Sandvik Coromant Threading User Manual

Contents

APPLICATION GUIDE

Threading

Thread turning and thread milling

Introduction

1 Basics in threads

2 Applications

Threading methods

Thread turning vs thread milling

Thread Turning

Thread Milling

3 Products

Thread Turning

CoroThread® 266

CoroCut® XS

CoroTurn® XS

CoroCut® MB

T-Max Twin-Lock®

Extended offer

Thread Milling

CoroMill® 327

CoroMill® 328

CoroMill® Plura

Grade information

4 Troubleshooting

5 Technical reference

Cutting data

Programming

Thread turning infeed recommendations

External thread milling recommendations

Formulas

Inch/mm conversion table

112

114

118

ntr

oduction

Introduction

Modern threading tools can produce complex component features with relative ease, but to gain consistent results there are a number of considerations to be made.

In this application guide, we show you how to achieve threading success with Sandvik Coromant tools. Our aim is to help you to choose the right tooling combinations to produce consistent, high quality threads and guide you towards the most productive and problem-free threading performance.

This guide also includes information on basic threading principles

- together with deeper application information, troubleshooting advice and  nally, a technical reference section to cover all of your thread machining needs.

Basic in threads

1. Basics in threads

What is a thread?

Threads are classi ed according to the main functions they perform in a component.

Primary functions of a thread:

• To form a mechanical coupling

• To transmit motion by converting a rotational movement into a linear movement, and vice versa.

• To obtain a mechanical advantage, by using a small force to create a larger force.

Threads are also classi ed into various pro les or forms. The selection of these forms will be in uenced by many other secondary, but still vital, functions.

Thread forms

The thread pro le de nes the geometry of a thread and includes component diameters (major, pitch and minor), the thread pro le angle, pitch and helix angle. The most common thread forms or pro les produced today are shown below.

Application Thread form Thread type Connecting

General usage

Pipe threads Whitworth, British Standard (BSPT),

Food and  re Round DIN 405

Aerospace MJ, UNJ

Oil and gas API Rounded, API Buttress, VAM

Motion

General usage

ISO metric, American UN

American National, Pipe Threads, NPT, NPTF

Trapezoidal, ACME, Stub ACME

Basic in threads

Threading terms and de nitions

1. Root/bottom

The bottom surface joining the two adjacent  anks of the thread

2. Flank/side

The side of a thread surface connecting the crest and the root

3. Crest/top

The top surface joining the two sides, or  anks.

P = Pitch, mm or threads per inch (t.p.i.)

= The pro le angle = The helix angle of the thread

d / D = The major diameter, external/internal d

/ D1 = The minor diameter, external/internal

/ D2 = The pitch diameter, external/internal

Pitch diameter, d2 / D

This is the effective diameter of the screw thread; approximately half way between the major and minor diameters.

Helix angle

The helix angle ()is the geometrical shape of the screw thread, it is based on the pitch diameter of the thread (d pitch (P) – the distance from one point on a thread pro le to the corresponding point on the next. This measurement can be represented by a triangle being unwound from the component.

, D2), and the

The same pitch on different diameters gives a different helix angle, see example above.

Thread designations

International standards

To ensure that the two (internal and external) halves of a threaded joint  t together properly to produce a connection capable of bearing a speci ed load, threads must maintain certain standards. International standards for thread forms have therefore been established for all common thread types.

Below are examples of Metric, UN and Whitworth thread designations.

ISO metric thread designations

The complete thread designation is made up of values for the thread form and the tolerance. The tolerance is indicated by a number for the tolerance grade, and letters for the tolerance position.

. Basic in threa

Examples:

M16 - 6h

Thread designation and nominal dimension Tolerance class for pitch and crest position

Pitch Tolerance class for pitch diameter Tolerance class for crest diameter

M10 x 1.25 5g6g

A  t between threaded parts is indicated by the internal thread tolerance class followed by the external thread tolerance class, separated by an oblique stroke.

Basic in threads

Tolerance positions

The tolerance position identi es the fundamental deviation and is indicated with an upper-case letter for internal threads and a lower case letter for external threads. A combination of tolerance grade and position give the tolerance class. The values of the tolerance classes are given in the standards for the different threading systems.

Tolerance positions

Internal threads H and G External threads h, g, f and e

ISO inch threads (UNC, UNF, UNEF, UN)

The UN system has three tolerance classes, ranging from 1 (course) to 3 ( ne). A typical UN thread is designated as follows:

¼” 20UNC – 2A

2A – Indicates a medium tolerance

UNC – Indicates a course pitch

20 – Pitch value: threads per inch (t.p.i.)

¼” – Major thread diameter

ISO - uni ed (UN):

. Basic in threa

Loose tolerance

Medium tolerance

Tight tolerance

Tolerance position

Types of UN thread

UNC thread diameter with course pitch UNF thread diameter with  ne pitch UNEF thread diameter with extra- ne pitch UN thread diameter with constant pitch

All of the above types of thread can be created using the UN insert from Sandvik Coromant

The pitch value is indicated in t.p.i. (threads per inch). To convert to metric, this should be divided by 25.4 using the following equation:

1A 1B 2A 2B 3A 3B

20 t.p.i.  25.4/20 = 1.27 mm.

Basic in threads

Whitworth threads (G, R, BSW, BSF, BSPF)

Whitworth screw threads are now obsolete, but Whitworth pipe threads are a recognized international standard. There are two tolerance classes for external-, and one tolerance class for internal Whitworth pipe threads.

Whitworth pipe thread designations

These threads are divided into 2 groups:

• Pressure-tight joints not made on the thread, ISO 228/1

• Pressure-tight joints made on the thread, ISO 7/1

Whitworth pipe threads:

BSW BSF BSP.F

Fine Only

Coarse

A B

one

class

Tolerance position

Examples of Whitworth pipe thread designations:

Pressure tight joints not made on the thread:

ISO 228/1 G

= G 1 ½ A

(external)

= G 1 ½ (internal)

= parallel thread

= pipe diameter, not thread diameter

1 ½

A or B = external tolerance class only

Pressure tight joints made on the thread:

ISO 7/1 = R

7/1 = Rc 1 ½R 7/1 = R 1 ½R

Sandvik Coromant’s WH inserts are to be used for parallel threads. The PT inserts are for the conical thread.

1 ½R

= parallel thread, internal

= conical thread, internal

= conical thread, external

2. Applications

Threading methods

Various methods and applications exist for generating screw threads. The choice of application will be based on the time taken to produce the thread and the level of thread precision required.

Different ways of making threads

. Application

Metal cutting

Within the metal cutting area, thread turning, thread milling and thread tapping are common threading techniques using cemented carbide cutting tools. The design of component and machine tool are the main factors when deciding which technique to use, and there are a number of important considerations to be made in order to maximize success.

Molding

Rolling

Metal cutting threading methods

Thread millingThread turning Thread tapping Thread whirling

Grinding

. Application

Thread milling vs. thread turning

This application guide focuses on thread turning and thread milling products and application techniques. Each technique has its own advantages in certain situations.

Thread turning Thread milling

Thread turning

• Normally the most productive threading method

• Covers the largest number of thread pro les

• An easy and well known threading process

• Provides a better surface  nish

• Can be used in deep holes with dampened bars

• Has dedicated thread programs in CNC machines

Thread milling

• Threading of non-rotating components

• Interrupted cuts offer good chip control in long-chipping materials

• Lower cutting forces make it possible to thread in long overhangs and thin-walled components

• Threads close to a shoulder or bottom, no need for a relief groove

• Enables machining of large workpieces which cannot be easily mounted on a lathe

Insert types

Three main types of threading principle can be used to produce a thread. The different technical and economic arguments for each insert are the main guide in the choice of application.

Thread turning Thread milling

Full pro le

. Application

V-pro le

Multi-point

. Application

Full pro le inserts –  rst choice for high quality thread forms

The most common insert type, used to form a complete thread pro le, including the crest.

• Ensures correct depth, bottom and top pro le for a stronger thread

• Extra stock should be 0.03 – 0.07 mm (0.001 – 0.003”)

• No deburring required after threading operation

• Fewer passes required compared to a V-pro le insert, due to the larger nose radius

• Separate insert required for each pitch and pro le

• Productive threading performance

Extra stock should be left on the workpiece for topping the  nish diameter of the thread.

Quality

Extra stock

V-pro le inserts – threading with minimum tool inventory

These inserts do not top the thread crests. Therefore, the outer diameter for screws and inner diameter for nuts must be turned to the right diameter prior to threading.

• Same insert can be used for a range of pitches - provided that the thread pro le angle (60° or 55°) is the same

• Fewer inserts needed in stock

• The nose radii is designed to offer the smallest pitch, which reduces tool life

Flexibility

Multi-point inserts – productive, economic threading in mass production

Multi-point inserts are similar to full pro le-, but have more than one insert point (two pointed inserts give double productivity, three pointed insert give triple etc.) Stable conditions are needed due to increased cutting forces as the cutting edge has a longer contact length.

Considerations should be made for thread turning and thread milling:

. Application

Milling

• Completes the thread in one revolution, when using solid carbide thread mills.

Turning

• Requires fewer passes, giving better tool life, productivity and lower tool costs.

• Requires longer passes beyond the workpiece thread to accomodate the extra points.

Thread turning with multi-point inserts requires longer passes beyond the workpiece.

Productivity

. Applications – Thread turnin

Thread turning

Thread turning is the most common method of producing threads. The many tooling systems offered by Sandvik Coromant cover internal and external applications and make it possible to produce threads of all sizes and pro les, across all segments of the engineering industry.

Indexable-insert thread turning tools such as CoroThread 266 and others offer high quality performance, providing dampening against vibrations, security in small holes, and in the toughest materials.

. Applications – Thread turnin

Insert geometries

Selecting the correct insert geometry is important in threading, especially in machines where there is limited supervision. Here, geometry A offers consistent tool life and quality and is the  rst choice for most applications, while geometry F is sharper, reducing cutting forces.

The chip-forming geometry C enables more continuous and unsupervised machining, free from sudden stoppages. This results in predictable tool life, and more active machining time.

First choice

Geometry A

First choice

• First choice for most operations and materials

• Rounded cutting edge for safe and consistent tool life

• Good edge security

Geometry F

Sharp edge

• Sharp cutting edge

• Clean cuts in sticky or work-hardening materials

• Low cutting forces and good surface  nish

• Reduced built-up edge

Geometry C

Chip-forming geometry

• Maximum chip control, minimum supervision required

• High security for all threading, particularly internal

• Optimized for low carbonand low-alloyed steels

• To be used with 1° modi ed  ank infeed only

2. Applications – Thread turnin

Insert geometries

MC CMC Geometries

ISO No. No.

P1.1.Z.AN

P2.1.Z.AN P2.5.Z.HT P3.1.Z.HT

M5.0.Z.AN

M1.0.Z.AQ M3.1.Z.AQ

K1.1.C.NS

K2.2.C.UT K3.1.C.UT

N1.2.Z.UT

N3.2.C.UT

S1.0.U.AN

S2.0.Z.AG S4.2.Z.AN

For ISO-H use CBN-insert, CB7015

First choice Second choice Alternative choice

01.1

02.1

02.2

03.21

05.11

05.21

05.51

07.2

08.2

09.1

30.11

33.2

20.11

20.22

23.21

AFC

. Applications – Thread turnin

Infeed

Infeed method dictates how the insert is applied to the workpiece to create the thread form. The three common infeed choices are modi ed- ank-, radial-, and incremental infeed.

The infeed method used in threading will directly in uence:

• Chip control

• Thread quality

• Insert wear

• Tool life

Modi ed  ank infeed Radial infeed Incremental infeed

Modi ed  ank infeed

Has many advantages over radial infeed, and most CNC machines are pre-programmed for this method which is modi ed (angled) slightly to avoid the insert edge rubbing on the component surface.

• Recommended for all operations and insert types

• Chip is easier to form or guide, compared to radial infeed

• Chip is thicker but generated only on one side of the insert, making it easier to cut

• Fewer passes than for radial infeed, as less heat is transferred to the insert

• Can be used on both  anks of the thread (opposite  anking) to steer the chip in best direction

• For larger threads, and to eliminate vibration problems

• Use 3-5° infeed angle for A- and F-geometries

• An infeed angle of 1° should be used for C-geometry.

2. Applications – Thread turnin

Radial infeed

The most commonly-used infeed method and the only one possible on many non-CNC lathes.

• Produces a stiff, V-shaped chip, which is dif cult to form

• Insert wear is even on both  anks

• Suitable for  ne pitches

• Insert tip is exposed to high temperatures, restricting the possible infeed depth

• Risk of vibration and poor chip control in large pitches

Incremental infeed - for pitches larger than 5 mm (5 t.p.i.)

This infeed type is the  rst choice for larger thread pro les.

• Even insert wear and long tool life

• A- and F-geometries should be used

• Special CNC machine programme is required

Very large thread pro les can be pre-machined with a turning tool,  nishing passes can be made with the threading tool For more information see page 33 (Threading large pro les).

. Applications – Thread turnin

Successful chip control in thread turning

Threading can present problems in machines where there is limited supervision. Chips can get trapped in chucks, often resulting in tool damage and lost machining time.

To avoid these problems and achieve the best possible chip control, use modi ed- ank infeed, together with a C-geometry (chip-control) insert.

Opposite  ank infeed

With this infeed type, the insert can cut using both  anks (opposite  anking) meaning that the chip can be steered in the right direction. This helps to ensure continuous, trouble-free machining, free from unplanned stoppages.

Standard modi ed

 ank infeed

Feed

direction

Chip direction Chip direction

Opposite

 ank infeed

2. Applications – Thread turnin

Infeed depths per pass

Decreasing depth per pass (constant chip area)

• First choice, most common

• First pass is deepest

• More ‘balanced’ chip area

• Even load on insert

• Last pass 0.07 mm (.003 inch)

Constant depth per pass

• Each pass is of equal depth, regardless of number of passes

• More demanding on the insert

• Can improve chip control

• Increases the required number of passes

• Should not be used for pitches larger than 1.5 mm or 16 t.p.i.

• A less-productive method

First choice

Normal CNC lathes are equipped with dedicated threading cycles, where pitch, thread depth and number of passes can be set in different ways – including the  rst and last passes.

For the last pass, we strongly recommend against using a spring pass (a cut without radial cutting depth). It is more bene cial to use the recommended infeed cycles to ensure better thread quality and longer insert tool life.

. Applications – Thread turnin

Number of passes and size of infeed per pass

The recommended depths of cut for the different passes are shown in the table below.

• These are recommended as starting values - the most suitable number of passes must be determined by trial and error.

• Infeeds of less than 0.05 mm (0.002 inch) should be avoided

• For Cubic Boron Nitride-tipped inserts, infeed should not exceed

0.10-0.12 mm (.004-.005 inch)

• For multi-point inserts, it is essential that the correct infeed recommendations are used

Infeed value recommendations

Number of infeeds and total depth of thread.

For tables and recommendations see chapter 5, Technical reference (page 96) or use the Sandvik Coromant threading calculator for more values.

2. Applications – Thread turnin

Tool holder selection

The choice of tool holder used in a threading operation is in uenced by many factors:

• Component shape

• Tool availability

• Machine type and condition

• Chip control requirements

• Hand of thread

• Tool holder choice

Coromant Capto®

Quick change coupling - for large, internal threads

Boring bar - for internal threading

coupling - for internal and external threading

Drop head - for external threading

QS shank tool - for external small part machining in sliding head machines

Shank tool - for external threading

Exchangable cutting head - for internal and external threading, with anti-vibration bars.

. Applications – Thread turnin

External thread turning

This is the most common thread turning method. It is often easier and less demanding on the tool and there are a number of different methods which can be used to achieve the desired results.

Upside-down tool holders

In many operations, it is bene cial to use a tool holder in an upside-down position, to help remove chips more effectively.

Drop-head tool holders are specially developed for threading upside-down and allow the correct centre height to be maintained, without having to change the clamping in the turret.

Conventional tool holder (right-hand)

Drop-head tool holder

(right-hand)

2. Applications – Thread turnin

Internal thread turning

Internal threading is more demanding than external threading, due to the increased need to evacuate chips effectively.

Chip evacuation, especially in blind holes, is helped by using lefthand tools for right-hand threads and vice versa (pull-threading). However, this also creates the greatest risk of insert movement.

Modi ed  ank infeed should always be used to generate a spiral chip, which is easy to guide towards the entry of the bore

Boring bar selection also has a strong in uence on the effectiveness of internal threading. Three main bar types can be used for internal threading, depending on the length of overhang and level of stability required.

• Steel boring bars - maximum 2-3 x bore diameter overhang

• Steel dampened boring bars - maximum 5 x bore diameter overhang

• Carbide boring bars - maximum 5-7 x bore diameter overhang

Boring bar type Max. overhang

Steel Steel dampened Carbide

Boring bar de ection is in uenced by the boring bar material, diameter, overhang and cutting forces. The recommended clamping length in a boring bar holder with a sleeve is 4 x bar diameter dm

2-3 x dm 5 x dm 5-7 x dm

External Internal

Right hand threads

Most common

Left hand threads

Right hand threads

. Applications – Thread turnin

Left hand threads

Right hand tool/insert

Left hand tool/insert

Right hand tool/insert

A negative shim must be used.

Right hand tool/insert

Most common

Right hand tool/insert

Left hand tool/insert

Right hand tool/insert

Thread turning methods

A thread can be produced in a number of ways. The spindle can rotate clockwise or anticlockwise, with the tool fed towards or away from the chuck. The thread turning tool can also be used in the normal- or upside-down position (the latter helps to remove chips).

Working away from the chuck

Using right-hand tools for left-hand threads (and vice-versa) enables cost savings through tool inventory reduction (a negative shim must be used). Care must be taken due to the risk of insert movement, particularly at the beginning of the thread.

2. Applications – Thread turnin

Insert clearance angles

Two types of angular clearance between the insert and thread are necessary for precise, accurate threading. These are:

• Flank clearance

• Radial clearance

Radial clearance

Flank clearance

Cutting edge clearance between the sides of the insert and thread  ank is essential to ensure that tool wear develops evenly, to give consistent, high quality threads. The insert should therefore be tilted to gain maximum symmetrical clearance from the  anks ( ank clearance angle).

The tilt angle of the insert should be the same as the helix of the thread, to ensure success.

Flank clearance

Flank

clearance

. Applications – Thread turnin

Selecting shims to tilt the insert for  ank clearance

Insert shims are used to give different tilts to the insert, so that the angle of insert inclination is the same as the helix of the thread. See table opposite for methods of selecting the correct insert shim.

• The standard shim in the holder is 1°, the most common angle of inclination

• Shims are available in 1° steps, in the range -2° to 4°

• Negative-inclination shims are required when turning left-hand threads with right-hand tools, and vice versa

= the angle of insert

inclination

The  ank clearance angle of the insert is adjusted by changing the shim under the insert in the tool holder. Standard tool holders have a 1° insert inclination angle.



2. Applications – Thread turnin

Methods for selecting the correct shim

Two alternative ways to select the correct shim:

A. Use the diagram, selecting shims. B. Use the formula to calculate the helix angle to choose the corresponding shim.

Workpiece diameter and pitch in uence inclination angles

Lead (Pitch) mm Threads/inch

Workpiece diameter

For a pitch of 6 mm and a workpiece diameter of 40 mm, a 3° shim is required. For a pitch of 5 threads per inch and a diameter of 4 inches, a 1° shim is required.

tan



d2 x π

Pitch

Effective diameter of thread

P = 6 mm d

= 40 mm

 = arctan

P = 5 t.p.i.

= 4”

 = arctan

mm inch

6 mm

40 mm x π

mm x



5 t.p.i.



4” x π



= 2.7° use a 3° shim



= .91° use a 1° shim

Relationship between  ank clearance, radial clearance and thread pro le angle

The smaller the thread pro le and radial clearance angles, the smaller the  ank clearance angle (see table below for  ank clearance values when the correct shim, equal to the helix angle, is used).

Please note that as the pro le angle becomes smaller, it is more important to choose the correct shim.

. Applications – Thread turnin

Threads with small pro le angles

ACME, Stub ACME, trapezoidal and rounded threads fall into this category and put extra pressure on the cutting edge. To minimize this pressure, choose the correct shim to tilt the insert.

Thread Pro le

Metric, UN Whitworth Trapezoidal ACME Buttress

Angle Internal 15° External 10°

( ()()

Flank clearance Flank clearance

60° 7.6° 5° 55° 7.1° 4.7° 30° 4° 2.6° 29° 3.8° 2.5°

10° / 3° 2.7° / 0.8° 1.8° / 0.5°

Radial clearance ()

Flank clearance

2. Applications – Thread turnin

Radial clearance

To give adequate radial clearance, inserts are tilted in the tool holder 10° or 15°.

It is important to use internal inserts with internal tool holders, and vice-versa, to ensure that the correct thread form is achieved.

Insert sizes 11, 16 and 22 mm

Insert size 27 mm (5/8 inch)

(1/4, 3/8 and 1/2 inch)

Modi ed bars for small holes

Internal boring bars can be modi ed to  t small holes and can be used in place of special tools. These modi ed bars retain their rigidity, as long as the recommended minimum dimension D retained – see main catalogue for further information.

min

+ 88 hidden pages

Sandvik Coromant Threading User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual