I left it unsupported, but was making very light cuts. Anyhow, I will try to center the tailstock, as I have a MT5 dead center, then I will mount a four jaw chuck and will try cutting a thicker piece of material with some other cutting tool.
I will try again, with a four jaw, bigger bar, and HSS. I will post my results.
Well, the profile of the cutting tool makes a big difference, and the speed also can affect the finish. You want to advance the tool as fast as you can, to avoid work hardening due to recutting the same area on each turn. Also, a cutting oil is pretty important to prevent "built-up edge", where the workpiece material builds up on the cutting edge and varies the effective tool position. You get those characteristic rings on the turned part.
To properly test for taper, you want to mount a hardened and ground shaft and use a dial test indicator on the surface. That eliminates almost all the deflection.
Jon
Don't involve the tailstock in this test. Regardless of the condition of the machine, if the tailstock is not dead concentric and in a common plane with the spindle, it will yield results that are not in keeping with what you're trying to establish-----if your machine can generate a straight turn. Do this with no support on the outside of the material-----no support of any kind.. Not a follow rest, not a steady rest. Use large diameter material to minimize defection, and insure that the chuck is not allowing the material to move with tool pressure.
Once you know your machine is cutting straight, you then use the machine to align the tailstock by either using a test bar, or by machining a long piece between centers, moving the tailstock such that you eliminate taper. You must do the free machining first, otherwise you won't know if the machine is right, or not.
Do not run the center with a part that is chucked. If there is the slightest misalignment between the spindle and the tailstock, you'll generate a compromise of not only straightness, but diameter. You may also generate a three lobed or four lobed cut, depending on the rigidity of the chuck and tailstock.
Harold
Harold
So, Iggy, you made any progress on the lathe?
Jon
I spoke to a very nice person who offered to loan me a test bar. I will hopefully clarify the taper in the headstock tonight and we'll be able to move on it. It may be easier to do with a test bar that fits into the Morse taper on the headstock.
Yes, I saw that offer. I usually use 1/2" or 3/4" hardened and ground shafts, like out of old printers and such. You have to check the bar to make sure it still is straight, of course. This has worked out quite well for these sorts of checks. Just mount it in the chuck, turn the chuck to make sure the bar is straight and not wobbling, and then ride a dial test indicator up and down it to determine how well the machine is aligned.
Jon
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