Taper Thread
A taper thread is a screw thread cut on a conical surface rather than a straight cylinder, so its diameter changes progressively along the axis. In CNC machining, the tool path coordinates axial feed with simultaneous radial motion to produce a helical thread on the taper. This design creates a wedging, interference fit that seals under load, as seen in NPT and Rc pipe threads.
On the shop floor, taper threading is a live-axial threading operation where the control slews the X axis while Z feeds, so the tool cuts a helical path on a cone. A programmer can use G32 with explicit end X and Z positions plus feed rate to synchronize both axes on every pass, or use G76 where the taper is set as a radial parameter in the second block when the control supports it. This matters most for NPT-style fittings, sealing plugs, tapered studs, and precision pipe connections, because the thread must not only engage mechanically but seat on the taper for pressure integrity. The setup is more demanding than straight threading because tool path, start diameter, taper amount, pass depths, and machine interpolation must all agree with the thread standard. If any of those are off, the part can assemble visually yet fail on gauging or sealing.
Is a taper thread the same as a tapered turning feature?
No. A tapered turn changes only the outside geometry, while a taper thread is a helical thread form cut on a taper, requiring synchronized axial motion and radial progression.
Why are taper threads used in pipe work?
Because the taper creates wedging contact that helps the threads seal under load, which is why pipe-thread standards commonly use a taper angle rather than a straight thread form.
What does the CNC programmer actually control?
The programmer controls pitch, taper amount, thread length, start/end diameters, and in some cycles the taper parameter as a radius value; the machine then interpolates the synchronized motion needed to cut the helix on the cone.