First thing I cut was some brass with a self ground hss tool and it cut fairly well. I came back later to practise some more and it was getting a way rougher cut. I'd assumed I must've chipped the end of the tool and so I was regrinding and regrinding it. Eventually I found out that i'd managed to set the lathe into reverse and hadn't noticed.
How 'tight' is your machine set up with the gibs and stuff? I'm definitely no lathe expert but I have noticed that my surface finishes seem to have gotten worse over the few years i've had the lathe. I've not adjusted it once since i've been waiting to get a milling machine so I can make some tapered gibs.