Machinist

[Lawrence London <lfljvenaura@gmail.com>]

Unusual 5C collets, soft collets, emergency collets, stepped collets
http://www.practicalmachinist.com/vb/general/unusual-5c-collets-277230/

Despite what the catalogs call them, they're not really "emergency" collets, they're more like soft jaws for a regular chuck. You bore them to the specific size, shape and/or depth you need.

For example, instead of using a 1" collet and an internal collet stop screwed into the body of the unit, you can bore the soft collet with an internal ridge to act as it's own stop. This can, among other things, help chip and coolant clearance.

Also, as the rectangular one shows, you can machine the soft nose to accept non-round and non-regular shapes, and/or hold parts offset to the spindle centerline.

People call them "emergency" collets because one of the many uses is to keep some in unmachined "blank" form laying around so it can be drilled and bored to either replace a broken or missing regular size in order to complete a job, or to be made into a specific, typically nonstandard size. (The "emergency" part assuming a deadline where you don't have time to order a replacement or specific size.)

I use soft collets quite a bit, and have a drawerful much like that photo. One time I got some slightly-oversize 3/4" round stock, and turned a .755" collet to get that job done. I had another job that used Sched 80 aluminum tubing, which was supposed to be nominally 1.062", but arrived measuring 1.054". Not a huge change, but well outside the accurate clamping range for a 1-1/16" collet, so I made another soft collet in 1.055".

Soft collets with shallow steps like that are also a great way to hold washers or thin spacers in order to either face them down or bore them out.

Doc.