Before the advent of modern computers, drafters used french curves to draw curved lines of various radii. These templates usually incorporated a number of curves over their entire length. Modern usage has dropped off, but drafters still find a use for the french curve in crafting and drawing. Making your own french curve takes time and preparation, but modern technology makes this task easier by providing you with a plethora of potential templates to choose from.
Find and print out a french curve template. Doing a quick image search online will provide you with templates. Print one out to the desired size, making sure the boundaries are clear.
Cut the outline of the french curve from the printout, and tape the template to the acrylic. You can also use a marker to transfer the pattern.
Use a jeweler's saw to cut out the shape. You can cut out the outline directly, but you will need to use a drill to cut a pilot hole to saw out any inside shapes.
Smooth out the edges with sandpaper. Use successively finer grits to smooth out all of the rough spots.
Mark out inches and fractions of an inch on the string. Stretch the string along the ruler and use a pen or marker to mark the measurements.
Use the string to mark out measurements on the french curve. Stretch the string along the curves and use a marker to transfer the measurements.
You can also use hard wood with a tight grain for french curves.
If you are looking for something for short-term use, you can use thicker cardboard.
Be careful when using the saw to ensure you don't cut yourself.