Lathe 2

Metalwork Lathe

In this lesson, we will cover the operation of a lathe in regard to tooling, tool setup, tool properties, and cutting terminology.

Lathe tools are sometimes referred to as single-point cutting tools. That is because all the cutting the tool does only happens on a single edge or point. The point that does the cutting is defined by the shape of the tool. Most high-end tools come pre-shaped these days, but the majority of manual lathes still use high-speed-steel cutting tools. These tools tend to be shaped by hand on a grinding wheel.

These cutting tools tend to come in Left-hand and Right-hand shapes. This is so that you can cut towards the left, or towards the right, depending on the shape you are aiming for.

The terminology that is used for cutting is called "feeding". This is because you are FEEDING the tool into the material when you cut. The rate at which you feed the tool is called FEED SPEED. This speed is typically measured in millimeters per minute or mm/m.

Your cutting feed, the speed at which you cut, will affect how deep a cut the tool does each revolution of the material.

The final surface quality will be determined by the shape of the tool, the feed speed, and the rotational speed. If the feed is too fast, the cuts per revolution will be too deep causing cusps (see image below) to form. It will also cause the tool to wear faster, and could also break the cutting point on the tool off.

If the rotational speed is too low, then it will result in the same effect plus material tears. (See image below)

It is important to always keep the rotational speed adequate and the feed speed in the correct range in relation to the rotational speed. You can refer to speed/feed charts for specific materials and diameters of material.

Tool Shapes

As you can see above, there are many different shaped tools that you can get. Each one will be for a different purpose, to cut a different shape, or to cut a specific profile into your material.

In addition, these tools can be specialized for only specific materials by adjusting the angles on the tools. For example, softer materials like Aluminium will require a more aggressive relief angle to clear away material, because of aluminium's tendency to not snap easily (ductility). Whereas with mild steel you require a less aggressive angle, because the material chips easily but also because it is a harder material. (see image below)

When you machine any type of material, there will be heat build-up. This heat will dissipate into the material you are cutting and into the tool. If the tool gets too hot it will cause the cutting edge to dull slightly, and the material will stick to the tool.

To combat this, we use coolant. Coolant is a cutting oil specifically formulated to dilute in water. The mix ratio is normally 35:1. 35 parts water, 1 part oil.

Using coolant can increase cutting performance, decrease cutting noise, and dissipate heat build-up.

It is important not to drink this coolant, or to get it on your clothes. It still contains oil, and oil will damage your clothes and make it more flammable. For this reason, each machine has a drip tray and will need to be periodically cleaned and emptied by the user. This tray also catches the swarf. The swarf is very sharp and should not be played with. Please always wear gloves when handling the swarf.

Below is an image of some of the basic turning operations that you will have to know and be able to describe.

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