Plans for "Fat Helicopter"



The Door

The door is like the one I have on my house. It is the third complete change in design I have tried, and it is completely satisfactory for us. My earlier doors, with curved frames of bent plywood, such as the one described in the last article, were functional, but not as good as the polygon one for hingeing. Curved doors present difficulties. I have worked out a door that is easy to hang on standard door hinges, and , despite its outward tilt, opens inward easily, keeping its bottom edge relatively level with the floor. I have done my best to minimize the momentum of this off balance door. My daughter in kindergarten can open and shut it. It is a tall hexagon with hinges on one lower side of the door. It is mounted in a 2x10 frame with the door flush with the interior edges of the frame. When it is left open the top flops back at an angle, and will stay open. The door itself is a lightweight sandwich type with outside layers of 1/4" luaun plywood (which measures 3/16") and an inner edge of pine boards or 2x4's, and an additional piece inside to provide stiffening across the middle. Since the door closes with a pronounced outward tilt,we didn't use a doorknob. We found a pretty piece of an apple tree branch with a good shape for a handle, and lagscrewed it on from the inside. We did another handle from the outside. Then we bought a deadbolt that locks from inside and out. Unfortunately, I made our door with 2x4 pieces around the edge between the plywood sandwich, and had to do a lot of chiselling to make a standard deadbolt lock fit the thick door. If you can find boards a full inch thick, or 1 1/8", that will work with a locking deadbolt. But the 1 1/2" dimension of standard 2x4's plus the thickness of two layers of thin plywood is too much for some standard door hardware. Standard doorknob sets worked on my earlier, equally thick doors. So 2x4's will do with some doorknobs, probably most.

The frame requires only one special angle throughout, 17 degrees from vertical. This is the angle I set my hand held circular saw for all the cuts. Look carefully at how the corners go together, carefully determine lengths of pieces from the dimensions. For instance, the top and bottom pieces show a measurement of 24" corner to corner, but that is the short dimension. The angles widen from there. This is a real measure twice cut once situation. I found it helpful to lay out the hexagon on a sheet of plywood, and assemble the pieces on there. Then the frame will not get distorted during assembly.

This hexagon can be drawn most easily and accurately by first drawing a tall rectangle 24" wide and 78" tall. A horizontal bisector (cuts it in half) extending 12" out on each side will reach the remaining corners. The door is of course smaller than the frame by the width of the frame all around (so it will fit inside) plus another 1/8" so it won't stick tight.

I fastened my frame together with metal plates made from leftover sheet metal (9" squares will do), and 1" #10 sheet metal screws. The plates are bent around the six outside corners of the frame. I fastened the frame to the plywood with 10 short blocks of 2x4 around the inside, lagscrewed through the plywood into the blocks, and nailed through the frame into the blocks. During this step I had the frame braced with diagonal pieces of wood to keep it from distorting. A stop running around the inside of the frame of 1x4 pine covers some of the nails and holds the door in place when shut. The door itself is fastened together with many 1 1/4" #10 sheet metal screws, through the plywood into the wooden braces. If you use 1" wood inside the door, use 1" long screws.

The virtue of this hexagonal door is that the door does not need to be lifted much when it swings inward, because it does not rise much, and does not have much momentum when it is closed, outward. The angle where the hinges mount on the door counters the outward tilt of the door and minimizes the unwieldy quality of other designs I have tried. I welcome innovators to try round doors. The hinges on round doors require special attention. A round door with a small, vertical flat side to mount the hinges would help the situation. Doors get a lot of use. We are a much happier family now that we have a door that functions properly. A poorly performing door is a constant annoyance.

I have included a drawing which shows how to locate the corners of the hexagon from the inside of the assembled dome. The corners of the triangular vertex holes, and the bottom center of a base sheet of plywood, are the reference points. Assume right angles where it appears to be so. Drill the six corners through to the outside, and connect them with straight lines, and saw the hole when you are satisfied it is a close fit to the frame. The frame, when properly braced to hold it rigid, can be held up to the inside of the dome, corners matched with marks or holes, to anticipate the fit.

Once the frame is in ,and the door hung, the frame should be flashed or caulked to seal it tight to the dome. A stop running around the inside of the frame of 1x4 pine or some appropriate trim covers some of the nails and holds the door in place when shut.


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