Having spent time as a mechanical engineer as well as product designer, I have taken many parts from concept sketch through to mass production. Below are a few examples of engineer drawings. For many of the parts I have designed I have also been responsible for creating the drawings and getting the part made, whether that means making it myself, a local machine shop, or mass producing a part in asia.
Below is a quick project I did for Wrightspeed, a company that was developing their own electric powertrain for heavy trucks. They had a box to enclose their motor controller that is mounted just above the motor. Since the application was for a heavy truck, the box was between the frame rails, exposed to the elements and visible to anyone looking at the truck. My project was to redesign the box to be more visually appealing ,communicate the brand and also be a manufacturer cast aluminum part. Below is a sketch and the CAD of what I created.
This is the original box as designed by Wrightspeed
Here is a quick sketch of the box I designed
The box I designed shown above