Modelling a small centrifugal pump that someone else could print

A job that started with nothing

Most enquiries arrive with something attached: a file, a drawing, a photograph, a broken original. This one arrived with none of those. The customer wanted a small centrifugal pump and wanted to be able to print it themselves, and that was the whole brief. There was nothing to measure and nothing to convert — the pump had to be designed before anything could be printed.

That makes this the purest modelling job of the five shown on this site, and the one that shows most clearly what the design side of the work actually is. The first photograph is the prototype housing: a cylindrical body with a side outlet and two flanged feet. The other two show the rest of the assembly that was modelled alongside it — the cover plate, the rotor, the shaft support and the mounting plate — and the small DC motor the whole design is built around.

Why these prints look the way they do

The black parts in the photographs were printed here, in the Partsmith workshop, as the prototypes for this design. They were run the way prototypes are run here: quickly, at a coarse layer height, to check that the parts go together and the rotor turns freely in the housing before any time went into finish. That is the right order. A prototype exists to answer a question about fit and function, and the answer arrives sooner when the print is fast. Finished parts from this workshop are printed at a finer layer height and cleaned up; the planetary gear set shows what that looks like where the surface itself matters. On this job the finish of the prototypes never mattered, because the deliverable was the design, and the customer would print the final version on their own machine.

Designing for somebody else's printer

The unusual constraint here was that the final parts would not be printed here. The prototypes were, to prove the design; the production version had to run on the customer's machine, which meant every design choice had to survive leaving the workshop.

In practice that shapes the geometry throughout. Overhangs have to stay within what prints cleanly without heroic support, because supports that need careful removal are exactly what goes wrong in someone else's hands. Parts have to sit on the bed in an orientation that is obvious rather than one that needs explaining. Wall thicknesses have to suit a common nozzle rather than a fine one. Anything that only works if the printer is well tuned is a bad decision, because the whole point is that the design keeps working when it is handed over.

Designing a part to be manufactured on equipment you do not control is a different discipline from designing one you will make yourself. It is closer to product design than to job-shop work, and it is genuinely more constrained.

Designing a printed pump properly

A pump asks more of a printed part than most jobs, and the design accounts for it from the start.

Sealing is designed in, not hoped for. An FDM part is built from stacked extrusions, so a housing that has to hold liquid is given thicker walls and designed around a bought seal or gasket — which is how a printed pump is made properly tight, and how it stays serviceable when the seal eventually wants replacing.

Material follows the duty. PETG for a housing that has to take knocks and daylight, flexible TPU where something has to compress and seal.

Scope is set at the quote. A printed pump is a working device for low-pressure, low-duty service — a project, a rig, a demonstration, a piece of equipment where reliability matters more than pressure. Where a job needs more than that, you get the recommendation before anything is designed, which is the most useful thing a supplier can tell you at that stage.

What this job shows

That a job can start from a sentence. If you can describe what you need something to do, that is enough to begin — a file is convenient, but it has never been the entry requirement. And when the design is the deliverable, the design has to account for who will be making it, not just for what it has to do.