Last Updated on February 25, 2022
Grading (to grade) is the act of bringing land to a certain elevation or slope. This process is necessary in almost all construction, roadbuilding, and landscaping applications. The activity is a work of engineering, serving as the base for buildings and infrastructure, and carries out other functions. One example is drainage, which allows for movement between different elevations. There are numerous ways to grade land, but one machine is designed for that sole purpose – the motor grader – making it one of the best equipment for grading.
The earliest graders (mid 19th Century) operated similar to today’s graders, but without any motor inside. They were two-axle machines with a seat behind the rear axle and no cab. The blade was situated between the two axles. These devices were pulled by horses, so grading took at least two people. One person operated the grader blades and other controlled the horses.
Eventually steam-powered tractors replaced the horses and diesel-powered tractors replaced steam-powered ones. All the while, the operation still relied on two people.
In 1919, Russel Grader Manufacturing Company introduced a motorized grader using the body of a modified Allis Chalmers diesel tractor. Other manufacturers began to follow suit, and soon many manufacturers had – as they called them – self-propelled graders.
Motor graders offer the best performance
Today, the motor grader is a long, narrow, wheeled machine. Its cab is positioned directly in front of its front rear axle (there are two rear axles). And directly behind the cab is the engine. There is a lot of open space in front of the cab. The grader blade is attached to one long, narrow beam that extends to the front axle with a turntable mounted underneath.
The amount of empty space directly in front of the cab allows the operator a full view of the grader blade. The grader blade can be lifted, tilted, and swiveled about 180 degrees. With these three motions, the operator contours the land by pushing dirt with the grader blade. The lift determines how much earth is being moved and therefore its elevation. The tilt determines the slope (or grade) of the earth being contoured. Then the swivel allows the dirt (or whatever material is being graded) to slide off the grader blade to one side of the machine. This device doesn’t have much pushing power like a dozer, so allowing dirt to slide off the blade is essential.
Motor Grader Market
Today, there are only a few manufacturers of motor graders – Caterpillar, Champion, John Deere, and Volvo Construction Equipment. The use of motor graders has fallen out of favor across most of North America. Though, the motor grader is still a popular choice in the state of California and the Canadian province of Ontario, which have really large markets.
There are two main reasons the motor grader isn’t used as often as before. The first reason is that now there are numerous other machines that can both grade and perform other tasks. The motor grader is often the best tool for the job, but its lack of diversity (and high capital costs) means equipment buyers and especially, departments of transportation, would rather spend their money on machines that can accomplish more tasks.
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Dozers add pushing power
Dozers are another type of machine used for grading. The motor grader has a grader blade located in between the front and rear axles. The dozer has a dozer blade located at the front of the machine.
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A dozer blade and grader blade appear similar, but there are some distinguishing features.
Dozer Blade vs Grader Blade
The grader blade is composed of three angles, the cut angle, the slide angle and the too-much material angle. The part of the blade that cuts into the earth is about 70 degrees perpendicular to the ground. The slide angle is 90 degrees perpendicular to the ground. Once material comes up the cut angle, it slides across the blade either to the right or left hand side of the machine. This depends on which way the blade is swiveled.
The top of the blade is the reverse angle to the cut angle. It is designed to dump material back in front of the blade. You should never cut deep enough that material goes over the halfway mark on a motor grader blade.
A dozer blade on the other hand is more rounded. This allows material to easily push up the blade while being cut. As material goes up the blade, it reaches the top where the curve pushes the material forward again. Then gravity drops it back in front of the blade. With a dozer blade, the material will reach near the top of the blade. That way you can make much deeper cuts with a dozer than with a motor grader.
The dozer blade can also lift, tilt, and swivel. However, the points to which the blade is fastened to the machine are near the center and edges. This helps with distributing pushing power. On a motor grader, the blade is fastened to the machine only at the center. This means it loses a lot of pushing power toward the sides. Also, the motor grader blade hangs down from a several inch diameter column. Conversely, a dozer blade is fastened to the front of the machine where you have the entire force of the machine behind the blade.
Scrapers move a lot of earth
There is another machine that is used for grading and little else – and that is the scraper.
A scraper is a real earthmoving machine, and grading is an earthmoving application.
Both motor graders and scrapers push dirt to the side of the machine, thereby creating a windrow of dirt. The scraper has a large bowl for collecting the dirt. This allows you to take dirt from where you just graded and move it away from the working area, instead of just few feet over.
Scrapers, like motor graders, started out as horse-drawn implements. Now, they can be motorized, and have grown in size. The largest scraper today has a carrying capacity of 63 cubic yards.
Most scrapers are pulled by a tractor or a converted articulated dump truck.
Scrapers in operation
With scrapers, a blade extends from the front of the bowl at an appropriate cutting angle. When the machine moves forward, the dirt moves up the blade and into the bowl. The scraper is also the only machine where the cutting action takes place behind the operator. Sometimes another bowl is trained onto the first one. A conveyor moves dirt from the first to the second, so you can move even more earth in one pass.
When an operator wants to deject the dirt from inside the bowls, they can do so from inside the cab. They can use the controls to open up the bottom of the bowl. The controls allow for metering of the material. This allows you two options: releasing a lot quickly or letting the dirt “drip” out. That means the scraper contours the land, bringing it to the desired grade both when removeing dirt and when dumping.
The operator doesn’t have a view of the blade, so scrapers aren’t great for precise grading. They perform mass excavating and general grading before the motor grader or some other machine adds the precision.
Excavators are versatile solutions
Excavators are very versatile, with more than one hundred different attachments. Each one allows the machine to perform a different task.
All excavators can be equipped with a dozer/grader blade at the end of the excavator’s arm. Some can be equipped with a dozer/grader blade at the front of the cab in between the tracks. The cab-mounted blade helps operators smooth out a surface after it has filled in a hole (dug by the excavator’s bucket). The arm-mounted grader blade can perform more precise grading. That is especially true when the excavator comes equipped with a 2D or 3D grading technology.
Loaders can be compact motor graders
Skid steer loaders (SSLs) and compact track loaders (CTLs) are small, fast and versatile machines. They resemble a tractor with loader arms that extend from the rear of the machine (as opposed to the front of the machine) and an enclosed and front-mounted cab. SSLs come equipped with construction tires and CTLs come equipped with tracks.
Again, there are dozens of attachments for SSLs and CTLs, including grader blades.
Unlike the excavator dozer/grader blade, the grader blade for SSLs and CTLs really does mimic the grader setup. The machines have the blade attached to a column hanging from a small frame, which has an axle with two wheels at the front. This becomes a single attachment that is connected to the front of the cab of the SSL or CTL.
When 2D or 3D GPS is added to the machines, they become better capable of precise grading.
2D and 3D GPS improve accuracy and speed
Grading isn’t an approximate science. When determining elevations and grades, it’s very important to have tools capable of measuring elevations and distances across uneven surfaces.
The most common way to measure grades and elevation throughout most of construction’s history is to use ground stakes, measuring tapes, levels, and string.
A ground stake is a short and narrow piece of wood sharpened on one side for easier ground penetration. Crews stake the grounds before grading. They measure the distance from the ground stake to the desired position of the next and then thrust one inside the ground. They repeat that process until the entire land is staked.
Then crews paint a line on one stake to mark the desired elevation. Next, they tie string to the stake at the paint line. Then they run the string to the next stake and pull it tight. They use the level to determine whether the string is running parallel between the two spikes. After determining the string is the same elevation on both ends, they paint the spike to mark the proper elevation and then tie the string to that spike. They repeat that process until all spikes are marked and tied.
If one spike is removed or the string is cut, the process is repeated to the damaged areas.
This has been the dominant process for grading until the past decade. Today, contractors are more often choosing 2D or 3D GPS systems for millimeter accuracy in grading operations.
GPS stands for global positioning system. GPS technology uses dozens of satellites to pinpoint location. The system can be added to earthmoving equipment and landscaping equipment in order to increase accuracy in grading applications.
3D GPS locates an object on an X, Y, and Z axis. Y represents elevation, while the other two represent longitude and latitude. 2D GPS locates an object on only the X and Z axes, so you know the hole that you’re digging is in the right place, but it’s up to you to make sure you are digging at the correct depth. 3D GPS informs the operator of how deep to dig.
GPS then and now
Prior to using GPS technology, achieving the desired grade consistently was difficult for operators. This is why after the excavator completed its work, crews would use shovels, rakes and lumber to make the earth the desired elevation and grade. The general practice on construction sites was to err on the side of removing too much dirt, because it was always easier to add a layer of dirt than to remove a layer of dirt. However, this increases the amount of time and labor required to complete grading projects.
GPS systems allow for more accurate and faster grading. And, when combined with machine control, GPS removes operator error. The GPS system warns an operator when the machine’s bucket or blade has reached the point of desired elevation. The operator will still have to control the machine in such a way that it doesn’t dig beyond the desired elevation. When machines are equipped with GPS and machine control, the machine takes over parts of the machine’s operation. It physically won’t allow the machine’s blade or bucket to move below a certain elevation or past a particular longitude or latitude, so you know your elevations and grades will be perfect.
Grading made easy
Grading the earth has never been easier in history. Technology eliminates human error and replaces would-be mistakes with pinpoint accuracy. There are always construction projects to be done. The motor grader, one of the best equipment for grading, is a great way to get started. If you’re looking to get a headstart on reshaping the land for your project, begin your search here for effective and affordable heavy equipment.