In the same way that drills can grab and pull into brass something similar can happen when turning soft materials with inappropriate tools.

Heat builds up quite quickly at the cutting edge with plastics as they don't conduct heat away as happens with metals. Once the melting point of the plastic is reached the cutting action changes dramatically. Light cuts can probably cause this as less heat is carried away in the swarf. Like parting off you may find it better to feed the tool in faster.

Martin C

Yes this will happen when turning soft materials with large loads or large cuts and highish feed rates. It just takes off at the helix rate of the ground tool. So when grinding the tool, to get the top rake, use a dremel or what ever and create a mini chip breaker that emulates what you see on commercial finishing carbide inserts. It can still take off, so small cuts that you can control is a good way. Not many manual lathes have the feed wheel like a Myford so finding a way to manually feed at some point of the turning process is essential. Your issue occured because you had too big of a cut and too high of an initial feed rate. Like mentioned above, brass will do this to a regular drill bit. To stop the brass from biting, most will put a small flat on the cutting edge. Another way is to just drill at a slow feed rate like at about 2 thou per rev or so. If you try and go at 6 thou per rev it will want to bite. Sometimes low feed rates is your friend.