February 12, 2016
Understanding Cross Slope
By Mark Johnson, John Deere Motor Grader Sales Consultant
The ability to hold and maintain an accurate cross slope is one of the most difficult skills an operator must acquire. It may take years to master, if mastered at all. As a motor grader is used to build a project, the operator is always trying to recognize and hold grade in two different axes: the grade in front as well as longitudinally. When trying to maintain this longitudinal grade, the operator will often follow grade stakes, a curb line, or other grade references. Following these reference points, usually with the "toe" or leading edge of the moldboard, will determine the height of the material on the job, or "elevation." While the operator establishes the correct elevation with the toe, he also has to feel and hold a lateral slope, or "cross slope," with the heel of the moldboard.
For construction applications, the use of grade stakes makes maintaining cross slope easier. But as job specifications get tighter, more grade stakes are needed for increased accuracy. The cost of engineering a project and the placement of stakes can be 20% or more of the total cost of the job.
Operators for municipalities have the same issues, but for different reasons. They are still required to identify and maintain slope on roads, but must do this for 8 to 10 hours a day, usually without referring to grade stakes at all. It is very difficult — some would say next to impossible — to hold the high level of concentration necessary to maintain a consistent slope for that extended period of time.
Cross-Slope Systems: A Better Way
Using a cross-slope system is a benefit to all operators, regardless of their skill level or application. It helps a less-experienced operator produce a finished product that meets job specifications, giving the job foreman flexibility in personnel assignments. But the system is also a huge benefit to the experienced operator. For example, when building a large retail store, the job specifications could be as tight as or tighter than a highway project. In order to have that finished 150,000-square-foot building pad meet the customer's requirements, the operator may need the grade stakes as close as 25-feet apart. Using a cross-slope system could allow the grid to be extended up to 50 or even 100 feet. This is a huge cost savings for the contractor and a time saver for the operator.
For municipal operators, it is very easy after just a few hours to lose the concentration levels necessary to hold a consistent percent of slope. Operators often eventually go back to just following the current levels and swells of the existing road. If there is a flat spot in the road where the water puddles and produces a pot hole, many operators will not effectively remove the problem and just make it smoother for a few days. Using a cross-slope system to maintain roads, operators can hold that 2% or 3% grade all day long.
Cross-slope systems are available as aftermarket components from a number of machine control suppliers. They are also available from some grader manufacturers at purchase time. At John Deere, we were the first to integrate a cross-slope system into our machines. Today, cross slope is standard on all our GP-Series Graders. The GP-Series Graders are the perfect platform for cross-slope technology. All cross-slope controls, buttons, and screens are integrated into existing components. Information on how the system is being used, its performance, gain settings, and step-by-step calibration instructions are all found in the LCD color monitor.
In today's competitive market, cross-slope systems are a must-have. They can help save significant project costs, speed job completion, and improve the quality of work.