Parts you should never 3D print: a five-question safety check

Most broken clips, knobs, covers and brackets are good jobs for a maker. A short list of parts is not, whatever the material, the printer or the maker's skill. This check takes two minutes and should come before any quote.

The five questions

1. Could someone be hurt if this part failed? Think about the worst case, not the usual one: a fall, a fire, an electric shock, a burn, a crash, a child swallowing a piece.
2. Does it touch gas, mains electricity, pressure or high heat? Gas fittings and burner parts, plugs, sockets and live-side housings, pressure-cooker and boiler parts, and anything inside an oven or next to a heating element.
3. Does it carry a person or a heavy load? Ladders, climbing and lifting gear, bike stems, handlebars, seatposts and forks, shelving that holds heavy items overhead.
4. Is it part of a children's product or a medical or mobility device? Toys for young children, cots, car seats, high chairs, stair gates and buggies; wheelchairs, walkers, hoists, care beds, hearing aids and breathing equipment.
5. Is it part of a vehicle's safety system? Brakes, steering, suspension, seat belts, wheels and hubs, airbag parts, and e-bike or e-scooter battery cases, mounts and chargers.

If any answer is yes, or you are not sure, do not have the part remade. Buy the manufacturer's part or a certified equivalent, and have it fitted by a qualified professional.

Why these parts are different

• Printed plastics behave differently from moulded ones. A UK government study of 3D-printed spare parts lists porosity, weak bonding between layers, and the effects of moisture, UV and ageing among the risks, and names electric shock, burns and appliance malfunction among the possible hazards [1].
• Common plastics soften at modest temperatures. The manufacturer's guidance says PLA "gets soft and deforms at temperatures over 60 °C" [3] and suits PETG to temperatures "below 80 °C" [4].
• Some work is licensed. In Great Britain, work on gas installations and appliances must be done by a Gas Safe registered engineer under the Gas Safety (Installation and Use) Regulations 1998 [2]. Other countries license gas work too.
• Some products are regulated. In the US, for example, a mechanical wheelchair is a Class I medical device [6]. In the EU, toys for children under 14 will come under Toy Safety Regulation (EU) 2025/2509, which applies from 1 August 2030 [5].
• No special law covers printed parts. The same UK study found no reviewed jurisdiction with 3D-printing-specific rules: general product safety and liability law applies [1].

What the EU repair law does and does not change

From 31 July 2026, the EU repair directive bars manufacturers from blocking independent repairers' use of compatible or 3D-printed spare parts, but only "when those spare parts are in conformity with requirements under Union or national law" [7]. It does not make a printed brake or gas part acceptable.

What a maker can make around these products

Non-structural extras are often fine: a cup-holder clip or bag hook for a wheelchair, a cosmetic cover that carries no load, a game piece for older children. Tell the maker exactly what the item is for, and expect a good maker to decline anything on the list above.