Twist Drill

Morse claims a helical flute doing three jobs: form the cutting edge, eject the chip, admit coolant. Write the three down; you will test each separately.

Examine one bit with the magnifier. Find the two cutting lips, the two flutes, the web between them, and the margin that rubs the hole wall.

Measure the shank diameter with the caliper and compare with the size stamped on the bit. The stamped name is a promise; check it.

Lay the bit on paper, trace the point, and measure the included angle with the protractor. General-purpose drills are ground to 118°.

Cut a right triangle of paper 40 mm tall with a 60 mm base and wrap it around the brass rod. The hypotenuse traces a helix. This is why a flute is a screw.

Cut a second triangle 40 mm tall with a 20 mm base and wrap it. The steeper helix is what a drill for soft metal uses — faster chip lift, weaker edge.

Mark a centre on the board. An unmarked start lets the point wander and the hole is oval before it is deep.

Drill one hole through the board with a 6 mm bit, steady pressure, letting the flutes clear.

Measure the finished hole with the caliper. It is almost always larger than the bit. Record the difference — that gap is why reamers exist.

Drill five holes and measure all five. The spread, not the average, is what an engineer designs around.

Drill deep without withdrawing. Feel the drill bind as chips pack. Withdraw, clear, continue. This is Morse's second job failing in your hands.

Try a #6-32 screw in a hole drilled to fit it. If it passes in every hole you drilled, you have made an interchangeable part.

Cut a hole the old way with the craft knife. Measure it. The comparison is the entire argument for the twist drill.

US 38,119, “Improvement in Drill-Bits”, Stephen Ambrose Morse of East Bridgewater, Massachusetts, granted 7 April 1863. Morse went on to found the Morse Twist Drill and Machine Company of New Bedford in 1864.

Not that Morse. Stephen A. Morse has no connection to Samuel F. B. Morse of the telegraph and the code. The coincidence of surname misleads often enough to be worth stating.

The manufacturing problem behind the patent. A helical flute is easy to draw and hard to cut. Morse's early drills were made by twisting a flat bar — hence ‘twist drill’, a name that describes an obsolete manufacturing method rather than the finished geometry. Milling the flutes into a solid round blank came later and gave a far more consistent tool. Joseph R. Brown's universal milling machine of 1862 was developed at the request of Frederick Howe specifically to machine spiral grooves in twist drills — the drill and the machine that makes it arrive together, each demanding the other.

Why it belongs in a metrology batch. A named drill size is a physical standard distributed to every workshop in the world. When a drawing says ‘6 mm hole’ and any shop can produce one, the drawing becomes portable. The Morse taper — his self-holding shank taper — is still a live standard on machine tools today, which makes it one of the longest-surviving dimensional standards in engineering.