Gents and Ladies,

yet another item that bamboozled me until I cracked its secret.

Quite an interesting item for those who have never seen one, i.e. me before I bought this.

In the central image the items inside the centre hole are hardened steel rollers that float freely. No manner of adjustment.

Bazyle, apparently these chucks were designed for production where stopping and starting the spindle wasted time, costing money.
If you’re constantly changing drills on a job it can come in handy. Plus the self tightening feature of the chuck in my original post is good for people with poor grip strength, I sometimes struggle with standard keyless chucks.

Bazyle I didn’t mean to teach you to suck eggs so I’m sorry old you thought I was.
I think you have a wahlstrom type chuck? A knurled collar and a plane tapered nose looking like a keyed chuck but without a gear ring.
I have one similar and it is quite a knack to change bits I admit, but I guess that workers would have gotten on with the job prior to elf and safety.
I hold the shank of the drill rather than the flutes and seem to be ok changing at 1300 RPM.
But obviously going from a 1/64 drill to 3/8 would need a speed change anyway.
Maybe I will fit it in my jig borer with variable speed pulleys.

Jimmy,
The chuck works by allowing the bit to.be removed and refuted while the spindle is turning.
Holding the knurled collar and pulling down releases the drill, holding the nose of the chuck closes it on the bit.
There is a video on YouTube if you look for quick release drill chucks.
One book I use advises their use is good on a mill where the spindle takes time to slow to a stop.
The chuck I posted about initially works by a set of cam operated rollers. Holding the collar while it is running opens the rollers and releasing it snaps them back onto the drill.
Both types are good if your changing bits often.