So as not to highjack GetShafted400's lathe thread, Kafie's post below got me thinking...

Quote:
Originally Posted by kafie1980
With 5C collets for quick release I was actually referring to the lever operated functions to be able to insert or remove the stock.

There is still a threaded portion holding the collet in place however the stock can be quick released via a lever rather than undoing the nut.

This is available for both collet blocks for milling and lathe spindle mounted setups.

Attachment 405676



I did a bit of number juggling as I was intrigued by this idea.
If I look at an ER40 collet, it's thread has a pitch of 1.5mm, and the taper angle is 8 degrees/ side. Therefore one revolution of the nut will change the diameter by 0.42mm
A 5C collet is tightened by a 20tpi thread (=1.27mm) and has a taper angle of 10 degrees/side. One revolution of the thread will change the diameter by 0.44mm

The issue of why a 5C releases and a ER40 does not is due to the taper angle. 8 degrees is a critical angle for steel-on-steel contact. A bit more than that and a taper is self releasing; less than 8 and friction will make it 'stick'. (coefficient of friction is related to the tangent of the angle) There is no easy answer as if you put some EP grease in the ER chuck it will lower the friction coefficient so it will release, it also means the chuck can not grab the collet as easily - it could spin in the chuck.

Any quick release ER chuck would have to have a way of moving the collet out of the taper to allow it to expand, either by moving the nut forward enough to pull the collet out of the taper or pulling the taper off the collet. Both of these are possible, but would take a bit of design effort to get something convenient, practical and safe to use.

Michael


Read the full thread at metalworkforums.com...