Jul 28 2016

Plastics routing

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Modern plastics vary greatly throughout their manufacturing processes. The differences between various types of plastics and the different uses machinists will have for their materials cause problems for some people. A good machinist, whether you are a hobbyist or a professional, should be aware of the problems you could run into and steps you can take to get around those problems.
Not all plastics are made equal, not even plastics that share the same name when you are purchasing your raw materials. Something as simple as a change in color can alter how one plastic cuts compared to another. You need to be able to recognize and classify what kinds of categories plastic falls under when you are working with it. To start, determine whether you are working with hard or soft plastic. This is easy to determine; you can check this by seeing how rigid or flexible your material is. Alternatively you can see what type of chip is produced when the material is cut. Soft plastic chips will curl while hard plastic chips retain their solid shape. A single type of plastics is not always universally hard or soft; some plastics can be hard or soft depending on how they were manufactured. Knowing the geometry of your cutting tool is the second step to success. Tools that are best suited for cutting plastic have high rake and low clearance. These days there are thousands of different tools made for plastics cutting that you can choose from. Soft plastics tools have “O” shapes and are usually straight or spiraled in shape. Hard plastics tools can have an “O”, spiral shape or a “V”, straight shape.

Routing plastics

Routing plastics

One of the most irritating problems you can run into is the plastics material welding. This problem can happen due to the direction of your cut, using a cutting tool that is too small or having a chipload (the thickness of a chip) that is too large. Chipload is the most common cause of this problem. Your chipload is determined by your spindle speed, feed rate and the number of edges on your cutting tool. In plastic routing you want your chips to be just the right size to distribute heat correctly. Another potential problem is your finished project having poor finish. Having good finish is extremely important on plastic items, especially ones that are made to be put on display somewhere. The quality of your finish is going to be heavily affected by your chipload. Problems aside from chipload tend to come from the condition of your CNC router. You want to make sure that your CNC router is up to speed on maintenance and performance at all times. Learning to work with plastic correctly is a matter of practice and with time you will become experienced enough that you will run into these problems less and less, until you stop running into them almost altogether.
Making sure you have the right bits for plastics is one of the most important parts of preparing for projects. Your best option for hard plastics is a solid carbide router tool. If you cannot get one of those a carbide tipped tool is a good second choice but they will not perform as well as a solid carbide tool. You can use the same kind of tools on soft plastics but high speed steel tools will also work well on these softer materials. Your CNC router should be capable of speeds of at least 15,000 RPM to work on plastic. A CNC router is the best type of CNC machine for working on plastic, being the machine that is best suited for working at the high speeds your projects will require. Ideally you want to be working at 18,000 RPM, if your machine can operate at that speed, at a feed rate of 200 in. per minute. This is a general figure for plastics in general and the exact speed and feed rate you should use will vary a bit between different types of plastic.