As you have a capstan lathe you could set up your first cut to the OD diameter with a heavy V shaped tool, then follow up with your parting blade this will get rid of all the interupted cutting giving you a better shot at the job.
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As you have a capstan lathe you could set up your first cut to the OD diameter with a heavy V shaped tool, then follow up with your parting blade this will get rid of all the interupted cutting giving you a better shot at the job.