My Atlas/Craftsman lathe has a 1-1/2 x 8 threaded spindle with a #3 Morse Taper ID - not easily adaptable to the common 5C collets used on many other lathes I've operated.  In considering which way to turn for a collet adaptation to this spindle I encountered the ER collet specification.  This is a collet set series from ER-8 through ER-40, the numeral indicating a nominal OD in millimeters.  The features of the ER design which appealed to me were that it was a "front closing" design requiring no drawbar taking up spindle bore space, it was parallel closing meaning that it gripped well, and each collet has a comparatively large working range of about 1/32" meaning that pieces slightly over or under nominal could still be gripped securely.  The ER-32 group goes up to about 3/4" which is a good match for the Atlas spindle through hole.  Hence a project to design and build an adapter to mate the threaded spindle to the ER-32 collet.

The machining for this adapter requires internal and external threading, precise angle setting and slightly ticklish internal turning for the feature in the closing nut that extracts the collet.  However, there are also some alternatives.  I have machined a nut without the extracting feature and simply have to tap the workpiece from the back of the spindle similar to releasing an R-8 collet in a mill.  Or, since the nuts are readily available as replacements, you could choose to make the external thread a metric thread to match the standard nut.  If you have used care in fitting and removing any chips, this adapter should provide a concentricity within tenths on your lathe - after all, it is made ON your lathe and FOR your lathe.

NOTE:  The completed adapter can also be supplied for other threaded spindles either metric or english.  Call or write to discuss feasibility and quote.

Order Collet Adapter Kit- $37             Order Collet Adapter Machined Complete - $160

ER-40 Collet Adapter for 1-1/2 x 8 threaded spindle using commercial closing nut.