A rudimentary ruling engine

klugesmith, Sat Mar 31 2018, 12:34AM

I needed to make many half-thickness knife cuts in plastic foam (for loop antenna in EMR forum).
Found it challenging to get them parallel and evenly spaced, using a hand-held straight edge connecting hand-drawn dots.
Adding to the hassle, it was important that the step size be 1/6 inch. None of the rulers on hand -- metric, decimal inch, and "fractional" inch -- had markings close enough to use without freehand interpolation.

The solution: mechanical aid, restricting each end of the straight edge to a set of fixed positions.

Original plan was to get #10-24 all-thread rod stock, before being reminded that 5/16"-18 is also standard.

The holes in one end plate are tapped, permanently fixing the phase of each thread (there are only two) with respect to the reference plane.
Then half-nuts were glued to the bottom of the straight edge:

The paper scales in picture were snipped from an old spreadsheet printout, that appeared to have 6 lines per inch. A good case for the English word serendipity.

It didn't take long to cut 16 lineal inches of 21 parallel slots.

Now the machine can be stored very compactly, as parts, until it's needed again.