Low-Cost Prototyping
Make a tool out of bottle caps, chopsticks, tape, and a few printed parts, then build it twice more, fixing what broke each time. The less a working version costs, the easier it is to sell.
Module sheet 3 of 5
- You make
- Three versions of one small tool, each fixing what failed in the one before
- You measure
- What broke, what leaked, and what each version cost in materials and time
- Bring
- Bottle caps, a plastic bottle, chopsticks, tape, rubber bands, and wire. A 3D printer helps but isn't required.
- Toward a sale
- What your last version cost to make is where the price starts in module 5.
Build it from scrap before you print it
Most first versions fail, so make them from things you would otherwise throw away. Once a scrap version works, print only the part that keeps breaking.
The lab's drip kit went through three versions this way, and every one of them is in the build log.
- Scrap first. Frames, joints, and handles from cardboard, chopsticks, and tape, so a failed version costs you nothing.
- Print what fails. When one part keeps breaking or leaking, replace just that part with a printed one.
- Test it in dirt. A tool that works on the table can still fail in wet soil or full sun.
- Count the cost. Materials and minutes for every version, written down as you go.
What to build it from
Start in the left column. Move a part to the right column only when the scrap version has shown you what it needs to do.
From the recycling bin
| Material | Becomes |
|---|---|
| Cardboard | Frames, templates, and spacing guides |
| Plastic bottles | Reservoirs and funnels |
| Chopsticks | Handles and stakes |
| Wire | Clips and hooks |
| Tape, rubber bands | Joints you can undo |
| Toothpicks | Plugs for emitter holes |
| Bottle caps | Blanks for adapters |
| Straws | Micro-tubes |
From the printer
| Printed part | Replaces |
|---|---|
| Adapters | A taped joint between a bottle and a tube |
| Valves and clamps | A knot or a pinch of tape |
| Emitters | A hole poked with a pin |
| Joints and brackets | Chopsticks held with rubber bands |
| Custom tips | Whatever shape the job turns out to need |
Tools to start from
- For seedlings
- Dibblers, soil scoops, mini rakes, pot packers, and transplant guides
- For watering
- Bottle-cap adapters, micro-emitters, flow controllers, soil anchors, and inline reservoirs
- For the garden
- Clip-on plant supports, moisture indicators, measuring tools, aeration sticks, and small planters
Six builds
Each one has a written result, so you compare versions on paper instead of from memory.
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Bottle-cap adapter
Print or carve a cap that turns a soda bottle into a drip reservoir, then hang it upside down over a sink for an hour.
Write downWhether it leaks at the threads, and how much
-
Micro-emitter lab
Try different hole sizes, angles, and shapes in a strip of tubing or a printed tip.
Write downThe flow and spray pattern of each one
-
Seedling tool from scrap
Make a seedling tool from a chopstick, a bottle cap, and one printed tip, then use it on a full tray.
Write downWhat you would change in version two
-
Soil anchor
Design a stake that holds a drip line in place, then pull it out of wet sand and out of wet clay.
Write downWhich soil held it better, and how the stake failed
-
Three versions
Build the same tool three times. Each version has to fix one thing that failed in the one before.
Write downWhat failed, what you changed, and what each version cost
-
Printed plus scrap
Combine a printed part with scrap, like a printed joint on chopstick legs or a printed clip on a bottle.
Write downWhich part gave out first, the printed one or the scrap
Before you print a part that lives outside
Three things that decide whether a printed garden part lasts a season.
-
PLA, the most common printing plastic, starts to soften at around 60 °C.
Its glass transition is about 55 to 60 °C. A part left in a hot car, or in full sun on dark mulch, can sag. PETG holds up better outdoors.
-
Most soda and water bottles in the US share one of two neck sizes.
The PCO 1881 and the older PCO 1810 neck finishes, both about 28 mm across, so one printed adapter fits most bottles you will find.
-
Printed parts leak between their layers unless the walls are thick enough.
Three or more perimeters, or a wall at least 1.2 mm thick on a standard 0.4 mm nozzle, is a common starting point for parts that hold water.
By the end, you can
- Turn a sketch into a working version made from scrap
- Decide which part is worth printing and which isn't
- Test a version and write down exactly what failed
- Say what a working version costs you to make
Take it into your project
Keep all three versions and their costs. They are your answer when a mentor asks why the tool looks the way it does, and the cost of the last one is where pricing starts in module 5.
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