Editing Collet (section)

====Autolock collets====
"Autolock" collet chucks (Osbourn "Pozi-Lock" is a similar system) were designed to provide secure clamping of milling cutters with only hand tightening. They were developed in the 1940s by a now defunct UK company, Clarkson (Engineers) Limited, and are commonly known as Clarkson chucks. Autolock collets require cutters with threaded shank ends to screw into the collet itself. Any rotation of the cutter forces the collet against the collet cap taper which tightly clamps the cutter, the screw fitting also prevents any tendency of the cutter to pull out. Collets are only available in fixed sizes, imperial or metric, and the cutter shank must be an exact match.<ref>{{Cite web |url=http://www.flightglobal.com/FlightPDFArchive/1942/1942%20-%201815.PDF |title=Archived copy |access-date=2013-08-08 |archive-date=2014-02-01 |archive-url=https://web.archive.org/web/20140201195425/http://www.flightglobal.com/FlightPDFArchive/1942/1942%20-%201815.PDF |url-status=dead }}</ref>

The tightening sequence of Autolock collets is widely misunderstood. The chuck cap itself does not tighten the collet at all, with the cap tight and no tool inserted the collet is loose in the chuck. Only when a cutter is inserted will the collet be pressed against the cap taper. The back of the cutter engages with a centering pin and further turning drives the collet against the chuck cap, tightening around the cutter shank, hence "Autolock".

The correct installation sequence as per the original specification is:
#Insert the collet and hand tighten the chuck cap (collet free to float)
#Insert the tool and hand tighten (tool engaged with rear pin and collet engaging cap taper)

As the tool is used further rotation tightens the collet and the centering pin ensures that tool extension and alignment remain unchanged. A spanner is only required to release the locked collet.<ref>{{Cite web |url=http://www.flightglobal.com/FlightPDFArchive/1942/1942%20-%201815.PDF |title=Archived copy |access-date=2013-08-08 |archive-date=2014-02-01 |archive-url=https://web.archive.org/web/20140201195425/http://www.flightglobal.com/FlightPDFArchive/1942/1942%20-%201815.PDF |url-status=dead }}</ref>

While threaded shank "Autolock" tools may be gripped by plain collets, such as ER, plain shank tools should ''never'' be used in an "Autolock" collet as they will not be properly clamped or aligned.