Making an A-frame
One does not need to have expensive soil surveying equipment to
locate the contour lines of the land. The Aframe is a simple and practical
instrument, which can easily be made by the farmer using locally available
materials.
Trees and a peasant
The steps in making the A-frame are as follows:
1. Secure the following materials:
· 3
wooden or bamboo poles with a 1.5 inch diameter (2 of which should be 2.1 In
long and one about 1.2 m)
· sturdy string for tying or
nail
· a rock about the size of a
fist or any similar heavy object object
2. Tie or nail the two longer poles at one end,
about 10 cm from the end. Make sure they are securely fastened. These will make
the legs of the A-frame. Make notches on the points of contact so that the poles
will not slip.
3. Spread the legs and brace with the shorter pole to make a
figure "A". Tie or nail the crossbar (about 10 cm from each end) to the middle
of the legs of the "A". The crossbar will support the legs of the frame and will
serve as guide in making the level ground position.
4. Tie one end of the string to the point where the two legs of
the A-frame are joined.
Measurements
5. Tie the other end of the string to the rock or any object for
weight. The rock should be heavy enough so that when it is suspended, it will
not sway with the wind. The rock should hang about 20 cm below the
crossbar.
Child Measuring
CALIBRATING THE A-FRAME
1. Locate a reasonably level ground and place the A-frame in an
upright position. Mark the spots where the legs (A and B) touch the ground. Then
mark the crossbar where the weighted string passes it.
Mark 1
2. Reverse the position of the Aframe's legs such that leg A is
exactly on the same spot where leg B was and vice-versa. Again, mark the
crossbar where it is crossed by the string.
Midpoint
If the two marks exactly coincide, this means that you have
found the midpoint on the crossbar and that the A-frame is standing on level
ground.
If the two marks are separate, make another mark at the midpoint
between them.
3. To check the accuracy, move one leg around until the string
passes the level point of the crossbar. Mark the point where the adjusted leg
touches the ground. Reverse the placement of the legs of the Aframe. If the
string passes the same point, the level position has been located.
4. Check calibration from time to time.
MARKING THE CONTOUR LINES
1. Cut tall grasses and remove other obstructions so that you
can move about easily. Two people will make the work much faster and easier. One
will operate the A-frame while the other marks the located contour lines.
2. Begin near the highest point. Drive the first stake at the
boundary of the area and position the left leg of the A-frame beside and just
above it.
3. Adjust the right leg such that the weighted string passes
through the midpoint of the crossbar. (This means you have found the contour.)
Mark this point by driving another stake just below the right leg of the
A-frame.
4. Move the A-frame to the right by placing the left leg on the
spot where the right leg previously was. Adjust the other leg again until the
string passes through the midpoint mark. Again, mark this with a stake. Follow
this procedure until you reach the other side of the field
5. Repeat steps 24 until you reach the bottom of the hill. The
vertical distance between contour lines should be 1.5 m (the actual distance
varies with the slope of the hill), which can easily be determined as shown in
the figure on this page
Height
6. After the contour lines have been determined, some of the
stakes will be astray from the general curve of the contour
line.
