The short version
- Flat ground: the gate is a square. Measure the width and one height.
- Single rake: the ground slopes. The top stays straight, the bottom follows the ground. Measure two heights.
- Double rake: the top and the bottom both slope. Measure four numbers from one level line.
- A datum line is a line that is perfectly flat. You measure from it. It is the trick that makes a sloping job simple.
- Measure the whole opening, not just one spot. The gate moves the whole way along.
- Try the pictures below, then open the same gate in CAD60 with one click.
What ‘rake’ means
Rake is just another word for slope. It means the ground is not flat. It goes up or down. A small slope is fine. A bigger slope needs a little planning.
A sliding gate slides sideways to open. The bottom of the gate has to stay above the ground the whole way it moves. If the ground rises part way along, the gate can catch on it. So you check the slope before you build.
A swing gate is easier here. It hangs on a hinge and swings through the air, well clear of the ground. A sliding gate has to clear the ground along its whole path, so the slope matters more.
The datum line: your flat starting line
A datum line is a line that is perfectly flat. Flat like still water. You make one with a string line and a spirit level, or with a laser. You stretch it across the opening.
Then you measure from that flat line. Down to the ground. Up to where you want the top of the gate. Every number starts from the same flat line. That is what keeps your numbers right, even when the ground is bumpy.
The dashed line in the picture is the datum. The blue shape is the gate. Below you will see this same line in all three jobs.
1. Flat ground (no rake)
This is the easy one. The ground is flat. Both sides of the gate are the same height. You only need two numbers: how wide the opening is, and how tall you want the gate. In CAD60 this is called Level mode.
Your CAD60 numbers
- Rake mode
- Level
- Width
- 4000 mm
- Height (both sides)
- 1800 mm
Drag the sliders. The gate stays a clean square. Both sides match because the ground does not move.
2. Single rake (the ground slopes one way)
Now the ground slopes one way, like a driveway running downhill. You keep the top of the gate straight and level. That looks tidy and lines up with the fence. The bottom of the gate follows the ground, so the gap under the gate stays about the same the whole way.
To measure it, stretch your level line across the opening. Measure from the ground up to that line on the left. Then on the right. Those two heights are all you need. Because the ground slopes, the two numbers come out different. In CAD60 this is Single rake.
Your CAD60 numbers
- Rake mode
- Single
- Left height
- 1800 mm
- Right height
- 1500 mm
Drag the two height sliders. The top stays flat. The bottom tilts to follow the ground.
3. Double rake (the top slopes too)
Sometimes the top needs to slope as well. Maybe the fence on each side sits at a different height and runs at its own angle. So the top of the gate follows the fence, and the bottom follows the ground. They tilt at different angles.
Now you measure four things, all from the same level line. At the left post: how far up to the top, and how far down to the bottom. Then the same two on the right. Four numbers. That is it. In CAD60 this is Double rake. The four sliders below are the four numbers you would write down on site.
Your CAD60 numbers
- Rake mode
- Double
- Up left / right
- 950 / 750 mm
- Down left / right
- 850 / 650 mm
Measure between the inside faces of the posts (the clear opening). CAD60 carries each slope out past the overlap for you.
See it in CAD60
Here is the best part. Once you have your numbers, CAD60 draws the whole gate for you. It works out the frame, the slope on each rail, and the length of every bar. The drawing below is real. It was made from the double-rake example. Spin the 3D model. Flip through the drawing. Then open the same gate and change it to suit your job.
Same numbers as the example. Change anything you like once it opens.
Two ways a gate moves, and why slope matters
There are two ways a sliding gate moves. The slope matters for both.
Track gates run on a wheel in a track set into the ground. The track has to be smooth and even. A bumpy or steep track makes the gate rock and clatter. Track gates like flat or gently sloping ground.
Cantilever gates hang from rollers fixed to a post on one side. There is no track in the ground. The gate can be almost any shape, and the rollers do not care what the ground does below. See the cantilever gate entry for how it works.
If your ground has a real slope, a cantilever gate is usually the simpler pick.
Mistakes to avoid
- Measuring in only one spot. The gate moves the whole way along. Measure across the full opening, and a few points in between, not just where the gate sits when it is shut.
- Forgetting the driveway might be redone. New paving can lift the ground by 30 to 50 mm. A small gap under the gate today can end up touching the ground later. Leave a little extra.
- Leaving the gap too small. Metal grows a tiny bit when it gets hot in the sun. A gate that just clears the ground in winter can rub in summer. Aim for about 30 to 50 mm.
- Guessing the slope. Two end points will not show a dip in the middle. Take a few points across the opening so you catch any bumps.
- Putting the gate motor on a slope. The motor needs a flat, level pad to run smoothly. The gate can slope, but pour the motor pad level.
Turn your numbers into a drawing in 60 seconds
Every sliding-gate model below handles level, single, and double rake. Pick one, type your width and your heights, and CAD60 draws the dimensioned plan, follows the slope on each rail, and lists every bar to cut.
Questions people ask
How do you measure a sliding gate on sloping ground?
Set up a level line across the opening with a string line and a spirit level, or a laser. Measure from that line. On flat ground you take the width and one height. On a slope you take the height on the left and on the right. When the top tilts too, you take four numbers: up to the top and down to the bottom on each side. Take a few points in between so you catch any dip, then type the numbers into CAD60.
What is a datum line when measuring a gate?
A datum line is a line that is perfectly flat and level. You make one with a string line and a spirit level, or with a laser, and stretch it across the gate opening. Every measurement starts from that flat line, down to the ground or up to the top of the gate. It keeps your numbers right even when the ground is bumpy.
How much slope is too much?
A small slope is easy. Think about 20 mm of drop for every 1000 mm across. Up to that, you can keep the gate square and just leave a slightly bigger gap at the low end. More slope than that, and you rake the bottom of the gate to follow the ground, or you flatten the ground first. A cantilever gate copes with slope better than a track gate.
Do I need to flatten the ground first?
Not always. A gentle slope is fine to build around. A steep slope is sometimes cheaper to flatten than to fight for the next 20 years. The tricky middle is when the slope is just enough to look wrong with a square gate. That is where a raked gate, or a bit of ground work, earns its keep.
Does a cantilever gate work on a slope?
Yes, and better than a track gate. A cantilever gate hangs from rollers on one post. There is no track in the ground to fight the slope. As long as the main rail it hangs from is straight, the bottom of the gate can follow the ground all it likes.
How big should the gap under the gate be?
Aim for about 30 to 50 mm at the closest point along the whole travel. Less than 30 mm and the gate catches on leaves and dirt. More than 80 mm and it looks gappy and a small child or pet can get under.
Can a track gate handle a slope?
Only a gentle, even one. The track has to sit smooth and follow the same slope the whole way. Bumps, dips, or a steep run make a track gate rock and clatter. If the ground really slopes, switch to a cantilever gate and stop fighting the track.
Should the bottom of the gate be straight or follow the slope?
Both work. A straight (level) bottom is the simplest to build, but the gap under the gate grows at the low end. A raked bottom follows the ground, so the gap stays even and the gate looks tidy, but it takes more work to build. Pick straight unless the gap looks wrong.
How do I measure the slope without fancy tools?
A long straight piece of timber and a spirit level will do for a short opening. Lay it down, lift one end until the bubble is centred, and measure the gap under the low end. For a long opening, hire a laser level for the day. It is the only sure way to take a few points across a wide run.
What if the ground dips in the middle?
Two end points will not catch a dip or a hump in the middle. Take a few points across the opening, not just the two ends. The lowest point along the whole travel is the one that sets your gap under the gate.
More to read
- Glossary: Rake
- Glossary: Datum line
- Glossary: Single rake
- Glossary: Double rake
- Glossary: Ground clearance
- Glossary: Clear opening
- Glossary: Overlap allowance
- Glossary: Sliding gate
- Glossary: Cantilever gate
- Glossary: Swing gate
- Glossary: V-track
- Glossary: Top roller
- Glossary: Gate motor
- Glossary: String line
- Glossary: Spirit level
- Glossary: Setout
- Guide: Which type of gate to choose
- Guide: Standard pedestrian gate sizes in Australia