10” divider 3mm plywood. Files will be available online under Creative Commons License.

What is a proportional divider?

It’s a 2 ended divider. One end measures the original ‘object’. The other scales in the selected proportion. Proportions can be 2 to 1, 3 to 1, 5 to 1 or anything in between. Precision is the definition of these tools. Some proportional dividers are pretty random in their scaling. Avoid those that don’ give precision measure.

This divider is set to a 1 to 2 ratio. The original on the left. This divider has ratios of 2 to1, 2.5 to 1, 3 to 1, 4 to 1 and 5 to 1.

My thinking for designing this was based on the canvas rectangles that I work with and their relationship to the photo references that I use.

I often start a painting with a 4 x 6 photo to do my initial sketch. The 2 x 3 ratio of the photo and the sketch relate well to a 20 x 30 or a 24 x 36 canvas.

In general I work from my sketch and a scaled photo for color. I draw the scene roughly with charcoal or a brush checking my proportions with the divider if the drawing looks wonky. I’m not a slave to the dividers unless I doing a very tight rendering.

I have made accurate proportional dividers using yardsticks from the home store on large canvases. Works OK.

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