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Spiral Bits are the one set of bits that can be confusing for many woodworkers. The main reason for this is the description given for these actually changes depending on where the bits are installed, in either a handheld wood router or CNC router, or ... upside down in a wood router table.
Watch it on Youtube: https://youtu.be/hTlx3FH39Bs
The nomenclature for router bits is - when the bit is vertical and the tip of the cutting edge is at the bottom of the bit.
Thus a Spiral Up Bit would have the cutting edge at the bottom of the bit and as it rotates in the wood it will drive the wood chips up the flutes and the tear-out will also be driven upward, which if cutting through the wood, will give clean cuts at underneath the wood.
Conversely and Down Spiral Bit will have the wood chips and any tear-out drive down into the wood or if cutting through the wood, the wood chips and tear-out will be in the bottom of the wood whereas the top of the cut will be clean.