Should I Machine My Plastic Part?

In many cases plastic components can be molded, however there may be many good reasons for machining.

Small to moderate quantities:

Low to medium production quantities are often a motive for machining a plastic part in place of molding. Depending upon the complexity of a plastic component, the cost of a mold can range from several thousands of dollars to as much as $250,000. Often when a customer has low to medium quantity needs, machining may be less expensive than molding, because the expense of the mold amortized over a smaller number of parts may prove to be cost prohibitive.

Very Close Tolerances

One of our customers had a need to hold very tight tolerances on a plastic part. The part feature tolerances couldn’t be held in the molding process. These tolerances could however be held in the CNC Swiss machine.

A Parting Line

A “parting line” may be another cause for choosing to machine a plastic component. Often when designing a mold, a parting line appears on the molded plastic part where the A-Side of the mold matches up with the B-Side of the mold. There are some occasions where that surface of a molded part must be free of blemishes, and in some cases a parting line renders the plastic part as nonfunctional. This would be another reason to machine a plastic part rather than mold it.

Draft Allowance

In the molding process, the term “draft” is used to describe the necessary taper build into the mold so the part can be ejected from the mold. In most cases, without draft, the part would either not release from the mold or be damaged during the ejection process. This may be an additional reason that a part would require machining rather than molding. Some components may need to be cylindrical and would not function when designed with a taper.

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