diagonal member of a fence gate

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Forum topic by bigmike2258 posted 05-04-2008 05:52 AM 14627 views 1 time favorited 18 replies Add to Favorites Watch
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11 posts in 3729 days

05-04-2008 05:52 AM

hi everyone

I am building a fence gate with a 2×4 rectangular frame….....inside dimensions are 29 hi x 46 wide….........i am trying to figure out the best way to make the diagonal brace, but i can’t come up with the answer… there an easy way to calculate that…’s not as easy as calculating the hupotenuse…....that didn’t work.
help would be greatly appreciated
P.S.——- i am trying to make 2 parallel cuts on the 2×4 29 inches apart…..but what is the angle?

-- bigmike lover in Ohio

18 replies so far

View Karson's profile


35111 posts in 4364 days

#1 posted 05-04-2008 06:00 AM


I’d draw the gate on a piece of plywood and get your angle cuts for it. It’s more accurate than doing it by math, if you are not into that type of calculations.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia †

View bhack's profile


349 posts in 3684 days

#2 posted 05-04-2008 04:26 PM

I agree with Karson. That pencil get dull sometimes.

-- Bill - If I knew GRANDKIDS were so much fun I would have had them first.

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John Gray

2370 posts in 3849 days

#3 posted 05-04-2008 04:34 PM

Make the frame and lay it on the 2×4 and mark your angles.

-- Only the Shadow knows....................

View Peter Oxley's profile

Peter Oxley

1426 posts in 3838 days

#4 posted 05-04-2008 04:41 PM

Build the rectangle frame, lay it on your workbench, and make sure it’s square. Then lay the diagonal member (rough cut long) on the frame and take your marks right off the frame.

You probably already know this, but as a reminder for others who might read this thread: the diagonal is supposed to run from the bottom on the hinge side to the top on the latch side of the gate. This way the weight of the gate pushes down on the brace. If you run the diagonal the other way, the weight pulls down on the hardware, which is likely to cause loosening.

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View dalec's profile


612 posts in 3852 days

#5 posted 05-04-2008 07:54 PM


I hadn’t thought about the layout of the diagonal relative to the hardware. It makes sense. Thanks for the information. Never know when this info will come in handy.


View brunob's profile


2277 posts in 4133 days

#6 posted 05-04-2008 07:59 PM

I agree. I’d build the frame then mark the diagonal.

-- Bruce from Central New, if you'll pardon me, I have some sawdust to make.

View bigmike2258's profile


11 posts in 3729 days

#7 posted 05-05-2008 03:17 AM

thank you all for the help…........i built the frame and then laid a long 2×4 across..marked it….cut it…....and it fit quite nicely….......i am not exactly sure what the brace is supposed to do….......i think it redudes racking and keeps the two rales parallel… is only fastened to the top and bottom rails…..again, thank you all for the help.

-- bigmike lover in Ohio

View Catspaw's profile


236 posts in 3779 days

#8 posted 05-05-2008 03:27 AM

assuming all joints and fasteners are tight and stay tight, the forces on the hinges are the same either way you put the diagonal. I know nobody will believe it, but it’s true.

I’m thinking the placement as stated above probably compensates for the fact that things probably won’t stay perfectly tight and it works alittle better that way.

either way, scribe.

-- arborial reconfiguration specialist

View Peter Oxley's profile

Peter Oxley

1426 posts in 3838 days

#9 posted 05-05-2008 05:22 AM

Catspaw – you are exactly right. If the joints and fasteners did not fail, the orientation of the brace wouldn’t matter … in fact, you probably wouldn’t even need a brace. But since wood changes shape and nails and screws may back out and joints can fail, the method I mentioned above helps the gate maintain it’s shape when it’s no longer new.

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View grumpycarp's profile


257 posts in 3709 days

#10 posted 05-05-2008 12:53 PM

Two issues here. To find for the length of the diagonal (hypotenuse) the Pythagorean theorem is in play. Side A squared times side B squared = side C squared or in your case 54.3783 or there abouts.

If your #s don’t work it is because your pulling them from the wrong place. Outside rather than the inside for instance. I don’t know much but on the following I will be firm, the Math is never wrong. The work that has gone before is.

View Peter Oxley's profile

Peter Oxley

1426 posts in 3838 days

#11 posted 05-05-2008 03:28 PM

I agree the math is never wrong, and the calculations would be pretty simple if you were trying to find length “A” and angle “B” ...
Gate Brace Measure

... however, you are trying to find length “C” and angle “D”, which are difficult to calculate until you know length “E”, which is difficult to calculate unless you know angle “D” ...
Gate Brace Measure

... there’s a reason why woodworkers have relied on story sticks for so long!

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View grumpycarp's profile


257 posts in 3709 days

#12 posted 05-05-2008 04:06 PM

If you think about it you will see that all the answers are already in your diagram. Just keep reducing, or enlarging the triangles. Find for the triangle. If you have the length “a” and angle “d” then its a trig function.

Also if you actually have the angle “d” then your cut is the reciprocal of “d” (I think thats the term) If “d” is 35 deg then the cut would be 65 deg (to net 90) the thing that hangs people up is it is measured “heel to toe” or “long to short” points.

I use story sticks all the time to transfer layout, etc. But, it is often easier to do the math when dealing with large systems, like roofs, where the mass of objects doesn’t really allow for the “Cut on er till it fits” method. A 20 ft. 4×14 LVL rafter is a bugger to put up and take down, takes a lot of time, costs big bucks and annoys the crane operator. So the math. And it’s just as easy to do it with the small, plus it gives an extra goof proofing layer to the exercise. I like to have my pinch sticks match what my numbers tell me. Then I know I’m still square as well.

View ronstar's profile


442 posts in 3674 days

#13 posted 05-05-2008 07:51 PM

You’re close. The hypotenuse angle is 32.23 degrees for 29” height 46” width. This is the inverse tangent of 29/46. The hypotenuse distance is 54.38 inches. but you need to calculate the additional angle for the width of the 2×4 (3.5”). So for an additional 3.5” over the 54.38” hypotenuse, take the inverse sine of 3.5 divided by the 54.38” hypotenuse. This equals 3.69 degrees. So the total angle is 32.23 + 3.69 = 35.92 degrees

-- Ron, Northern Illinois

View dirtclod's profile


169 posts in 3824 days

#14 posted 05-05-2008 09:32 PM

I agree with everything Peter O said. I’ve built a number of gates for cattle. They’re much more durable than what you can buy at a local farm center and can hold even determined animals in tight quarters. Just watch what happens even to a new/heavy gate that a 1200 lb cow tries to go over on the latch side when the diagnal brace is running down from the hinge. It’s not only the hardware – it’s the compounding of hardware. The brace compresses against the ends and picks up the hardware that hold the ends on. Therefore the brace, its hardware, and the hardware holding the ends on all work in unison. An analogy is to brace a free-standing wall with spring boards that are nailed at both ends on only one side. It holds well as long as the wind is blowing the wall toward the brace, but fails miserably when the wind blows the wall in the opposite direction.

-- Wonderful new things are coming! - God

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Peter Oxley

1426 posts in 3838 days

#15 posted 05-06-2008 05:44 AM

Grumpy – well, that was kind of my point – the original poster didn’t know angle “d”, and since knowing where the heel of the brace is depends on knowing “d” ... well it gets complicated. The math is certainly do-able (as ronstar showed us), and necessary in your example of large, heavy construction items, but for a gate member it seems a little much. I offer as evidence the fact that our guy already had his brace cut and installed while we were still talking about how to figure it!

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