Somebody else finds the customer. You print the thing.

• A marketplace of printers. You list your machines and capabilities on a service, customers upload a model, and jobs are offered to you. Open to anyone, priced by competition, and the work is unpredictable in size and difficulty.
• A local service of your own. You are the person in town who prints things. Word of mouth, a Facebook group, a line in a local directory. Best margins, slowest start, and every job is a quote.
• Printing one product for one brand. You learn a single part properly and print it to order, for a fixed amount per unit, for as long as the orders come. The least varied and by far the easiest to be good at.

The third shape is the only one where your print gets better and your minutes per order get smaller every week, because it is the same print every time.

Per-unit work either pays or it does not, and you can tell before you accept it. Take what you are paid per unit, subtract filament, power, hardware and postage, and divide what is left by the minutes the job takes from you — not the hours it takes the printer.

A worked example with real figures, our own: a GigTag and its clamp are 94 g of PLA and about 3 h 51 m on the plate. Call the filament £1.50, the power £0.12, the bolt and nut £0.12, the large-letter box and the A5 card inside it £0.30, postage £1.90 as a second-class large letter and a 7% failure allowance, so £4.06 of costs. Against the £9.99 we pay for a UK tag, that leaves about £5.95 a tag. The printing itself is unattended; what it takes from you is a plate change, 3 filament swaps at the colour pauses, a few minutes of assembly and a trip to post it. Perhaps twenty minutes a tag at first, and under ten once you have the rhythm.

That is not a wage. It is what otherwise-idle machine time pays, and the test is whether twenty minutes and four hours of plate time are worth six pounds to you. For some people that is obviously yes; for others it is obviously no. Both answers are fine, and it is better to know before you apply.

Batching is what moves it. Several tags on one plate means one plate change, one set of filament swaps and one trip to the Post Office spread across all of them, and the margin per tag stays the same while your minutes per tag fall. See what a print costs you, and what to charge.

Anybody paying per unit is buying consistency rather than printing. The part has to come out the same every time, because the person opening the parcel bought a product, not a 3D print, and has no interest in layer lines, elephant's foot or a stringy first colour change.

• Dimensional accuracy. Parts that fit something else must fit it. Calibrate flow and shrinkage once, properly.
• The visible face. Whatever the customer sees first — the face, the lid, the front — gets your best surface. Print it against the plate if you can.
• Repeatability over speed. A profile that finishes nine out of ten plates perfectly beats one that is 20% faster and fails one in four.
• Honesty about a bad print. Scrap it. Everyone who does this at volume has a bin; the people who send the marginal one get a refund request and lose the work.

Most people who stick with printing for money end up doing some of both: their own small range for the enjoyment and the margin, and per-unit work to keep the machines busy between orders.