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G10 3/32” fin warp fix

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base890

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I’m building my first fiberglass kit (MACH1 Alien Interceptor) and looking for advice to correct a bent fin. Dry fitting the parts I found one fin wouldn’t slot; looked it down the edge to find it warped by 1.5mm each end when flat along the root chord, and a little bit along the span. I can flex it down flat and wonder about heating it up and cooling under weights... any tips?
Also, there are some surface scratches maybe fillable with a filling primer but if this was balsa I’d be putting sanding sealer on first. How do you all prep fiberglass surfaces for paint?
Blue Skies,
Craig S
 

Banzai88

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Me, I'd contact they guy you bought it from and get a new fin. For the price you paid, you didn't pay for a warped fin (or a mis cut fin). Give them a chance to make it right.

Prep is to wash with soap and water, dry, and sand with 80 grit where you want glue to stick. If you think that's too aggressive, go to 120. Any scratches that you're concerned with will be filled with primer.

Primer/paint surface prep for me on fiberglass is a 320 buff, wipe with alcohol rag, wipe with lacquer thinner rag, dust with tack cloth, prime, sand, prime, sand, paint.
 

Banzai88

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I'll say that in nearly 3 years of building fiberglass kits from everyone out there but where you purchased this, I have NEVER had a warped flat piece. Same with my raw plate that I've purchased from McMaster-Carr. (I've had mis-cuts, but never warps).

One of those is unacceptable, the other is marginal, depending on how tight the slots are. In any case, you wouldn't want any tension in the fin with the slot holding the bent fin straight.

Contact the supplier and see what they say.
 

base890

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Steve said this is normal and straighter than any wood fin, that it won’t affect the flight. I’m not sure as the span is affected too, which won’t have a slot to support it.
I tried lifting the tips on some balsa and overnight kept a heavy weight on it the opposite direction to straighten it but within a few minutes it was back to the way it started.

Does humidity affect FG? I wouldn’t imagine but it’s been raining a lot here.
 
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base890

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Maybe I should just buy a sheet and cut my own. Does anyone know a cheap source for a small amount?
 
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nemoc1987

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Buying a sheet will probably be your fastest solution. I wouldn't build with the warped fin. It will affect how it flies.
 

base890

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The sheets I’m finding almost cost as much as the rocket kit
 

Titan II

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Steve said this is normal and straighter than any wood fin.
Wrong on both counts and I would not accept them. I am with Tom (post 5). Over many years with several manufacturers, I have never had a warped flat composite component. In addition, one can also have flat wood fins.
 

Banzai88

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Steve said this is normal and straighter than any wood fin, that it won’t affect the flight. I’m not sure as the span is affected too, which won’t have a slot to support it.
I tried lifting the tips on some balsa and overnight kept a heavy weight on it the opposite direction to straighten it but within a few minutes it was back to the way it started.

Does humidity affect FG? I wouldn’t imagine but it’s been raining a lot here.

Ummmmm.......that's a load of bunk. Twisted/warped fins 100% will affect how a rocket flies.

I've never seen warped fiberglass, and I have TONS of wood fins that don't display 1mm of warpage over their length or span, REGARDLESS of humidity or anything else. I live in the Tidewater area of southeast VA, average rainfall is 10 inches a year MORE than Seattle, WA, with humidity to match.

Another prominent seller of all fiberglass kits has issues with being able to cut 3 fins the same, but they're never warped or twisted. They'll replace them until you're happy. I've since learned how to get fins cut properly from another vendor.

If the seller of this kit is a business and won't replace the fin set, you now know everything that you need to know.
 

Banzai88

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Check McMaster-Carr for cheapish prices on fiberglass plate. That's where I get what I need for small projects or limited use stuff. Caution: their shipping charges are stupid.
 

Rex R

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one could try gently warming the fin(s) to about 120 - 150F (most home oven thermostats may be +/- 50F(50 degrees low to turn the heat on to 50 degrees high to shut off)).
Rex
 

base890

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I’ll try this Rex- do you think bending the other direction(s) during heat and cooling will allow the “fix” to stick and stay? Or just keep things dead flat with weight ? I’ll try flat first and let you know. I requested replacements but still waiting to hear back from Steve.
 
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Wallace

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I’ll try this Rex- do you think bending the other direction(s) during heat and cooling will allow the “fix” to stick and stay? Or just keep things dead flat with weight ? I’ll try flat first and let you know. I requested replacements but still waiting to hear back from Steve.
Warpage is common in any flat/sheet stock material. I've never had an instance where fins or sheets were truly flat no matter if it was wood, g 10, carbon plate or phenolic. Can usually be easily resolved by "over bending" and clamping overnight in the opposing direction. If you think any of these materials are immune just try leaning a sheet against a wall at a good angle and leave it for a few days...1/8" carbon fiber plate. Was fairly flat when I received it. Now this..
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Wallace

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1/8" G 10 fin. Was worse prior to me simply setting it on a flat surface opposing the warp a bit over a month ago...
GetAttachmentThumbnail (4).jpg
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Wallace

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And yes, winter has officially arrived in southeast Wisconsin..
 

Wallace

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Won't even mention wood, we are all aware of it's properties. A handy technique for warped wood is to lightly dampen the concave side and apply a bit of heat. Weather or not any of these "fixes" are truly permanent? Guess you have to go take a look at some of your finished rockets...
 

Wallace

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Hope it helps. I'm a retired carpenter with over 30 years experience working with bent,bowed,cupped,warped and twisted materials. It it extremely rare to find ANYTHING (granite being an exception) flat and straight. You just have to try different approaches to make them comply.
 

rcktnut

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Hope it helps. I'm a retired carpenter with over 30 years experience working with bent,bowed,cupped,warped and twisted materials. It it extremely rare to find ANYTHING (granite being an exception) flat and straight. You just have to try different approaches to make them comply.
Agreed, especially with treated lumber, but when you pick out the lumber yourself you have the option to reject the twisted, warped stuff. Not saying it will stay that way, but at least your starting out with straight stuff. When you order it and have it delivered, you can put the bad stuff aside and exchange it for straighter stuff, or use it for short cuts. Also agree that improper storage of flat stock materials will be subject to the effect of gravity over time. The bigger the sheet the bigger the problem. OP's problem is a twist/warp near the tip of the fin. Had it been a gradual warp in the middle of it would not be much of a problem, easier to straighten. OP, I say demand a new fin or two!!
 

base890

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Thanks all for your thoughts

I requested a replacement and Steve at MACH 1 is going to send one. Thanks Mach1!

Meanwhile I’m going to see what heating and clamping does or doesn’t do. Heated my granite and fins until pretty warm with a heat gun, my wife will love what I’ve done to the kitchen! Clamped them under a dead flat 2x2.
 

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base890

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36 hours later the clamps were removed and fins All had worse warping than before! Hand bending them helped two, the other continued to slowly rewarp. I’m going to scratch that one and wait for the replacement.
 

Wallace

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Well, Ya tried. For future reference, try overbending in the opposing direction. Where and how much is more art than science. If you're gonna scap 'em anyhow you really have nothing to lose.
 

base890

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Well, Ya tried. For future reference, try overbending in the opposing direction. Where and how much is more art than science. If you're gonna scap 'em anyhow you really have nothing to lose.
That's what I've been doing, I don't understand how this got it's memory/mind of it's own.
 

rcktnut

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Might have gotten heated up while being cut. Might have had a "glitch" in that spot during manufacture that let loose after being cut in that spot, who knows. There are somethings that just don't return to normal no matter how hard you try to fix it. Just have to replace.
 

DankMemes

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Maybe Steve Skinner has some tips, he’s Designer Fly on here
 

base890

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MACH1/steve skinner has resolved this concern of mine... I'm excited to get building now!
 

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