Well, almost 20 years working on/for mori, I can guarantee the old sl you have won't ridged tap without live tool. A few of the newer triple digit sl's could as a special order option, and usually only on the sl153/154 models. Im sure its available on the newer nl's as well. Those were integral spindles. Now, it's not to say you couldn't turn on the fanuc option and tweak parameters to make it work for a particular part weight. Mori sold it with the full c axis contour control, and by the time you paid for that, it wasn't much different in price to buy the live tool option.