How to Answer: Why are screws generally not ideal for location in fixture design? What is a better way to do it?
Advice and answer examples written specifically for a Mechanical Engineer job interview.
4. Why are screws generally not ideal for location in fixture design? What is a better way to do it?
How to Answer
Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, fixtures are generally responsible for locating parts in three dimensional space in addition to providing clamping force to secure the part. Parts can generally move or rotate in one of twelve degrees of freedom. These come from rotation or translation on the X, Y, and Z axes. Screws are not ideal for location because they have relatively loose tolerances, allowing the part to vary in location slightly every time it is installed. A better way is to use dowel pins, which are tightly-machined cylinders that are usually pressed into one end with an interference fit and slid into the other end with a clearance fit or location fit.
Written by Jason Toby on October 12th, 2020
Answer Example
"In fixture design, screws are not ideal for location because they have relatively loose tolerances compared to the precision required in a work fixture. If I design a fixture that relies on screws, then the part can still move slightly in the X and Y axes, where Z is the axis of the screw. A better way to do this would be to use two dowel pins, which have much tighter tolerances. I believe that kinematic mounts are also used in some cases to further restrict the degrees of freedom."
Written by Jason Toby on October 12th, 2020