3D printing: bring a file, or have the file made

3D printing quotes confuse people because two completely different jobs hide under one heading.

If you already have a model, you are paying for material, machine time and the labour to finish the part. If you do not have a model, you are paying for the design work first, and that is quoted on its own before anything goes near a machine. Keeping those two apart is the fastest way to understand a 3D printing quote.

You already have the file

Send the model and it gets printed. STL, OBJ, 3MF and STEP all turn up regularly.

They are not equivalent. STL and OBJ are meshes — a surface made of triangles, with no memory of the dimensions or the features that produced it. 3MF is a more modern mesh container that can carry units and other information alongside the geometry. STEP is the useful one, because it is a solid model: it keeps real dimensions and can actually be adjusted. If a hole needs to be a millimetre wider, that is a small edit on a STEP file and a reconstruction job on an STL.

What the price is built from. Material used, machine time, and the labour to remove supports and finish the part. Quantity and labour, in plain terms — which is why this one is quoted rather than listed.

What surprises people. Print time follows part height and layer count as much as it follows volume. A tall thin part can take longer than a short fat one that uses more plastic, because the machine is laying down more layers.

What goes wrong before printing. Files often need repair before they will run: holes in the mesh, inverted normals, or the classic millimetres-versus-inches mix-up that arrives as a part ten times too big or ten times too small. Those get flagged before anything prints, not after.

You do not have the file — from $150

CAD modelling from a description, a drawing, a measured part or a 3D scan, followed by a printability review before anything goes on a machine.

The work involved is mostly not the modelling. It is working out what the part mates to and what load it sees, measuring the things it has to fit, modelling it parametrically so it can be revised rather than rebuilt, and then checking wall thickness, clearances, orientation and support strategy.

The real deliverable is the iteration loop. Test print, check the fit, revise, print again. That loop is what is actually being bought, and it is why design is quoted separately from printing rather than folded into it. A part that fits on the first attempt is luck; a part that fits on the third is process.

Choosing a process

Which process a part should run on is a decision about what the part has to survive, not about which machine happens to be free.

• FDM (filament). The workhorse. Cheapest per part, the largest sizes, and genuinely strong functional parts. The trade-off is visible layer lines.
• Resin (SLA/DLP). The detail process. Smooth surfaces and crisp small features. More brittle than filament, and every part needs washing and UV curing after it comes off the machine, which is real labour rather than an afterthought.

If the part is going to be looked at closely — a miniature, a display piece, a fine texture — resin. If it is going to be used, held, loaded or bolted to something, FDM is usually the honest answer.

Choosing a material

• PLA. Display models and props. Easy to print, rigid, and not happy in a hot car.
• PETG. When it has to be tougher, damper or warmer than PLA can manage.
• ASA / ABS. When it lives outdoors. ASA is the one with real UV resistance, which matters for anything that sits in sunlight for months.
• TPU. Flexible. Gaskets, grips, bumpers, feet.
• Nylon. Tough and low-friction. Gears, hinges, and moving mechanical parts.

The useful way to arrive at this is backwards: describe what the part has to survive — heat, sunlight, impact, flexing, rubbing against something else — and the material follows from that. Describing a material first usually means importing an assumption from a different part.

What people actually print

The honest range of what a job shop gets asked for, so you can tell whether yours is one of them:

• Prototypes. Form and fit models before committing to tooling.
• Jigs and fixtures. Assembly aids, gauges and holders for somebody else's production line.
• Replacement parts. The knob, clip, bracket or housing that is discontinued and cannot be bought at any price.
• Props and models. Cosplay, miniatures, architectural and display pieces.
• Signage. Dimensional letters and logos.
• Short runs. Enclosures and product parts in quantities too small to justify a mould.

That last one is the real economic case for the technology. Moulding is cheaper per part and vastly more expensive to start, so there is a band of quantities where printing is simply the right answer, and it is wider than most people assume.

What to send

If you have a model: the file, ideally STEP, plus what the part does and how many you need. If you do not: photographs, measurements, the broken original if there is one, and a description of what it mates to. Say which surfaces matter and which do not — orientation on the build plate is a trade-off between strength, surface finish and time, and knowing which face has to look good changes how the part is oriented.

If you are not sure whether the thing in your head is printable, it usually is. Describe it and it can be worked out from there.