D & L Thomas Equipment Corporation

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A simple optical device - to measure angle and direction of blast holes - for better and safer blast results! Part # SLGN-20 (includes Stemalign optical device, flashlight and wood case)

USE OF THE STEMALIGN

All measurements of the Stemalign are taken from a flashlight lowered into the borehole on a string or a tape measure. A baseline is set up using a string drawn tightly across the rims of the boreholes in a row. This would normally be parallel to the free face.

TO MEASURE THE BOREHOLE INCLINATION:
(From the vertical)

1. Hold the Stemalign vertically over the borehole with the level on the left side.
2. Center the bubble and move so that you can see the light on the vertical cross-hair.
3. Where the light intersects the vertical cross-hair is the inclination of the borehole. (The angle of the borehole from the vertical.)

See the diagram below.

TO MEASURE THE BOREHOLE DIRECTION:

1. Direction readings are taken relative to a baseline on the surface. This baseline would normally be a line between boreholes parallel to the free face. The direction readings are the angle (right or left) from the baseline.
2. Holding the Stemalign telescope fashion, sight down the borehole directly at the flashlight.
3. Rotate the Stemalign until the bubble level is at the bottom of the instrument and the bubble centered.
4. Read the direction of the borehole by noting the image of the baseline in one of the sectors which are marked 0 to 30 degrees to the right or left.

NOTE: The actual direction of the borehole is in line with the vertical cross-hair of the instrument. The image of the baseline shows the angle of deviation of the hole. If the borehole was drilled correctly, the vertical cross-hair would be perpendicular to the baseline.

If the collaring error is greater than a foot, a short straight edge should be placed parallel to the baseline across the top of the hole so that the direction can be read.

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