1. Relation Between Spindle Speed and Lead Screw Speed:
The speed of the lead screw (or the feed rate) is determined by the spindle speed and the pitch of the lead screw. The relationship is:
\[
\text{Lead screw speed} = \frac{\text{Spindle speed} \times \text{Pitch of lead screw}}{\text{Pitch of thread to be cut}}
\]
2. Substituting Values:
\[
\text{Lead screw speed} = \frac{60 \, \text{rpm} \times 6 \, \text{mm}}{2 \, \text{mm}} = 20 \, \text{rpm}
\]
3. Conclusion:
The speed of the lead screw is 20 rpm to cut the screw threads with a 2 mm pitch.