Introduction: Cardboard Weighing Scale
For my 30th instructable, I will show you how I made this tiny weighing scale from cardboard! It is an easy and useful project, give it a try!
WARNING: I used the metric system here, so the weights I am referring to are in grams (g).
This project started here:
For christmas, my girlfriend got a box with a set of plants (medicinal and aromatic) to make her own infusions. And with this set, there is a book of recipes, explaining the benefits of each recipe, the plants to add to the infusion, and their weights. But at the moment we had no weighing scale, and I challenged myself to find a solution.
And I remembered this little letter weighing scale I got many years ago. It is very simple, with just 2 plastic parts and a clip, and it is quite useful to weigh letters.
So I decided to use a similar shape, and browsing on the internet I found the "The International Society of Antique Scale Collector" website , where you can see very nice pendulum scales. The model I made is similar to number 3, called "Letter balance by N.B. Paris, markings indicate date 1869-1875".
But the project does not stop to the reproduction of a pendulum scale. And the problem I faced was: How to calibrate it, without... another scale? Read further if you want to find out the technique I have used!
To summarize, this is what you will find here:
- Step 1: Materials and Overview
- Step 2: Feature 1, the Counterweight
- Step 3: Feature 2, the Arm (with the clamp)
- Step 4: Feature 3, Arrows
- Step 5: Feature 4, the Scale (and how to calibrate)
- Step 6: Examples
- Step 7: Conclusion
Step 1: Materials and Overview
Tools I used:
- A pair of scissors / A utility knife
- A hot glue gun
- A pen
Materials I used:
- A4 paper sheets (80 g/m2), so 1 sheet weighs 5g. This is important because I used the sheets to calibrate the scale
- Yarn, I used nylon yarn
- A clip. The one I used comes from an old crocodile clip, but you could also use a tiny clothespin
- A toothpick
First, I made patterns to cut the shapes out of the cardboard. No need to explain how to cut these patterns, just use the appropriate tool.
You can make your own patterns, but there are important characteristics to keep. In the following steps, I will explain these characteristics in more detail, but here is a summary:
- Feature 1: the counterweight, so the scale is properly balanced.
- Feature 2: the arm, to attach the object.
- Feature 3: arrows, to point to the weight values.
- Feature 4: the scale, to read the weight of the object.
Step 2: Feature 1, the Counter Weight
On this little weighing scale, a counterweight is required. The counterweight is opposed to the weight of the object and allows the scale to find a stable position.
I decided to use something common, relatively dense, and easy to use as counterweights: coins. So I designed the pattern with 6 long "fingers", 3 "fingers" on each side to hold a coin. This way I can place up to 2 coins for the counterweight.
To do this I folded 3 "fingers" on each side and glued them together with hot glue. Make sure to alternate the bending of the fingers: bend fingers 1, 3 and 5 on one side; bend fingers 2, 4 and 6 on the other side of the weighing scale.
Below you can see how the weighing scale behaves with different counterweights. The lighter the counterweight, the more sensitive the weighing scale.
Step 3: Feature 2, the Arm
The arm is important to hold the object. Without going into details, its length is directly related to the torque of the scale:
- If it is too short, the scale will not be precise and sensitive, and it will require heavier objects to move
- On the other hand, if it is too long, the scale will be very sensitive and require lighter objects
On the patterns I made, it is 35 mm long, and I chose this length empirically.
Just make a hole in the arm, and attach the clip with the yarn.
Step 4: Feature 3, Arrows
Bend the pattern with the pointing arrows, and pass a yarn loop. Make holes in the center of each arrow, another hole at the base of the arm, and pass the toothpick inside these holes to maintain everything together.
Now make sure the hole in the main part of the weighing scale (the one in the middle) is large enough so that there is as little friction as possible with the toothpick.
Step 5: Feature 4, the Scale and How to Calibrate It
The scale depends on the counterweight:
- On one side of the weighing scale, I used a counterweight with one single 2€ coin (weight=8.5g). This way I can weigh objects from 0 to 25 g, with a precision of 5 g. Perfect to weigh letters!
- On the other side of the weighing scale, I used a counterweight with one single 1 cents coin (weight=1.67g). This way I can weigh objects from 0 to 8 g, with a precision of 1 g. Perfect to weigh the plants for my infusions!
How to calibrate it with paper sheets?
The paper sheets I have used are A4 sheets (21 cm x 29.7 cm, or 1/16 m^2), and they have a grammage of 80g/m^2. So one single A4 sheet has a weight of 5 grams (80/16=5), and I have used this reference to calibrate the weighing scale as shown below.
To write the scale with a precision of 1 g, I just cut the A4 sheet in 5. There are many techniques to cut paper sheets in 5 equal pieces without any tool, click here to find out.
Step 6: Examples
As I said previously I use both sides of the weighing scale:
- The first side, with a counterweight made with 1x2€ coin, goes from 0 to 25g every 5g and is suitable for letters.
- And the second side, with a counterweight made with 1x1cent coin, goes from 0 to 8g every 1g and is suitable for weighing the plants to add to my infusions.
For the plants, it is a bit trickier than for the letters. I just placed them in a piece of paper and subtracted the value to the weight I read.
Step 7: Conclusion
To conclude, the precision of this weighing scale can be controlled with 2 features: the length of the arm, or the weight of the counterweight. While you cannot change the length of the arm once done, you can change the coins to modify the counterweight.
And as you can see, it weighs 5 g.
Second Prize in the