When I was actively drawing in pen & ink, I used to do practice exercises like the one above. The purpose was to train my eye and develop the control and muscle memory in my hands. Like the exercises music students do to train their ears and eye/hand coordination for the instrument they’ve chosen, creating a set of consistent lines and tones is a foundation skill for doing more complex work with the pen.
In looking at the model so far, I determined that inaccurate measurements and layouts were a prime source of the errors I outlined in this post. This is something I can fix by practicing on scrap material to develop more precision in my working methods.
In the past I’ve used a mixture of techniques to mark and layout parts. After some study, I decided to exclusively use dividers or a caliper to take measurements from my scale rule for marking off the dimensions on the stock. Both tools have advantages and drawbacks. For general dimensions, I lean heavily toward the dividers as it is much easier to locate the sharp points to the exact dimension needed, and then transfer that spacing to the material. Trying to mark the stock directly from the rule creates all manner of variables that will negatively impact the results. If multiple locations are needed, such as equally spaced holes for rivets, it’s easy to set the dividers and step off the points.
The caliper is great for marking off lines from the factory or other prepared true edge of a sheet (see the fourth photo below). I often do this to cut thick sheets into strips of equal width. I rough cut them slightly oversized, so I can true up the raw edge and bring the strip to exact dimension with hand files or the milling machine.
For greater visual contrast and clarity, I put a black coating on the brass with a Sharpie brand marker as a shiny scribed line against the black background is easier to see.