Quote:
Originally Posted by asid61
We have two lathes, one that is so terrible it cannot make straight cuts of any depth (and I mean any depth) and another smaller one that belongs to a teacher. The teacher one was just bought this year and has runout of well under 0.001" with the stock 3-jaw, which I bored out slightly for accuracy. The larger one, for all it's junk, has only .003" TIR on the 3-jaw. I've gotten the tailstock inline with it once before to within 0.001", but the machine didn't hold up very well over time. I've never experienced a failure with plastic encoder mounts regardless of mounting, just because they are so flexible. I'm all for magnetic encoders, but as far as the COTS options go they are pricey compared to AMTs or similar.
If our lathe can do it, any lathe can do it.  Seriously though, getting stuff within 0.006" is not difficult if you check it every once in a while. Grinding the chuck jaws and using a good indicator help immensely. |
On the 3 jaw chuck, please make sure the jaws are installed in order 1-2-3. (Number Stamped) If someone installed them in a mixed order you will have a really hard time.
A procedure to setup lathes.
First you need to use a decent level (preferably a precision level) to make sure the entire bed is level. Adjust if it's not.
Lubricate and adjust the Gibs on the sliding and compound rests and the saddle to remove any free play. ** Edit - Mini Mills can take a real beating machining a lot of Hex Stock. We trashed the saddle gib on our first small mill. Needed to completely take it apart to repair. Do check these. **
You will need:
1) A Dead Center with the correct Morse Taper for your Lathe. Typically MT2 for small lathes and MT3 for larger.
2) A lathe dog for (1/2?) round shaft.
3) A micrometer
4) A large piece of unhardened steel or aluminum bar the same size as your lathe dog.
Procedure:
1)Cut off 5 inch piece of bar and set aside.
2) Cut a Piece of bar that will fit easily between centers. Face Each side and Center Drill & Counter Bore.
3) Install the dead Center in the tail stock.
4) Take the 5 inch section of bar and clamp in your 3 Jaw. Move the adjustable rest and tooling so as to make a 60 degree point at the end of this bar. Don't remove it.
5) Install the lathe dog on the large bar, and install the bar between the two centers by moving the tail stock in.
6) Machine at least .01 off the OD of the bar for the entire length.
7) If the Diameter of the Bar is wider at the tail stock than the spindle, adjust the tailstock 1/2 the difference toward the tool post. If it's narrower adjust the tail stock away from the tool post.
8) Repeat the machining the diameter and adjusted the tail stock steps, until the error is acceptable.
You can adjust the cutting tool quite high, and use the similar method to adjust the tailstock height if adjustable.