Parts with cylindrical, conical and shaped surfaces
On the lathe the blank is first turned to a cylinder, and cones or shaped surfaces are made from it. A conical surface differs from a cylindrical one in the direction of tool feed: the tool is moved at an angle, not parallel to the line of centres. The slope angle is given in the drawing. Shaped surfaces – long (200–350 mm) surfaces made of spherical, conical and cylindrical parts – are worked with special profile tools, and the finished surface repeats the tool’s profile exactly. In the school workshop this method is used for parts such as tool handles, mallets and the legs of small furniture. Marking is done with a pencil or compasses; with a pencil, sizes are taken from a scale ruler. Vertical necks, stepped surfaces, rectangular grooves and concave surfaces are made to the marks, and groove depth is measured with a vernier caliper or inside caliper. The finished surface is checked with a template and sanded. All turning is done on the lathe only with the teacher’s permission; measuring, holding the template and sanding are done after the machine has fully stopped.
Surface types: the teacher shows pictures of finished parts (mallet, handle, leg); pupils mark the cylinder, cone, sphere, step and groove sections in coloured pencils. No real turning is done, only drawing practice.