Many parts in the machine shop will require the operator to turn a part with a taper
and a tangent radius or fillet. With the advent of numerical control machines, the
machinist will not be asked to perform radius turning as frequently as in the past, but
certain situations will demand that the machinist be competent in this operation.
Producing radii on parts can be done a number of different ways, but in this instance we
will be discussing form turning tools.
Smaller radii can be produced easily through the use of a forming tool. Forming tools
are cutting tool blanks with the required radius or form ground into them. Form grinding
cutting tools takes knowledge of cutting clearances and angle,. If you need to refresh your
memory on cutting tool relief and clearance angles, go to the cutting tool unit in this
|When producing a radius on a part, it is necessary to leave enough material on the
part to create the radius (Figure 10-1).
|The straight portion of the part will need to be rough turned. Keep in mind the
location and size of the radius by laying out the part. Once the initial diameter of the
part is turned to within 0.015 inch, you will rough in the radius. To produce a good
finish on the radius, the part should revolve slowly. The RPM should be about 1/2 to 1/3
that of the rough turning speed. Set up the radius tool making sure that it is square with
the work (see Figure 10-2).
|The radius tool should be fed into the work slowly while plenty of cutting fluid is
being applied. To avoid chatter, plunge the tool slowly into the workpiece using a slight
longitudinal back and forth motion (Figure 10-3).
|Once the radius is roughed in, take the finishing cut on the part. When the tool gets
to the radiused corner, allow it to finish the fillet, but dont let the tool dwell
in one spot. Retract the tool as soon as possible.
When you are creating a combination
transition radius to a tangent angle (Figure 10-4), you must first adjust your compound
rest to the proper angle.
|Rough in the radius by moving the tool to the shoulder and turning the compound rest
out (Figure 10-5).
When you have the area roughed to within 0.015 on the diameter and length, take the
finishing cut on the part. When the radius tool gets to the corner allow it to finish the
fillet, but dont let the tool dwell in one spot. Retract the angled compound rest in
a smooth, steady motion.