Thread: Collett Sizes

I am not a expert although no I believe they are made to suit one type

No, they are different sizes.

Thanks for the confirmation.

You'll need to be careful but it's possible to fit a hold a larger collect chuck in an smaller chuck.
For example if you have a ER16 you can fit a ER20 so you can run bigger collets.
It all depends on the precision required, bit size (length/diam) and materials being machined.
I wouldn't do this on more precise milling of say steel, but cheesium, or wood is probably OK especially if the cutter speed and feed is reduced.
There's another reason for doing the reverse is smaller in larger chuck and that is so the cutter can get closer to things like shoulders.
I have several long ER16s that I mount in an ER32.

I don't claim to have the practical experience, but can't you just change the collet extension by substituting something along the lines of these -
https://www.ebay.com.au/itm/ER20-A-T...30l:rk:10:pf:0
https://www.ebay.com.au/itm/ER20-A-T...30b:rk:13:pf:0

As Bob has said the only thing to be concerned about would be a potential loss of precision.

Not having seen two spindles or collets together my question revolved around whether the spindle shaft is sized specifically for each collet size. Are the two shafts a different ID/OD to match the collet type?

This is, again, as I understand it so don't take it as gospel. All of these CNC motors have a bare shaft end that the collet carrier is attached to using grub screws. The two collet carriers (extensions) that I linked to are designed for 8mm and 12mm shafts and there are probably other sizes as well. So all you need to do is remove the supplied collet carrier, establish what size is appropriate to your motor and then buy and fit an appropriate collet carrier. As long as you can find the correct internal diameter ER collet carrier you can use any size of ER collets you want, ER20, ER25 etc.

Have a look at this - https://www.cnczone.com/forums/chine...-er16-one.html - not a ringing endorsement, but

That'd make sense Dave from a manufacturing POV, make a universal motor and put the specific collet adaptor on it.

I think that you'd find that as the motor went up in power and the collet holder up in size the motor would have more substantial bearings to handle the increased loads, particularly the side load. But when we're talking about machining wood and only going from ER16 to ER20 it shouldn't present any problems.