Introduction: Automatic Double-Gate Closer
We have a few laying hens, and we let them have the run of the yard during the day, but we wanted to keep them out of our patio area. We needed something that would deter them from the patio, but would allow our dog to go in and out. I tried various combinations of springs and magnets, and they worked, most of the time. But they were finicky, and our dog kept forgetting to make sure the gates closed behind him after he did his thing. Finally, I came up with the right combination of weights, levers, and pulleys to get the gates to close every time. We have two sets of gates; the pictures are a mix from both projects. I hope that isn't too confusing.
Note: anyone who has raised chickens will laugh at our short little fence. The hens know they can fly over it, but there is plenty of scratching area in the yard, so they usually don't bother. We just needed way to deter the hens without making it too inconvenient for us and the dog. We still have the occasional plops on the patio to deal with, but it's much more manageable than before we got the gates.
Parts list for two gates:
1 1/2-inch, by 1/8-inch 48-inch long steel bar
2 Small eye-bolts with nuts
2 Locking nuts (to fit eye-bolts)
2 Small pulleys
2 Necks from plastic water bottles
2 Wide hose clamps (one-inch)
2 Narrow hose clamps (3/4-inch)
2 Super strong hard-drive magnets
6 feet of string,
2 feet of galvanized wire
Black spray paint
2 Rocks or other suitable counter weights
Step 1: Materials
Sorry this post-project photo doesn't show several of the items used in the instructable. I do show some pieces of the half-inch bar material that I used for the "L" pieces, and the half-moon things are the hard-drive magnets.
Hose clamps do all the hard work of holding this project to the fence. For attaching the "L" pieces to the gates, I used wide hose clamps, like you would use to repair a garden hose. For attaching the funnels to the fence, I used the smallest hose clamps I could find that would still fit around the fence tubing. You want them to be narrow so they will fit under the wires that hold the clamp to the funnel.
Galvanized wire is indispensable around the yard. I forget what gauge wire this is, it's about the same diameter as a coat hanger. It takes about a foot of wire per funnel attachment.
Electrician's Tape: what more can I say.
Drill, and drill bits: check the diameter of the eye-bolt to get the appropriate sized drill bit to drill holes in the "L" bars.
String: Nylon string, about two-millimeters in diameter, about three feet per gate. Hack saw and file are needed to cut the metal bars.
A hammer to bend the metal bar. You really need a vice to hold the bar while you're bending it, but if you are a person without a vice, CONGRATULATIONS!, and you're going to have to get by clamping the bar to the corner of a bench or something.
Black spray paint, you don't want Rube Goldberg rolling in his grave because you let your wonderful contraption get all rusty.
Step 2: Make String Funnels
To make the funnels, I just cut the tops off of some water bottles. There is a flange (a little ring of plastic) just below the threads on the bottle neck. You need to file one side of this flat, so it will rest tight up against the clamp we'll use to attach it to top bar of the fence.
Put two wraps of galvanized wire around the bottle-neck, one wrap above the flange and one below, and twist the wires to hold the wraps in place. Before you twist the wires tight, feed the end of one of the narrow hose clamps under the wires, so the clamp fits tight up against the sanded off place on the bottle neck. Twist the wires fairly tight, but gently, you don't want them so tight that it weakens the wire. Also, do the twist off to one side of the flat place, you need that to stay clear. Clamp the hose clamp to the top rail of the fence, about a foot from the gatepost and leave it loose for now so you can adjust it later.
Step 3: Make "L" Bars
Sorry I don't have pictures of the process for making these, really, you just cut the half-inch steel bar to size, mark where to bend it, clamp it in a vice and check that that it's square. Then beat on it with a hammer to make a 90 degree bend. The trick is figuring out how long the legs of the "L" need to be. You need one leg long enough to attach to the gate, and extend up high enough for the other leg to clear the gate post when you swing the gate. For me this was 8-inches.
The other leg is tricky. There are a couple of things to consider, you need the length of travel for the string to be long enough so you can swing the gate all the way open, but short enough so the weight won't hit the ground before the gate closes. I did a bunch of trigonometry and slide rule calculations to figure out exactly how long the arm of the "L" needed to be--I joke--actually, I just eyeballed it and used a tape measure to estimate how far the end of the "L" arm would be from the fence (where the funnel will be attached), when the gate was open as wide as necessary. I decided (somewhat arbitrarily) to make the arm a foot long. Drill a hole near the end for the eye-bold. File off any burrs and round the corners on the long end. Clean the pieces with solvent if you have it, and apply a couple of coats of spray paint. If you're sharp, you may notice that I actually wound up with brown spray paint, but at least they're painted.
The "L" piece is attached to the gate with a wide hose clamp. I'll see how it works with just one clamp and add another clamp if it gets loose. You need some way to attach the string; at first I just used some split rings that I had lying around. I didn't like how they flopped around and would get hung up on one side or the other of the "L" piece. This interfered with how far the gates would swing shut. I found some little eye-bolts (sorry I don't remember the specs) that had short threads and came with their own nut. Because these will be bouncing around a lot, I wanted to make the eye-bolts secure to the arms, so I got some locking nuts; the original nuts are moved down, so the "L" arm piece can be clamped between the two nuts. Align the eye-bolts so they are perpendicular to the "L" arms.
Step 4: Add String, Pulleys, and Counterwights
Now, you're ready to set up the counterweights. First, clamp the hose clamp with the funnel to the top rail. so the opening is just below the eye-bolt on the lever arm. I bought some pretty pricey little pulleys ($3 each), but you could use salvaged pulleys from old window blinds to make the weight stand away from the fence. This is really just so the rocks I'm using for weights don't clang on the fence every time the gate is opened. Bend the extra ends of the wires to make it so you can attach the pulley a few inches below the funnel and a few inches away from the fence. Tie the counterweights to the string (I'm hoping to find something better than rocks in the future), and rout the string over the pulley, through the funnel, and tie it to the eye-bolt. Repeat for the other gate.
Now, tune things up: you may need to bend the "L" piece arms a bit to get them to line up with the funnel at the same time the gate's are closed.
Step 5: Attach the Magnets to Keep the Gate Closed
I salvaged some super-strong magnets from some old computer hard drives. You can also get these from on-line "science and surplus" stores. If you can find a computer hard drive, these magnets can be tricky to get off of the metal parts they're fused to. There is a good instructable for salvaging these magnets, just search hard drive magnets. I hadn't seen the instructable, but I came up with a way that worked--most of the time, I did have some failures.
I just grabbed the metal part that the magnet is fused to (loosely) in a vice, with the magnet resting against top of the jaw of the vice, and the metal part sticking up. Whacking the metal part downward will, hopefully, shear the magnet away from the plate. Otherwise, use the method described in another instructable, where they bend the metal plate till the magnet breaks loose, much less drama.
These magnets are no joke, they're so powerful that they will hurt your fingers if you let them smack together. They are also so powerful that when they inevitably get stuck together, you can damage them just by trying to pry them apart. Putting the narrow edge of one magnet against a sharp corner of a table, or something, and pushing the other magnet in the opposite direction, it is possible to slide them apart. Be careful with these, they are not for kids to play with.
Attaching the magnets to the gates is straight forward. Just stick one to the metal edge of the gate and wrap electrician's tape around it till it's thoroughly attached, then align the other magnet on the opposite gate so it matches forces with the first magnet, tape it in place and the gates should come together smartly. If the gates are too close together the magnets will hit and the tape will wear. You may need to adjust your gate posts if they're too close together. These closers took our dog about two tries to figure out. So far the hens just think they are sorcery.
This mechanism is just a variant of the type of gate closers farmers have been using since they first started making gates. These two gates needed some help to stay closed, and the magnets really make them stay secure. If you have a gate situation, you can make adjustments; it's much easier just getting one gate to close in one direction, but even if you have a more complicated situation, there is always a way to make this style of closer work.