Assembly: parts list, order and fit
Assembly is joining finished parts to make a product. A good assembly follows four rules:
- Check the parts list. Count and inspect every part before you begin.
- Plan the order. Some parts hide others, so the order matters. Write the steps down, like a recipe.
- Check the fit before fixing. A part should go in with a small, even gap. If it is too tight, file or reshape it. If it is loose, add a washer or remake it.
- Fix with the right fastener. Use screws (can be undone), glue or solder (permanent) as the design says. Do not over-tighten.
Work on a clean bench and keep small parts in a tray.
Testing the assembled product
After assembly, test the whole product the way a user would use it. Compare what happens with what the design said should happen. If it matches, it passes. If not, you have found a fault.
A test only says that something is wrong. It does not say where. For that you need debugging.
Debugging: find and fix the fault
Debugging means finding the cause of a fault and removing it. Follow these steps:
- Look for easy faults: loose wire, flat battery, switch off, part the wrong way round.
- Split the system in the middle and test there with a meter or a probe.
- If the signal is present, the fault is after that point; if not, it is before. Keep the faulty half and split again.
- Fix the one fault you found, then test again. Change one thing at a time, or you will not know what worked.
This is the half-split method. With 6 parts you need about 3 tests; with 100 parts, only about 7.
Try it
Make a simple circuit with a battery, a switch and a bulb, and ask a friend to secretly loosen one wire. Find the fault using the half-split method, and count how many tests you needed. Then use the probe slider in the last 3D step.
Key formulas and definitions
- Assemble: check list → plan order → check fit → fix
- Debug: look → split in the middle → keep the faulty half → fix → test again
- Tests needed with the half-split method ≈ log₂(number of parts). 8 parts → 3 tests, 16 → 4
- Change one thing at a time
Worked examples
1. A circuit has 8 parts in a line and the lamp is off. How many tests might the half-split method need at most?
Each test halves the search: 8 → 4 → 2 → 1. That is 3 tests.
2. You test the middle of a 6-part chain and find no signal. Where is the fault?
Before the middle point, in the first half. Split that half in the middle next.
3. A shelf bracket will not fit its slot because it is 1 mm too wide. What should you do?
Do not hammer it. File the bracket a little, check the fit again, and repeat until it slides in with a small, even gap.
Common mistakes
- Fixing parts for good before checking the fit.
- Testing every part from the start instead of splitting in the middle.
- Changing three things at once, so you cannot tell which one fixed the fault.
- Forgetting to test again after the repair.