Threading tolerances

All thread standards have dimensional tolerances to
acheive the required fit between the shaft and the nut.

The shaft (in most cases) has a larger root radius and
closer tolerance than the nut, which is designed to
prevent shaft breakage.

The standards for the ISO and UN (Unified) thread
profiles are shown here.


Partial profile:

Partial profile inserts can be used for a variety of thread pitches and standards,
however, incorrect nose radius on the insert can result in rejection of the com-
ponent. This style of insert will not deburr the major diameter of the thread and
will, therefore, require a secondary operation.
Full profile:

Full profile inserts are designed to produce the correct root radius and depth
requirements for an individual pitch. Tool life and thread quality are always
improved when selecting this style of insert, because the thread profile and
depth is dedicated to that pitch, therefore, fewer passes are required to com-
plete the thread.

Inserts for small Pitches

With this inserts threads can be produced much closer to the shoulder.
Available for pitches 1mm (24TPI) and finer, and also produced in partial
and full profile styles.


Threading cycle times can be reduced up to 50% with this style of insert, and
tool life is greatly increased due to fewer passes. More HP is required when
using this type of insert, therefore, a stable component and rigid set-up are

Chip control is much easier with this new insert geometry, chips are divided
into 3 manageable portions. The first tooth cuts the flanks of the thread, and
the following tooth generates the root radius.

Clearance angles

The side clearance angles on QuadCut are generated by
tipping the insert 10° (QuadCut external) and 15° (Quad-
Cut internal). Note that the clearance angle is larger for
ISO Metric, UN and Whitworth profiles than it is for ACME
and Trapezoidal. More care is required when selecting
cassettes for Trapezoidal and ACME profiles, to ensure
that the helix angle is as close as possible.

Helix angles

Over 98% of all common profiles have a helix angle between 0.5° and 2°. We have chosen 1.5°
as the standard angle for QuadCut when no other angle is specified. In the diagram below, the
helix angle () is shown as a function of the diameter (D) and the thread pitch (P).

Pitch mm
Pitch TPI


D Ø mm   10       20      30       40      50       60       70      80       90     100     110     120    130     140     150

Other helix angles

When threading Trapezoidal and ACME profiles, or when producing a left-hand thread with a right-hand toolholder,
cassettes other than the standard may be required. QuadCut cassettes are available in increments of 1.5° helix.

QER 25-12- 4.5
QER 25-12- 3
QER 25-12
QER 25-12- 0
QER 25-12- 98.5
QER 25-12- 97

Methods of infeed

Radial infeed

This is the most common method of infeed on short chipping materials. On long
chipping materials, it is difficult to break or control the chip as it shears from the
flanks of the thread. The high heat generated from this method of in-feed on the
tool nose radius causes premature tool failure.

Flank infeed

Angular infeed progammed at the same angle as the thread flank. Although the
heat generated from this method is greatly reduced, the rear flank of the insert
removes very little material, which can cause work hardening in some materials,
and unsatisfactory surface finish on the rear flank of the thread.

Modified flank infeed

Angular infeed modified to generate additional work by the trailing insert edge
and still maintain a smooth chip flow with reduced heat at the tool nose. Highly
recommended for most types of material, however, the infeed angle should be
reduced on more abrasive materials to prevent work hardening. Recommended
range 27-10°.

Alternating flank infeed

An excellent solution for optimizing tool life. Many of the latest CNC machines
offer this canned cycle sub-routines and its use is highly recommended for most
materials. The one disadvantage is loss of chip control in certain applications.

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