Taper turning

The method used to turn a taper depends upon the angle of taper, its length and the number of workpieces to be machined. Three methods are commonly used with a form tool, with the top or compound sUde and with a taper-turning attachment. 

Short tapers of any angle can be produced by grinding the required angle on the cutting tool. Fig. 9.28. The cutting tool is then fed into the work until the desired length of taper is produced. 

This method is normally used for short tapers such as chamfers, both internal and external. The long cutting edge required by the long tapers has a tendency to chatter, producing a bad surface finish. 

Turning the angle is done by winding the top slide handle by hand. The tool will feed at the angle to which the top slide is set. After the first cut, the tool is returned to its starting position byrewinding the top slide. 

The feed for the second cut is achieved by moving the cross-siide. 

The cross-slide is positioned so that the knurls are above the centre of the workpiece where they are adjusted to contact the workpiece surface using the adjusting screw. Slender work may have to be supported using a centre in the tailstock. 

With the lathe running at a low speed and cutting fluid applied, the knurls are tightened until the required form appears on the workpiece surface. 

The knurls can then be fed along the workpiece to give the desired length. 

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In a later report, a 96-lane CE glass chip was used to carry out DNA sequencing. Tapered turns were employed to increase the channel length, and hence the DNA read length [972], More recently, a 384-lane plate for DNA sequencing has also been reported [973],... 

Taper turning can be carried out from the top slide by swivelling it to half the included angle required on the work. Fig. 9.32. Graduations are provided on the base plate, but any accurate angle must be determined by trial and error. To do this, set the top slide by means of the graduations, take a trial cut, and measure the angle. Adjust if necessary. 

Tubes are typically 20-30 mm long and 5-10 mm in diameter after the design of Massman. In the past, the tube may have been turned down at the centre to increase the temperature at that point, or the whole tube may have tapered towards the centre ( profiling ) to shape the tube to the optical beam and increase the free atom density at the centre. Modem tubes tend not to have either of these modifications made to them. The graphite tube is held in place between two electrodes, axially in line with the light source, as shown in Fig. 3.4. 

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