I have had a South Bend 9 lathe for a while, and I am still having difficulties with parting. I think I know what the problem is. Actually, there were lots of problems. The first one was too much rake on the parting tool. The cross slide has too much backlash and the tool gets sucked in, causing a crash. A lot of internet posts say that backlash does not matter as long as you wind it all out, but that is not quite correct. Also, tightening the gib screws for both cross slide and compound helps.
Another problem I had was not feeding aggressively enough. I developed a timid habit after reading an internet post that suggested increasing the feed rate at the first sign of chatter. This is true. Kind of. The first time I tried this, I snapped the tip off a parting blade. It seems that sometimes this is good advice and sometimes not. You have to listen to what the machine is telling you and "do the right thing." The second time I did this, I was using a homemade parting tool holder with a trimmed down blade that was for a larger lathe. This time, the blade had zero rake, due to previous bad experiences. The material was aluminum, and as soon as I touched the bar with the tool, there was a bunch of scary chatter. I doubled the feed rate and the chatter instantly stopped. Not only that, a beautiful curled ribbon chip was produced, and the tool sailed right through the bar. The finish was beautiful, and I saved the piece that I parted off.
So, the time came to part a larger steel bar (about 1.5"). Slow feed caused chatter, so time to crank it faster! This didn't work. The blade jammed, and in a scary way. Finally, the belt slipped. It appears that there wasn't enough torque, so I used the back gear. This gave plenty of torque, but the feed became very fiddly. I could only feed slowly, else the blade would catch and stall the lathe. I was afraid of breaking something! This problem was probably due to insufficient power. I could part by feeding very slowly with little crumb like chips. This was no good, but as soon as I tried feeding faster it would jam again. The job could be done this way, but it would take forever, and also be risky. I didn't want to damage anything.
This experience reminded me of a parting lesson that I saw at Techshop. The instructor told the students to part at minimum speed, which on the 14x40 lathe is pretty slow. Feed slowly and carefully, barely getting a chip. This took a long time to part, but at least he said it was safe. These 14x40 lathes had a lot of power, and parting was easy at almost full speed for the material, but this was an intriguing technique. It seems that it does have its place with an underpowered lathe.
Could my parting blade be too thick? I have a grooving tool which is thinner, and has no trouble with steel. The parting tool is 0.089", which is similar to the Empire P-2 blades which seem to be the correct size for a South Bend 9. I have a China-made HSS tool, but it looks and feels cheap, and I'm afraid to use it. It measures 0.053" thick on the top and 0.054" on the bottom. It has a slight taper like the old fashioned blades. My large 7/8" blades start at 0.125 on the top and are 0.090" in the middle and thinnest at the bottom. This Chinese tool is thicker at the bottom. But it is thinner, Could 3/32" (Empire size) be a little thick for the South Bend on steel? For aluminum, I think I have it down. Easy and smooth with the 0.089" blade.