| 摘要 |
<p>A sight tube is mounted perpendicular to the floor of a portable drilling rig used for drilling earth boreholes and is parallel to and offset from the drilling axis by a predetermined amount. A stake is driven into the earth's surface at the predetermined drill point. A sight board having a pivot hole bored through one of its interior portions is pivoted on the stake. A line having a first end anchored near the location of the drilling rig has its other end attached to a first end of the sight board. A sight mark is placed on the second end of the board which is offset from the pivot hole by the same amount that the sight tube is offset from the drilling axis. The driller or rig driver lines the rig up above the line leading to the board by looking through the sight tube and making direction corrections while still a considerable distance from the stake. Thus, the drilling rig is traveling in a substantially straight path as the stake is reached. The rig is driven straight past the stake for the same distance that the sight mark is in front of the drilling axis. The drilling axis is thereby stopped pointing directly toward the stake. Means are provided on the drilling rig to level the floor of the rig with respect to true horizontal to thus enable a true vertical hole to be drilled. Such means include leveling legs which are perpendicular to the rig floor. As the rig floor is lifted, the entire floor swings forward and the sight tube continues to substantially point toward the stake.</p> |
