A door latch for the shedHaving built the doors for the shed, I still needed some way to latch them shut.
Normally, for double doors, one locks one door to the top and bottom, and then the second door latches onto the first. But I started thinking about a way of locking the two doors together in one plane without latching the other door at the top. A "barricade bar" that fits into hooks on either side of the double door would do the job, but that would make locking the doors quite awkward.
So I had the idea for making a really long sort of "deadbolt". I needed a means of transferring rotating motion from a handle to the linear motion of the latch. And a rack and pinion would be just the solution for a very long latch.
I designed the rack and pinion using my gear generator program. I used a 3.5 cm tooth spacing, and a seven tooth pinion against a rack. I left all the other parameters at their default values.
I smoothed the faces of the teeth and rack using my strip sander. The resulting rack and pinion moved very easily. I made sure to cut away all of the line when I cut the pieces out to ensure my rack and pinion would have a little bit of play. A little bit of play is not a problem, and I don't want these to become tight with humidity changes.
I used birch plywood for the gear and rack. I cut a rabbet into the corner of what would be my "bolt" and screwed the plywood rack to it. I wanted to make the rack out of plywood so the teeth aren't liable to break off, but I wanted the main bolt to be from solid wood for better stiffness. It's also thicker and less expensive that way.
I used a 1.5" hole-saw to cut a hole through the sheet metal and door. I then attached a flange to the outside to provide more bearing surface for the dowel shaft, and to get the handle away from the sheet metal ribs. I made the flange out of some exotic hardwood, though I'm not sure exactly what it is, probably mahogany - it's very dark. I'm hoping that it's fairly weather resistant. I held it in place with one of my long reach clamps while I screwed it on.
I could have made it slightly longer still, but the scrap of 2x4 that I used to make it was only so long.
I added a stop to prevent the bolt from extending too far (not shown). Otherwise, I might extend the bolt past the rack teeth, and then it would be impossible to crank it back!
I'm thinking the handle and flange would be ok without it, but the dowel is only maple, and maple is not that rot resistant.
You can also see how the gable end is slightly forward of the doors. That way, even with driving rain, any water that may hit the gable will run down and drip off in front of the doors, not behind them.
So with the bolt fully extended, it locks the two door halves into alignment with each other, which makes sure both doors are closed, even if the door to the right (seen from the inside) wasn't locked at the top. With just the one bracket near the edge, it locks the doors against swinging outwards. The doors already can't swing inward because the door's sheet metal hits the front of the shed.
I wanted to see how well the doors held shut without that, but then realized that it was nearly impossible to close the doors without engaging that latch. Basically, gravity pulls that latch vertical, which closes it.
They usually fall down just from closing the doors, so when opening the door, they are often already dragging on the ground. A good feature, I think.