Ditch Witch OnGrade - Manual (Page 39)

Grade Boring Concepts - 38
OnGrade Operator’s Manual
Theory of Operation
CMW
Theory of Operation
Job Plans
For most jobs, engineers will lay out the line and will establish the manhole locations, the depth the sewer
line needs to run, and the recommended grade for the installation. On jobs where a connection is being
made to an existing service, the position of the existing sewer line will dictate the depth.
Engineers commonly base the plans for a sewer line on the invert, or flowline, of the installation. This is the
elevation of the lower surface of the internal diameter of the installed pipeline. Drillers depths are from the
center of the beacon which equates to the center of the installed pipe. If the engineer has specified
elevations based on the invert, the driller must subtract half of the internal diameter of the pipe to be
installed from the values given by the engineer to obtain the correct centerline depth for the housing.
Laser Plane
The laser emits a 360° plane. This allows for offset
location of the laser plane by the grade pole.
The laser plane is also directional meaning that it
will slope up from horizontal in one direction and
down from horizontal in the other direction.
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