Draft for Part Release: Rigid Material vs. Elastomers
Draft is required in order for a part to be removed freely from the mold. As a general rule of thumb, 1” of draft is a good starting point, though there are times when more may be required. In some cases, it may be required to use less draft where there are deep ribs or tall bosses.
Parting line (or shut-off draft) is when a tool steel must make a vertical transition and wipe across another steel component in the mold. Parting line draft is required so the mating steel doesn’t gull or reduce mold life. These faces should have a minimum of 3°, though there are situations when more draft is required.
In special draft situations, minimum draft is recommended on highly polished surfaces of SPI A-3 and above 2° to avoid visible drag and scuff marks.