Thinking of a couple mini mill modifications...

[AlanR]

One thing I don't understand about ER collets: Do you have to remove the ER nut every time you change a collet?

I can answer that one. The nut and the collet become basically integral. The collet kind of snaps into the nut and when the nut is loosened the collet is jacked out of the chuck taper by an eccentric ring in the nut. So yes the nut comes off every time but it's painless.

My ER25 chuck takes about 2" of headroom, I think they're great.

Edit: With extra nuts you can leave commonly used tools together with the appropriate collet and the nut. Makes tool changes very quick, the nuts are inexpensive.

 

[martik777]

It only takes seconds to remove the nut and collet, so I do not see much advantage to getting a spare nut, besides the nuts are $14 vs $17 for a whole collet chuck including the nut. One nice thing is that you can push your smaller drill bits right up inside the collet and hold the bit by the spiral portion. I got my ER tooling from ctctools - good quality for the price. The metric collets are quite a bit less but still fit everything the imperial ones do. If you want exact fits for the common sizes like 3/8, just get those separately, they are under $3 each.

 

[KenS]

I can answer that one. The nut and the collet become basically integral. The collet kind of snaps into the nut and when the nut is loosened the collet is jacked out of the chuck taper by an eccentric ring in the nut. So yes the nut comes off every time but it's painless.

My ER25 chuck takes about 2" of headroom, I think they're great.

Edit: With extra nuts you can leave commonly used tools together with the appropriate collet and the nut. Makes tool changes very quick, the nuts are inexpensive.

Thanks Alan. Very helpful.

Ken