Fun with window frames (updated 19/06/10)

I’m now into my sixth week of shell-building and I’m nowhere near as far along as I’d hoped to be. The last three weeks has been taken up with trying to sort out the window framing of the enclosure, and this has turned out to be the most difficult part of the build by far.

The real problem with the window frames is the multiple compound angles required to frame and join parts that are angled in three axes simultaneously. My experimental approach to building falls down here, and a recourse to maths, diagrams and head-scratching is required. I abandonded the first attempt at a frame because the framing members were too big and deep and it would have looked very odd.

My second attempt began by taking the base frame from the first and making that secure and stiff. I removed the front-centre baton that was in place and put in three 1m-high posts upon which the frame was screwed, the whole assembly then being screwed to the A-frame to give a window enclosure.

I decided to make the frames out of 18mm x 44mm pine strips, so they’d be thin and not disturb the outside view. The plexiglass would be screwed into the back of them to give the appearance of a frame from within the cockpit. This left me needing to work out the exact angles to cut the strips so that they would meet at the right points and give a seamless fit. With a 20-degree back-angle on the windows, this required me to make a difficult compound cut – lucky I bought that mitre saw!

After a little trial and error I worked out that the magic angle was 8 degrees, so the compound cut was 20 degrees by 8 degrees across the width of the strip. Once cut, the strips are secured down to the frame base with metal braces bent to fit, and then secured at the top with a further brace. The overall effect is pretty convincing, and with some filling and painting, it should look like a custom-made metal and plastic part.

I took a quick snap at the 2/3 point, just for this update:

Now I must finish the post for the other side, create a top frame to top it off, then measure the precise dimensions for the plexiglass to go in each frame. Over the weekend I bought a router attachment for my Dremel which will let me rout a groove in the frame parts into which the plexiglass will fit. The whole frame then needs painting (black outside to be as little visible as possible, and aircraft gray on the inside to match the rest of the build). I can then use some silicone gel to seal it all off and complete the effect.

Given the glacial pace at which things have been going of late, I imagine it’ll be a couple of weeks before this part is done.

UPDATE 19/06/10

Not worth a full new post, but I’ve gotten a little further with the window frames (lack of some necessary bits and screws stopped me early last weekend). Now I have 3/4 of the top frame in place, and I’ve also filled the inside void of each of the window posts with an adhesive filler to keep them together and get rid of tiny imperfections. The effect is quite nice if I do say so myself…

Lots of finishing to do on this and the rest of the frame, and then I’m on to the framing for the main instrument panel.