Definition of a taper
Taper is a gradual increase or decrease in the diameter along the length of the job.
Tapers are used for:
- easy assembly and disassembly of parts
- giving self-alignments in the assembled parts
- Transmitting the drive in the assembled parts.
The different standard tapers and their uses
- Morse taper (MT)
- Brown & Sharpe taper (BS)
- Jarno taper (JT)
- Metric taper
- Pin taper
1. Morse taper (MT)
It is the most commonly used standard taper in the industry. It is a self-holding taper. This taper is usually used in bores of spindle noses of lathes and drilling machines, shanks of drills, reamers, centres, etc. The
Morse taper is denoted by the letters MT. They are available from MTO to MT7. The numbers MTO to MT4 are commonly used on taper shanks of twist drills, reamers and lathe centres. The included angle of Morse taper is
approximately 3° and the taper per foot is 5/8″. A chart showing the angles and TPF of different Morse taper numbers in detail may be referred to for specific use.
2. Brown & Sharpe taper (BS)
Both quick-releasing and self-holding tapers are available in Brown and Sharpe tapers. The taper used in the arbors of milling machines is the quick-releasing Brown and Sharpe taper having a taper of 3 1/2″ T.P.F.
Brown and Sharpe self-holding tapers are available from BS1 to BS18. The taper per foot is 1/2″ except BS 10. BS10 has a taper of 0.5161″ taper per foot.
3. Jarno taper (JT)
Jarno tapers are also used on the external taper of the lathe spindle nose where chuck or face plate is mounted. They are available from No.l to No.20. The amount of taper per foot is 0.6″. Jarno taper is mostly used in die-sinking machines.
4. Metric taper
It is available as both self-holding and quick-releasing tapers. A self-holding metric taper has an included angle of 2° 51′ 51″. The commonly used self-holding metric tapers are expressed in numbers, and they are 4, 6, 80,
100, 120,160 and 200. These numbers indicate the highest diameter of the taper shank up to which the gauge or mating part is to match.
Quick-releasing metric tapers are used as the external tapers of lathe spindle noses. Metric tapers are expressed by numbers which represent the big diameter of the taper in millimetres. The equivalent quick (self) releasing taper in metric also has a taper of 7/24 and the available sizes are 30, 40, 45, 50.
A 7/24 taper of No.30 will have a maximum diameter of 31.75 mm at the larger end and No.60 will have 107.950 mm. All other sizes fall within this range.
5. Pin taper
It is used in taper pins. It is a self-holding taper. It is available both in Metric and British systems. The amount of taper is 1:50 in the Metric system and 1:48 (1/4″ TPF) in the British system.
A taper pin is used to assemble parts which must be held and positioned for accurate, quick and easy assembly. It also permits to transmit the drive.
Lathe Taper Turning Methods
- Form Tool method
- Swivelling compound slide method
- Tailstock offset method
- Taper turning attachment method
1. Taper Turning By Form Tool method
Form tool method is used in mass production for producing a small length of taper where accuracy is not the criterion. The form tool should be set at right angles to the axis of the work. The carriage should be locked while turning taper by this method.
2. Taper Turning By Swivelling Compound slide method
In this method the top slide of the compound rest is swivelled to half the included angle of the taper, and the taper is turned.
Advantages of Taper Turning by Swivelling Compound slide method
- Both internal and external taper can be produced.
- Steep taper can be produced.
- Easy setting of the compound slide.
- Only hand feed can be given.
- Threads on taper portion cannot be produced.
- Taper length is limited to the movement of the top slide.
3. Taper Turning By Tailstock offset method
In this method the job is held at an angle and the tool moves parallel to the axis. The body of the tailstock is shifted on its base to an amount corresponding to the angle of taper. The taper can be turned between centres only and this method is not suitable for producing steep tapers.
Advantages of Taper Turning By Tailstock offset method
- Power feed can be given.
- Good surface finish can be obtained.
- Maximum length of the taper can be produced.
- External thread on taper portion can be produced.
- Duplicate tapers can be produced.
Disadvantages of Taper Turning By Tailstock offset method
- Only external taper can be turned.
- Accurate setting of the offset is difficult.
- Taper turning is possible when work is held between centres only.
- Damages the centre drilled holes of the work.
- The alignment of the lathe centres will be disturbed.
- Steep tapers cannot be turned.
4. Taper Turning By Taper Turning Attachment Method
This attachment is provided on a few modern lathes. Here the job is held parallel to the axis and the tool moves at an angle. The movement of the tool is guided by the attachment.
Advantages of Taper Turning By Taper Turning Attachment Method
- Both internal and external tapers can be produced.
- Threads on both internal and external taper portions can be cut.
- Power feed can be given.
- Lengthy taper can be produced.
- Good surface finish is obtained.
- The alignment of the lathe centres is not disturbed.
- It is most suitable for producing duplicate tapers because the change in length of the job does not affect the taper.
- The job can be held either in chuck or in between centres.
Disadvantages of Taper Turning By Taper Turning Attachment Method
- Only limited taper angles can be turned.