What do I mean by this? Lets look at a 1797 plan book by Asher Benjamin and see. If you wanted to build an interior door today you would buy a set of measured drawings for a 2/8, 2/10 or 3/0 door which would give you the standardized width of the stiles, bottom, top and lock rails, dimensions for the molding, etc. If you look below at a plate from Benjamin's 18th century plan book, you will see that the drawings are far simpler.
|Asher Benjamin, The Country Builder's Assistant|
(1797) plate 12.
The genius of this approach is its simplicity and flexibility. If your door opening is an odd size like 2/9, 2/11 or 3/2 (as is common on older homes), you simply step off 9 parts on the door opening's width with a pair of dividers and there you have your base measurement. You then use the dividers to lay out the width of the stiles (1 divider step or part), the dimension of the bottom rail (1 1/2 divider step) and so on until you have your stock ready to cut and plane. Regardless of how wide or narrow the door, the proportions of each component to the entire door are exactly the same.
What's better yet is you don't even need a ruler or to know the dimension of the opening. You simply mark the width of the opening on a scrap piece of wood or story stick, use your dividers to divide it into 9 parts and start laying out your door. The idea of not knowing or needing the dimension of a door is hard for modern tradesmen to wrap their heads around, but in the 18th and 19th century this was standard procedure.
|Ca. 1849 Greek Revival Door|