There are three modes for configuring stems in BikeCAD.
If the goal is to configure a quill stem for a threaded headset. it may seem unclear which of the three modes should be chosen. Although the diagrams associated with the input fields in each mode depict stems for threadless headsets, the fact is that any of the three modes can be used to model a quill stem.
The key dimension to change, regardless of the mode selected, is dimension F. In a stem for a threadless headset, dimension F represents the outer diameter of the collar which slides over the steerer tube of the fork. In a quill stem, dimension F represents the diameter of the quill which is inserted into the steerer tube of the fork. The typical diameter of the quill in a quill stem is 22.2mm (7⁄8").
The simplest mode for defining a stem is the first mode. If using the first mode to define a forged quill stem, dimension E can be tweaked so the quill does not extend beyond the top edge of the stem body. To slide the stem up and down, one must change the spacers dimension in the Headset dialog box. Although spacers are not actually used in a quill stem, assume these spacers simply represent the length of exposed quill.
A quill stem can also be modeled using the second mode. The advantage with the second mode is the length of exposed quill can be modeled as part of the stem. It does not have to be represented by spacers. The trouble with using this mode for a quill stem is dimensions E, G and Y must all be increased or decreased uniformly when raising or lowering the stem. Furthermore, the handlebar clamp is located by X and Y coordinates rather than by a length and an angle which would typically be the published specifications.
Finally, the third mode can also be used for defining a quill stem. The defining characteristic of the third mode is the body of the stem is tangent to the quill. When using the third mode, one must select the Curved checkbox in order to offset the handlebar clamp from the steerer tube. By applying a curve to the stem, one can simulate the rounded contour of a forged quill stem.
