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hadjcues
06-23-2005, 12:19 PM
I have a problem with my tailstock... when I drive it close to the chuck and have it centered properly dead on [the tram 1.5" out]- then I pull the tailstock back around 8" and move the tram forward towards the chuck to check for centering again... it's veered of slightly to the left prolly by half a millileter... could the problem be in the bed or on the tailstock tram?

How could I get this right and check it properly?

SGW
06-23-2005, 02:00 PM
Well, the first step is to be sure the bed is straight. You can play around with a precision level or whatever, but maybe the easiest way to know, for sure, is to chuck a piece of maybe 1" stock so it hangs out maybe 8" fron the chuck, and take a light skim cut for its length -- a light cut, so the force of cutting doesn't deflect it. (Don't use the tailstock for support while doing this.) Then measure the o.d. up near the chuck and again at the outboard end. If the o.d. isn't the same, you have either a misaligned headstock or a twisted lathe bed (or both, I suppose).

If that checks out okay, then the problem is likely in the alignment of the tailstock.

Forrest Addy
06-23-2005, 04:48 PM
Don't be too quick to condemn the tailstock ways on the bed. Check the tailstock itself first.

Tram in your tailstock close to the spindle. Separately release the tailstock quill clamp and the tailstock base clamp then retighten being carefull not to bump anything. If the tailstock dials in OK after all then then the problem isn't in the tailstock - but it probably is.

The tailstock base is probably "rocking chaired" by some amount. If you can rack the tailstock in pitch and yaw you're doomed to battle it everytime you move it. The only fix is to hand scrape the bottom of the tailstock to bring the quill back in parallel to the spindle axis and shim between teh loer plate and the upper casting to spindle height.

The quill is a separate problem. If the quill has more then 0.002" side shake then it's worn almost beyond economical use for precision work. You need to bore out the housing and make a new quill so they have 0.0003" to 0.0005" clearance.

This brings us to the tailstock ways. Chances are they are worn but you don't know by how much or whether you can live with it without first re-building the taistock.