3D Printed Spare Parts: Purpose & Limits

Lisa Ernst · 20.11.2025 · Technology · 12 min

The moment a small plastic button breaks knows no mercy: the coffee machine stops, the office chair wobbles, a cover in the car suddenly rattles. Genuine spare parts are often expensive, have long delivery times – or are no longer available at all. In our workshop at 33d.ch, precisely these kinds of cases constantly come up, usually with the question: "Can you print this quickly?".

In such situations, 3D printing seems like the perfect shortcut. At the same time, we also see projects where a self-printed spare part is simply not a good idea because safety, temperature, or liability issues speak against it. Using Tom's project as an example, we show how we systematically evaluate spare parts, which applications have proven themselves in practice, and where we clearly advise our customers to use original or certified parts.

Source: Own Representation

Introduction & Basics

The failure of a rotary knob on an office coffee machine can paralyze an entire team. Tom, an engineer and enthusiastic 3D printing user, saw this as an opportunity to solve everyday problems with self-printed spare parts. His goal was to manufacture knobs, brackets, and covers for the coffee machine, office furniture, and the interior of his car without compromising safety functions. At the same time, he wanted to avoid long delivery times and high prices for original spare parts. The fact that manufacturers like Philips now even offer official, 3D printable spare parts shows how strongly this topic has arrived in industry – and confirms much of what we observe daily at 33d.ch.

Tom manages a small technology office with five employees. They have an FDM 3D printer equipped with PLA and PETG filament. He wanted to replace typical small parts without compromising safety functions. Companies and service providers confirm that 3D-printed spare parts can play a sensible role in such cases, provided that material selection and application limits are clearly defined (

This exact combination – high practical benefit with clear limits – is also the basis for us when we plan projects with customers. 3erp.com). The framework conditions for Tom's project were very typical for many inquiries we receive at 33d.ch:

• FDM printing (layer-by-layer build-up from molten plastic).
• PLA for simple, cool applications, PETG for moderately warmer environments.
• Application areas: Coffee machine (hot water, steam), furniture (static loads), car interior (summer heat, vibration).

Furthermore, FDM printed parts are not equally strong in all directions. The layers adhere to each other less well, which makes components weaker, especially in the print direction (Z-axis), and leads to anisotropic behavior ( facfox.com). Especially with loaded spare parts, we therefore always plan how the part will be oriented in the print space.

Practical Example: Tom's Project

To approach the project systematically, we defined a simple four-step process together with Tom, which has since proven to be a good guide for many spare part inquiries:

1. Categorize parts into risk classes.
2. Understand material and temperature limits.
3. Clarify legal and liability issues.
4. Test prototypes and only use non-critical parts permanently.

Define risk classes

We first collected all the desired spare parts and divided them into three categories – a step we also recommend in the workshop at 33d.ch before anyone slices the first part:

a) Non-critical parts: Pure brackets, decorative covers, knobs without structural function. If they fail, nothing dangerous happens. Examples include dashboard organizers, covers, or clips that do not bear any load ( crealitycloud.com). Precisely these types of parts make up the majority of inquiries that we can safely implement in practice.

b) Functionally critical but not safety-relevant parts: Drawer handles or cable holders. A break is annoying but not dangerous to people. Here, we usually consciously discuss with customers how much annoyance a failure really causes and whether a test print is worthwhile.

c) Safety-critical parts: Anything related to personal safety, high temperatures, pressure, or electrical safety. This includes brake or steering parts in a car, load-bearing furniture parts, components carrying hot water or steam, as well as anything that needs to insulate mains voltage. Expert sources clearly advise against manufacturing such components with hobby 3D printers ( lab3d.dk). In our workshop, we draw a very clear red line here.

Understand material and temperature limits

For Tom's applications, we primarily examined PLA and PETG more closely – precisely the two filaments with which many beginners start:

• PLA: Easy to process, but temperature-sensitive. It softens at around 60 °C and loses strength ( dbe.unibas.ch).
• PETG: Better temperature resistance, with a glass transition temperature around 70–80 °C and dimensional stability up to about 70 °C ( ultimaker.com).
• ABS: Even more temperature-resistant, with a glass transition around 105 °C and heat distortion temperature around 85–100 °C, but more difficult to print and with stronger emissions ( salesplastics.com).

Practical temperatures:

• Brewing water from coffee and espresso machines: 90–96 °C ( brewistabrand.co).
• Car interior on sunny days: up to 70 °C, dashboard close to 100 °C ( joe.uobaghdad.edu.iq).

For orientation purposes, we often use a rough rule-of-thumb table internally:

*Guidelines that may vary depending on the manufacturer and component design – when in doubt, plan and test conservatively.

In practice, this means for us: PLA is unsuitable for areas near coffee machines or car interiors in summer. PETG is only comfortable there with distance from heat sources and without high continuous load. ABS or special materials are more suitable for higher-load areas, but even then only for non-critical parts and with very careful design.

Law and Liability in Simple Terms

The question of liability for damages caused by self-printed spare parts is complex – and, based on experience, often underestimated in discussions. Under European product liability law, the manufacturer of a defective product is liable ( mills-reeve.com). In the case of 3D-printed parts, the responsibility can be difficult to separate between the filament producer, the platform operator for CAD files, and the private printer ( cooley.com).

The new EU Product Liability Directive explicitly includes digital files and modern manufacturing processes, thereby expanding the circle of potential liable parties ( reuters.com).

For Tom – and generally for anyone who passes on 3D parts to others – this means:

• If he prints only for himself privately, he bears his own risk.
• If he prints or sells parts for others, he can be considered a manufacturer and held liable ( europa.eu).

Prototypes, Tests, and Clear Stops

Together with Tom, we decided to only print parts from categories a) and selected parts from b). Category c) – safety-critical components – is taboo. This includes no brake levers, no chair roller mounts, no water-carrying or pressure-loaded components in the coffee machine, no parts on seatbelts, airbags, or steering systems ( jlc3dp.com). We recommend precisely this boundary in our customer projects as well.

Technical Details & Learning Moments

The broken rotary knob of the coffee machine was the first project. It sat on the outside of a metal shaft, had no direct contact with water, and was mainly subjected to mechanical stress. We have implemented such knobs in various forms at 33d.ch – from inexpensive office devices to semi-professional machines in break rooms.

Source: 3ddruckmuenchen.com

Diverse 3D-printed spare parts demonstrate the adaptability of the technology.

Material Choice and Settings

In our workshop, the following settings, among others, have proven effective for such knobs – always to be understood as guidelines, because every printer and every filament reacts slightly differently:

• Material: PETG, due to higher heat distortion temperature compared to PLA and dimensional stability up to about 70 °C ( 3dtrcek.com).
• Wall thickness: 3 perimeters for sufficient material around the metal shaft.
• Infill: 40% Gyroid for a good combination of strength and print time ( ncbi.nlm.nih.gov).
• Print orientation: Shaft mount oriented so that the layers run circularly around the shaft to avoid layer separation in the critical zone, as FDM parts are weakest in the Z direction ( formlabs.com).

Stumbling Block 1: PLA knob becomes rubbery

An initial test knob made of PLA became soft during longer espresso sessions and could be pressed in. PLA loses significant stiffness at around 60 °C, and the coffee machine reaches these temperatures near the brewing unit ( salesplastics.com). We observed precisely this behavior in early test runs in our own coffee corner as well.

Learning Moment: PLA is only conditionally suitable for coffee machine front parts, especially when metal parts conduct heat. PETG or ABS are more robust alternatives, as long as there is no direct contact with brewing water or steam ( filamentive.com).

Stumbling Block 2: Part in the car interior warps in summer

A PETG clip for the ventilation grille in the car held up in spring but deformed on a hot summer weekend. Interior temperatures in parked cars can reach up to 70 °C, dashboards even close to 100 °C ( joe.uobaghdad.edu.iq). Since PETG loses its dimensional stability at 70–80 °C, the thin, loaded clip was a borderline case ( wevolver.com). The solution was a more massive design with a shorter cantilever and darker filament, with the clear instruction that a break would at most drop the phone and not slip into the pedals or steering wheel ( 3dtrcek.com). We also see such "summer surprises" with customer parts that remain in a heated car for a long time.

Stumbling Block 3: Food safety with the coffee machine

The idea of printing an adapter bushing for the water supply was discarded. FDM-printed parts can promote bacteria and residues due to layer lines and micropores, which is problematic for continuous food contact ( jlc3dp.com). Even if filaments are advertised as "food safe," dyes or additives may be unsuitable. True food safety requires tested materials and often additional coatings ( formlabs.com). This is precisely why we at 33d.ch routinely reject such inquiries regarding water-carrying parts for coffee machines or refer to original parts.

Therefore, the project was limited to external controls and covers. Anything that comes into contact with hot water or steam remains an original part or a certified spare part.

Sensible Applications

Tom's office project resulted in a practical list of 3D-printed spare parts that have proven themselves in everyday use. All examples are chosen such that a defect would be inconvenient but not dangerous. This pattern strongly aligns with the projects we implement in our daily business at 33d.ch.

Source: formlabs.com

Functional 3D-printed spare parts such as fan wheels and brackets in practical use.

Top 10 List of Safe Spare Parts from a 3D Printer:

1. Rotary knob on the coffee machine (outer knob only): Replacement for broken plastic knobs on a metal shaft without direct water contact.
2. Covers and caps on furniture: Small caps for visible screws, holes, or old fittings.
3. Cable holders and clips under the desk: Brackets that guide cables or fix power supplies without bearing load.
4. Drawer and cabinet handles: Handles that are only pulled by hand.
5. Feet and spacers for furniture: Small feet under sideboards, spacers for walls, or distance pieces for shelf boards.
6. Phone holder in the car (with safety margin): Holder on the ventilation grille or adhesive plate, designed so that a break at most drops the phone, but does not slide into the pedal area or steering wheel.
7. Covers in the car interior: Caps for screws, missing blanking plugs, or small trim pieces without safety function.
8. Tool holders in the workshop: Wall holders for screwdrivers, pliers, or bits; if it breaks, only the tool falls down.
9. Holders for sensors or small electronics: Housings and holders for Raspberry Pi, sensor boards, or low-voltage power supplies, without direct mains voltage.
10. Organizer inserts for drawers: Inserts for cutlery, tools, or office supplies, where material failure only causes disorder.

Results: What Came Out in the End

After a few weeks of everyday use by Tom – and in comparison with similar projects of ours – a clear picture emerged:

• The PETG rotary knob on the coffee machine runs stably, even with intensive use, as long as it is not directly attached to hot metal areas. 3dtrcek.com).
• The furniture parts (handles, feet, covers) have held up for months and are in no way inferior to comparable manufactured parts, as long as the loads remain manageable (
• In the car, all parts were non-critical if they were sufficiently dimensioned, placed in a shaded area as much as possible, and limited to non-safety-relevant functions. Practical guides mainly recommend 3D printing in car interiors for organizers and decorative elements ( crealitycloud.com).

In numbers:

• The original coffee machine knob would have cost about ten times the material cost of 3D printing, including shipping, and would have taken several days for delivery. With the printer, the spare part was ready for use in under an hour, with material costs in the range of a few euros ( 3erp.com).
• By consistently self-printing non-critical parts, several minor repairs were carried out that otherwise would likely not have been done, contributing to the extended lifespan of the devices – an effect that sustainability reports on 3D-printed spare parts generally highlight ( formlabs.com).

Applying to Your Situation

When we plan spare parts in the workshop, we essentially always ask customers the same questions:

Question 1: If a defect occurs, is it "just" an annoyance – or can someone be seriously injured?
If a break only causes disorder or loss of comfort, a 3D-printed spare part is often justifiable. Expert sources explicitly mention organizers, handles, decorative panels, or brackets as typical, non-critical applications ( 3dspro.com).

Question 2: How hot, wet, or loaded will the part really get?
Anything near 90–96 °C (coffee machine, steam, near stove) is already in or above the range where PLA softens and PETG can become critical under load ( dbe.unibas.ch) (3dtrcek.com).

Question 3: Are you legally more in the private sphere – or are you providing parts to others?
If you publish models, print for others, or sell parts, you are moving closer to the role of a manufacturer in terms of product liability ( cooley.com).

Critical Applications & Warnings

As enthusiastic as we are about 3D printing: Several sources surprisingly agree on which applications with hobby 3D printers are problematic or simply too dangerous ( creality.com) (lab3d.dk), and we also consistently advise against it:

Source: mark3d.com

A small, precise 3D-printed spare part that fits perfectly in the hand.

• Parts on brakes, steering, or chassis of a car or bicycle.
• Load-bearing components of chairs, ladders, shelves, or wall cabinets.
• Water or steam carrying components of coffee machines, boiler systems, or pressure vessels.
• Components intended to safely hold children (e.g., car seat components for children).
• Housings or supports that must safely insulate mains voltage or high currents without corresponding testing.

If there is uncertainty whether a part could become dangerous in case of failure, the safe answer is: it is better to use an original or certified part. Safety authorities generally warn against circumventing inspection and approval procedures for safety-relevant products through uninspected 3D parts ( cpsc.gov).

Quick Questions & Objections from Practice

Question 1: Can I print brake levers for my bike or parts of the brake myself?
In short: Don't do it. FDM parts are anisotropic and have different strengths in different directions; the layer boundaries are mechanical weak points ( sciencedirect.com). Critical components like brake levers are subject to high, alternating forces, and failure can directly lead to serious accidents. Technical guides explicitly mention safety-critical car parts as examples of what should not be made with hobby 3D printers ( jlc3dp.com). We have exactly this discussion repeatedly in consultations.

Question 2: What about parts in the engine compartment or near the windshield?
Temperatures in the engine compartment can exceed 90 °C significantly, sometimes even higher in direct proximity to exhaust components ( zeal3dprinting.com.au). FDM plastics like PLA, PETG, or standard ABS are often overwhelmed there; even PETG loses significant stiffness from around 70–80 °C ( wevolver.com). Therefore, only specially tested, high-temperature-resistant plastics or metal parts are suitable for the engine compartment, as used in the automotive industry under defined testing conditions ( raise3d.com). We do not print such parts at 33d.ch for safety-critical applications.

Question 3: Isn't it overkill to be so cautious with a simple adapter bushing in the coffee machine?
Water-carrying components combine several risk factors: temperature, pressure, hygiene, and often electrical proximity. Brewing water and steam operate in the range of 90–96 °C, pushing many standard filaments to their limits ( brewistabrand.co). At the same time, bacteria can settle in the layer lines of FDM prints, which is why scientific articles on food safety are cautious about FDM parts and often only recommend "food safe" use in combination with suitable coatings or special materials ( formlabs.com). Therefore, it makes sense to stick to original parts or certified spare parts in such areas – and we consistently recommend this to our customers.

Question 4: How dangerous are the fumes and particles during 3D printing anyway?
Studies show that during 3D printing – especially with ABS – ultrafine particles and volatile organic compounds can be released, including some potentially harmful substances ( researchgate.net). Therefore, professional organizations recommend good ventilation, filters, or enclosed systems, especially in small rooms ( raise3d.com). In our workshop, the printers therefore never run in a poorly ventilated office.

Conclusion & Outlook

For us as a 3D printing team, Tom's case study makes it very clear: Spare parts from a 3D printer are particularly sensible when they clearly remain within the zone of comfort and optics – i.e., where a defect is annoying but does not endanger anyone. Expert literature and practical guides recommend precisely this direction: clips, brackets, knobs, covers, and organizers used in moderately loaded environments ( creality.com) (3erp.com).

However, as soon as heat, pressure, personal safety, or electrical safety come into play, the balance tips: The combination of material limits, anisotropic layer structure, and unclear liability makes safety-critical spare parts from hobby 3D printers an unnecessary risk ( sciencedirect.com). Anyone who follows the simple rule of thumb – print non-critical parts themselves, use original or certified parts for critical ones – uses the potential of 3D-printed spare parts wisely and avoids exactly the damages that would cast the topic in a bad light ( lab3d.dk).

Open Points and Next Steps

Several aspects remain open and will continue to engage us in the coming years:

• Material development: Fiber-reinforced and high-temperature-resistant filaments promise better mechanical properties, but their long-term durability in everyday use is still under research ( tandfonline.com).
• Quality control: Industrial users use non-destructive testing methods like X-rays. This is usually not available to hobby users, which is why the focus should be on non-critical applications ( improprecision.com).
• Legal framework: The new EU Product Liability Directive will clarify the legal framework for digital files and 3D printing, but implementation in member states is partly still pending ( reuters.com).

For Tom, the next steps are:

• Systematic labeling of all printed spare parts with material, print date, and location of use for traceability ( ul.com).
• Small load tests for new designs, e.g., gradually increased weights on furniture handles or temperature tests in the oven for non-food-related parts, to gather experience ( 3erp.com).

Mini-Conclusion for Your Spare Parts

• Only print spare parts where a defect is maximally annoying but does not endanger anyone.
• Think in risk classes first, then in materials – not the other way around.
• Consciously plan for temperature, load, and installation situation, rather than just "quickly printing something."
• For safety-critical areas and water/steam zones: prefer to use original or certified parts.
• If you print for others or publish models, you automatically have to consider liability.