Dynalab Corp custom plastic fabrication department machines products for use in laboratories, industry, education and even the home. Plastics fill an interesting machining niche somewhere between wood and metal. Until recently there were no specific tools for plastics; wood cutting and metal cutting tools had to be tweaked to perform machining tasks on plastics. Turning, milling, boring, reaming, and threading are all easily accomplished on most plastics. There are a few basic rules to follow.
Plastics are generally poor thermal conductors and care should be taken to control heat. Some possible methods to achieve this include employing a liquid coolant and keeping spindle speeds low. Water soluble cutting fluids can work very well.
Another key element is the cutter material. We have found that uncoated cutters work best as they have dead sharp edges. It is important to put enough load on the cutting tool to create a good chip.
Feeds and speeds are combined to permit the best cut, and there are as many combinations as there are plastics. A common mistake is to feed too slowly with the spindle speed too high, causing great heat. Small diameter tools run at higher speeds than larger diameter tools. Also, try to listen to the cutter, chirping, singing, and chatter are all bad sounds.
Fixturing your workpiece properly is crucial. Top plates for drilling, toe clamps for milling, chucks & collets, and of course vices. Most plastics are non-porous which makes them excellent candidates for a vacuum table hold-down system.
|The CNC in the photograph above is machining a sheet of white polypropylene that is being held to the table by a vacuum table hold-down system.The CNC is equipped with special bits for use with plastics that account for the heat limitations of the materials. Some possible methods for dealing with "melting" are to employ a liquid coolant and keep spindle speeds low. Water soluble cutting fluids can also work very well.