ER25 collets in a vertical mill, why?

In a bridgeport type mill why use an er25 collet chuck and collet? I assume it is easier to eject. But what advantage does it offer over r8 or mt3? I have never heard of a native mill spindle in ER size. Are the collets more accurate and grip better with more fingers?
Bill D

Bill D said:

In a bridgeport type mill why use an er25 collet chuck and collet? I assume it is easier to eject. But what advantage does it offer over r8 or mt3? I have never heard of a native mill spindle in ER size. Are the collets more accurate and grip better with more fingers?
Bill D

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ER are dirt-common on Asian "mill drills" and "native" as well on loose building-block spindles some folks use to make a vertical head add-on. Also CNC tool-changers and their magazines, residing on taper-tail (NMTB/ANS/ISO, CAT, BT, and newer-yet).

TG might be more beloved for "live" tooling, CNC world, but ER serve that market, too.

Most things grip better than Are Ate. As with 5C, it has a narrow "collapse range".

ER, TG, SK have very low runout even in "standard" grades. There are extra-precision ones as well.

The "handy" advantage to ER, TG, SK, on an all-manual machine is that once in place, there is not as much need to mess with a drawbar - tool changes are done right in front of you with a spanner wrench - be it hex, castellated, or "hook", all of which nut types fit the same collets and body.

The ER family claim to globally wide acceptance (which it has earned a great deal of) comes off the back of very good grip over a very wide "collapse range".

A full millimeter per collet, though half-mm sets are better, and "zero collapse" or "on-size" are better-yet for taps and such.

Already half-mm "TG" has even Tighter Grip at the downside of needing twice as many collets for the same coverage.

Both (and SK) are "meant to be" precisely tightened with a torque wrench, but as they work well-enough with "feels right", it doesn't happen often.

FWIW-nothing-really, the "number" in ER is the length of the collet, not the max diameter. One has to look that up in a table. I have ER 20 and ER 40. ER 50 exists. ER 60 is 'mentioned", very rarely. In theory, the design scales, could go larger, yet. But I have never seen even an ER 50 "in the metal", nor an ER 60 even for sale.

NB:

ER 32 is perhaps a better size than ER 25 as to torque to support BirdPort-class spindle power?

There is a trade-off between clamping nut size and stick-out, vs max diameter & grip, though.

Bill D said:

In a bridgeport type mill why use an er25 collet chuck and collet? I assume it is easier to eject. But what advantage does it offer over r8 or mt3? I have never heard of a native mill spindle in ER size. Are the collets more accurate and grip better with more fingers?
Bill D

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Getting back to the question, Bridgeport type mills tend to have a limited selection of spindles. Old M-heads have 7 B&S or 2 MT. J-heads mostly have R8 or QC 30 or NTMB 30. I don't think Bridgeport ever made a spindle that takes ER collets. But there are plenty of R8 and other type collet chucks that accept various size ER collets.

Why use an R8 ER collet chuck? Grip? I have read that the ER collets grip an end mill better than an R8 collet and they have that wide clamping range. Accuracy? You have the concentricity of the R8 chuck plus the ER collet, so just a good (Hardinge) R8 collet by itself could well be more accurate than a random Chinese R8 chuck and Chinese ER collet. Overhang? An R8 collet has the least overhang, which is a good thing. An R8 end mill holder may have overhang similar to an R8 ER chuck, depending on end mill size.

Larry