I am having trouble parting with my new to me South bend 9 lathe. It never achieved a continuous chip and the tip dug in with a bang noise. I broke two parting blades on one piece of 3/4" mild steel. This is really a hassle since the parting blades are time consuming to make. These blades are cut from a defunct carbide wood circular saw blade.
All the standard set up precautions were taken including setting center height, aligning perpendicular to the axis, plenty of oil, etc. These parting tools have been very successful on the smaller Craftsman AA 109 lathe. They have routinely parted 1.25" HR round and even worked on a 2" piece (difficult to hold in the small chuck). They also work great on the Techshop Jet 14-40 lathe. They cut a nice ribbon like chip. They are used in a solid steel block holder, which is very stable.
The main difference with the South bend lathe is that there is a lot of cross slide backlash. The screw is worn and the backlash is about 0.048". But, there are a lot of web posts saying that backlash doesn't matter at all. Here's my theory. It does matter if the tool has a lot of rake like these circular saw blade sourced parting blades. The blade skips and chatters until it is fed sufficiently to dig in, lock and snap the carbide. Does this sound correct? Is there a simple solution that doesn't involve a new cross slide screw and nut (since the Internet posts may be correct and it will be a waste)? I kind of thought that parting was a skill that only had to be mastered once. I'd rather not just do the parting on the little Craftsman 109 lathe, since the heavier South bend should have the advantage. In nearly every other way the South bend is the superior lathe, except for this one.
All the standard set up precautions were taken including setting center height, aligning perpendicular to the axis, plenty of oil, etc. These parting tools have been very successful on the smaller Craftsman AA 109 lathe. They have routinely parted 1.25" HR round and even worked on a 2" piece (difficult to hold in the small chuck). They also work great on the Techshop Jet 14-40 lathe. They cut a nice ribbon like chip. They are used in a solid steel block holder, which is very stable.
The main difference with the South bend lathe is that there is a lot of cross slide backlash. The screw is worn and the backlash is about 0.048". But, there are a lot of web posts saying that backlash doesn't matter at all. Here's my theory. It does matter if the tool has a lot of rake like these circular saw blade sourced parting blades. The blade skips and chatters until it is fed sufficiently to dig in, lock and snap the carbide. Does this sound correct? Is there a simple solution that doesn't involve a new cross slide screw and nut (since the Internet posts may be correct and it will be a waste)? I kind of thought that parting was a skill that only had to be mastered once. I'd rather not just do the parting on the little Craftsman 109 lathe, since the heavier South bend should have the advantage. In nearly every other way the South bend is the superior lathe, except for this one.