VOCABULARY TERM: FORM MOLD

Form Mold. A holding device made of lead or epoxy to hold large circular medals one at a time in a lathe while they are being trimmed. The form mold acts as a chuck to hold the medal secure while its flash or excess material is turned off on the lathe. Removing the flash is only required from medals struck by open face dies (medals larger than two inches and not struck with a collar). A form mold is a kind of jig and is also called lead form or lead chuck. Workers at the U.S. Mint call these chucks "carriers."

Lead forms. Form molds are made by taking a sample medal to be trimmed, and using this as a pattern, building a fence around it, then pouring molten lead within the fence; it is then shaped with a shank to fit into the chuck at the head of the lathe. After cooling, the form mold is placed in position on a lathe and trimmed to the diameter of the intended medal, or somewhat less. Untrimmed medals can then be placed into position – by finger positioning – then secured tightly as the tailstock is clamped against it.

The medal used as the pattern should be discarded as the lead discolors one side of it. Normally only one such medal is required to make the form mold, even if several form molds are required (as for use on several lathes simultaneously). After use, of course, the lead form molds may be melted for reuse of the lead.

Epoxy forms. An epoxy form mold is made much the same method as lead forms. A fence is built around a pattern metal. Epoxy is mixed and poured within the fence. After setting (curring) it forms a much harder and permanent composition. Epoxy forms look like a plastic die (without very distinct detail). Epoxy cannot be used again, as can lead.

To read the complete entry on the Newman Numismatic Portal, see:
Form Mold (https://nnp.wustl.edu/library/dictionarydetail/515951)

	NBS (coinbooks.org) Web