Lathe Machine Operations “Taper Turning”

Taper turning means, to produce a conical surface by gradual reduction or increase in diameter from a cylindrical work piece. This tapering operation has wide range of use in construction of machines. Almost all machine spindles have taper holes which receive taper shank of various tools and work holding devices.

Taper Turning Methods:   A taper may be turned by any one of the following methods:

  • By a broad nose form tool.
  • By setting over the tailstock centre.
  • By swivelling the compound rest.
  • By a taper turning attachment.
  • By combining longitudinal and cross feed in a special lathe.

Taper Turning by a Form Tool:  A broad nose tool having straight cutting edge (form tool) is set on to the work at half taper angle, and is fed straight into the work to generate a tapered surface. In this method the tool angle should be properly checked before use. This method is limited to turn short length of taper only. Tool will require excessive cutting pressure, which may distort the work due to vibration and spoil the work surface.

Taper Turning by Setting over the Tailstock: The principle of turning taper by this method is to shift the axis of rotation of the workpiece, at an angle to the lathe axis, and feeding the tool parallel to the lathe axis. The angle at which the axis of rotation of the workpiece is shifted is equal to half the angle of the taper. The body of the tailstock is made to slide on its base towards or away from the operator by a set over screw. The amount of set over being limited, this method is suitable for turning small taper on long jobs. The main disadvantage of this method is that the live and dead centres are not equally stressed and the wear is not uniform. Moreover, the lathe carrier being set at an angle, the angular velocity of the work is not constant.

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(D= Large Diameter of Taper, d= Small Diameter of Taper, L=Length of work,

 l= Length of taper, α= Half taper angle, S = Set over)

Taper Turning by Swivelling the Compound Rest: This method employs the principle of turning taper by rotating the work piece on the lathe axis and feeding the tool at an angle to the axis of rotation of the work piece. The tool mounted on the compound rest is attached to a circular base, graduated in degree, which may be swivelled and clamped at any desired angle. Once the compound rest is set at the desired half taper angle, rotation of the compound slide screw will cause the tool to be fedat that angle and generate acorresponding taper. This method is limited to turning a short taper owing to the limited movement of the cross slide. But a small taper may also be turned. The compound rest may be swivelled at 45°on either side of the lathe axis enabling it to turn a steep taper. The movement of the tool in this method is being purely controlled by hand, thus giving a low production capacity and poor surface finish. The setting of the compound rest is done by swivelling the rest at half taper angle, if this is already known. If the diameter of the small and large end and Length of taper are known, the half taper angle can be calculated from the equation {Tan α = (D-d) / 2L}.

Taper Turning by a Taper Attachment:   The principle of turning taper by a taper attachment is to guide the tool in a straight path set at an angle to the axis of rotation of the work piece. A taper turning attachment consists essentially of a bracket or frame which is attached to the rear end of the lathe bed and supports a guide plate pivoted at the centre. The plate having graduations in degrees may be swivelled on either side of the zero graduation and is set at the desired angle with the lathe axis. When the taper turning attachment is used, the cross slide is first made free from the lead screw by removing the binder screw. The rear end of the cross slide is then tightened with the guide block by means of a bolt. When the longitudinal feed is engaged, the tool mounted on the cross slide will follow the angular path, as the guide block will slide on the guide plate set at an angle to the lathe axis. The required depth of cut is given by the compound slide which is placed at right angles to the lathe axis. The guide plate must be set at half taper angle and the taper on the work must be converted in degrees. The maximum angle through which the guide plate may be swivelled is10to12°on either side of the centre line.  If the Large diameter (D), Small diameter (d), and the taper length (L) are specified, the angle of swivelling the guide plate can be determined from equation. Tan ά = (D-d) / 2L.

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Advantages of Taper Turning Attachment – The advantages of using a taper turning attachment are:

  • The alignment of live and dead centres being not disturbed, both straight and taper turning may be performed on a work piece in one setting without loosing much time.
  • Once the taper is set, any length of a piece of work may be taper turned within its limit.
  • Accurate taper on a large number of work pieces may be turned.
  • Internal tapers can be turned with ease.

Taper Turning by Combining Feeds – Taper turning by combining feeds is a more specialized method of turning taper. In certain lathes both longitudinal and cross feeds may be engaged simultaneously causing the tool to follow a diagonal path. This is the resultant of the magnitudes of the two feeds. The direction of the resultant may be changed by varying the rate of feeds by change gears provided inside the apron.

4 thoughts on “Lathe Machine Operations “Taper Turning”

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