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getting cloth to lay around a corner? - 10/3/2012 7:34 PM   
thunderchief


 

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Status: offline 		Does anyone who has laid up molds have any special technique for getting the cloth to go around a radius or lay in a corner with out creating a bubble?
Thanks
Glenn

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RE: getting cloth to lay around a corner? - 10/3/2012 10:39 PM   
wyowindworks


 

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quote:

ORIGINAL: thunderchief

Does anyone who has laid up molds have any special technique for getting the cloth to go around a radius or lay in a corner with out creating a bubble?
Thanks
Glenn


Often you have to fill tight corners with a thickened resin (resin + cab-o-sil + a little cotton flock) before you lay in your fabric.  I scoop the thickened resin into the corner of a cheap sandwich bag, spin in around so the resin goes further into the corner, and then just nip the corner off so you can pipe it into the corner.  You can see some examples in the phots below.  The thickened resin is the white-ish colored stuff under the fabric layup.  Notice how the tip of the fuselage doesn't need any before the layup but the thickened resin is added after the layup to reinforce the nose.

Using bias cut fabric can help get fabric conform in some tigher shapes.   Also using fabrics like harness satins (H8) will help.



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RE: getting cloth to lay around a corner? - 10/4/2012 12:57 AM   
thunderchief


 

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Status: offline 		Thanks for the information about the cloth. I have been doing lay ups for 25 years and still have trouble in corners but mainly around sharp corners not really into corners. I had my F-106 go in and I want to lay up another but when you only do a lay up every couple years you never really develop the right techniques.
Glenn

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RE: getting cloth to lay around a corner? - 10/4/2012 2:22 AM   
speedracerntrixie


 

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Status: offline 		Have you thought about bagging the molds with some peel ply and breather? Doing so correctly will help you with the corner issue ( Would require less thickened epoxy ) but would yeild a lighter, stronger part.


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RE: getting cloth to lay around a corner? - 10/4/2012 4:55 AM   
lfinney


 

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Status: offline 		have you tried crowsfoot weave cloth

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RE: getting cloth to lay around a corner? - 10/4/2012 6:02 AM   
wyowindworks


 

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quote:

ORIGINAL: speedracerntrixie

Have you thought about bagging the molds with some peel ply and breather? Doing so correctly will help you with the corner issue ( Would require less thickened epoxy ) but would yeild a lighter, stronger part.



The parts will definately come out lighter but not necessarily stronger (unless you add more fiber).  The wall thickness ends up being thinner than an unassisted hand layup so our thin walled structures are much more prone to buckling.  Buckling is the most common form of failure in in thin walled composite structures.  Whenever you increase the Vf (Fiber volume fraction) the laminate must become thinner (unless it's heavily aerated).  When you start increasing the Vf you often have to add more fiber to offset the reduction in thickness.  The end result can be lighter and stronger but with a higher degree of labor due to having to add more fiber..

Put another way, if you take two identical layup schedules and one is bagged and one is not, the unbagged layup is almost always stronger.




< Message edited by wyowindworks -- 10/4/2012 3:44 PM >

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RE: getting cloth to lay around a corner? - 10/4/2012 11:43 AM   
sidgates



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Status: offline 		WyoWindWorks
This morning I was in the process of ordering a batch of cloth and have been using 3.2oz crowfoot for going into tight corners. I am considering the following cloth:
"Style 120 - 3.16oz - Silane finish for epoxy resin or Volan finish for any resin used in RC models, aerospace applications and other composite structures.

Style 120 is a 3.16 oz Crowfoot Weave fiberglass fabric. It has a count of 60 x 58 ends per inch, a thickness of 0.0035" and uses the ECD 450-1/2 in the warp and fill. It is similar to 220 with the exception that 220 uses the thicker filament glass fiber E(7 microns) instead of D which is 5 microns."

You can see it is available in Silane or Volan finish. I am not sure which is best for models using only epoxy resins.

Could you share your opinion?



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RE: getting cloth to lay around a corner? - 10/4/2012 1:41 PM   
thunderchief


 

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Status: offline 		What is crowfoot cloth? I am not familar with it. I usually purchase from Fibreglass Developments or US Composites.
Glenn

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RE: getting cloth to lay around a corner? - 10/4/2012 3:21 PM   
sidgates



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Status: offline 		Glenn,
I hope Adam will answer your question about crowfoot cloth. To me it is a more flexible weave and lays in corners and edges better.
I like your F-106. How is it powered?

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RE: getting cloth to lay around a corner? - 10/4/2012 3:41 PM   
wyowindworks


 

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Status: offline 		Style 120 and 220 are good choices.  The 120 will be slightly more flexible while the 220 is a little stronger.  Either will work well.

Crowfoot is the same as a Harness Satin 4.  The yarns go over 3, under 1, over 3, under 1, etc.  This weave allows the fabric to be more conforming than a plain weave.  It also allows the yarns to lay flatter.  This is theoretically stronger since the frequency in the crimp of the fiber is reduced.


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RE: getting cloth to lay around a corner? - 10/4/2012 3:52 PM   
sidgates



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Status: offline 		Adam,
Thanks again for the explanation. I knew I liked the flexibilty but didn't know how crowfoot rated in strength. I use the 3.2oz crowfoot for my first layer a lot of times.
Sid

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RE: getting cloth to lay around a corner? - 10/4/2012 5:23 PM   
SCALECRAFT



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Status: offline 		Thunderchief, your model is very nice. Did you make the plug for it as well?

Steve

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RE: getting cloth to lay around a corner? - 10/4/2012 10:17 PM   
GREG DOE


 

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Status: offline 		Here's a recommendation for a source for all kinds of cloth, at reasonable prices. Thayercraft Inc. Their web site is thayercraft.com the owner is Steve Thayer, who is a modeler, and full scale pilot. I've been doing business with him for over 20 years, and ordered cloth by the bolt several times. That's usually between 120,and 130 yards, but he will sell it in smaller amounts. There are several terms to discribe the different cloth weaves, but for our model airplanes we usually want a cloth that will drape around contours. Crows foot weave has already been mentioned as a good choice. Here is another suggestion if you are having problems with the cloth laying down in the mold, if you are not already doing this, try say 4 layers of 4oz. per sq.yd. instead of 2 layers of 8oz. per sq.yd. The lighter weight cloth will conform better to curves. As already mentioned cutting the cloth on the bias (45 degree angle) is a big help, but may generate a lot of waisted cloth. Sometimes there is no other choice than to cut the cloth at a sharp cornor, and over lap the edges. Since we are giving away trade secrets, no I mean "TIPS", try this suggestion. Use the lightest closest weave for your first layer of cloth in the mold. Something like 2 to 4oz. per sq.yd. This will result in the least amount of cloth weave on the exterior of your finished part, and fewer and smaller pin holes. Some people brush in a "skim" coat in the mold first, and some use a "surface coat" which is the equivalent to a "gell coat" when using polyester resin, to reduce pin holes. The different finishes on the cloth help in the wetting out of the cloth with the resin. Some finishes are better with epoxy, and some are better with polyester. Volan seems to work well with both. Good luck, Greg


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RE: getting cloth to lay around a corner? - 10/5/2012 12:58 AM   
thunderchief


 

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Status: offline 		Guys thanks for the information about the cloth. The F-106A was lost on its maiden flight a tuff way to go. The first two I had were powered by ducted fans. This one was turbine powered. It had a Jet Central Bee ii ks in it. About thirty years ago I acquired a 1/10 USAF display mold of and early 106. The mold was crude but I was able to make a plug from it, add scale changes and bring it up to date and then make a new rc type mold. The wing was scaled up from drawings I got from Wright-Patterson AFB
Glenn

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RE: getting cloth to lay around a corner? - 12/11/2012 1:19 AM   
RAPPTOR


 

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Status: offline 		WOW .. WHAT A BUNCH OF BALCK MAGIC..JUST CUT THE CLOTH ON THE BIAS... 45 DEG.. WILL DO ANY SHAPE THEN..

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RE: getting cloth to lay around a corner? - 12/18/2012 2:31 AM   
Foxman


 

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Status: offline 		Yes RAPPTOR is correct about cutting the fibre at 45 degrees. It is a lot easier to get into and around corners.
Also the stiffness of the particular fibre you are using. I have some very soft 30 grm and 60 grm but the 48 grm I have is so stiff I can't use it on anything with a small radius.
30 grm is around 1oz, 60 grm is 2oz more or less.
You need to have a look at the fibre you are buying and choose a soft one as there can be a big difference.
When making the wing skins I prefer the stiffer material though as it keeps it shape better.
Jim

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RE: getting cloth to lay around a corner? - 12/18/2012 2:41 AM   
wyowindworks


 

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Status: offline 		Laying bias cut fabric on +/-45 is helpful but fibers at 45* to the loading axis are significantly weaker and less stiff than those aligned with the loading axis.  When maximizing the strength for a given weight you need to consider the fiber orientation.  The tensile and compression strength of 0/90 is higher than +/-45 even though half the fibers are not being loaded.  On fuses I often use 0/90 layers and +/-45* layers.  If you put all fibers going in the same orientation then the laminate will "zipper" along the fiber weave upon impact.  If toughness is desirable then you need the fibers going in at least 4 directions.  If weight is the primary objective then you align most of the fibers with the loading axis at a sacrifice to toughness.  You can't have it all.


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