Loctite and acrrylic (bad)

Discussion in 'Workshop Tips and Secrets / Tools' started by FritzW, Nov 4, 2018.

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  1. Nov 4, 2018 #1

    FritzW

    FritzW

    FritzW

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    I post this information for the "next guy" ...(I'm remembering the good 'ol days before the HBA shut off it's ability to be seen by search engines)

    First of all: I won't benefit from anyone telling me that I shouldn't have done it because 'XYZ' (no s#it, I know that now). And deep down inside I knew it was wrong, but everything I could find on f@#*&^g google said it was okay...

    A couple of CSK screws on the canopy came loose during the initial flight testing of our chapter Waiex. I googled around and consulted experts, the consensus was it'd be okay to use a wee dab of Loctite on the CSKs to keep them from coming loose.

    Bottom line: Loctite shatters acrylic, even "rubberized" acrylic like a Sonex canopy. The plans probably say "don't use Locktite" but if I read every note on the Sonex plans I'd still be waiting to squeeze my first Cleco.

    20181103_105005_resized.jpg CM181103-105726002_resized.jpg Interesting: Every screw hole on the canopy failed, but none of the windshield holes failed. ...Yes, Loctite is anaerobic and I would (maybe) have been okay if I'd let it "dry" for a while before I put the screws in....

    Learn from my expensive f%@#up :roll:
     
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  2. Nov 4, 2018 #2

    MadRocketScientist

    MadRocketScientist

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    Wow! That is bad, looks like it must expand when curing?
     
  3. Nov 4, 2018 #3

    FritzW

    FritzW

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    $400 for a new canopy, I can live with that. The hard part is apologizing to the guys (I was one one them) that spent weeks getting the canopy to fit perfectly.

    It was a chemical reaction, not a physical reaction (expanding) that caused the problem. But I'll have to let the build team guys calm down and put down their pitch forks and torches before we can psychoanalyze exactly what happened.

    ...this is my first screwup ever :roll:
     
  4. Nov 4, 2018 #4

    MadRocketScientist

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    I would suggest trying some silicon on the bolts to stop them coming undone. I say this because a lot of the model aircraft guys use high temperature silicon on the exhaust bolts on their engines when they keep coming loose.
     
  5. Nov 4, 2018 #5

    FritzW

    FritzW

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    From what I've read, the solvents in silicon do the same thing. I've used CA glue and T-88 on Home Depot Lexan (slimier material?) and it worked...

    Save the scraps from your canopy and test any chemical you plan to use on/near it ;)
     
  6. Nov 4, 2018 #6

    MadRocketScientist

    MadRocketScientist

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    The silicon is used a lot on shower cubicles and things like that, a lot of those are now being made with acrylic sheeting. The plans for my canopy say to use some Sikaflex to bond it to the frame. I have some Sikaflex 11FC (polyurethane rather than silicon) that I intend to use. Maybe some testing is in order..

    I would say to use caution with superglue as it may depend on the exact composition of the particular brand if it reacts with the lexan or not. In my experience the superglue does tend to etch into plastics and may cause a failure at a later date. The epoxy 'might' be a bit safer in that regard.
     
  7. Nov 4, 2018 #7

    pictsidhe

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    Polycarbonate is even more picky about chemical stress cracking.
    Save the shards and test any other chemicals on them. It may be an idea to find a list of permitted chemicals and adhesives from the acrylic manufacturer, rather than going by what Internet Ian suggests you try on the next $400 canopy...
     
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  8. Nov 4, 2018 #8

    MadRocketScientist

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    Or just use locknuts on the back sides of the bolts, not as tidy but will stop the chemicals attacking the canopy.
     
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  9. Nov 4, 2018 #9

    FritzW

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    Plan 'A' is to drill through the canopy bows and use longer bolts with fiberlock nuts.
     
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  10. Nov 4, 2018 #10

    Daleandee

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    Sorry I missed where the question was asked because I did know the answer about Locktite and a Sonex canopy ... but now you know the answer too. BTW ... the cost of the canopy is bad enough but the shipping is really off the chain so get ready for that number.

    I have used silicone (clear) on a Sonex canopy without any concerns. I used it once to repair a canopy that got cracked from some idiot (me) letting the canopy get away from me while holding it slightly open during a ground run. :mad2: I actually used some scrap canopy material to cover the cracks and used the clear silicone to glue it into place. But that is something you can test now that you have a broken canopy to experiment with.

    I hate it for you but sometimes bad things happen to good people ...

    Dale
    N319WF
     
  11. Nov 4, 2018 #11

    pictsidhe

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    ex - has been
    spurt - drip under pressure

    Acrylic can be solvent welded. Maybe you can turn a learning experience into another learning experience?
     
  12. Nov 4, 2018 #12

    BBerson

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    The solvent glue for acrylic also attacks and starts cracks. (PS40 I think it is).
    I had cracks from epoxy. I don't know why, maybe the epoxy was old.
    Some acrylics are low quality. Or maybe canopies have locked stress and is more crack prone.
     
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  13. Nov 4, 2018 #13

    mcrae0104

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    The canopy's acrylic, but the windshield is Lexan IIRC. Is that right, Dale?
     
  14. Nov 4, 2018 #14

    lr27

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    Maybe if you take the canopy off and figure out how to apply a load putting compression on the cracks, solvent glue will work. The liquid type will probably make for clearer results than the solid type. Acrylic cracks if you hold your mouth wrong. Don't the Long EZ guys secure their canopies with epoxy? It might pay to find out just what they're using. OTOH, that's a lot of cracks!

    I gather the canopy frame, i.e. metal, is threaded? If so, there are threaded fasteners with little nylon patches in or on the male threads to prevent them from coming loose. For instance:
    https://www.mcmaster.com/92805a144

    Are the holes in the canopy oversized, so that the material can move around a bit as it expands and contracts?
     
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  15. Nov 4, 2018 #15

    TFF

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    I doubt the Locktite did that. I think the warning about the Locktite is busting the plastic out if you had to remove it. As you said, the Locktite is anaerobic. it will not dry in the air. My "guess" it was over tightened along with the holes too close tolerance. The holes should be just about rattle loose. I also like to be able to just turn the screw when "tight". Almost loose when done. You might wrap the screws in teflon tape or use some of the liquid kind. The coolest screws/ washers i have used for that are what is standard for AS350 helicopter windshields. I forget the designation.
     
  16. Nov 4, 2018 #16

    pictsidhe

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    Uncured cyanoacrylate is known for cracking acrylic.
     
  17. Nov 4, 2018 #17

    Dana

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    Countersunk holes in the canopy with flathead screws? That alone will put a lot of stress on the canopy. A common approach is rubber bushings around the screws in oversize holes so there's some give.
     
  18. Nov 4, 2018 #18

    lr27

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    He's got some kind of washer, it looks like, between the flat head and the plastic.
     
  19. Nov 4, 2018 #19

    FritzW

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    Where are you seeing flat head screws?

    They're counter sunk screws and counter sunk washers, the holes are counter sunk and drilled oversized and the screws wern't over tightened.

    ...It was the Loctite.
     
  20. Nov 4, 2018 #20

    lr27

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    What's the difference between a flathead and a countersunk screw???
     

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