Self-Watering Planter with Ball-Float Water Gauge (40 mm Table-Tennis Ball) – 3 Sizes

A self-watering houseplant pot in three sizes, printed in four parts, with a water gauge that uses one bought standard 40 mm table-tennis ball as the float. The lower part of the pot is a water reservoir; the soil sits on a riser plate above it and is meant to draw water up through a wick column. A gauge column on the side of the pot holds the ball, and a light printed rod resting on the ball rises through a funnel cap: when the rod's two small V-notches have just fully appeared above the cap, the reservoir is at MAX; when the rod is at its lowest, it is time to refill. The funnel cap is also where you pour the water in.

Validation status (please read): digitally validated only: CAD geometry and interface checks, slicer checks without supports, and float calculations. It has not been physically printed or tested with water, soil or plants: whether a print holds water, how well the potting mix wicks, whether the rod slides freely after printing and how the gauge behaves over months are all unverified. Leak-test the printed pot over a towel before you plant in it. All pictures are 3D renders, not photos; the plant, soil, water, ball and room in them are simple stand-ins.

How it works

• A riser plate on four legs holds the soil above the water. A slotted wick column in its middle stands on the reservoir floor and is filled with the same potting mix, which is meant to draw water up to the roots.

• The gauge column is joined to the pot. Three narrow slots at the bottom of the shared wall let the reservoir water in, so the water in the column stands at the same level as in the reservoir.

• A small air vent just under the plate connects the reservoir's air space to the column. It is meant to keep the gauge from lagging while you fill or while the plant drinks (without it, the air could only escape through wet soil).

• The ball floats in the column and lifts the rod. The MAX notches are placed from the geometry, including how deep the loaded ball floats (about 11 mm).

• The MAX water line is 6 mm below the plate (checked on the CAD model), so the soil is meant to sit above the water.

Who it is for

For houseplant owners who want a pot that shows when to refill, in the size and colour they choose. Printed pots with a gauge tower and a floating ball already exist. This one is built around a bought, sealed 40 mm table-tennis ball, with the MAX mark calculated for that ball, an air vent between the reservoir and the gauge column, a riser plate with a wick column, a funnel cap and three sizes. A sealed bought ball is used because a printed float can take on water through its layers and sink, which makes a gauge read wrong. It is not cheaper than a retail multi-pack of self-watering pots.

Self-watering pots are usually used for plants that like evenly moist soil; cacti and succulents that should dry out between waterings usually do better in a normal pot.

Features

• The float is a standard 40 mm table-tennis ball: sealed, cheap and widely sold. No printed float, no special float print settings, no foam ball or fishing bobber to hunt for.

• The gauge column sits outside the pot, so it takes no soil space. Its funnel cap (45° cone with six drain slots) catches the water you pour and guides the rod.

• Riser plate 2.4 mm thick with 2 mm holes at 10 mm spacing, to let excess water drain from the soil and air in; the small holes are meant to limit soil falling through.

• Every part is designed to print without supports (checked in the slicer). No threads, no glue.

• Three sizes (115 / 140 / 160 mm) plus the parametric CadQuery source for other sizes.

Which file?

Each size has three size-specific parts (shell = pot + gauge column, plate, rod). The cap is the same for all sizes: self-watering-planter_all-sizes_cap.stl (print one for any size).

The root-ball sizes compare the soil depth with typical nursery root balls and keep about 15 mm of headroom; measure your plant's root ball. Plant directly in the pot on top of the plate, not in a nursery pot standing on the plate.

Ready-to-print PrusaSlicer projects (self-watering-planter_<size>_print1of2 / print2of2 ... .3mf, PrusaSlicer 2.9 or newer): two prints per size with every part already oriented and set up with the recommended per-part settings; each was checked by slicing the saved project. Open, select your printer, slice, print.

Dimensions

All values in mm, from the CAD model. Width includes the gauge column. Soil depth = plate top to rim.

Water volumes are calculated for the pot plus the gauge column up to MAX, before subtracting the legs and the wick column (a few percent less in reality); the dimension drawings list the pot alone (255 / 490 / 758 ml), and the sizes picture rounds the pot + column values as ~294 / ~539 / ~815 ml. The "Volume" printed on the drawings is the plastic volume of the shell, not the water it holds. With the rod up at MAX the gauge stands about 141 / 174 / 200 mm tall (rod top); the pot rim is at 121 / 147 / 168 mm.

Print settings

• Material: PETG in an opaque colour (light getting into a translucent reservoir or column grows algae). The rod can be printed in a bright contrasting colour so it is easy to read. PLA is not recommended for a part that holds water long-term.

• Nozzle / layers: 0.4 mm nozzle, 0.20 mm layers.

• Supports: none on any part (sliced with supports disabled).

• Shell: 4 perimeters and at least 8 bottom layers, so the 1.8 mm walls and the 1.6 mm floor print solid.

• Plate: 8 top + 4 bottom layers, so the 2.4 mm plate prints solid (meant to stay flat under wet soil; strength not tested).

• Rod and cap: normal settings (3 perimeters, 15 % gyroid infill).

• Orientation: print every part on the face it was exported on (do not tip it over or lay it on its side); turning it flat on the plate is fine, e.g. 45° so the 140 mm shell fits a 180 mm bed: shell upright; plate soil-face down (legs and wick column pointing up); rod flat; cap top face down (the funnel prints as a cone).

• Do not rescale the STL files: the gauge column and the rod are sized for a 40 mm ball. For other pot sizes use the source (see Customising).

Print time and filament for all four parts of one size, with the settings above (slicer estimates, not measured prints):

The shell is most of it (140 mm: 16.6 h / 241 g with the generic profile, 3.9 h / 228 g on the MK4S).

What you need

• The 4 printed parts of one size (shell, plate, rod, cap).

• 1 standard 40 mm table-tennis ball, any colour. A cheap recreational ball should work: the 43 mm column bore leaves 1.5 mm of play per side, cheap balls vary slightly, and no ball has been tried in a print yet. The gauge is calculated for a 40 mm / 2.7 g ball, the size and weight set by the ITTF rules; no approved or competition ball is needed.

• Potting mix and your plant.

Assembly

1. Leak test first: fill the empty shell with water up to about half its height and leave it on a towel overnight.

2. Drop the ball into the gauge column.

3. Lower the rod into the column, crossbar foot first, so it rests on the ball.

4. Thread the cap down over the rod and set it on the column.

5. Put the plate into the pot, legs down. Fill the wick column with potting mix first, then plant directly into the pot on top of the plate.

Use

• Pour water slowly into the funnel cap until the rod's notches have just fully appeared above the cap (MAX). If the notches sink back after a few seconds (the column fills a little faster than the reservoir), top up.

• Stop at the notches: the pot has no overflow, so overfilling floods the soil.

• While a new plant settles in, also water from the top as usual.

• When the rod is at its lowest (its top about 3 mm above the cap), refill. At that point a third or a little more of the water is still in the reservoir (about 120 / 190 / 250 ml for the three sizes; see Limitations).

• To take the ball out, tip the pot over a sink when repotting.

Customising

self_watering_planter_model.py is the parametric CadQuery source. With Python 3.10+ and pip install cadquery trimesh shapely: python self_watering_planter_model.py --preset large (presets: small, default, large) or python self_watering_planter_model.py --set d_top=150 for a 150 mm pot; it writes the parts as STL and STEP (the usage lines inside the file still call it model.py). The digital checks also ran on other sizes (pot diameters 100-164 mm and other height ratios), but only the three included sizes are offered as checked files. STEP files are included for the default 140 mm size (the cap STEP is named all-sizes, like the cap STL).

Limitations

• Not physically printed or tested with water, soil or plants yet (see Validation status).

• Whether a printed reservoir holds water depends on the printer, the slicer settings and the filament. Test it over a towel first; nothing here promises that a print will not leak.

• The gauge reads only the upper part of the reservoir: the ball floats only once the water is about 11 mm deep. Below that the rod shows "empty" while a third or a little more of the water is still there (about 120 / 190 / 250 ml). That is a reserve on the safe side, not a fault.

• The MAX notches are placed for a rod printed 100 % solid (about 3.9 g at 140 mm). A rod printed with normal infill is lighter (about 3.2 g as sliced), so the ball floats about 0.7 mm higher and the notches show slightly before the water reaches MAX (more air under the plate, the safe side).

• No overflow: stop filling at the notches.

• Roots may eventually grow into the reservoir and through the narrow inlet slots into the gauge column (normal in self-watering pots). If the rod stops moving, check the column when repotting.

• The ball stays in the column until the pot is tipped out; algae or sediment around it are cleaned when repotting.

• The ball, rod and cap are loose: hold the cap when carrying the pot tilted.

• The gauge column makes the pot about 45 mm wider on one side.

• No drainage holes and no saucer: the reservoir is closed at the bottom.

• Print times and grams are slicer estimates for the named profiles, not measured prints.

Pictures

All pictures are 3D renders of the exported model or drawings made from it: a clean cover render, a cut-in-half view of the FULL and REFILL states, a lifestyle render on a windowsill (a second pot in another colour, a spare ball and a watering can as props), the gauge read from outside at FULL and REFILL, a gauge close-up showing the MAX notches and the fill opening, a dimension card for all three sizes, the three sizes side by side and the four parts in print orientation with the ball. Plants, soil, water, the spare ball, the watering can and the room are stand-ins. None is a photograph of a print.

The ITTF is mentioned only as the source of the standard 40 mm / 2.7 g ball size. This design is not affiliated with or endorsed by the ITTF.