I'm confused, you did a .002" doc and got taper of .0007" over 6"? I would think this is quite decent for an old lathe.
If you want a more accurate test, I would use a HSS bit instead of carbide, you can get a better cut at those low doc's. Also wait till the steel cools off before measuring.
Lots of things can factor into there being a taper in this scenario.
- bad seating of chuck on spindle
- Spindle bearings not preloaded properly, taking very small doc will help offset this though.
- chuck jaws tapered, allowing piece to move while cutting
- headstock not aligned to ways, you would need a test bar to check this
Gerrit