When I’m carving a ball and claw foot, I use a gauge that includes all the info needed to carve the foot. The information is transferred to the gauge from an original or from a prototype that I’m satisfied with.
Most feet I carve are from 3″ stock, so the foot will live inside this 3″ cube. Initially, two circles are scribed on the bottom of the foot, one is the diameter at the equator of the ball and the other is the footprint where the ball meets the floor. Usually I just write these dimensions on the gauge. I will then scribe diagonals across the bottom of the foot to locate the nails. For demonstration purposes in this article, I’m using a roughed out Massachusetts type foot of mahogany. 
The first dimension I rough out is the maximum diagonal from opposite claws. On the gauge this is the larger of the two cutouts. When this is snug across the claws the maximum width has been reached. 
Next, the gauge is used to locate the apex of each knuckle, the first being the lowest. One side of the gauge has the front knuckles and on the other side are the sides. Sometimes these will be the same. When carving, this is my second step- to bridge these points with cuts that define the profiles of the knuckles. I eyeball these angles until they look identical from side to side. 
Next, the gauge is used to measure the diameter of the ball at the equator. I measure the equator from a note on the gauge that gives me this height off the floor. Once the gauge fits across the equator I’ll use a large gouge to shape the ball both above and below the equator. The gauge has a note on it that is the ball height. Note the triangle in the previous photo for one of the ball heights. Depending on the style of foot this will be either where the ball meets the web or the maximum height of the ball before it passes under the claws, as in a Newport foot. 
Once the ball has been shaped and the claws rounded over, I’ll model the nails. Usually I will eyeball these as they are all the same height off the floor just below the first knuckle. Rear claws usually have only the first knuckle and then smoothly merge with the back of the ankle, so the only measurement I use from the gauge is the first knuckle location. Sometimes I cut a mousehole on the gauge somewhere to indicate the width and height of the knuckles off the ball, but I rarely use it because these dimensions are created by the gouge that I use to shape the claws, almost always an 8-13.
Lastly, I’ll measure the ankle thickness with a cutout for that dimension. 
The great advantage to measuring a foot and carving a foot with this tool is that all the info can be on the gauge with no need for reading tape measures and juggling several pairs of caliper.
Sometimes I’ll even write the tools used to carve the foot on the gauge so that all of the information lives in one spot. I make the gauges out of either 1/8″ or ¼” plywood. Solid stock tends to break too easily, and the thin ply is easy to shape. Once you try this method, I’m pretty sure you’ll be hooked! 
How to Use Carving Tools
Learn design, tool selection and sharpening, as well as how to break a project down into its basic elements.
One Day Ball and Claw Class
An enormous amount of skill can be acquired in a day spent carving a basic ball and claw.
