I normally don’t have the time anymore to hang around the forums but this thread came up in our domain notifications and there’s just too many things I want to say to not post.
Quick preface: I work for Think & Tinker (PreciseBits) so I’m biased about everything. I try to keep the information I post brand agnostic and as general use as I can (other than when addressing specifically things about us). But keep that in mind for the below.
Thanks for the link and mentioning us. Wouldn’t have seen this without it.
Thanks. We actually measure at 2 points in the tolerance spec (face and 1”). More details in the tutorial for collet selection.
Be careful if you do this that you are getting the right nuts. There are 3 “standard” designs. They all take the same ER collets but they have different threads and spanners.
A/UM/Hex
ER11 thread M14x0.75
Typically 17mm hex wrench
M/Mini/slotted/castle
ER11 thread M13x0.75
Castle or slotted wrench
E/slotted
Never seen this type for ER11
This gets into an issue of empirical vs marketing spec.
Short version:
Anytime you see someone list a balance spec of GX at/for X RPM this is a ISO 1940-1 spec. It doesn’t mean that it’s only balanced for use up to that specific RPM. Balanced to 100KRPM with no other spec means functionally nothing. EVERYTHING can be called balanced to a million RPM at some absurd error level. Well, assuming it stays in one piece I guess…
Long version:
GX at/for X RPM is, as stated earlier from the ISO 1940-1 (although I believe it’s been revised to a new version). As an example if you have G2.5 at 20KRPM this is also ~G6.3 at 70KRPM. This is due to the fact that it is based on the same static with a base permissible residual unbalance in g.mm/kg. Not going to post it, but a .mil may have put online the entire 1940-1 spec with the table in it if one were to google for it.
What spec you need can’t really be determined by this alone as it also depends on the dynamic load that the bearings can take, tool mass, etc. I can tell you that the G2.5 at 20KRPM is the spec regularly used in Colombo 40K spindles for their collets and toolholders. So that should give you some baseline.
The “official” minimum length by DIN standard is 4x the diameter if I remember correctly.
In most cases the reason you see a counterbore in the back of the collet is to help with manufacturing tolerance. The longer you bore a small hole the more likely it will move off center. So ideally we would have a perfect bore with no counter bore all the way though the collet. But functionally you are picking between more accurate collets or a longer bore.
If you do get a nut for each collet make sure that you take them apart and clean them or at the very least blow them out after changing tools. If you don’t then you may not get the accuracy out of them as debris stuck in either taper (spindle side and nut side) can force it off center. Not to mention grind away at your precision ground surfaces if it’s abrasive.
Not to be pedantic but runout is specifically a rotational error. So you can’t get it from mounting issues. You can get other errors from mounting like movement, orthogonality, etc.
One last thing to watch for if you are specifically looking for high precision collets. Most TIR specs are listed as “typical”. This means that they could have more or less TIR than listed. They are usually done with either an average of a number of the batch (e.g. average TIR of 10 out of a batch of a 100) or AQL (e.g. less than X spec failures in X percentage measured of the batch). I only know of 3 companies that measure the actual collets that you receive Us, Techniks’ UP grade, and REGO-FIX. There are probably more but those are the ones I’m aware of. To make it extra fun we all use different measurement standards. As mentioned, I’m biased so I won’t comment on what ones I think are better.
Hopefully that’s helpful and doesn’t come off as “marketing”, advertising, or defensive. If there’s anything I can help with or answer let me know.