Turning plastic: tools, speeds and surface finish
When turning plastic on a lathe, there are several factors that affect the result. We need to choose the right tool, speed and cutting conditions to achieve a good surface finish and avoid problems such as heat build-up and poor cutting results.
One important factor is tool geometry. A tool with a positive rake angle and sharp edges is often better suited to turning plastic than a tool with a negative rake angle and blunt edges. This is because a positive rake angle provides better cutting force and reduces the risk of heat build-up.
Choice of tool
When selecting tools for turning plastic, we must consider the properties of the material. For example, PE-HD and PE-1000 are both soft and ductile materials that require a tool with sharp edges and a positive rake angle to prevent the material from ‘clinging’ to the tool. On the other hand, POM C is a harder and more brittle material that can be machined using a tool with a smaller rake angle and blunter edges. So how do we choose the right tool for our plastic material? A good starting point is to read the material’s data sheet and look for information on recommended cutting conditions and tool geometry. We can also try out different tools and see which one works best for our specific material and application.
Cutting speeds by material
Cutting speed is another important factor when turning plastic. If we turn too slowly, the material may become too hot and start to melt or deform, whilst excessively high speeds can result in a poor cut or even tool damage. So how can we choose the right cutting speed for our material?
- For PE-HD and PE-1000, we recommend a cutting speed of 50 to 150 m/min.
- For POM C and PA6G, we recommend a cutting speed of 100 to 250 m/min.
- For PC and ABS, we recommend a cutting speed of 150 to 300 m/min.
But what if we do not have access to the material’s technical data sheet, or if we are unsure which cutting speed is appropriate? In such cases, we can always start with a lower speed and increase it gradually until we achieve a good cutting result.
Surface finish and heat build-up
A good surface finish is important for most applications, and we can achieve this by selecting the right tool, cutting speed and cutting conditions. How can we avoid heat build-up, which can result in a poor cutting result or even tool damage? A good strategy is to use a tool with a positive rake angle and sharp edges, and to maintain a suitable cutting speed. We can also use a coolant, such as water or air, to reduce heat build-up. But what if we do not have access to a coolant? In such cases, we can always try to increase the air flow around the machining area or use a tool with built-in cooling.
Long chips and short chips
When turning plastic, we may sometimes encounter problems with long or short chips. Long chips occur when the material is too soft and ductile, and can result in a poor cutting result or even tool damage. Short chips, on the other hand, occur when the material is too hard and brittle, and can result in a good cut but also in tool damage. How can we deal with these problems? A good strategy is to adjust the tool geometry and cutting speed to suit the material’s properties. For example, we can use a tool with a more positive rake angle and sharp edges to deal with long chips, whilst a tool with a smaller rake angle and blunt edges may be more suitable for short chips.
We hope this article has provided you with some useful tips and advice on turning plastic on a lathe. If you have any further questions or need help with your plastic project, please do not hesitate to contact us for more information and guidance.
Turning Plastic: Tools, Speeds, and Surface Finish