce location - 2 days shipping to AZ with no expedited charges, unfortuneately Wicks is nearer a week for shipping here.
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  #14  
Old 05-12-2009, 05:26 AM
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carlrai carlrai is offline
 
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Default Great Source

Quote:
Originally Posted by n8zg View Post
Thayercraft ( www.thayercraft.com ), on the other hand, is a goldmine of glass.
For roughly 8 years I produced hundreds of R/C Pattern fuselages using glass from this supplier.

Great folks. You'll have to purchase material in bolts, usually mill ends making it more likely for group purchases. The prices were (seven years ago) incredibly reasonable. If you can put together an order with a few buddies, give them a try.


Carl Raichle
RV-9A N194CR
Lutz, FL
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  #15  
Old 06-01-2009, 07:46 AM
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Geico266 Geico266 is offline
 
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Location: Huskerland, USA
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All, can some one walk through the process of finishing fiberglass? After sanding as smooth as you can feel what primers do you use and what do you use to fill pin holes, imperfections, ect?

I realize this is a fiberglass "form" tip, but I didn't know where else to ask.
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  #16  
Old 06-01-2009, 08:12 AM
RVadmirer RVadmirer is offline
 
Join Date: Dec 2006
Location: Kalifornia
Posts: 466
Default Finishing

Larry,
Dan will probably give you some good advice but here are a couple places I've gone for help from composite award winners and had good luck:

http://curedcomposites.netfirms.com/finish.html
(PS: I'd avoid the polyester fillers....)

Cory Bird's masterpeice Symmetry used a resin wipe to fill pinholes and provide a durable finish that eventually became almost optically perfect:

http://www.sportsmanpilot.com/AL/art...Spring2003.htm
(PS: he describes it later in the article a couple paragraphs above his picture)

Here is a good explanation of the process with pictures:
http://www.maddyhome.com/canardpages...kimcoating.htm

Good luck,
Dave

Last edited by RVadmirer : 06-01-2009 at 08:39 AM. Reason: added info
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  #17  
Old 06-01-2009, 08:48 AM
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DanH DanH is offline
 
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See the very good articles Dave referenced, and the later posts in this thread:

http://www.vansairforce.com/communit...ication&page=2
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  #18  
Old 06-01-2009, 11:11 AM
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Geico266 Geico266 is offline
 
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Vad, & Dan, Good stuff! Thanks!

I really appreciate the help.
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Last edited by Geico266 : 06-01-2009 at 11:13 AM.
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