Spindle RPM, tap drill size and cycle time for cutting an internal thread — set thread size, material and hole depth.
Tapping RPM uses the same surface-speed formula as drilling, but at a much lower cutting speed — typically a third to a half of the equivalent drilling speed — since the tap is cutting a full thread form rather than just clearing a hole: RPM = (tapping speed × 1000) ÷ (π × thread major diameter). Because rigid tapping synchronises feed to spindle rotation, the feed rate is fixed at exactly one thread pitch per revolution: Feed rate = RPM × pitch. Cycle time includes both the forward tapping pass and the reversal back out, which this calculator assumes takes roughly the same time as tapping in.
Tap drill size follows the same thread-diameter-minus-pitch rule covered in the tap drill size chart guide. For the hole itself before tapping, use the drilling calculator to work out the right RPM and feed for that tap drill diameter.