I have a Sieg C3. I use either a 1/32" wide blade or a 1/16" wide blade, both from AR Warner in the USA. The lathe can part off 25mm diameter 12L14 (free cutting) steel very well at something in the order of 200 to 300 rpm, with lots of squirted on oil, I use Inox. The difference is the spindle is run "backwards" (i.e. clockwise looking from the tailstock), and the cutter is mounted upside down. As the C3 is a modern machine with a bolt on chuck there is no danger of the chuck unscrewing.
Here are a couple of pictures.....
Best of luck!!
cheers
Bill