Mechanical Design Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Before your Mechanical Design Engineer interview, it helps to see the questions from the interviewer's side. We have picked eight from our set of 16 and added the reason each one gets asked.

Eight Mechanical Design Engineer interview questions, and what the interviewer is thinking

1. Talk me through the stages you would follow to take a mechanical product from a customer brief to a released design, and what you enjoy most about that process.

Why they ask: They want to see that you understand the whole design cycle, not just CAD modelling.

2. How would you design a bolted joint that is subject to fluctuating loads, and how would you control its preload?

Why they ask: Bolted joints are a bread-and-butter design task and they fail often when badly understood.

3. Tell me about a time you had to solve a design problem with conflicting requirements, such as weight, cost and strength. How did you reach a solution?

Why they ask: This is a core design engineering skill, and they want to see structured thinking and trade-off decisions.

4. How do you choose a sensible factor of safety, and which design standards or codes might you refer to when sizing a structural or pressure-carrying component?

Why they ask: They want to see engineering judgement rather than blind use of a default number.

5. How do you select a bearing for a rotating shaft application, and what does L10 life mean?

Why they ask: Bearing selection is a typical design task, and they want to see calculation and practical judgement.

6. During validation testing, a prototype you designed fails after sixty per cent of its target life. What do you do?

Why they ask: They want to see calm, structured failure investigation and honest communication.

7. How would you select a gearbox or design a gear stage for a machine, and what factors affect gear life?

Why they ask: They want to know whether you can apply drive-train fundamentals to a real machine.

8. What do you need to consider when specifying seals, for example an O-ring, in a design, and why do they fail?

Why they ask: They are checking your knowledge of a detail that often causes service problems.

A sample answer to question 1

Talk me through the stages you would follow to take a mechanical product from a customer brief to a released design, and what you enjoy most about that process.

I start by turning the brief into a clear requirements specification, including loads, environment, life, cost, standards and interfaces, and I get that agreed with the customer or product owner. Next comes concept generation, where I sketch and calculate a few options, then compare them using a weighted decision matrix or Pugh method. Once a concept is selected, I move into detailed design: 3D CAD, hand calculations, FEA for critical areas, tolerance and fit decisions, and material and supplier selection. I use design reviews at concept and detail stages and an FMEA to catch risks early. Prototypes then go through validation against the specification, and findings feed back into the design before drawings and the bill of materials are released through change control. What I enjoy most is the moment when conflicting requirements, such as weight, cost and stiffness, come together in a solution that works first time, and then seeing it on a production line or in service.

Common mistake to avoid: Describing only CAD modelling; skipping requirements and validation

Want the rest?

Full model answers, key points and common mistakes for all 16 questions are on the Mechanical Design Engineer interview questions page. The first five are free, no sign-up needed.