ER40 collet retaining nut is bad! Check your items as soon as you get them!

[macardoso]

Not sure? I've definitely seen it happen with a 1/4" endmill on an ER20 holder. I use a solid nut, a clean dry collet, a clean dry chuck, and a lightly oiled nut when assembling. I hope that the oil on the nut taper reduces this twisting effect.

John Saunders at NYCCNC also has a video where he explains that you can torque a chuck halfway and then indicate the endmill true by tapping it with a soft metal bar (copper). After it is true you can torque it all the way down. This is important for small tools where 5 tenths of runout might be equal to the desired chipload where 1 tooth would end up not cutting and the other cuts double.

 

[Robo_Pi]

Don't feel bad. I've been working with machines for years. Never used an ER collet system. I recently decided to buy a set of ER 20 collets. When I saw the offset inside the collet nut I thought precisely the same thing. "How could anyone have made such a horrible machining mistake and not catch it!".

Then like you, I quickly discovered that I'm the one who is totally ignorant of how an ER collet nut works!

Pretty clever design actually. But yeah, nothing in any instructions said anything about this. Apparently we're supposed to be born knowing how ER collet nuts were designed.

 

[pontiac428]

I seem to recall a thread on this forum where the recipient of a new collet holder chucked his collet nut into his lathe and "fixed" the eccentric ring.

I much prefer lessons learned on someone else's dime. I mean that without offense. The unplanned down time kills me!

 

[mikey]

There is a Haas tip of the day that discusses the different kinds of nuts and the benefits of each. Collet twist is a real thing that adds error into your assembly. Basically, friction between the nut and the collet causes the top of the collet to twist relative to the bottom (which is fixed in the much steeper lower taper). This can cause uneven spacing of the slits in the collet which pushes the tool off center.

I finally had a chance to look at this video. Two things I noted. Bearing nuts have evolved and are now in favor. The second thing is that nowhere in the video did I hear him discuss this collet twist thing. He referred to a collet stop in one of their holders but nothing to even suggest that the collet can twist. There was one instance where the slots of the collet were not even but this was due to an improperly installed/torqued nut. My takeaway is that not much has changed and proper care and use of your collets matters. The nuts, specifically bearing nuts, have gotten better and I'll have to consider buying a good one to test for myself.

One other point he made, and many others have also raised this, is that proper torque is important for both accuracy as well as tool holding power, regardless of the nut in use. My big problem is that I don't want to spring for a spigot nosed torque wrench from a European maker like Norbar but almost all the torque adapters for ER nuts use this type of wrench. You would think that some enterprising hobby machinist would buy a big arbor press and some broaches and make "crow's foot" wrenches out of them and sell them to us. You can buy these types of adapters but they are not common and are expensive beyond what they're really worth. I plan to buy the wrenches that fit my nuts, cut the long handles off and drill and file a square hole to fit my torque wrenches. I'll also break down and make fixtures for all of my ER chucks. And yes, I know most of us don't bother torquing these things but I'm going to give it a go and see if it makes a difference in tool performance, just because I'm curious.

 

[macardoso]

The second thing is that nowhere in the video did I hear him discuss this collet twist thing.

Whoops! Must've been a different video then. Been doing a lot of research on ER collets since I just bought a ton of chucks.

 

[macardoso]

Not what I originally found, but same idea:

https://www.mmsonline.com/articles/be-kind-to-to-your-collets

"6. When tightening the nut, torque down on it only to the value specified for this nut. Use a quality torque wrench to observe this limit. Exceeding the torque does not provide more clamping force; it just leads to runout. In fact, the more force is applied, the more the top of the collet wants to twist with the nut. Too much force can actually twist the collet’s top, deforming the collet, which will increase runout and reduce clamping force.
7. Avoid this collet-twisting phenomenon by using a nut that reduces the friction between the nut and collet. Different varieties of nuts achieve this low friction using an impregnated coating, a ball bearing or a friction bearing."


About the author: David W. McHenry is a product engineer for toolholder and collet supplier Rego-Fix Tool Corporation (Indianapolis, Indiana).

They designed the ER collet

 

[mikey]

Yeah, I know Rego-Fix developed the ER collet. I just wanted to make sure we all understood that a good coated nut, used properly and using proper torque, will not deform the collet.

The friction effects and slot deformation thing has been known for quite some time. This is what led to the development of coated nuts and, subsequently, ball bearing nuts. As far as I know, the cheap Chinese nuts that many hobby guys use are not coated. Most hobby guys also do not use fixtures or torque wrenches. That leads to undetected tool slippage, poor finishes, inaccuracy and excessive tool wear. When you point these things out, the commonest response I've seen is "Meh, this is just a hobby and it's good enough for me. I'm not making parts for NASA." Okaay ...

 

[macardoso]

When you point these things out, the commonest response I've seen is "Meh, this is just a hobby and it's good enough for me. I'm not making parts for NASA." Okaay ...

I don't subscribe to that philosophy. There is a lot of room between NASA and treating your tools like crap.

 

[darkzero]

Well I make parts for NASA, but they always ignore me & never buy from me.

Ok ok, of course not true but I do pretend to make parts for space shuttles. Maybe that's why it takes me so long to finish stuff.

I knew Rego-Fix invented the ER system but after watching that HAAS video I had no idea that they invented them i the 70s. Never thought ER collets were that old. Cool that HAAS mentioned Lyndex bearing nuts in that video, that's what I use on all my ER-40s. Oh, I couldn't find my Rego-Fix nuts, I must have sold them which is odd, I rarely sell any of my tools. I couldn't even find my standard Rego-Fix nuts, I know I had 2 of them & 1 friction bearing nut. But I did find 2 extra brand new Lyndex bearing nuts & a Lyndex ER-16 straight shank collet chuck with bearing nut that I forgot I had.

Speaking of HAAS. Saw this today. Someone in Argentina is getting 2 big new machines soon. HAAS is not that far away from me & I see HAAS shipments all the time on the fwy. But they're usually wrapped in plastic, first time I have seen them fully crated. Those are some big crates! I guess they only crate them for overseas shipments.

 

[mikey]

I think you can't go wrong if you use nuts from an established maker of ER equipment - Lyndex, Rego-Fix, ETM, Techniks - they all make good nuts that most of us can afford. I only use coated nuts but after seeing the Haas video I think I will try a Rego-fix bearing nut to see what kind of accuracy I can get from it.

I watched the Haas video on making one of their CNC machines. Impressive, and yes, those things are big!