While doing some pocketing cuts on the CNC Router, the bottom surface of the pocket turned out a little bit ragged. This is caused by the router’s spindle not being perpendicular to the machine bed. Instead of a flat bottom, it was ‘saw-toothed’, the size of the ‘teeth’ being a function of the cutting tool diameter, the offset distance between passes and how out-of-square the spindle is to the bed. Click ‘continue reading’ below to see an exaggerated graphical example.
This is not a unique problem and there is definitely a solution. There is a thing called a tramming gauge. It is super simple: a piece of metal that holds an indicator a certain distance from the spindle. The tramming gauge is loaded into the spindle and a measurement is taken in one position and again after the tramming gauge is spun 180 degrees. If both measurements are the same, the spindle is square. Here’s a great video on Tramming a Bridgeport Milling Machine Spindle.