I am interested in designing a rocking chair. I have found plenty of information on chairs but nothing basic about the geometry of a rocker. Can you explain seat placement and back angle relative to the rockers; provide a geometry for the rocker linkage with respect to the ground; and a seat geometry for an average person?
Answers to your questions
You raised a number of legitimate and important questions regarding the design of a rocker. However, I’ve found that there are no clear and singular answers. There are so many things to consider when designing a rocker. I really couldn’t dictate curves, angles and lengths as a formula because they might change depending on a particular design.
Because of the special demands put upon a rocking chair (as compared to a regular chair), every aspect of its Chair design dimensions and construction should be carefully considered. For instance, a rocking chair’s legs must be shorter than those of a chair to compensate for the addition of rockers. And a rocker’s back should be only slightly angled; otherwise, a sitter might feel like the chair will tip over when in use.
In my experience, it takes three or four tries to come up with a successful original design, but there are a few ways to speed the process along. The simplest approach is to use an existing rocker as a model. After measuring, inspecting and trying the chair, you can make adjustments and changes for your version.
Another method that helps me in the shop is to experiment with the position of the legs on the rockers. On a Windsor rocker, for instance, the legs are slotted to receive the rockers (see What makes a rocker work). This construction allows you to temporarily clamp the legs to the curved rockers as well as experiment with the position of the chair on the rockers. A small 1/2-in. shift in the chair’s position along the rockers can shift the sitter’s weight and dramatically change how the chair rocks.
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