Thread: ER40 Collet nut dimensions

Hi Scott,
The ID is around 40.75mm, being the average of two samples I have - they differ by about .02mm.

As you will be aware, the ring is eccentric to the axis of the collet - let me know if you need the eccentricity measured as well.

My experience is that the if the collet has been tightened firmly, there is a noticeable (but not large) torque required to unseat the collet. You may find that it can be removed quite easily without including that ring, but it may not be an elegant operation unless you can get a drift in behind the collet to tap it out.

Cheers,
Bill

Aha, I knew it was a good idea to ask - I had no idea it was eccentric, though that makes sense. If you could measure its runout, id be very appreciative Bill

Originally Posted by scottyd

.....Does it need the ring there? Does the collet wedge into that taper hard enough to require it? Obviously, not machining it at all would be the easy way to go......

Scott, the excentric puller ring is entierly optional. Especially if used as a lathe chuck, as you would rarely need to tighten it up near as much as a toolholding collet.

That said, the excentric puller is a standard feature with ER collets. If you want to have it, you will have to grind/make/buy an internal grooving tool. Such a grooving tool will, if you choose to buy it, likely cost more than a commercially made, hardened collet nut. These ER40 collet nuts go for around $15 a piece on eBay with free postage, from China of course: http://www.ebay.com.au/itm/Milling-C...item46209096c0

You could also go the luxury way of a ball bearing collet nut. These nuts have much less friction due to a sleeve filled with small balls, so for lathe use you probably could go away tightening it by hand (without spanner or tommy bars). An example here: http://www.ebay.com.au/itm/ER40-Cast...item416fd016c2. Maybe adding a nice polished sleeve ring around such a ball bearing nut would be an idea to try too for a lathe chuck. That would also cover up these nasty castellations for the ER spanner. On a lathe you do not want these castellations around the nut, they prevent you from working close up to the nut with your hands, as the castellations like to tear flesh off ones knuckels. That is why most commercially made ER lathe chucks do not use castellated nuts, but smooth cone shaped nuts that use tommy bars for tightening/loosing.

Now before someone poor soul comes out again with Google.... I have owned and used a dedicated lathe ER collet chuck for about 30 years, that is why I know about the advantage of tommy bars over castellations and the other things about them.

Originally Posted by cba_melbourne

These ER40 collet nuts go for around $15 a piece on eBay with free postage, from China of course:

Where's the fun in that? I dont actually have much of a use (yet?) for a collet chuck, it just seemed like a fun thing to make.

Im not using castellations, Ive gone with an array of holes for pin spanners (which im also making). Ive not got a milling machine at home, so Im limited in my abilities at this point. If push comes to shove, Ive got one at work, but so far, I can see all the work required to finish the tool not needing anything more than a lathe and drill press. Ill have a go at turning the eccentric ring, but if I cock it up, its no biggie. Grooves are no problem, ill grind a boring tool to take care of it.

Scott,

Eccentricity of the ring measures at about 1.9mm offset from collet axis to ring ID axis. Once again, the average of two samples.

Not a classy measurement because I did it quickly with a digital caliper (reference being the OD of the nut) rather than setting up in the 4 jaw and using a dial gauge.

cba is quite right that you would not need to tighten a collet very hard on the average turning workpiece, but if you have no milling machine at home you may want to do some milling in the lathe, and ER collets need to be tight to grab an end mill shank reliably (that's where the ball bearing nuts shine). But as you say, it's more fun to tackle it yourself.

Cheers,
Bill

It is possible to drive the collet out with a soft flat end of a bar such as brass, but it is not an elegant solution. Position the edge of this bar in the slot that the eccentric ring sits in and angle it as vertical as possible before tapping with a hammer.

Don't ask why I know how to do this!!

Dean