Dividers aka a Compass

This post is undergoing revision to make it clearer - my editor stopped by and gave advice, but I have not yet acted on her suggestions.

I ignored them, much as I ignored those pages of geometry in the pattern books.

But if you use proportions to determine how big something should be, dividers - or a compass - are how you transfer a dimension from one place to another. Dividing your window into 6 parts to find the width of your casing? Use the divider to transfer that dimension from the window to your piece of wood.

Today we would discuss it this way: "6 inches +?" "6 1/4 inches?" "How about only 6 3/8 inches?" Tricky to figure out, right? The divider is easier.

A compass serve a similar function as a ruler or a measuring tape, but it always refer back to a real thing. Intellectually, inches and feet are abstract numbers, with no relationship to any other thing at all. If you ask, "Why use a 5-1/2 inch casing for that window rather than one that's 6-1/2 inches?", an answer might have to do with cost or personal preference. The answer, "Is the 5-1/2 inch casing a better proportion for the window?" doesn't come automatically. When you get to that question using dividers you have already included the window, that's where you began.

I find I am in uncharted territory. At first I thought I was talking about 'calipers'. Then I found the tool I was thinking about is called 'dividers' or 'a compass' .

So far I haven't found very much written that confirms what I am seeing. I do know that proportions and relationships in medieval construction were often based on the circle and how it can be divided and combined. 17th and 18th century woodworking tool box lists include dividers and compasses. However, the drawing comes from Eric Sloan's Museum of Early American Tools , and he places it among the wheelwright's tools, not with the joiners'.

Measuring - Proportions

How did carpenters measure in 1797?
What does Asher Benjamin assume his readers know when he writes his first pattern book?

Instructions today for building a simple bookcase  - for example - assumes the carpenter will use  a tape measure and a steel carpenter's square.
By comparison, in 1797, a carpenter had a square and perhaps a folding rule.
 He also had dividers and a compass. He used both to determine dimensions.


 Here are Asher Benjamin's  instructions for the moldings around a door (at the end of the descriptions for Plate 1).  Click the picture  to enlarge it - for easier reading!

He gives no dimensions, just ratios:  'seven or eight parts',  'one fourth or one third wide'.
The reader would have used his compass and dividers to  layout the geometry, to divide a door or window width into  7 or 8 parts.


When Asher Benjamin writes his books, we were still making the parts for a house specifically for that house - no buying off the shelf.
When it came to finish work, each molding added at a door opening or chair rail was made to order, regardless of how it was measured.
Uniform measurements for construction were not necessary until people wanted interchangeable parts. If your yard was 36" and mine was 35" it didn't matter.

Benjamin's introduction to geometry - his first plates - and his descriptions of how to draw the profiles of various moldings show his readers to how adapt his patterns to their specific buildings.

The Country Builder's Assistant, by Asher Benjamin, 1797,  shown above,  is a reprint by Applewood Books, Bedford, Massachusetts, 1992.  The originals, (worn. well used and well loved!) are often available in rare book libraries.

TOOLS

I am curious about the tools carpenters had around 1800. Asher Benjamin wrote for the trade. He was a 'joiner' himself. He knew what his readers were working with. His books will make more sense if I too know what was in those carpenters' tool boxes.
It is not easy to find any information that's not prefaced with, " I think..." The list so far includes hand saws, chisels, hammers, plumb bob, planes, wooden squares, bits and braces.

No rulers, no measuring sticks. This last fact really interests me.

Eric Sloan wrote about early American tools in the 1960's. His books have beautiful pictures, some dates, and basic information. He knew a great deal more than is in the books. I wish he had written more.