3 Jaw self centering ER chuck

Hi All

I Stumbled on this web site
An Australian engineer living in Vietnam.
An unusual way of holding an ER collet.

**LINK**

Video Link
**LINK**

Regards
John

Edited By John McNamara on 19/02/2019 15:02:11

Thanks for the link, John

An interesting idea !

MichaelG.

EXCELLENT!

It's a significant geometrical compromise and not a very clever way to use a dual taper collet.

.

Admittedly, ignoring the front taper is a novel way to use a dual taper collet

... I wonder what the internal profile of the soft jaws might be.

It does, however, seem a neat way of holding thin tubes in a hefty 3-jaw.

MichaelG.

I beg to differ.

The workpiece is a thin wall tube, while it would be easy to make a special set of soft jaws to hold the part, using this method will allow an easy change to a wide range of sizes.
The chuck itself is fitted to a high end CNC machine, I am guessing that the the hydraulic chuck body is very high accuracy and that the soft jaws were bored in situ dead true.

I have always suspected the ER system's main flaw is that the front taper is centered by a screw cap. I have seen a number of experienced machinists videos that show the cap being given a smart tap with a soft hammer to improve the centering of the cap.

I think this is a good solution, Looking at the other videos on the site it appears the shop produces a lot of differing small parts.
Does it produce parts that are within spec efficiently? that is the only question that needs to be answered.

... hopefully from Nick, not me

MichaelG.

Yes Michael I was responding to Nick.

Holding something in a collet has normally been more accurate than using a 3-jaw chuck.

This a 3-jaw holding a collet. How accurate is that ?

Paul.

Hey John, I like it. That is quite a trick setup , especially the fact that the chuck has a limit on the opening.

As for accuracy I am sure it is better than 0.01mm if the collet is a precision collet. For it's application with full contact engagement in the collet looks really good to me.

It would also lend itself to the use of distortion collets as well. Very interesting.

I might have to make up a set of jaws to allow this to happen.

Neil

Michael if you follow John Mc's link to teh FB page you can see the jaws have a tapered cone turned into them and small lip to retain collet via it's groove.

Like Nick I wonder how that can apply an even force all around the collet rather than just give 3 points of contact which would be more so the further the collet was closed down. At best it spreads the load more than using standard 3-jaws and saves having to make dedicated soft jaws for each size.

Edited By JasonB on 20/02/2019 07:26:23

.

I avoid FaceBook as much as possible ... but that ^^^ is exactly what I surmised when responding to Nick.

MichaelG.

Reading some of the comments and replies he says "it is important that the jaws are machined to the collets CLOSED size" so unless you are only holding work at the upper end of the collets range you would need a rebore of the jaws every time eg if holding 1/4" stock in a 7mm collet so can't see that being any quicker or easier than machining soft jaws.

It sounds as though this works but in very qualified situation for a very specific purpose. This is not an alternative ER chuck but a special purpose tool utilising an ER collet. Worth filing for reference and may be a seed for other applications. Interesting.

Mike

Looks like it would be optimum for a fixed diameter only.

regards Martin

Are the jaws air operated ?

Martin

My thoughts are:

For small bore collets which are counterbored, ideally you need more compression at the front.

It prioritises convenience over accuracy. On my lathes changing chucks takes about as long as changing jaws, but that may not be the case for this hefty machine with six mounting screws.

Neil

Again if you read the link he says changing the 3-jaw to a collet chuck takes a long time so quicker for him to swap jaws.

I think if you have a cnc machine with an air operated 3 jaw chuck then with the addition of 3 special jaws you have an adaptor to take the full range of ER collets and can safely hold thin walled tube. Not a bad result for not much outlay.

regards Martin

also worth noting that this setup would allow the easy integration of a depth stop through the back-end of the headstock spindle ... something typically considered an advantage of the 5c over the ER collet.