Premises

Jobs that allow ground plastic	About half of the resin runs on jobs whose customers allow regrind. This is the plant's own record. If this is wrong: fewer jobs allow it, and the figure falls with the share. Each tenth of the plant's resin that turns out not to allow regrind takes about $11,300 per year off the figure.
Pounds worth grinding	About 1.5 percent of that resin ends as runners and rejected parts clean enough to grind. Our estimate, against the 5 percent of all resin that the records show did not ship as good parts. If this is wrong: the bins weigh less than about 8 pounds per job per shift, and the grinders pay back more slowly.
Grinders needed	Six grinders reach those pounds. We assume a few long-running jobs make most of the leftover plastic. If this is wrong: the pounds are spread over many small jobs, and one central grinder fits better than one per press.
Parts made with ground plastic	Regrind within the customer's limit does not raise rejects. A US safety standard lets a molder blend up to 25 percent into new resin of the same grade without new tests. If this is wrong: specks, streaks or brittle parts appear on a job that takes regrind, and its share comes down.