Threading inserts
Thread-turning insert profiles, cutting points, holder and shim compatibility, chip control and worked lead-angle calculations.
Tags: tooling, cutters, turning, threading
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At 2.0 mm pitch and 18.0 mm pitch diameter, one start has 2.0 mm lead and 2.026° lead angle. Three starts give 6.0 mm lead and 6.057°. At 400 rpm the feeds are 800 and 2,400 mm/min. Select the insert inclination or shim using the actual tool system.
A thread-turning insert cuts a profile while axial motion follows workpiece rotation. Verify the tool and shim against the required thread.
A thread's root joins adjacent flanks at the bottom, while the crest joins them at the top. The profile angle is measured between flanks in an axial plane. These features describe the thread form; they are distinct from the helix angle around the part. Sandvik Coromant, Threading formulas and definitions
Full profile, partial profile and multiple cutting points
Sandvik distinguishes three thread-turning insert concepts:
| Concept | What the edge forms | Application distinction |
|---|---|---|
| Full profile | Complete profile, including the crest | Separate insert for each specified pitch and profile |
| V-profile / partial profile | Thread groove without topping the crest | Covers a bounded pitch range; prepared diameter remains important |
| Multi-point | More than one cutting point in a full-profile concept | Requires stability and exit space for the final tooth |
These distinctions concern the cutting form. Sandvik separately discusses sharp, flat and chip-breaking geometries. A chipbreaker designation is not another name for full profile. It also distinguishes radial clearance from clearance at the thread flanks, with holder shims controlling insert inclination to suit the thread helix. Sandvik Coromant, Choosing thread-turning inserts and shims
Explanatory synthesis: the number of indexable edges available over an insert's life is different from the number of cutting points engaged in one pass. Likewise, a matching included angle does not establish the correct root radius, crest shape, pitch range or holder interface. A generic 60° description is insufficient to establish a complete thread specification.
A named profile example comes from Seco's December 2018 announcement of 13 full-profile inserts for internal UNJ and MJ threads, extending its external/internal range. The announcement identifies stainless steel and heat-resistant nickel and titanium alloys as applications and pairs the inserts with Jetstream Tooling directed-coolant holders. This historical product announcement establishes neither current availability nor universal interchangeability with other thread forms. Seco Tools, Full-profile precision threading inserts
Internal access and holder compatibility
ISCAR's threading overview lists distinct insert families and bore limits. Its internal examples include GEPI partial profile, minimum bore 12.5 mm, TIPI partial profile, 20 mm, and UMGR partial profile 55°/60°, 5.2 mm. Those are named family examples, not minimum bores for all inserts of the same profile angle. Bore access is a tool-system constraint, separate from whether an edge matches the required thread. ISCAR, Main types of threading inserts
Sandvik relates internal-threading vibration and bar deflection to overhang, bar material, diameter and cutting forces. Insert-seat condition and clamping also affect the result: excessive screw torque can damage the insert or screw, while insufficient torque permits movement and vibration. The specified tightening torque belongs to the actual holder; no universal torque or overhang limit follows from an insert's nominal size. Sandvik Coromant, Thread-turning tool setup
Chip control, infeed and prepared diameter
In Sandvik's application guidance, modified flank infeed helps direct chips, while prepared workpiece diameter affects first-pass loading and final thread size. The nose radius, speed and infeed affect edge loading and wear. Coolant delivery can influence evacuation and temperature, but very low temperature in sticky materials can also promote built-up edge. These relationships do not produce a material-independent cutting recipe. Sandvik Coromant, Thread-turning application tips
A full-profile cutting edge controls more of the thread's shape, but a completed thread still has separate requirements for diameter, lead, flank angle, surface condition and runout. Tool geometry alone does not prove those finished-part characteristics.
Worked example: pitch, lead and insert inclination
A single-start thread advances one pitch per workpiece revolution. For multiple starts, lead equals pitch multiplied by the number of starts. Sandvik explicitly uses lead when discussing multi-start shim selection. Sandvik Coromant, Multi-start threading
Use the hypothetical pitch, pitch diameter and spindle speed stated above.
From an unwrapped helix, the lead angle is φ = atan(L / (π × d2)), where L is lead. This is the pitch-diameter relationship given by Sandvik's threading formulas.
| Quantity | One start | Three starts |
|---|---|---|
Lead L = starts × P |
2.0 mm/rev | 6.0 mm/rev |
| Lead angle at 18.0 mm pitch diameter | 2.026° | 6.057° |
Synchronized axial feed n × L |
800 mm/min | 2,400 mm/min |
| Ideal traverse time over 24.0 mm | 1.8 seconds | 0.6 seconds per traverse |
The pitch and pitch diameter stayed constant; lead angle and synchronized feed changed. Using pitch alone in the three-start helix calculation would incorrectly return the one-start angle.
The time calculation excludes entry, runout, retract, acceleration, synchronization, return motion and additional passes. Three starts also require separate grooves; the per-traverse result is not a total-cycle comparison. The computed angles are geometric quantities, not a direct catalog shim choice: the insert, holder and available inclination range must support the actual thread system.
Coverage and source limits
This reference describes insert concepts and selected manufacturer examples, rather than a catalog cross-reference or a thread acceptance standard. Substrate, coating, edge preparation, thread hand, internal/external application, seat and clamping interface remain specific to the actual tool. No generic productivity multiplier, grade equivalence, achievable tolerance or pass schedule is adopted.
The Seco announcement states December 2018. The other cited web pages display no issue date in the content reviewed on November 2, 2026; crawl dates and copyright years are not treated as publication dates.