Cutting the Slit

Cutting the slit is the step in which the round airway at the mouth end of the mouthpiece (stem) is turned into a flat opening. This opening is called the slit, and the thickened tip where it is cut is called the button. The step falls into place after the stem has been drilled and roughly shaped, and it is carried out by hand; on ready-made cast mouthpieces, it is often left as it comes from the factory.

Geometry and Its Effect on Draw

The cross-section of the airway is not uniform from end to end. The hole, usually around 1/8 to 3/16 inch in the shank, narrows to roughly 1/16 inch toward the tip of the mouthpiece; once drilling is finished, about half an inch at the end of the stem is left at that narrow bore. It is in that final stretch that the slit is cut, and its purpose is to recover the volume lost to the narrowing bore in a flattened form. However carefully the rest of the airway has been drilled, leaving the last few centimeters at the tip closed is considered to erase the openness of the draw; sharp corners and abrupt steps are likewise counted among the things that break up the flow. For the mouthpiece's material and overall shaping, see the entries on mouthpiece craftsmanship and mouthpiece materials.

Workshop Practice

The toolkit for cutting a slit is modest: a rotary tool (a Dremel-type) with fine burrs, a very small diamond burr, a 1/16-inch drill bit, needle files, narrow sanding strips, and polishing compound. In shops that use a lathe, the drill bit is mounted in the tailstock chuck; the details of lathe work are covered in the entry on drilling on the lathe.

The work proceeds in three directions. First, a fine burr cuts a narrow guide notch at the end of the airway that only sets the direction; this notch alone does not count as an open airway. The corners left at the bottom of the notch are then flattened out with a small diamond burr, and the opening is widened roughly an inch inward with the drill bit. Throughout, the symmetry of the two sides and the openness of the draw are checked continually. Finally, needle files and sanding strips remove any roughness, and the inner surface is polished by drawing a pipe cleaner soaked in heated polishing compound through the slit.

Marks of a Good Slit

The received view is that the finished slit should be no taller than the original 1/16-inch drilled airway, gaining the cross-section it needs by widening sideways instead. Keeping the height limited lets the button stay thin, so the mouthpiece sits comfortably between the teeth. No special tool is needed to check it: drawing on the mouthpiece alone should produce no noticeable resistance, and the two sides of the slit should look symmetrical to the naked eye. For where this step fits within the overall process, see the entry on pipemaking.