A spare part buyer is not browsing. They own something that stopped working or lost a piece, and they want that exact fit. That changes the economics: an obscure part can carry a high price, but each exact model is a tiny market. A good repair business in this niche is mostly a measurement and catalogue operation that happens to use a printer.
Who buys
- Hi-fi and radio owners chasing a matching set. One AudioKarma member could not find Fisher 500 knobs on eBay and looked at having them printed, and Studebaker owners discuss the same idea for car radios.
- Sewing machine collectors, since old machines often arrive with parts missing, according to the ISMACS collector society.
- Retro computer owners, whose original plastics crack and yellow with age.
- Gamers with limited reach or one working hand, or the people buying for them.
Four products, ranked by how they fail
Vintage audio and radio knobs
Vintage audio and radio knobs are the natural starting point because one parametric file can cover many shaft sizes and diameters. Used originals have their own eBay browse page, and an Etsy amplifier knob shows printed versions already on sale. They fail on looks, since layer lines show beside original metal or spun caps. Finish matters more here than anywhere else in this list.
Retro computer case parts
Retro computer case parts have devoted buyers, and the margin sits in bezels, Gotek cases and repair supports. They fail on size. Ami64 sells refinished Amiga cases from GBP 120 with a lead time of about 90 days, which shows both the demand and how slow full shells are. Keep to the small parts and sell on eBay and retro forums.
Vintage sewing machine parts
Vintage sewing machine parts are a gap with an untested price. The range comes from conventional metal parts, and no printed seller with listed prices turned up. They fail on wear, so stay with slide plates, spool pins and the cams and templates Hackaday covered. Anything near the hook, feed or needle needs metal, and an error of a fraction of a millimetre can stop a machine.
One-handed controller adapters
One-handed controller adapters fail as generic listings. The Controller Project offers mods free, and Microsoft's official joystick costs about $30. What remains is a fitted service for a specific person's needs, which takes real support time. Treat it as a service you price honestly, and point people to the free options where those suit them.
Comparing the numbers
The hourly figure is estimated for a typical specific product in each niche, at its midpoint price and print time, after estimated costs and selling fees. In this category it needs more scepticism than usual, because the "price" is often someone else's product.
Read the table with these points in mind:
- The sewing machine figure is for a bobbin tray at $10 to $18, an idea to test rather than a listing seen, and metal part prices do not carry over to a printed slide plate.
- The sailboat figure comes from rated commercial blocks. A printed block does not earn that price, because it does not carry that rating.
- The retro computer figure is for a floppy emulator case at $15 to $28. Full shells of up to 40 hours would earn far less.
- Adapter prices mix an official $30 product with one sponsored listing at $72.50.
- Low competition partly reflects how small each model's market is, so do not read it as easy sales.
Jobs to turn down
- Sailboat deck hardware, when it carries load. A Harken 16 mm block is rated at about 250 lb working load, layer lines are the weak point of a print, and a failure can injure crew. Sailboat owners also report UV failures on pulleys. Low-load caps and covers in ASA are the most that could work.
- Child seat and seatbelt clips, however polite the request. A repair shop will eventually be asked, and car seat makers generally warn against third-party parts.
- Full retro computer shells as a stock item. These need a large bed and many hours, and warping and print time eat the margin.
How to make a part that is yours
Measuring an original part and modelling it yourself solves two problems at once: it gives you a better fit and it avoids file licences. Some popular retro case files are non-commercial and no-derivatives Creative Commons, and files for specific radios are scattered, with most licences unchecked.
- Build one parametric master per family, such as a knob with shaft size, diameter and skirt as inputs.
- Ask buyers for photos beside a ruler and a caliper reading, and keep every confirmed fit as a catalogue entry with the model number in the title.
- Change what failed. If an original bezel cracked at a tab, thicken the tab.
- Sell a paid fit sample when a customer's model is unconfirmed.
Etsy requires printed items to be based on a seller's original design, so a self-modelled part is also the one that fits there. If you would rather sell the modelling itself, a broken part CAD service is the same skill packaged differently, and classic car parts follow the same logic.
Rules that apply
- Trademarks: write "fits Marantz" or "fits Singer 28", and leave brand marks off the part. Copying a logo adds trademark risk to a simple repair. Car owners have seen brand-driven removals, as noted under classic car parts.
- EU design law: a Lewis Silkin note says design rights now cover creating and sharing 3D print files, and describes a repair exception for parts that restore a product's original appearance, provided their origin is made clear. Label repair parts as yours, and take advice if a registered design is involved.
- Controllers: do not copy an original controller's shape as a replacement shell.
- Disability claims: describe what an adapter does and for which controller. Avoid promising it will suit a medical condition.
- Scope: write down what you refuse, so you can decline safety-critical work quickly and consistently.
Estimates are ours unless a source is linked. This guide was drafted with AI and reviewed before publishing.
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