HOW TO BUILD A ZERO COST SENSITIVE BALANCE
When dealing with chemistry experiments or tests it is often necessary, for the preparation of a reagent, to dose small quantity of substances, generally of the order of a few milligrams up to one gram.
High precision is generally not mandatory, since a reagent works well if the concentration is within 10% of the nominal, and the balance below described, which you can build at absolutely no cost from a paper sheet and a few wood sticks, is more than adequate for this purpose.
You can draw the balance parts yourself, or better make a print of the drawings here enclosed. Start with the balance body, depicted in the image below.
On the bottom of the picture a 10 centimeters scale is shown. The balance body should be 21 centimeters long.
Cut the balance body and the balance needle. Make a small hole with a sewing needle through each dot. Bend accurately along the lines to form a triangular body with two lower lips. Glue the interior of the lips and join them together to get a body with the section shown.
Bend at 90° the pointing extremity of the paper needle and glue it to the center of the lips. Try to get the paper as straight as possible or bend slightly in the middle for some rigidity.
Shape two copper wires to get the hooks.
Build the balance holder with some wood pieces to get a fork around 15 cm high.
With the help of a sewing needle insert some cotton thread through the central holes in the balance body and position the body between the fork arms as shown.
Secure the cotton thread to the top of the wood arms by some glue.
Apply the two hooks.
Cut two balance pans, one of which is shown here below.
Make a small hole on the two extremities, bend the paper to form a shape as shown.
Keep a sewing needle through the hole while pressing the extremities after having glued them.
When dry, hang up the two pans on the hooks at the extremity of the body.
The body will generally be inclined because of some imprecision in the construction.
Cut a small strip of paper and place it on the higher arm and adjust its size and position on the arm until they are horizontal.
Glue on the wood just under the paper needle a reference mark like the one shown,
Adjust again the paper strip until the paper needle points exactly to the mark.
You have just completed the balance! You should have in front of you something like this:
To use it you need some known reference weights. Normally you can buy at modest price a set having the following composition:
one 5 mg piece
two 10 mg pieces
one 20 mg piece
one 50 mg piece
two 100 mg pieces
one 500 mg piece
You can also build a set of reasonable accuracy by cutting small pieces of paper, provided you know its weight per square meter.
I used a 80 grams per square meter paper, then one square centimeter of it weighs eight milligrams. To get the above set I prepared the following items.
5 mg : 0.5 x 1.25 cm piece
10 mg: 1 x 1.25 cm piece
20 mg: 2 x 1.25 cm piece
50 mg: 2.5 x 2.5 cm piece
100 mg: 5 x 2.5 cm piece
500 mg: 5 x 12.5 cm piece
Fold the larger pieces or compress them to make a small paper ball.
The use of a tweezer is recommended to place weight and samples on the pans.