[alpinelakespilot2000]

I know it's OK to drill #40 with a normal drill then increase the hole to final size with a plexi bit, but is it also OK to drill #40 and then increase the size with a unibit? I'm ready to drill the hole for my canopy latch handle and would like to use the #40 to make sure that my hole is centered. Thanks.

 

[cleve_thompson]

We have just finished doing just what you plan and we had no trouble. However, when we were enlarging the #40 holes to 5/32", we found that the steps on our particular step drill bit were too close together to allow us to drill all the way through the plexi so I ordered a plexi drill from Air Craft Spruce and it did just fine.
Good luck! I know I am tired of fooling with this canopy business, aren't you? We're installing the rear canopy block now and trying to figure out how to get the angle of the hole for the spike just right!

 

[pierre smith]

Like this

Hi Cleve,
I'm assuming that you're speaking of the two blocks that house the pointed hold down pins? Get in the airplane and let your helper close the canopy until the point touches the rear of the block. Hold a ruler at the same angle as the pointed rod and transpose that extended line onto the side of the block with a colored marker. Open the canopy and stand on one side of the airplane while the driller aims the drill with you looking at the drill's angle compared to the line on the block. Tell him to raise or lower the drill to match the line and drill away. Later the entrance to the hole can be enlarged into a funnel shape to help guide the pin in as the canopy closes.

Regards,
Pierre

ps You may have to start drilling perpendicular to the block until the drill starts going in and then angle it up while it spins.

 

[alpinelakespilot2000]

We have just finished doing just what you plan and we had no trouble. However, when we were enlarging the #40 holes to 5/32", we found that the steps on our particular step drill bit were too close together to allow us to drill all the way through the plexi so I ordered a plexi drill from Air Craft Spruce and it did just fine.
Good luck! I know I am tired of fooling with this canopy business, aren't you? We're installing the rear canopy block now and trying to figure out how to get the angle of the hole for the spike just right!

Thanks Cleve-

Yes, this canopy stuff is getting old! Still, I just made my first cuts in trimming off the fwd. and aft flanges. Did one test cut and then went right up to the edge of the flanges and cut them very cleanly and left a finished edge smoother than what came from Van's. I'm very relieved that it went well and that the plexi didn't break just by looking at it wrong!

The steps on my unibit are too shallow too, so maybe I'll have to get a big plexi bit for the canopy handle hole if my friend doesn't have one.

Good luck on those rear blocks. Thanks for asking the question before I got there!

 

[mburch]

The steps on my unibit are too shallow too, so maybe I'll have to get a big plexi bit for the canopy handle hole if my friend doesn't have one.

Don't forget that you can drill halfway through the hole with the unibit, then come at it from the other side and finish it off. Worked for me!

mcb

 

[Bob Axsom]

The Canopy Stuff Gets Old?

I didn't think so. This is one of the most eye catching parts of the whole airplane and impatience at this point is a bad thing. I compromised nothing on this part of my plane and took several extra precautions to assure a good closure seal. I've never regretted it but we each have our own priorities. Good luck. I would never have tempted fate with anything but plexiglass drills on the canopy and lenses but obviously it works.

Bob Axsom

 

[Captain Avgas]

Don't forget that you can drill halfway through the hole with the unibit, then come at it from the other side and finish it off. Worked for me!

mcb

It's a good suggestion. Actually finishing off the hole with the unibit from the rear is safer. Damage to the plexi always occurs on the break-out side of the plexi....and increases in risk with larger holes.

Go most of the way through from the front and then come in from the rear to just finish off. If you have any microscopic damage on the rear it will clean it up.

 

[alpinelakespilot2000]

I didn't think so. This is one of the most eye catching parts of the whole airplane and impatience at this point is a bad thing. I compromised nothing on this part of my plane and took several extra precautions to assure a good closure seal. I've never regretted it but we each have our own priorities. Good luck. I would never have tempted fate with anything but plexiglass drills on the canopy and lenses but obviously it works.

Bob Axsom

Not sure whether you are trying to encourage me or discourage me Bob. Sometimes it's hard to tell on the internet. I don't think I'm being impatient and am not trying to compromise anything. Like you, my priority is building my canopy to the best of my abilities. Van's instructions say to use a unibit for this process, so my first thought is to follow directions and use a unibit. If you have a source for 5/8" plexi bits I'm interested in hearing where. Spruce doesn't carry anything that big that I can find. That said, I'm glad you really enjoyed the stressful/high dollar $$$ part of the building process. I've enjoyed learning a new skill but will be quite pleased when it's all done and I don't have to do it anymore.

Matt and Bob B.--Thanks for the suggestion at using the unibit I've got and coming at it from both sides. My initial thought was that maybe I wouldn't be able to center the bit perfectly on the backside given that most of the material will have been taken out on the first side. I'll give it a try though on some of the scrap.

Thanks again, Matt, especially for your canopy notes. They've been really helpful.

 

[Bob Axsom]

You got me!

WOW 5/8"! I don't have a plexiglass drill larger than 3/8" so I decided I better back check. I got my photo log (album) down and found the series where I was working on the canopy. I saw no evidence of what tool I used for the large latch hole but all of my photos have the date they were taken written on the back. It was in September of 1998 that I first set the plexiglass on the round tubular canopy frame and rollover structure. On 10-17-98 I found the following entry: "... I've drilled and enlarged the hole for the latch." Still no clue as to the tool used so I got out the instruction manual. On page 9-9 in my RV-6A manual it says "A large hole must be cut for the latch tube - - use a Unibit and drill this hole as accurately as possible. If the canopy must be adjusted after the hole is drilled, it may be carefully "ovaled". The trim strip along the top tube will cover it up later." Based on the evidence I can only guess that I drilled a pilot hole with a 1/8" plexiglass drill, then enlarged it to 3/16" or 1/4" with another plexiglass drill so the smallest diameter of the unibit would enter it and then enlarged it to the final size. I bought my plexiglass drills from Avery Tool and the 3/8" drill for the wing tip lens mounting holes was the largest. I do not know if they have larger diameters. I was wrong in my apprehensive reaction to the use of the Unibit for plexiglass applications - thanks for straightening me out - I'll be more careful in the future.

Bob Axsom

 

[Captain Avgas]

My initial thought was that maybe I wouldn't be able to center the bit perfectly on the backside given that most of the material will have been taken out on the first side. I'll give it a try though on some of the scrap.

Thanks again, Matt, especially for your canopy notes. They've been really helpful.

Matt, go as far through from one side with the Unibit as you can and then come in from the other side to finish off the last bit ....then you won't get misalignment. But your intention of practicing on scrap is excellent. I NEVER practice anything on my plane.

I actually bored out all my canopy holes to 1/4" and used silicone bushings to allow for differential thermal expansion. I used a plastic drill up to 1/8' and then a unibit above that. In reality a good unibit with small steps is better (read safer) than a plastic drill but in practical terms you need a 1/8" hole to get started with the unibit.

Keep things warm. Be very careful with countersinking as well ...big danger there. The less flutes on the countersink the better. One flute is best, two flutes just OK, 3 flutes dangerous.

I would suggest that most of the cracking seen in canopies (and there's a LOT of cracked canopies) is cause by one of 3 things: a) initial microscopic damage to holes by poor technique in drilling and countersinking. b) misalignment between holes in the canopy and holes in the frame. c) poorly fitting canopy on frame resulting in localised plexi stresses being built in.

I'm with Bob Axom when he says the canopy needs to be done carefully and with patience. Many builders I know are using the 'take-no-prisoners' approach to building....they just keep throwing things together. But that approach will not work for the canopy. Every really nice fitting, well finished, smooth sliding canopy I've ever seen had a LOT of time spent on it to get it that way. Come to think of it....it's the same with the rest of the plane.

 

[mburch]

Be very careful with countersinking as well ...big danger there. The less flutes on the countersink the better. One flute is best, two flutes just OK, 3 flutes dangerous.

I hadn't heard this before but it makes sense. Thanks for the tip. I think I have some single-flute cutters around here somewhere...

Good idea about using bushings in oversize holes. Did you just make these by cutting pieces off a length of tubing? Also, did you size the I.D. of the bushings to just fit the fastener (e.g. 1/8" I.D. for a pop rivet) or did you also make the I.D. of the bushings oversize compared to the fastener?

thanks,
mcb

 

[Captain Avgas]

Good idea about using bushings in oversize holes. Did you just make these by cutting pieces off a length of tubing? Also, did you size the I.D. of the bushings to just fit the fastener (e.g. 1/8" I.D. for a pop rivet) or did you also make the I.D. of the bushings oversize compared to the fastener?

thanks,
mcb

I used surgical grade silicone tube 1/8" ID and 1/4" OD. I then cut it to the required lengths (approx 3/16"). I believe that silicone is the best option because it has very good UV resistance, good elasticity, and importantly, excellent deformation recovery.

So the bushings are not oversize to the fastener, nor undersize to the hole...they are a perfect fit.....but they have really good elasticity so they compress easily to allow movement of the fastener inside the plexi hole...and then they recover.

The fact that there is no slop around the bushing means that when you instal the canopy and set the fasteners, the 1/4" hole in the plexi is nicely centred on the smaller hole in the slider frame.

I also countersunk the plexi on the 1/4" holes so that the dimpled aluminium has exactly the same dimension for lateral displacement as the fastener.

In fact I used a small ceramic stone tool (ground to 100 degrees) in a dremel to make all my countersinks. Absolutely no chance of chipping or cracking the plexi. After that I simply used a 100 degree standard hand deburring tool (same as you use for deburring your drilled aluminium rivet holes) to clean them up. Just a couple of light turns by hand does the trick. Beautiful.

At the side curtain location I moved all holes in the aluminium 1/16" closer to the edge (moved them up). This enabled me to move the 1/4" holes in the plexi up 1/16" as well and thus provide some additional edge distance.

If I was doing it again I'd probably fabricate new custom aluminium side curtains to allow even more edge distance on the plexi...not a big job but you'd need access to a folder to make the cranked inside strips.

In reality, even with the standard design I didn't think Vans allowed enough metal to capture the plexi. They make it tough going for everyone.

Anyway, I hope I haven't confused you.

Initially I was very keen to use Sikaflex but the more I researched it the more concerned I became. So I decided to use mechanical fasteners but develop a design that would allow differential thermal expansion without stressing the plexi.

 

[LettersFromFlyoverCountry]

Re: bushings. Amit Dagan had an article in the RVator a few years ago where he used fuel line tubing for RCs. This sounded like a great idea. I've asked around to see if anyone else tried something like that and I haven't really heard much; but this is the way I'm leaning toward.


Now, let me ask you this question: I have a unibit and I have an Avery plexiglass drill bit set.

Which is better?

 

[fl-mike]

Steve,
Canopy latch:
First, grind the tube down flush with the top of the canopy frame. It's not necessary and you can then delay drilling the latch shaft hole until you have finished the initial fitting of the plexi to the frame.
After the plexi is fitted and you've drilled and clecoed the plexi to the frame, make a 3/16 drill bushing the fits in the latch tube (what, you don't have a lathe?) for your plexi bit. Now you can back drill the plexi with your 3/16 plexi bit for a perfectly centered latch hole. Next, open up that hole with your unibit as needed for the latch shaft.
Polish the edges, make burnt offerings to the plexi gods, etc.

You can also use that drill bushing to center the hole in the center cover strip. (before passing it along to your other builder buddies)

 

[alpinelakespilot2000]

Thanks Mike-
That (grinding off the top part of the frame) is something I've heard elsewhere before, but for another reason. Can't remember what it was, but it does sound like it has the advantage of being able to center that hole perfectly. Another option to consider anyway.

 

[Bob Axsom]

Modified Unibit

I remembered that I had two Unibits, one bought at a local store that had too small a range for all the work and one that I ordered from one of my aircraft builder sources. I knew I had ground down the some of the larger steps on the small one so it would pass through the part I was working on when the hole was enlarged to the desired size without cutting in with the next step size. I never remembered what that tool sacrifice was for but ... the final size is 5/8" - I think I found the answer. In the course of building our RV-6A, I modified and created several tools like this as needed (ground down the thickness of open end wrenches, cut off most of the handle of stubby screwdrivers, multiple coupled drill extensions, etc.). The tool Gods are angry but the airplane is put together well.

Bob Axsom

 

[Captain Avgas]

Re: bushings. Amit Dagan had an article in the RVator a few years ago where he used fuel line tubing for RCs. This sounded like a great idea. I've asked around to see if anyone else tried something like that and I haven't really heard much; but this is the way I'm leaning toward.


Now, let me ask you this question: I have a unibit and I have an Avery plexiglass drill bit set.

Which is better?

I use the plastic drills from Avery up to 1/8". Beyond that I use a fine step unibit. Never had a problem and all my holes were drilled out to 1/4". I'd say that beyond 1/8" the unibit is WAAAAAY safer.