SPEX SamplePrep 6870D Freezer/Mill Forums . Find SPEX SamplePrep 6870D Freezer/Mill Forums, Questions, Troubleshooting, Discussions at LabWrench Productivity, Performance, and Flexibility The 6870D Freezer/Mill® is a highthroughput, dual chamber cryogenic grinder with a selfcontained liquid nitrogen tub and insulated case.