RivetBangers.com

Well, I learned a valuable lesson yesterday...don't tighten the screws in the canopy too tight.
I was putting the three screws in each side of the canopy so that I could drill the side skins to the frame. Well, I was tightening the screw, and heard the wonderful sound of acrylic cracking! Unfortunately the crack went both ways, to the bottom of the canopy, and also about 3/8" upward as well. I stop drilled the crack (twice, as the first hole sent the crack farther up!) and now have a 1/8" hole about .5" above the canopy frame.

I talked to Airplane Plastics (referred by Ken at Van's), and they said to stop drill the crack, and then fill the hole with laminating epoxy. I've got some clear RTV, and they said that would work as well.

So the moral of the story is to not tighten down the canopy screws too tight...and try to go very slow when you do tighten them!

I'm curious as to the size of the screw versus the size of the hole. Do you have an pictures of your mounting, etc?

-- John

It's a #6 screw for all of the canopy mounting. The canopy was c-sunk for the #6 screw and the dimple on the side skin.
I don't have any pictures of that area yet...I'll try to shoot some tonight.

spike wrote:I'm curious as to the size of the screw versus the size of the hole. Do you have an pictures of your mounting, etc?

-- John

Hey Ron,
What a bummer Just out of curiousity, what was the temperature of you're shop?

High 60's low 70's when I was cutting and drilling.
Most likely low 60's when I was tightening the screws. I'm sure hoping that I don't have to have temps in the 70's just to tighten the screws on the canopy!!!

Ron wrote:Hey Ron,
What a bummer Just out of curiousity, what was the temperature of you're shop?

Ron,

I was wondering about the dimpling of the skin under the countersink in the canopy? Depending on the depth of the dimple, how did it match-up with the countersink? Seems like you'd have to be very careful about a the match to keep support under the countersink edge of the canopy and avoid stress on the plexi. Just wondering how that works.......Larry

Larry,

At the time that the canopy cracked, I did not have the side skin on and dimpled. I was attaching three #6 screws through the canopy and the side rails so that I could drill the skins to the sides, and then drill the holes for the #6 screws through the canopy to the side skins.

l & d lewis wrote:Ron,

I was wondering about the dimpling of the skin under the countersink in the canopy? Depending on the depth of the dimple, how did it match-up with the countersink? Seems like you'd have to be very careful about a the match to keep support under the countersink edge of the canopy and avoid stress on the plexi. Just wondering how that works.......Larry

Well, I did the cracked canopy thing too while I was building - and its still there to remind me. BUT, I have a much better solution than stop drilling for anyone else unfortunate enuf to crack theirs...

...I just wish I could remember the name of the stuff. Anyway, go down to your local glass (house, automotive, etc) shop and ask some questions. The guys in my hometown gave me some clear, high viscosity (really really thin), plexiglass glue. Put the glue in a syringe for application and just drip (yes just one) or touch the end of the wet syringe near the center of the crack. Capillary action draws the glue entirely into the crack and its fixed - stronger than the plexi around the repair - yes, I tried it on a sample!

Do NOT stop drill the hole. I marked the end location of the crack using a sharpie pen on the canopy and I now have just shy of 500 hours on my RV4 and its seen the full temperature, g load, airspeed, etc spectrum and the crack has NOT budged!

m.

The solvent/glue stuff for plexi is called methylene chloride i believe. It melts the edges do the crack and should make for a very strong repair G

gsimatos wrote:The solvent/glue stuff for plexi is called methylene chloride i believe. It melts the edges do the crack and should make for a very strong repair G

D'oh why didn't I look here when I cracked my landing light lens this weekend, and before I ordered a replacement from Van's??? Oh well, only $12.

How'd you crack the lens?

How?

Short answer, impatience and inattention.

Technical answer... when enlarging one of the holes, the #30 bit acted like a screw diving throught the hole and putting a small crack in it as it blasted its way out the back. It is no big deal, but it will probably grow over time, so I figured it would be easier to replace now before the screw holes are dimpled. Now I have plastic drill bits on hand.

They say you can use regular drill bits in reverse. Has anyone ever tried that?

CJ

captain_john wrote:They say you can use regular drill bits in reverse. Has anyone ever tried that?

I tried that... I held the drill in my left hand, behind my back, while standing on my head... it still cracked!

Hmmmmm, note to self...

Get some plexi bits!

CJ

captain_john wrote:Hmmmmm, note to self...

Get some plexi bits!

CJ

Don't bother C.J., I already have them, and you can borrow them when the time comes. I'll only charge ya a beer

CJ, I was joking, I didn't try it with the bit turning in the reverse direction.

WS, cool... Thanks!

Brad, do you still have the fractured pieces? Can ya try it for us?

CJ

CJ, for you? Sure

Actually, for all of us here!

Thanks!

CJ