FR-1 is a hard, flat material that consists of a thin layer of copper over a non-conductive phenolic resin. It’s usually about the thickness of two or three credit cards. It's primarily used for making circuit boards. The thin copper layer can be milled or etched away, leaving traces to which electronic components can be soldered.
Unlike FR-4, which is fiberglass-based and generates dangerous glass-shard dust when milled, FR-1 is safe to use if you keep it away from your eyes, lungs, and skin. We recommend vacuuming up the debris after you’re done milling (never blow on it).
We sell FR-1 PCB blanks in our store. It’s generally hard to find in small quantities elsewhere.
It’s good to store the FR-1 blanks on a flat surface to prevent them from bowing (aka warping). Before using a board, check if the board is bowed. You can check for bowing by placing the board on a flat surface and pressing on the left side then the right side and see if it's flat or if it's see-sawing on the flat surface. If it's warped, you can try to gently bend it back the other way until it looks straight. This will help make sure the board lies flat, which is very important when using smaller end mills and milling small features.
When machining circuit boards using the Desktop CNC Milling Machine, we recommend using our removable spoilboard and high-strength double-sided Nitto tape that we carry in our store. Be sure to place strips of double-sided tape across the back of the board until most or all of it is covered with a single, even layer of tape, without any overlap or wrinkling.
Note: For more info about fixturing with the Desktop CNC Milling Machine, see our Fixturing support guide.
Most circuit boards can be milled with either a 0.005” PCB engraving bit or a 0.003” PCB engraving bit to isolate the traces and pads, and a 1/32" flat end mill to cut the holes and board outline. Sometimes you might need to use a 1/64" flat end mill. Less commonly, a 1/16", 1/8", or 1/4" flat end mill can be used if you need to remove large sections of copper. Typically, to mill small features, it's best to use a PCB engraving bit instead of a 1/100" flat end mill because the engraving bits have a smaller cutting diameter and are more robust.