🔍 It depends on the size of your machine and the project. Common diameters are **1\"**, **2\"**, or even **3\" for surfacing bits. On a smaller CNC (like desktop size), a 1\" or 1-1/4\" bit is plenty – larger bits might strain a small spindle. For bigger CNCs or handheld router sled setups, a 2\" or 3\" bit covers more area faster. For example, SpeTool offers a 3\" diameter insert surfacing cutter which is great for large slabs. The key is to choose a bit that your router can spin at the proper speed without struggle. Also consider your router’s collet: larger surfacing bits usually have a 1/2\" shank for stability, so you’d need a router that accepts 1/2\" bits. In summary: use the largest bit your router/CNC and project comfortably allow – bigger bits flatten faster, but you must ensure your machine can handle them.

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