You need to make the 3d tabs longer than your regular tabs, due to the way that they ramp up and down.
Found this out the hard way =p
haha, will do!
Some refer to those as dwell marks. It happens because travel is stopped as the bit is raised and plunged straight up and down. It will happen at the start point as well as it stops to plunge each time around. So use ramped plunges as well as 3d tabs.