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Saggy Gate Physics/geometry


JT!

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This is a picture of my gate.

post-4715-0-88402900-1340663663_thumb.pn

Red are 2x4's, yellow is 2x2's. Green are the hinges, orange arrow is the sagging.

The gate sags by a couple on inches. Basic knowledge of physics leads me to believe gravity might be the culprit. Basic knowledge of geometry tells me that the arse who built this thing only used wood vertically and horizontally, and nothing diagonally, making it like an accordion.

I was thinking about cutting up a 2x4 and putting it across diagonally. Would this actually help the sagging? If it would, should I put it A to D or B to C?

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What sort of size is the gate?

As Ali mentioned, one way puts the new support in tension and the other compression. I don't really know the tensile/compressive properties of generic wood, but I'm guessing there wouldn't be much real-world difference either way.

Do it with carbon fibre for additional points.

Do it with carbon vinyled wood for pure win.

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I think it would help and I would put it from A to D, it would put the diagonal piece in tension rather than compression.

What sort of size is the gate?

As Ali mentioned, one way puts the new support in tension and the other compression. I don't really know the tensile/compressive properties of generic wood, but I'm guessing there wouldn't be much real-world difference either way.

Do it with carbon fibre for additional points.

Do it with carbon vinyled wood for pure win.

So do I want the support in tension or compression? :geek:

B to C seems most popular and what I instinctually thought would be best, and I was going to push the gate up opposite of the way it was sagging, and then past the level point too before I screw it in, then hopefully the little sag in then has would bring it down to a level point.

B to C, however it's all dependent on the size of gate, one diagonal may not be suffecient.

It may not, but this gate is a little f**ked anyone so as long as it helps a little it'll be fine.

Could you not put one either side one A to D and the other C to B?

I could, but that would mean having to cut a slot down the middle of one of them and twice as much stuff to do.

...with a lap joint would do the job nicely!e.

I don't have the skills. :(

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B to C, I used to make windows and doors for a living for the best part of 5 years. If you go the other way your effectively pushing the far corner into the ground whereas packing it B to C would make the top corner C push down onto the bottom corner B to hold itself up

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as above, in this instance tensile bracing would not be the best option due to both the sides being equal in length, however tensile bracing could be used if the hinged beam was say 50% higher, that way you could fix the diaganol above point A and down to point C, thus eliminating the pivot points.

Edited by ezgonzo
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Put some extra screws in first. It can only sag if each wood:wood interface is allowed to pivot. If you put extra screws in (E.g. at the top / bottom of each slat, make sure there are at least 2 screws) then it can't twist. YMMV

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I think that was the logic of whoever put it up in the first place. Problem is most of the screws have worked loose because of the constant sagging and lifting.

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Problem is most of the screws have worked loose because of the constant sagging and lifting.

Then tighten them, dear boy. In other potential win solutions, attach a length of wire or rope to corner C and, by means of an over complicated series of weights and pulleys, counter balance the sag. If done right this could also probably be used to create a self-close feature. Extra win points for using titanium fixings.

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I have.

I also took off the wire that was helping only a little. The wire kept stretching though and constantly needed tightening. Will put a 2x4 up asap.

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Support in tension is usual so A to D diagonal brace.

Can also be done B to C which is usually how farm gates are done. if you can get the new brace inside the outer frame it will be in compression which is where timber is best (compression along grain) and not solely on the screw/connection pieces

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