Ultimate Quickie Information Package!

Login Form

Q-talk 144 - Creating a Q2 Canopy

Before you can begin creating a canopy, you first have to build a large oven.

This sounds a bit more involved than what it really is, it’s just an open wooden box 2.4m x 1.3m x 1m (sorry I grew up metric) [Editor's Note: That's 94.5" x 51.25" x 39.5"], with insulation. You have to make it deep enough (1m), to prevent the heating elements from burning the Perspex before it reaches proper molding temperature.

Line the box with roofing insulation, shield it off with tin-foil, and staple checken wire over it to keep everything in place.

Four conventional oven elements, straightened, and connected in parallel will be more than enough for heating it up really fast. Put some sealing foam on the top edges, cut a peep hole in the side, and lastly install a light inside the box, since it is very important to see what’s happening and when to start inflating.

The lid is made of 32mm super-wood, slightly bigger than the top of the box to ensure you can get a grip on it when it’s time to lift it up for the heat to escape. This is also the backing for the canopy bubble. The inside face of the lid has to be lined with foil: just lay down a few lines of silicon sealer to hold it flat against the wood, then you have to remove a strip of the foil under the oval shape of the frame to get a sealing surface where some more silicon has to be put down to seal it airtight just before the Perspex goes on for final tightening.

In the center of the frame a hole needs to be drilled and a nipple mounted which will be used for inflating the bubble in due time. Like Plexiglas, Perspex also cracks easily, and the easiest way to mount the sheet is to sandwich the whole lot together and drill the mounting holes, all the way though in one go, first widely spaced and bolting them down just to keep everything in place, then drill that multitude of holes evenly spaced all the way around. We used a total of 110 x M6 bolts (1/4 inch I think is close enough).

Pre-drilling the holes.

Now take the frame, and Perspex off, to clean all the shavings and dust which would have been stuck between the lid, and what is going to be your canopy, they leave very ugly marks when the Perspex softens.

Everything cleaned, back in place, silicone sealed, and tightening up.


Here's a quick shot to show the spacing, and the foil under the Perspex.

Our oven is only 1.2m [47.25"] wide, and the oval frame was resting on the sides, so we had to add a sealing frame of the same thickness. This is also the reason we could not mount a cross beam (height gauge) on the lid. So we installed it in the oven.

The frame is simply two parallel lines with two semi circles closing each end.

A true oval will give you a "bulge" towards the front, instead of the flatter profile a Q should have.

This is what I mean by "bulge."

This was our first attempt, which at the time,
we thought was just perfect . . . .

OK HERE WE GO. . .

This whole assembly (The lid) has to go on to the oven, and it is heavy, if you don’t have at least four relatively strong guys together, make sure you have a chiropractor’s number saved on speed dial!…?

The lid is in place, and we’re sealing off the edges.

Once you have the lid in place, make sure all the edges are sealed to keep the heat inside, and connect your compressor hose to the nipple in the centre of the lid. The compressor hose should have an in-line gate valve to control the inflating (blowing) process. Take a look trough the peep hole to make sure there is nothing in the way of the bubble, especially the birds wire didn’t get hooked on the bolts, and hanging from the side. Leave the light on, close the peep hole, and switch on the oven.

Now you have to look at what’s happening inside rather often, but try to limit the amount of heat escaping when you open the hole, and from time to time you have to measure the temperature on the surface of the Perspex (an infrared thermometer works great). It will start sagging when it reaches about 140°C [284°F], and you can start blowing some air into it, but not too fast, because the compressed air cools it down considerably, and cold spots on the Perspex whilst you are stretching it is not a good thing. . . Try to keep the surface temperature below 160°C [320°F] by switching the elements on, and off as required, and finally when your bubble is just touching the height gauge, don’t switch it on again.

Connect the air hose to the nipple, and turn on the air.
The rest happened really fast, and the excitement killed
the last thought I had about taking pictures.

Keep an eye on your bubble, because it now egin to act like a big baloon. If air leaks out, it will get smaller and you’ll have to inflate it back to where it should be. Lift the lid and place some blocks on the corners to allow the heat to escape. As the bubble cools down it will harden again.

This sounds like a lengthy process, but it happens fast, and it should now be about 15 minutes from the first time the oven was switched on. When the bubble cooled down to about 50°C [122°F] it is safe to call your three buddies closer to lift it out of the oven, but be careful, don’t try to open the oven like a tool box, the bubble will scratch against the birds wire, just lift it straight up until the bottom of the bubble will clear the edge of the oven, move it over to the side of the oven, and rest it on two sawhorses. Now take a short breather, and turn it right side up.

And there it is on the sawhorses.

The last part is cutting the flange off where the frame was holding it down, and then cutting the bubble in half to finally end up with two canopies. If you work carefully you could have a spare for whatever happens in time to come, but since the trimming and fitting is likely to cause scratches on it, my idea is to use one of them to make a template to fit perfect on the canopy-frame, then cut the right one to size and glass it in to limit the handling of it.

1, 2, 3 right side up, and our two helpers are un-doing the bolts.


The best tool for cutting Perspex is what we call a baby grinder, with a 2mm stainless steel cutting disc. Sorry, no picture of that one, I felt it would be like showing a picture of a hammer.

 
The flange is off, and the split line marked with masking tape.

And there we are, still needs a lot of trimming but the line looks good.

Yes . . . it is too dark, so the whole process started again,
and we made another using neutral pigment,
and it came out just the way I wanted it.

One Final TIP:

Buy a full sheet of Perspex, and have them cut your 1.2m x 2.3m piece from the center of the sheet. The sheet is thicker on the edges, and will stretch unevenly, leaving you with a lopsided bubble.

Credits:

I want to thank Arthur Smith for all his help, tools, oven and everything. Without him, this article wouldn’t have been possible, and I would have still been without a canopy. Anyone in need of a canopy and not wanting to go through all of this is welcome to contact us. We know how to do it….done it before.

Bernhardt Jansen
Johannesburg, South Africa
www.poynting.co.za