Lathe Tools

The cutting and clearance angles of a lathe tool will be dependent on the type of material they are to be used on and the required quality of finish. The basic angles are shown below:

The shape of the tool in plan view is as important as all of the other angles and should be set according to the material being worked. The tool shown is suitable for roughing out the shape. The angle of the tool in plan view should be less than 90° if a step is required in the diameter of the workpiece. The nose radius should be kept large for roughing purposes, but may need to be reduced for finishing into the corner of a step.

Increasing the rake angle on the side or back will produce a force that will draw the tool into the workpiece. The tool will tend to run and as such the cut will not be so controllable. It is important that the height of the tool tip is on or just above the centre of the workpiece. If the tool is too low the tool will be drawn into and under the workpiece and for small diameter material may result in them bending or breaking. The front clearance is there to stop the tool rubbing on the workpiece. When machining some materials, of note is aluminium, some of the material may build up on the tip of the tool and so produce a new cutting edge. The result will be a poor finish.

The overhang of any tool should be kept to a minimum as it is important that the tool is as stiff as possible. If the tool starts to chatter check that is held firmly. This may be particularly true if too many shims have been used to adjust the height of the tool. However, there is the odd occasion where a large overhang is required, especially on small lathes, to work into an area where the saddle or tool post will not clear the workpiece. On this occasion the cutting rate should be reduced to reduce the forces on the tool and hence reduce the displacment of it and hence chatter.

Bell Mouth

The flaring or tapering of a machined hole, usually made at the entrance end because of misalignment or spring of the cutting tool.

Boring Tool

A boring tool is used to enlarge a cylindrical hole, sometimes the tool bit the boring bar and the tool holder are incorporated in one solid piece.