Before you can mill or pave with a 3D system, you need to properly set the system up. "The first few times out, until the learning curve is behind you, there is no significant time advantage other than the cost advantage realized by not expending the labor to set the stringline," says Kevin Kline, vice president of engineering/research and development, GOMACO. "Once the learning curve is behind you, I do not believe it takes any more or less field time to set a paver on stringline compared to setting it to run on 3D."
However, it can take more back office preparation. "There can be significantly more time spent in the engineering office getting ready to perform the construction in the first place by preparing 3D design files and 3D machine control files before even moving to the field."
Fritz Matthias, Wirtgen, adds, "The setup time for the system itself is very minimal. It requires some initial preparation of the machine itself, which is usually done within three hours, including the fine tuning of hydraulics and other calibration processes. Once in the field, it requires probably 15 minutes setup time for total stations or even less when GPS is being utilized."
"Both the conventional stringline and 3D system require preparation time in the office," says Matthias. "The design engineers have to work out the final layout of the project, do some checking and send the data out to the field. There is not much difference between data for setting out stringlines or storing it in a machine computer."
"You have to understand the machine," notes Jim Cleary, Cleary Machinery. "A paving machine requires travel time for a change to happen. The screed has to float up or float down to get to grade. You may not be on grade when you step behind the screed, but you are trying to get there. It is in transition. So you have to be patient with the paver. You don't want to turn the dial too much trying to chase the grade."
According to Cleary, a milling machine is "a different beast." "It is a more instant result. However, the milling machine is still tricky because the teeth wear out," he notes. "When you are doing a GPS application with a milling machine, the teeth start to wear and the drum gets smaller. If you have a guy walking behind the machine with a GPS rover pole and he is taking grades within a hundredth, you can see it."
The hydraulics on the milling machine always try to achieve grade. "The drum is going to go up and down trying to find grade," says Cleary. "Don't dial the machine up or down trying to hold it because you are in transition. Let the machine do its job. You are close enough. That has been one of the problems. You need dealers who are experienced enough with machinery, not necessarily GPS. You need experience with machines to keep them on grade."
He adds, "If you have the model and your system set up right, I don't care if it is a milling or paving machine, you are going to be able to mill or pave within .25 in. of the electronic design 70% to 80% of the time."