Got a Clarkson NT30 chuck with metric and imperial collets some time ago (auction ?) that I have only recently tried to use.

The metric collets work fine, a number of various sizes screw in appropriately.
But, I cannot get any imperial tool to screw into an imperial collet.
This means the shaft diameter does not slip into the parallel part of the collet, AND, the thread does not screw into a reversed collet.
The same tools screw easily into a Taiwan made clone.

Note that this affects all 4 collets in the set.
Did numerous checks of diameters etc, but no revelations there.

I initially assumed that is was due to previous operators screwing them down tight on to metric tools.
But, there is the mystery of the refused thread engagement.

The set looks absolutely genuine, blue metal box, expanded foam liner, chuck labelling, included spanner etc. Cannot fault it.
It all looks like a genuine ex-industrial set, same as what I used at TAFE.
I didn't include a photo because everything looks absolutely normal.

Any suggestions on what gives ?
Is there any acceptable resolution ?
Did the post-machining hardening step shrink them ?

It is Ok for me to just bin the collets, as I have full sets of ER32 available.

Don't you just love a mystery,
John.


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