A lathe chuck whose four jaws move independently, so a part can be dialed in to run true within tenths, gripped off center on purpose, or held by square and irregular shapes. Setup takes longer than with a self-centering three-jaw, but accuracy is limited only by patience and the indicator. Veterans judge a newcomer by how fast they can dial in a four-jaw.
Re-chucking a finished part, so put it in the four-jaw and dial it in under a tenth on the bore.
Adjust opposite jaws as a pair: loosen one and tighten its partner by the same amount, and halve the indicator reading each time.
Also heard as
- four-jaw chuck
- independent chuck
- 4-jaw
Related terms
Indicate
To align a vise, part or bore to the machine axes using a dial or test indicator.
Collet
A slotted, tapered sleeve that squeezes evenly around a tool shank or bar stock to grip it accurately.
Chuck key
The T-handle wrench that opens and closes a geared drill chuck or lathe chuck, never left in the chuck.
Soft jaws
Vise or chuck jaws of aluminum or mild steel, machined in place to cradle a specific part.