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Chapter 1

Q. 1.2

Explain the various taper turning methods on a lathe.

Step-by-Step

Verified Solution

Taper turning. Tapered surfaces can be turned by employing one of the following methods :

1. Compound rest Method. The compound rest is swivelled to the required angle, (Fig.1.69). The angle is determined by the formula :

where α = Half taperangle.

D = larger diameter of the taper
d = smaller diameter
l = length of the taper

After swivelling the compound rest to this angle about the vertical axis, it is clamped in position. The taper s turned by hand wheel by rotating the handle. The method can be employed for turning short internal and external tapers with a large angle of taper. The workpiece is commonly held in a chuck.

2. With a Form tool. Short external tapers with various angles of taper can be turned with a form tool, Fig 1.69, using cross feed. The width of the from tool slightly exceeds that of the taper being turned. The work is held in a chuck or clamped on a faceplate.

3. Setting over the Tail-stock. Long workpieces with a small angle of taper (not exceeding 8°) are usually turned by setting over the tailstock centre, (Fig 1.69 c). Tailstock setting over or offset can be determined from the formula,

h=\frac{L(D-d)}{2 l} mm

where, L = full length of the workpiece

l = length to be taper turned

4. Taper turning attachment. Long tapered work is frequently turned with a taper turning attachment, Fig. 1.69(d ). Bracket 1 is attached to the lathe bed. It carries guide bar 2 which can be turned to the required angle and clamped in place. Guide block or slide 3, linked to the lathe cross slide 5 by tie member 4, is free to slide along the guide bar. The cross slide is disengaged from the cross feed screw. Upon travel of the saddle along the bed ways, the guide block slides along the guide bar, and through the tie member, forces the cross slide with the cutting tool to travel parallel to the guide bar at the given angle and the work is turned to the specified taper. The angle of taper can be found out by the relation :

\tan \alpha=\frac{D-d}{2 l}

In some taper turning attachments, the bracket carries in mm, instead of in degrees. In such cases, the guide bar has to be swivelled through mm divisions, which can be found out as :

S=\frac{D-d}{2 l} \times \lg

where lg = Half of the total length of the guide bar or plate.

Conicity or taper, T, is defined as the ratio of the difference in large and small diameters to the length of taper.

∴                    T=\frac{D-d}{l}

In the case of compound rest method,

T=2 \tan \alpha

In the “Setting over all stock” method, h=\frac{L \times T}{2} ,when the length of taper is less than of workpiece and , h \times \frac{T}{2} \times l ,when the length of taper is equal to length of work.

In the case of “Taper turning attachment” method, again

T=2 \tan \alpha

1.69