CNC Setup, Workholding, and Tool Setting
Locating and holding the part
Workholding should follow 3-2-1 locating: three points establish the primary plane, two the secondary, one the tertiary - avoiding over-constraint that twists a part. Know vise technique (parallels, soft jaws, jaw lift, tapping the part down), fixture plates, clamps and strap support, chucks with proper jaw boring and grip length, collets, vacuum and magnetic chucks, and tombstones for multiple parts. Materials and cutting forces dictate clamping force: enough to resist chatter, not enough to distort.
Setting zeros and tools
Understand the difference between the work offset (G54) that locates the part and the tool length offset that locates each tool's tip. Know edge finding with an edge finder (offset the radius), probing routines, touch-off on a gauge block or presetter, and the importance of clean tapers and proper drawbar torque. Check tool runout (TIR); a worn or dirty taper destroys both finish and tool life.
Proving the setup
Standard sequence: verify program and offsets, dry run with the tool clear of the part, single block the first tool, confirm clearances and retracts, cut a first article, inspect it, then run production. Always know how to recover from a mistyped offset.
Traps
Confusing work offset with tool length offset, forgetting to shift by the edge finder radius, over-tightening a vise and springing the part, or leaving chips on a taper. A worn tool set as a different tool number is a common distractor.
Rule of thumb and worked example
Edge finder Ø0.200 in: touch off until it kicks, then move 0.100 in toward the part to establish the true edge as the work offset.