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Clear fin repair?

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Cabernut

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What is the best method for repairing clear fins? My Falcon 9 took a hard landing and broke one fin, cracked another. I was thinking of trying plastic cement however I'm not sure if that will hold. I'm not really sure what material this is. Clear plastic/polycarbonate/acrylic?

Perhaps a small strip of fiberglass over the fillets? Plastic cement? Both?


 

rstaff3

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Someday I will link to one of micromeister's posts that outlines what solvents work best on which plastics. My gut says it's acrylic vs polycarbonate. My Lexan fins on much bigger models have hit hard and have not broken. If it were me, I'd wait to see if anyone can conclusively identify the material. Meanwhile, research micro's post and get the best solvent. I'd then sandwich an outer layer of some thin, clear packing plastic along the crack. Won't look as good but it will help. I've done that on fins made out of thin packing plastic and used liquid hobby glue on them. Ugly, but it worked and it avoided surgery.

I bet thin fiberglass would work using some good ol' 5-min epoxy. Drilling small holes along the crack will form glue rivets.
 
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Micromeister

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While I am not familar with this particular kit, Most clear fin materials I've seen used in kit models is a Modified Acrylic. (Really NOT a good choice but much Cheaper then Polycarbonate.)
As such you can use a number of "Solvent Welding products to fix the problem but ALL will distroy the Clear surface wherever the solvent hits the plastic. I would not suggest using Testors tube type plastic cement, but would go with either Plaststructs Acrylic solvent, Acetone, MEK, or best Solvent welding agent is (MC) Methylene Chloride. All of these water thin solvents should be applied with a fine tip brush (Not the applicator in the bottle). Solvent is sparingly stroked on both broken surfaces three or four times without letting the solvent run down the edge being treated (NOT EASY). After application of three or four coatings quickly join the broken parts, Holding in contact for a minute or two. You can use little pieces of tape to secure the parts together but these tape pieces WILL LEAVE a noticable mark.
Set the model aside to completely dry (overnight) with NO stress on the joint at all. I generally use some form of motor mount stand to get the rocket vertical with no pressure on the fins.
If you need more info on "Working with Plastic" in the library section on the www.Narhams.org website you'll find Tech-Tips. Look up Tech Tip-017 it's a 12pg in-depth study on what sticks to what and some good info on most of the Plastic we encounter in the hobby. There is also a additional Photo file that shows most of what is mentioned in the text.

As mentioned above: if you can't make a decent repair on the material you have I'd suggest removeing the broken and cracked fins and replaceing them with clear Polycarbonate (Lexan). These will not break, Unless flown in the dead of winter where the temperature is below freezing. Lexan and other polycarbonates are Highly Break Resistant but not Unbreakable at very low temperatures.:)
 

Cabernut

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Thanks for that resource. I'm going to try some acetone first. Once that's dry then I'm thinking I might lay on a couple small strips of 2oz fiberglass over the break. That's going to be very visible however I'm more on the side of strength vs clean looks for this model - as is apparent by the oversized fillets.

I'm going to look around for some polycarbonate sheets should I decide to perform surgery on this one and replace the fins completely.
 

Micromeister

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Dichloromethane. If properly applied, with a syringe, will leave no trace.
Just so you know: Methylene Chloride or MC are the common names used in industry for Dichloromethane CH2CL2.

Regardless of application method used to apply this water thin agent will destroy the clear apperance at the break line.
With extreme care this distortion & clouding can be minimized, However the distortions will remain. Some Surfrace clouding can be polished out with Finessit -II and/or Flame polishing, but the interior break joint will remain cloudy to semi-reflective.

Edit: Thought a couple photos might help understand the use of just about any of the solvent welding agents. As you can see the Flat flood joints remain clear while the end joints show the tell-tail non-clear joint.

Plastics-1b_ Acrylic-Acrylic solvent Welding_01-02-10.JPG


Plastics-1d_Close Acrylic-Acrylic MEK solvent lap joint_01-02-10.JPG


Plastics-2b_Close-up Solvent welded Mod Acrylic pcs_01-02-10.JPG


Plastics-2c_3 major solvent welding agents(MC-MEK & Actone)_01-02-10.JPG


Plastics-2d_Close-Up Clear Mod Acrylics Welded_01-02-10.JPG
 
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