What causes swirls in the bottom of the engraving?
If the cutter is sharpened properly, the spindle perpendicular to the material, and the speed and feed rates are correct, the bottom of the cut should be smooth with the swirls uniform, close together and barely visible. As a rule of thumb, slower feed rates and faster cutter speeds produce smoother cuts.
If the swirls tend to be uniform but further apart and more visible, the cause is probably that the feed rate is too fast for the cutter speed. In essence, the cutter is moving forward at a rate faster than its ability to cut cleanly. (Figure 1)
If the swirls are somewhat uniform, but the bottom of the cut is rough, the problem may be that the clearance angles on the tip of the cutter are too radical which can result in the cutter tip scribing grooves as it rotates. (Figure 2) The problem can usually be remedied by reducing the angles and making the tip flatter.
The other cause of swirling has an appearance similar to the above situation, however, the pattern in the bottom of the cut will generally not show a complete circle and the swirls will be more semi-circular in appearance. (Figure 3) This is most often caused by a spindle that is out of alignment and the cutter is not perpendicular to the material. If this is the case the spindle needs to be adjusted on its carriage. The procedure for this is generally available in the machine manual or from the machine manufacturer.
