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.