Spiral Router Bits

CNC Router Tool Finder

Spiral router bits are a huge help for improving or tuning performance on a CNC router. Depending on which way the spiral goes [up or down], you get a cutter that either moves the waste in the direction of the spiral. The direction of the waste also exerts a force on the workpiece in the same directions.  So, an up-cut router bit will move the chips up and clear the cut well, but it will tend to pull up on the workpiece [so the clamping needs to be better and it has the disadvantage that it wants to pull up and has a tendency to cause break out along the top edge.]

Why should I choose a down-cut router bit for my CNC?
For wood and materials that may chip, a down cut is cutting into the material, not lifting it; as the downcut pushes down, it gives a cleaner finished edge on top, but can break out the bottom edge. If you are working with spoil boards and backing jigs it's not problem. The down-cut also increases work pressure helping to keep the workpiece firmly on the table. The disadvantage to them is that they force the chips down to the bottom of the slot or pocket, which is far from ideal. Think about using a downcut for a final finish pass where there is less waste to clear and you want the best finish.