Jur's RV7 Aircraft Factory
2917 hours and counting
Some decisions in life are bare of any obvious logic

The "all feared" canopy cutting and trimming work can finally start. After all the time I've spent on bending the frame, it's a welcome change in type of work.
The plexiglass canopy comes molded in one piece and needs to be both trimmed down, and later cut in two halves when you are building a slider canopy like mine.

The long feared "big cut" as Vans builders tend to call it is coming real closeby now.

As this is my first article on plexi, I'll try adding all my tips here in the list below as I go.
A number of things that are very important when working with plexi is that :

- it is very brittle when cold. Do not try to work on the canopy in temperatures less than 25 degrees celcius. Once over 25, the material becomes very flexible, more bendable and has less risk of forming cracks during drilling.

- never ever use a traditional drill bit. The sides will "bite" on the last bit when you're almost through the material and will rip and crack it. I tried grinding down the edges of a traditional drill bit as you can find in some video's on EAA video's and did a lot of test drilling. But I still do not feel confident about this. I bought some real plexiglass drills at Abbeon.com and they work great.

- I found that the plexi glass cutting disc delivered with the kit works best in a die grinder. It gives you greater precision while cutting.

- Don't worry about having to stop half way through a cut. You will have to do it anyhow to secure the loose end with duct tape. So no problem in using an air pressured die grinder with small compressor.

- When drilling the plexi to the canopy frame with plexi tip drills, it's impossible to drill with the plexi drill in the canopy frame. You will break or dull them. A good tip here is to clamp the bubble on the frame, then insert some wooden popsickle sticks between the frame and the bubble and drill through. Then remove the popsickle sticks and change drill to a regular drill bit to drill through the canopy steel frame.

- practice your cutting skills with the die grinder on the scrap parts behind the molding marks. This will help you build confidence when you move closer and closer to the big cut seperating the bubble in two halves.

Since it's getting colder in Belgium, there was no way I could heat my garage workshop to 25 degrees. The living room had to be reshaped in an airplane shop. No need to tell you my girlfriend loves me very much.
A little less now, but still enough to get away with it. I have a wood stove in my living room so combined with the central heating I could crank the temperature up quite rapidly.

I have a garmin biking gps which also shows temperature. As you can see below, i put it on the bubble and read a nice 33 degrees C.

I marked the molding flanges front and back and started cutting away. The molding flanges are the parts in the canopy where you see striped markings from the mold.
In the image below, you see I already cut half way through.

Then layed the frame in the bubble and did some more alignment checking. Notice the duct tape strips. You really want to do this to ensure the bubble won't open too much. It's still ok now, but the more you cut away the more flexible it becomes. After the big cut it will be even worse.

You will need a zillion clamps. The more the better.

What worried me most at this point was the big gap underneath the front bar. I could stick my fingers under it. As the bubble is still in one piece, there is no flexing.
I sent a mail to vans support to ask them about this and they told me not to worry. It would fit well after making the big cut.

Then I made a first attempt to define the cut line for the big cut.

You need between 1/16 abd 3/32 overhand from the front bar which is shown on DWG43 Detail B

I made this little tool block in hard woord and measured 3/32 from the front. Then filed away they wood behing. That way, I could put the sharpie pen in the gap and draw while moving the block along the front of the canopy bar.

It leaves a nicely defined edge. This is definitly the way to go.

Then I cut away the front mold. Here also you see the molding marks in the canopy.

Enough sweating for today.

With the big cut done, it's now time to reclamp the slider part of the canopy bubble back on the frame and trim back the back and sides to fit the frame.

Used a sharpie pen to mark the line above the side bows.

Final checked by clamping it to the frame. You want to keep checking that the forward line remains in it's perfect position in front of the forward frame bow.

Keep supporting the plexi with strips of duct tape. The last thing you want to happen here is the canopy to fall open. The bubble is very flexible at this point.

Here, the cut is completed and you can see that the canopy lays a bit higher than the canopy frame. This is to give room for C-759 which will act like a clamp together with the side skirt C660 to keep the plexi in place.

Other side done.

Close up picture of the mating at the forward bow

Then mark the aft line 1/2 to 1 inch back of the rear canopy frame bow. I went for the full 1 inch. I had to search quite a bit to find these measurements on the plans but you find them on Section G-G on dwg 43.

I used a little wood block to slide along the frame bar and mark the line.

Cutting back the rear plexi with the plexi cutting disc.

A lot of smoothing and sanding edges later, I'm finally done for today.
As you see it's already dark outside. It's a job where patience is required.

 Another close up shot of the plexi to front bow relation.

The rear clamped in place with a zillion spring clamps

The distance looks about pefect as well as the alignment to the centerline.

Today is "The Day". the day of "the 1000$ cut" or the "big cut".

Actually for European builders it's more like the 2000 euro cut because breaking this thing will cost a fortune as you not only have to buy a new one but also ship an odd and big form to Belgium again and add 33% tax and tva on top of that.

So you can imagine we are even more stressed about this than our US friends.

The big cut is the nickname for seperating the windscreen from the sliding canopy. In other words, cut the whole damned thing in halves.

Before I could do that, I had to continue where I left of yesterday. Heat the place back up to 30 degrees and cut off the side molding marks.
I don't want  to go any further than that as I want to make sure that I keep enough material on the windshield side that will be cut off. I decided only to trim back to the size above the vertical square side bows of the canopy frame until after the seperation is completed.

In the image below, I started cutting the side molding marks off. As you can see I'm cutting and immediatly restoring the duct tape support strips as I pass the point.

 Cut through the suport strip

and restore it underneath the cut to control the stress on the bubble.

This cutting process is easy and it helps you to build confidence for the big cut.

When done, immediatly sand down the edges so that you remove all possible stress marks in the material. Whatever you do, do not put this aside until the next day as the bubble will cool down and stress marks may lead to unpleasant surprises in the morning. I used a thin hand-belt sander of 1 inch wide and 200 grit. Move constantly from left to right and back to avoid heat building up in the material. Too much heat can also lead to cracks. Keep moving and once it looks smooth, use sand paper to sand it down to 300 and finally 400 grit.  I took it all the way to 600  for the final pieces but 400 will be enough for intermediate cuts like the one on the sides. I will have to trim them more down tomorrow anyway.

Then I reclamped the frame in the bubble. Look at the amount of clamps. Yes, that's how many you will have to buy. Get as many as you can while they are on a discounted sale.

Another shot of the gap between the front bow and the bubble. Vans reassured me the bubble will comply once the cut is done. Crossing fingers at this point. Not much you can do now as the hole in the canopy for the latch defines the position and not much you can do about this now. If I would have to redo it, I would pay more attention to this when defining the position for the canopy latch hole.

I took of the protecting platic from the bubble front and back and re-did the procedure I tried out yesterday. Used a wooden hardblock to define the spacing between the front of the canopy front bow and a 1/16 to 3/32 gap. Putting the sharp in the gap of the block and moving the block perpendicular along the front bow line.

Here is a shot of the hard-wood tool. The leg is 3/32 inch.

A well defined line is the result.

Next I put painters tape on the inside. Partly to protext the bubble, secondly to highlight the line.

With the bubble turned over, you can now clearly see the line.

 Last picture in one piece. As you see in the image below, I also made some wood beams with wood stops in the end to control the sliding process of the bubble. As you cut, the bubble becomes more flexible. The last thing you want to have is that the sides start moving outwards and creating stress on the cut line. Guaranteed crack coming up. So make sure the side are secured well. Don't press them inwards either. Just let them rest without in or outwards pressure.

Ready for the big cut. Sweating like crazy and shaking hands from the stress. I decided to go from passenger side to pilot side .

Here the cut is started. To keep the bubble from moving, I put duct tape strips over the freshly cut line every couple of inches. This ensures that the bubble won't tend to move by it's own weight.
You want to make sure - especially at the last couple of inches - that the windscreen does not tear off. As I started cutting, the stress faded away and concentration took place of fear.

An image says more than a thousand words, but a video puts you right into the moment. My girlfriend shot the entire process, here are some key moments.
You can see in the first video how nerveous I am and how it's trying to find the right angle to position yourself. Then last movie shows how the canopy stays nicely in place and there is no cut-off movement at all in the last fractions.

 The next picture is taken after the full cut is completed. Again, adding duct tape every couple of inches. The windscreen did not move at all until the end of the cut.

All done, ready to seperate.

Tada... we have two halves !

I carefully removed the sliding half and put the bubble on the cut-side. This is according to me the safest way to store the canopy for now. This is just temporarily as I will immediatly sand the edges of both sides.

Sanding starts on the windscreen side. Same procedure as before using the hand-belt sander and 200 grit sandpaper to start. 200 grit takes away excess material fast so move left to right rapidly to get an even sanding and avoid taking away too much in one location.

After sanding to 300, 400 and 600 grit, this is what the edge looks like.

Then I did the same on the sliding canopy half and set the windscreen safely aside.
When all was done, I put the frame back in the canopy to check the overhang in the front.

As you can see on the picture below, the gap between the frame and the bubble disappeared. The plexi nicely adjusts to the shape of the steel frame with little stress.

I will leave it for now and continue trimming the sides in the next session.

A most feared task is behind me and turned out to be a succes. I deserved a good beer !

If you think you are done with frame bending, you are wrong. Sadly but true.

When clamping the canopy to the frame, you will noticed that the rollers now make a terrible sound and hardly move in the perfectly aligned canopy tracks. That is because the load of the plexi on the frame stretches it out a significant amount.

It's about 1 inch in the front and half an inch on the the rear bow.

You will have to re bend the frame inwards front and back to compensate for the springload. Make it just enough so that you get a perfect alignment agin of the rollers in the canopy tracks.
Another job where patience is in your favour and a lot of fitting and refitting of the bubble is required.
Be patient, once you will be drilling the holes in the plexi, you are locked in forever.

Got to a point where I'm satisfied with the result. Notice also the side clamping with a wood strip to support the side of the plexi all along the lenght of the side bow.