rv9av8tr

rv9av8tr

Well Known Member
OMG?. Almost done & my tip-up cracked!!

Conditions preceding the event:
Canopy holes were countersunk and drilled out with a 5/32? plexiglass drill bit. Canopy was held in place on each side of the frame with three #6 screws and outside skirts were cleco?d in place. Using a #27 standard drill bit, commenced match drilling from the inside through the tip-up canopy frame/canopy assy into the outside skirts.

All went well exactly as planned.

The event:
After removing the skirt cleco?s and the 3 screws on each side, I reinstalled the skirts with clecos so the last 3 holes on each side could be match drilled. When it was all said and done, I found the forward most hole on the left side had a huge crack (about 6" long) in the canopy, coming out of the hole!!!!!!! I nearly had a heart attack on the spot!!!!!!! You know? one of ?those? moments when you experience utter denial. NO NO NO? this can?t be happening.!!!!

The Cause:
After performing a through investigation and root cause analysis, it was concluded the builder (me) is a flaming bloody idiot!!

For some reason, the forward most hole had not been drilled out from 1/8? to 5/32? with the plexiglass drill, nor had it been countersunk. Some how, I missed ?finishing? that hole. When I match drilled, using the #27 bit, it caused a stress riser in the original 1/8? hole and off went the crack about 15 minutes later!!

The Punishment:
I could have lived with an ?accident?, but this was my doing? or should I say ?undoing?!! Tonight will be the flogging with a cat-of-nine-tails? followed by a soak in the hot tub to calm down. Holy mackerel?. I?ve read about not drilling plexiglass with standard twist drills? now I stand before my peers to attest, NEVER EVER let a non-plexiglass drill bit remove so much as a sliver of plexiglass!!

How?s that old flying adage go? something to the effect: Building in itself is not inherently dangerous, but it is terribly unforgiving of any carelessness, incapacity or neglect.

Now? to start over?
 
Mike, you're taking this very well. Welcome to the club....I have a small crack in mine....Ross cracked his....I can go on....

Anywho, I'm sorry it cracked. At least you're close to the replacement living so close to Van's!

Sorry again.
 
ouch

sorry to hear that.. you know i drillled nearly ten dozen holes in test strips with normal avery bits and it never cracked. it did however chip out the backside. this just goes to show that it will, and when you least expect it. i feel your pain . better luck next time. or should i say pay attention next time? either way good luck.;)
i cringe even posting here as it is bad ju ju.
 
I'm sorry too! If it was 90 to a 100 degrees or so, you could almost knock a hole with a hammer and nail, and it probably won't crack!:D

I took some scraps in hot summer weather, and got very abusive with drill bits of all conditions. The stuff just held up.

L.Adamson
 
Sorry to hear about the crack. And, yeah, it's a big club.

FYI, I decided not to drill the most forward hole (in the plans) in the canopy. I'd heard that there is a lot of cracking on that hole.

That it turns out, my cracks is in the most rear hole.

Crazy world, this RV stuff.
 
Sympathy - Empathy

Thanks for the encouraging words..... I needed that. Redoing the work isn't as daunting having to fork out $$$$$$$ that could've / would've / will still have to be spent yet going forward................

Anyone have experience with Todd Silvers canopies?? Rumor has it his canopies aren't as sensitive to cracking as those from Van's. Must be a different plastic????

Any thoughts?
 
rv9av8tr said:
Thanks for the encouraging words..... I needed that. Redoing the work isn't as daunting having to fork out $$$$$$$ that could've / would've / will still have to be spent yet going forward................

Anyone have experience with Todd Silvers canopies?? Rumor has it his canopies aren't as sensitive to cracking as those from Van's. Must be a different plastic????

Any thoughts?
Click to expand...

If it makes you feal better I've cracked TWO canopies in the last 10 days. T-minus 2 days before being "flyable" I was standing on the right side of the -4 and was closing the canopy, but had to drop it the last 8 inches or so because I can't reach all the way across. Done it a hundred times, but it was around 28 deg out and it cracked around the front. AHHHHH! I'm 3 hours from vans so I bought a new one, (ouch) had it cut and drilled ready for rivets after 3 evenings' work. I removed it from the frame to peal the inner plastic off so it wouldn't be in the way and as I set it down on the saw horses... *tink* a 6 inch crack ran from one of the holes in the back. (sigh) my throat got dry, eyes got moist... I turned the air compresser off, the lights off, and went home. Um, honey...?

The first canopy was from aircraftextras.com (I'm not sure if these are Todd silvers) and I would say was 3/32 of an inch thicker than Vans and it was gauranteed not to break during instalation. $150 cheaper too I think. Took a month to get it tho. We should start a support group.:)
 
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Sympathy and empathy

Mine's cracked in almost the same place, so I feel your pain.

Before you order a new bubble, consider repairing it. It can be done, at considerably less cost than a new bubble.
 
I have a Todd's Canopy on my Cozy IV project. Todd is an AWESOME guy and his work is fantastic. I have scratched my cozy canopy (my fault entirely) and Todd told me a few years back he would replace it for $100 instead of the $350 original price. Mine is also a slightly bigger canopy than the standard cozy for no extra charge. Check the canard lists for testaments to Todd and his work. According to his website he does not have a -9 canopy but I bet he could build you one if you asked.

FWIW I believe he uses a slightly thicker material and that is the reason they are resistant to cracking.

Ryan
Hillsboro, OR
Cozy MKIV
RV7?/8? who knows at this time
 
OMG Joe B..... TWO?!?! :eek: I'd be hiding all sharp objects in case of self inflicted wounds!! In reading these posts, I'm surprised to hear of all this cracking.

I messed around with the scrap cuttings after my first trim cut and I could hardly snap this stuff when folding it over to put the pieces in the garbage can. It seemed indestructible... Oh nay nay moose breath!!

I'm thinking it may be a good idea to very slightly counter sink the holes on the inside face of the canopy also, such that a bevel there won't leave a sharp faced edge, like a drill hole does.

I heard back from Todds Canopies this morning, he doesn't make canopies for the 6,7,9 series. Bummer!!
 
rv9av8tr said:
Anyone have experience with Todd Silvers canopies?? Rumor has it his canopies aren't as sensitive to cracking as those from Van's. Must be a different plastic????

Any thoughts?
Click to expand...

Its a thicker (and heavier as a result) canopy. I do not know if this lessens the chances of cracking.
 
rv9av8tr said:
I'm thinking it may be a good idea to very slightly counter sink the holes on the inside face of the canopy also, such that a bevel there won't leave a sharp faced edge, like a drill hole does.
Click to expand...

I used my deburring tool to take the sharp edge off....scraping the corner. I also used that yellow swivel tool deburring thing to smooth the edge of where the countersink ends and the hole begins. And I took a very small piece of folded up sandpaper and ran it through all the holes.
 
You guys are making me nervous!

Last week I made the big cut, the sides etc are within fractions of where they need to be, back window is looking good. Now i have to drill all the holes...
I have the avery plexi bits, i have my work area around 80-90. I have read a pile of builders logs... Do i have to still worry or can I relax and start drilling. Uggh.
 
Hey, check out the current issue of EAA's Sport Aviation. There's a really interesting article on a guy who repaired a much-more-messed-up plexi canopy (turret on a B-25) than anything most of us have seen. VERY interesting.
 
Sorry to hear about your Canopy. One thing I am going to try is using reamers to bring the holes up to size. I was toolmaker for many years( now a CNC programmer) and have worked some with plexi-glass. After cracking many pieces trying to make holes in plexi, I found that starting with an 1/8 " hole I could drill fine with no cracks. Then I could use reamers at about .030 increments to produce any size hole I wanted. Let me rephrase that, maybe up to 3/8". Never had a reason to go bigger than that. Never had even the hint of stress or cracking using a reamer.

That said, I will be making lots of test holes in the scrap peices of my canopy before I start on the real thing, but I'm feeling pretty confident that it will work. Drills and plexi make me very nervous
 
Tip Ups Crack in Operation

Once you get it built the tip up (wind sail) canopy is vulnerable to cracking during operation. Be careful with it in the field, especially alignment during closure.

Bob Axsom
 
RickWoodall said:
Last week I made the big cut, the sides etc are within fractions of where they need to be, back window is looking good. Now i have to drill all the holes...
I have the avery plexi bits, i have my work area around 80-90. I have read a pile of builders logs... Do i have to still worry or can I relax and start drilling. Uggh.
Click to expand...

"No worries"... famous last words!! Yep, start drilling... start with 1/8", then do the countersinking, THEN drill out to 5/32". Using the Plexiglass drills!!

Picked up my replacement today.... $930!!:eek:
 
Another thought Mike, even though I've cracked two, I found heating the drill bit with a bbq lighter helped the drill bit slice through the plexi, rather than scratch its way through. If anything it made me less nervous about the actual drilling process. My neigbor has a plexiglass welder at work he said he'd let me use... never heard of one of these before... we'll see how it does.

I think the airplane itself ought to be afraid of me inflickting it with wounds than myself =)
 
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HIGH Speed, NO pressure!

Let the drill "burn" it's way through. I've done lots of RV canopies in the last 18 years. Haven't had one crack yet.
BTW, I've never used a "plexi" drill bit.
 
practice on the old one some more

with the tecniques mentioned here. i used the plexi bits and they are so smooth its crazy. the guys in the military do waht mel is talking about on helicopters. remember heat heat heat.80-90 is nice to the plexi. at 90 deg. with deburred edges i could fold over a 2" x 3' strip and almost if not touch the ends at 90 deg.
 
Cracks...?

Ummm... Sikaflex, anyone...?

dsc08215qy2.jpg
 
Mike is active in our builder's group; in fact our last meeting was at his place to see his progress on his canopy. He has been helpful to others and is doing nice work.

What can be done with his cracked canopy? If it were a slider, maybe someone could use the back half. But it's not.

So how can he/we get some good out of this? Any ideas?

Richard Scott
RV-9A Fuselage
 
Avoiding cracks

Most of the large cracks on drilled canopies start as microscopic chips caused when the drill breaks out the rear side of the plexi. They ultimately enlarge and become visible due to the "work of fracture" principle.

My sliding canopy was drilled out to 1/4" holes and I used silicon bushings to let the whole canopy "float" to avoid stresses caused by differential expansion. Each hole is additionally countersunk to allow floating clearance around the aluminium dimples (and around the stainless tinnerman washers that I used on the front bow and roll bar).

As the holes (and countersinks) in plexi get bigger the probability of cracks being generated increases. Therefore this is what I did.

1. I used a plexi drill up to 1/8" (but not above....I don't trust them over 1/8).
2. Above 1/8" I used a step drill with fine progressions (best thing).
3. Before drilling any hole to a larger size I used a 100 degree ceramic countersink (absolutely cannot cause a crack because it has no cutting edge) to countersink the rear of the hole. The countersink diameter was always just larger in diameter than the intended drill size. When the drill breaks through into a countersink it cannot cause chipping.
I never used standard countersinks because they can definitely cause damage. If you prefer to use standard countersinks I recommend a single flute. Double flutes are more likely to cause damage and triple flutes are the worst.
4. All finished holes therefore have a final countersink on both sides. On the outside a large countersink to allow for "float" and on the inside a very small countersink merely to prevent stress risers forming.
5. I sanded the inside bore of every hole as well.
6. I heated up the canopy before performing ANY operations.
7. I never use ANY cleaners or agents on the plexi other than Plexus or kerosene. The damage you initially do with agents like methylated spirits cannot be seen (microscopic) but with time the microscopic crazing propagates into visible cracks.
8. In any location where a threaded fastener passed through the plexi the threads were machined off.

Incidentally the Sikaflex 295UV that many builders use does not in fact adhere well to plexi at all. That is why they need an adhesion promoter such as Sika 209 Primer. The adhesion promoter "bites" into the plexi. It does so because it contains approx 25% MEK and 20% Ethyl Acetate. Both of these chemicals fall into the worst category for causing microscopic crazing of plexi. Down the track it may well be that those builders who used Sikaflex to avoid cracks may develop them anyway. I believe one case has already been reported.

Anyway I hope I've been of assistance.
 
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Thanks Bob!! Great tips and ideas... I like the bushing idea a lot!! After dropping $930 at Van's today for a replacement, this is NOT something I want to do again.... ever.:(

I was wondering about the Sika adhesive, makes sense not to use it in this application. The local plastic outfit (Tap Plastics) suggested using E6000 as an adhesive with the plexiglass.

Seems the only place on the tip-up to use an adhesive/sealant is around the front of the canopy to the 701 skin. Then do the fiberglass fillet overtop. To use an adhesive elsewhere would make a mess of trying to replace a broken canopy down the road.

Another suggestion to others is to not "suck up" the canopy to any part of the frame where it can impact the frame in a stressful manner. The front side curves, where the side rails joins the front weldment is a clear and present danger zone. I can already see I need to make some refinements there before I do this the 2nd time!

Good luck to all while crossing this bridge. Tread carefully!!:eek:
 
Actually.. THANKS EVERYONE!! This is such a great group and a way to brain storm and commiserate at the same time!!!!
 
Pick up a 10X lighted magnifier for a look at the holes you just drilled in a canopy. They look fine to the naked eye, but up close you'll see all kinds of scary edges, mostly from chip-out at the backside edge of the hole. I'm talking about holes done the "right" way, very low pressure, high speed, properly ground drill bit.

A standard countersink does a terrible job, walking around the hole and scooping chunks. A single hole CS is better. The best was a pointed rock to grind the hole edge smooth.

My fastback canopy is bonded to the fiberglass frame, and has alternating cleco sized holes and 1/4" holes for Hysol "pegs" to squeeze through during bonding. I kinda think the big holes are safer than the small ones; for a given drill RPM the outer edge of the drill flute has higher velocity, ie, more chance for the drill to melt through the plexi. It's also a lot easier to finish the edge of the hole after drilling.
 
Drilling plexi

FWIW on my -9A slider, I drilled first of all with a normal drill bit, but one of the right initial pilot hole diameter that would fit in my Dremel. Then set the Dremel on high and let the drill almost melt its way through. Did all of the holes in this manner, and after one year have no cracks at all. But maybe i was lucky, and I hope to h*ll I haven't spoken too soon.

Allan
 
Microscopic chipping

DanH said:
Pick up a 10X lighted magnifier for a look at the holes you just drilled in a canopy. They look fine to the naked eye, but up close you'll see all kinds of scary edges, mostly from chip-out at the backside edge of the hole. I'm talking about holes done the "right" way, very low pressure, high speed, properly ground drill bit.
Click to expand...

As usual, a very astute observation from Dan Horton. I inspected early plexi fabrication trials under a high powered stereo microscope. The amount microscopic chipping that could not be seen with the naked eye at the backside edge of holes using convention drilling techniques (including Avery "plexi" drills) was very considerable. I suspect that many builders have these flaws just waiting to propagate.

As I said previously, I found that if I countersunk the rear of the hole BEFORE upsizing drilled holes (with a ceramic stone CS) there were NIL microscopic imperfections on the backside of the hole.
 
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ceramic stone cs??

Can you clarify a ceramic stone counter sink that has no cutting edge? Are you talknig the small cone shaped bits that come with the dremel type tools? I asked a couple gear heads i know.... they shook their head and had no idea what a you were talking about. Source, or pic? Time sensitive...i just marked my holes today, drilled side frames...but just stared and the plexi...we had a stare down and it won. Maybe thursday.. hahha. I swear it was laughin at me.
 
RickWoodall said:
Can you clarify a ceramic stone counter sink that has no cutting edge?
Click to expand...


Technically it's a ceramic stone deburrer and it has no cutting edge. But you say you have a dremel tool, so just grind down one of the miniature grinding stones on a bench grinder to approximate a 100 degree countersink (that's 100 degrees inclusive). It will work just fine with no clogging at all. You'll be surprised at how little pressure you'll need to produce an instant countersink in the plexi.

As always...practice a few times on scrap first. Never practice on your plane.

After you have drilled the plexi to 3/32 you can use the stone to countersink the rear hole to be just larger than your next drill size. This will clean up any microscopic cracks from the 3/32 drill and prepare the exit hole for the next drilling. You can use the next size drill as a measuring tool to ensure that the countersink diameter is just larger than the drill diameter.

And don't forget to warm up the canopy before any drilling.
 
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