Drilling and Sawing Operations
What this domain tests
Drilling and Sawing Operations tests drill geometry, speeds and feeds, workholding, hole finishing, tapping, and saw blade selection. The exam expects safe setups and a hole that meets size, location, and finish requirements.
Core rules and concepts
- A standard twist drill has a 118° point for general steel; 135° split points reduce thrust and are common for tougher alloys. Lip clearance must be equal on both lips.
- Inch drilling speed: RPM = (4 × cutting speed in ft/min) / drill diameter in inches. Use coolant or cutting fluid for steel; reduce speed for stainless and high-strength alloys.
- Clamp the work to the table or in a vise; never hold a part by hand under a drill press. Use a center drill or spot drill to establish location.
- Reaming follows drilling and removes a small amount of material for size and finish. Ream at about half the drilling speed and twice the feed, with the reamer aligned.
- Tapping on a drill press or mill requires a tapping head or a floating holder; start the tap square and use the correct tap drill.
- Bandsaw blades: coarse pitch for thick solid stock, fine pitch for thin sections and tube. Break in a new blade at reduced feed, and use coolant where recommended.
Worked example
A 1/2 in diameter hole is to be drilled in mild steel at 100 ft/min. RPM = (4 × 100) / 0.500 = 800 rpm. With a feed of 0.008 in/rev, penetration rate = 800 × 0.008 = 6.4 in/min. Reasoning: the constant 4 combines π and the 12 in/ft conversion for inch units; using diameter in inches keeps the units consistent.
Traps that cost marks
Holding work by hand on a drill press; using a dead-center drill without a pilot; reaming at drilling speed; forgetting to break the chip when tapping; and using a fine-pitch blade on thick stock, which clogs the gullets. Also watch for a drill with unequal lips, which cuts oversize.