I saw a needle tool used in a video by a Russian artist to cut a curved shape out of a sheet of clay. It seemed like a better way to cut curves than an Xacto blade, especially with templates made of card stock. An Xacto blade would nick their sides.
Below is the sewing needle tool I made from the smallest sewing needle I had. I used a small electric eraser refill to cover the ends so I wouldn’t poke myself. Polymer clay would make a good handle for this tool.
Here I’m using it to cut a slot for a pin back on a brooch. I try to hold the needle straight up and down.