Simple question on Z-brace for gate


Hello,
I'm building two exterior redwood gates, 34.5" x 62", using a frame of 2x4s and a z-brace. I understand that the z-brace should go from the bottom hinge side, so that z-brace is in compression. Does it matter how the diagonal of the frame is aligned with the edge of the z-brace? I can think of five different arrangements, from attaching the brace to both rails and both stiles, to attaching it to only to the rails, etc.
Is it purely a matter of aesthetics, or are some arrangements structurally superior? Intuitively, I would think that attaching the brace to the upper rail and the hinge-side stile would be strongest, but perhaps it would look odd being off center.
Thanks, Wayne
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On Sun, 04 Sep 2005 16:12:30 -0500, Wayne Whitney

In most stile and rail situations the rails go between the stiles, but on a gate the stiles should go between the rails.
Many folks don't do it this way because it doesn't look like what they're used to, but when you think of the applied stresses, it starts to make more sense.
The diagonal that forms the Z should be double mitered so that the point fits into the intersection of the stiles and rails. This allows you to pin the brace from both directions, and adds rigidity to the frame.
If you really want to get good service life out of the gate, let corner irons into the interior of the stile and rail intersection. This gives you the opportunity to get a good face grain connection for your screws, rather than going through the face and into end grain.
Your diagonal will hide these and, in conjunction with a dab of exterior construction adhesive between it and each of the pickets, give you a strong and long lasting job.
It is worth your time to seal the end grain of all members before assembling your gate. Even redwood will open and close on the end grain and the mechanical effect will degrade the joints.
Tom Watson - WoodDorker tjwatson1ATcomcastDOTnet (email) http://home.comcast.net/~tjwatson1/ (website)
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Is it that the applied stresses are different with a gate and with, say a cabinet door? Or is it that for a small door, the stresses are small and so the difference doesn't matter, and "rails between stiles" is conventional or aesthetically more pleasing? I noticed that all my 1908 house's interior 5 panel doors have rails between stiles.
I guess I don't properly understand the applied stresses. I always thought that "rails between stiles" was because gravity would have to pull the stile farther down to disconnect it from the rail, assuming the tenons are shorter than the rails are wide.
Cheers, Wayne
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On Sun, 04 Sep 2005 16:55:45 -0500, Wayne Whitney

Cabinet doors and residential doors use joinery that relies on face grain to face grain contact that is pinned by glue.
A typical gate relies on mechanical fasteners that join face grain to edge grain, and the failure profile is different.
You've already cottoned onto the idea of the Z brace going from the bottom hinge side to the upper latch side, and there's a good reason for that.
The stresses are greatest at that high inside point and the frame wants to sag away from that.
If you live near farm country, drive around and try to find a "Can't Sag Gate", which could be as much as twelve feet wide, although only three feet high.
A gate wants to fall apart from side to side. Running your screws from the top of the rail into the stile gives you a better shot at resisting the implacable desire of gravity, aided by by long term impact forces, to tear your gate apart.
My previous description involved techniques that would provide face grain to face grain fastening, which is way more resistant to withdrawal than face grainto edge grain joining via mechanical fasteners.
Now, all that being said, you could choose to use mortise and tenon joinery for your gate, which would give you the face to face contact that was optimal. Then the reason to run the stiles between the rails would be that you don't want edge grain to face up towards the weather.
Tom Watson - WoodDorker tjwatson1ATcomcastDOTnet (email) http://home.comcast.net/~tjwatson1/ (website)
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Thanks for your long insightful comments. This is the one thing I don't understand the reason for, though. I assume you mean side-to-side in the plane of the gate. My naive reaction is that gravity pulls down. Where does side-to-side come from? Considering the gravitational torque about the bottom hinge?
Thanks again, Wayne
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Another question: are screws stronger in resisting pullout or in shear?
Thanks, Wayne
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Wayne Whitney (in snipped-for-privacy@localhost.localdomain) said:
| || In most stile and rail situations the rails go between the stiles, || but on a gate the stiles should go between the rails. | | Another question: are screws stronger in resisting pullout or in | shear?
On pullout, it's the small amount of wood around the threads that tears. In shear the wood either has to split or allow a large chunk to be torn out - or the screw has to break (normally unlikely).
The answer may depend on the wood and the direction of grain relative to the shearing forces. If you want a best try at one answer fits all, I'd say that screws are stronger in resisting shear.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto/solar.html
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[...]

You might be confused now because you often see the advice never to put shaer stresses on screws, but that comes from mechanical engineering in metal parts, where you would anyway not rely on a screw to fix a position but would rather use a pin.
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto: snipped-for-privacy@physik.uni-bonn.de Phone: +49 228 73 2447 FAX ... 7869
  Click to see the full signature.
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May I offer the suggestion of a Gate Kit. I have built my last z braced gate as all have eventually sagged. As the wood dries out and weathers it tends to shrink. The gate kits let you build your gate frame out of 2x4's for framing but also include hinges and steel reinforcement in all 4 corners to prevent sagging. About $35 Home Depot.
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