To prevent large burrs and tendency for the drill to grab, a machinist should ________ the spindle pressure when breaking through the material.

To prevent large burrs and the tendency for the drill to grab when breaking through the material, decreasing the spindle pressure is the appropriate approach. When a drill reaches the end of the material, maintaining a high spindle pressure can cause the drill bit to grab, leading to potential damage to both the workpiece and the tool, as well as creating large burrs that can affect the finish of the hole and subsequent machining processes.

By decreasing spindle pressure, the machinist allows for a more controlled exit of the drill bit from the material. This reduction in pressure helps to avoid excessive force that can lead to the drill snagging or tearing the material, which can produce those problematic burrs. It promotes a cleaner hole and a more precise finish, while also extending tool life and improving overall machining efficiency.

Maintaining, increasing, or stopping spindle pressure does not sufficiently address the issue of burr formation and grabbing. Instead, these practices could exacerbate the problem, leading to poor results in the machining process.