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Comparing surface finish of a molded part to a machined part

The company I work for currently is machining a part that I want injection mold. If the surface finish of my machined part is 32 microinch what SPI surface finish do I need to meet on my molded part?

James Wolfe
mfgr - Memphis, Tennessee, USA
2005

Not very much info to give a satisfactory answer but, as a rule, molded plastic parts replicate the interior surface finish of the mold pretty accurately. Mirror finish is required for transparent parts whereas sandblasted, EDM'ed or chemically etch interior surfaces will show the reverse pattern on the plastic. So, a straight answer would be, a 32 RMS finish inside the mold is what you need. Whether it would be suitable for the injection process is unknown.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

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