Quote Originally Posted by MrWiz73 View Post
Hey James, I am using a 3mm Diameter Straight Twin Fluted Wood Cutter. My current spindle speed is 12000 and feed rate is 12mm/sec. To be honest i really have no idea if i have the right settings, it was a half-educated stab in the dark as i have had no CNC training. When using thicker MDF the shapes seem to be coming out spot on but with the 4mm i am getting bad furring on the edges.
What depth per pass? I'd keep the depth low to start with and increase the feed rate, or decrease the spindle speed. At the moment your chip-load (the width of each chip) is 0.03mm when it should be about 0.23mm. That implies you need to feed about 7 times faster or decrease the spindle speed by the same factor ... but both of those would break the cutter as the deflection is too high. The best will be somewhere in between...

If you're doing a lot of this it's worth getting a single flute carbide cutter. Since it only has one flute you only have to use half the feedrate to get the right chip load.