Balance a 3D-printed crankbait in two passes: first set the finished mass for the intended floating or sinking behavior, then adjust ballast position to compare rest attitude and action. Include the shell, internal print structures, bill, hooks, rings, attachment hardware and modeled coating. There is no single ballast position or weight that works for every body.
Separate weight from placement
The amount of ballast changes total mass. Moving the same ballast changes the center of mass and the moment arms acting on the lure. For an unchanged sealed exterior, moving an internal weight does not itself create more displacement. In a printable design, however, moving a pocket can also change its supporting structure or attachment clearances, so recheck finished mass after every rebuild.
Use the as-built mass readout once the print calculation is ready. It adds the generated internal structures and the attachment hardware represented by the print setup to the design model. If the readout is pending or has fallen back to the design-only model, do not record it as a verified finished-part estimate.
In the model, positive net buoyancy means an upward force and negative means a downward force when fully submerged. The readout expresses that force as an equivalent mass in grams. Near neutral buoyancy, a small unmodeled amount of glue, coating, water ingress or different hardware can change the real outcome.
A public design to start from
Use the 60° version of our published square-bill design as an inspectable starting point. The table below summarizes its recorded inputs; the downloadable JSON contains the complete design, print and simulation settings. This is one configuration from the bill-angle experiment published on October 31, 2026, not a ballast-placement experiment or a physically tested recommendation.
| Input | Recorded setting |
|---|---|
| Body | 60 × 24 × 17 mm |
| Square bill | FR-4, 11 × 15 × 1.0 mm, 60° |
| Shell and modeled coating | Hollow ASA, 1.2 mm wall; 0.15 mm epoxy coating |
| Ballast | One Ø5.5 mm tungsten ball; station 19 mm; height fraction −1 |
| Rattle | Two Ø4 mm steel balls; station 34 mm; height fraction 0 |
| Hooks and rings | Two size 6 trebles, size 2 split rings; belly station 24 mm and tail station 60 mm |
| Print setup | Split halves, 0.25 mm clearance, alignment pins, Ø1 mm through-wire, 0.16 mm layer height |
| Published finished-model mass | 11.502 g |
Station is measured from the nose toward the tail. Height fraction −1 requests the lowest fitting position against the inner belly wall, 0 the middle of the feasible range, and +1 the highest position. The actual center can be constrained by the cavity and ball radius; inspect the cutaway and fit warnings rather than treating a requested station as proof of clearance.
The case page’s “Open 60° model” link opens an anonymous read-only snapshot with the recorded settings. To change ballast, sign in and copy the design first. Keep its source JSON, a variant name and the print settings together; later software versions can produce different estimates.
1. Set the finished weight before comparing positions
Choose the intended buoyancy class and check the shell material, wall thickness, bill material, coating thickness, hooks, rings and attachment method first. In the automatic-ballast panel, select an existing ballast item and the target class. The tool changes that item’s sphere diameter; it does not search for an ideal location or optimize swimming action.
Wait for the as-built recalculation and read the actual result and any warning. Available diameters and body space may prevent the requested class. Confirm that the selected diameter exists in the material you plan to install, that the pocket fits, and that the wire path and hook hangers remain clear. An automatic result is a model estimate, not a substitute for weighing the finished lure.
2. Compare placement without quietly changing everything else
Make named copies of the same design. Keep the body, bill, material, ballast diameter and count, rattle, hooks, rings and print setup fixed while changing one requested ballast station or height at a time. Record the requested setting, inspect the placed ball in the cutaway, and note finished mass, center of mass and predicted rest attitude after each rebuild. Start with fitting locations, not a universal percentage of body length.
A fore-and-aft move changes the weight’s moment arm; a vertical move changes the center of mass relative to the buoyant body. Neither tells you the complete swimming action by itself. If the printed structure or total mass changes, label the result a complete-design comparison. If you resize ballast to restore buoyancy, record that second change instead of calling it a position-only test.
3. Compare equal simulation runs
For a first comparison, use the public case’s tank setup: steady 0.6 m/s tow, 3 m towline, 0.30 mm monofilament, water density 998 kg/m³, kinematic viscosity 0.000001 m²/s and zero current. Use 20 substeps per 1/60 s frame, reset each run, run for 10 seconds and compare seconds 6–10. Keep all remaining settings from the recorded JSON unchanged.
Read depth, pitch, wobble, roll and line tension together. Use the same analysis window; a changing live rolling window is not automatically the published final-four-second summary. These instructions define a repeatable comparison protocol. This guide publishes no new ballast simulation results and no tank measurements.
4. Weigh, seal and test the physical build
Weigh the printed parts and the actual ballast, hooks, rings and attachment hardware. After assembly, sealing and the coating’s required cure, weigh the finished lure again. Record material, slicer settings, coating and glue. A decorative paint scheme in the editor does not change the mass model; the shell’s modeled coating setting does, while a real finish still needs to be weighed.
Check rest attitude and leakage in controlled water before comparing action. Record water conditions, hardware, line and tow or retrieve method. Repeat each trial under the same setup and keep video or observations for both successful and failed variants. If a prototype takes on water, investigate the leak before correcting its behavior with more ballast.
The CSV below is a blank record sheet: its first row contains field names and units, with no measured or simulated results. Add one row per variant or trial. It is not a file to import into the studio, and the website does not collect the values you enter.
Use the evidence for the next adjustment
Update inputs that differ from your build, then change one documented factor and repeat. Do not turn this starting design, a predicted buoyancy class or an attractive animation into a promise of diving depth, durability or catch performance. The useful result is a record of what you changed and what happened under known conditions.