Machining plastic: tools, speeds and surface finish
When we machine plastic on a lathe there are several factors that can 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 buildup and poor cutting results.
An important factor is the tool geometry. A tool with a positive cutting angle and sharp edges is often better suited for machining plastic than a tool with a negative cutting angle and dull edges. This is because a positive cutting angle provides a better cutting force and reduces the risk of heat buildup.
Tool selection
When we select tools for machining plastic we must consider the material properties. For example, PE-HD and PE-UHMW are both soft and ductile materials that require a tool with sharp edges and a positive cutting angle to avoid the material sticking to the tool. On the other hand, POM-C is a harder and more brittle material that can be handled with a tool with a smaller cutting angle and more dull edges.
How do we then choose the right tool for our plastic material? A good starting point is to read the material datasheet and look for information on recommended cutting conditions and tool geometry. We can also try different tools and see which one works best for our specific material and application.
Cutting speeds per material
Cutting speed is another important factor when we machine plastic. If we machine too slowly the material can become too hot and start to melt or deform, while too high speeds can result in a poor cutting result or even tool damage. How can we then choose the right cutting speed for our material?
- For PE-HD and PE-UHMW we recommend a cutting speed of 50-150 m/min.
- For POM-C and PA6G we recommend a cutting speed of 100-250 m/min.
- For PC and ABS we recommend a cutting speed of 150-300 m/min.
But what if we do not have access to the material datasheet or if we are unsure about which cutting speed is suitable? 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 buildup
A good surface finish is important for most applications, and we can achieve this by choosing the right tool, cutting speed and cutting conditions. But how can we avoid heat buildup, which can result in a poor cutting result or even tool damage?
A good strategy is to use a tool with a positive cutting angle and sharp edges, as well as to maintain a suitable cutting speed. We can also use a coolant, such as water or air, to reduce heat buildup. 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.
Stringy chips and short chips
When we machine plastic we can sometimes encounter problems with stringy chips or short chips. Stringy 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 cutting result but also in tool damage.
How can we then handle these problems? A good strategy is to adjust the tool geometry and cutting speed to suit the material properties. For example, we can use a tool with a more positive cutting angle and sharp edges to handle stringy chips, while a tool with a smaller cutting angle and more dull edges may be more suitable for short chips.
But what is the biggest challenge when we machine plastic? Is it not to find the right balance between tool geometry, cutting speed and cutting conditions? How can we ensure that we achieve a good surface finish and avoid problems such as heat buildup and poor cutting results?
We hope that this article has given you some good tips and advice for machining plastic on a lathe. If you have more questions or need help with your plastic project, do not hesitate to contact us for more information and guidance.
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