i probably baught the wrong item on ebay--i am a newbee to lathes etc

what is teh best way to take a morse taper spindale and get it down to
about 5/16 of an inch ( i plan to adapt a collet chuck with a mt3
spindle) to my smalljewlers lathe

i know nothing about a mt spindle google gives all sorts of purchasing info

i assume the spindle is made of very strong steel and cannot be cut say
with a carbide tool


any advise really appreciated---i suspect the prucase will be a disaster
but the phots look good--


tia
peter