Tuesday, December 23, 2014

Uphill Gate Hinges

I used SketchUp to design some up-hill gate hinges for the rental property, and to work out the intial amount of metal I need to buy for the frame.  My SketchUp File is here, if anyone wants to see it, and details are below.

We built a fence at the rental property, but I need to make a gate.  I was going to make a gate that went sideways on rollers, but we have limitations.  1) It has to be as thin as possible, because the fence is already at the edge of the parking area.  2) Our poles are only 6 feet out of the ground, but the fence is 8 feet high, so the rollers can't be higher than 5 1/2 feet or so.

I was going to make a short gate, going from probably 1 foot off the ground to 5 feet, 6 inches up and use boat trailer rollers for the rollers.  The gate frame would be made out of the fence poles, which would make it strong enough to support the wood and let me use the top and bottom edge as rails.

My wife didn't like the idea of a short gate, and making it taller would require putting the guide rails on the outside of the gate (in order to prevent having a guide system on the other side blocking the parking) and she thought that would be ugly.  So I am making a swinging gate.

It's 18 feet long, and has to swing uphill.  I found these hinges online.  They are really expensive, but just looking at the picture didn't really tell me how they work.  But, the site has a link to the installation instructions.  All they are is regular hinges with really long leaves.  (Although they are heavier duty than regular, probably.)  After seeing the instructions, I went into SketchUp and started doing some tinkering.  It's the first time I've done serious engineering in SketchUp, but it worked out.  I'm attaching my gate file.  Basically, you end up with the hinge pivot line tilted so that it is 90 degrees to the slope, but the gate is 90 degrees to gravity.  So the gate ends up tilted to the slope, and you can see that when you open it.  Another way to look at it is that you are making the pivot radius on the bottom of the gate larger than the top.  So the bottom travels further from the pole and tilts the gate up.

My initial design, before I actually measured the slope and such, had a 4ft rise over 25 feet, and the hinges still work.  But the tilt meant that the bottom of the gate stuck out quite a ways into the driveway.  So I designed a bent version that would offset the pivot point away from the driveway.  I ended up not needing to do that, though, as the realistic version shows that the "kick-out" is less than the pole is offset from the driveway, so it won't actually block anything.

The included file has both designs.  Both gates in the file have an attached arrow pointing at the pivot axis, and rotated to align with the rotation plane, to make swinging the gates for testing easier.  You'll notice that the pole is not plumb in the realistic version.  When I measured the opening, it was smaller 6 feet up than at the ground.  I didn't actually measure plumb-ness, though.  I imagine that the offset is a combination of the poles on both sides being slightly off, and the face fence being slightly off as well.  More likely, it is the fence face, since we didn't measure those for plumb when we installed them, but we did try to plumb the poles when we set them.  But I designed for worst-case scenario just to make sure that the hinges still worked, and they do.

The reason for two wheels is because the gate is so far from the pole that it may need support at the hinge side, especially with the bent hinges, since I will probably just weld extensions to cheap standard hinges from lowe's.  Plus, even if the hinges were strong enough to hold the gate on their own, I know the poles aren't.

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