I've had this lathe proably 2 years now and never turned anything very long. Well yesterday I was turning a piece of 1.75 stock down to 1.40 and took a measurement.
It is running .003 in bigger at the chuck end of lathe . Question is should I try to get it better, or this close enough?
I don't do work for nasa, just hobby.
I call that pretty good. You can play with adjusting the tailstock but depending if that is coming off your 16" American or you're Logan 820. Can make a difference. That's about the same amount I get off my 13" Sheldon that's 60 years old! It does have some wear in the bed, too. Ken
.003" @24" doesn't sound too bad.
a slight amount of twist may be present or as Ken said you could have slight misalignment of the tailstock, or wear or the combination of all.
try to correct for half of the TS error and test again, you may surprise yourself
I should have said , it' the American that's doing it. It was made in 54 and has very little wear. I don't know what it had been used for.
I think I will set up a dial indicator and try adjusting the tail stock.
There is no standard, rule of thumb or conventional wisdom. What the Customer requires is what you produce. If the component works for the amount of time required then it is acceptable. if not then adjustments must be made, accuracy is application dependent. If this were not so every simple mechanical device would be significantly more expensive to produce, do you measure the diameter of the lead screw in a Chapstick™ dispenser or the thread lead of a lipstick package screw?
Make the parts so that they work together, this is the only important consideration, one could spend the remaining days of their lives chasing tenths, if however so inclined have at it.
Possible and wouldn't rule it out. But the wear ratio between the bed ways and the bottom of the tailstock is like 1 to 20, for every 1 thousandth worn off the bed you will take off 20 plus on the bottom of the tailstock. This is if the bed is harden. And of course how well it has been oiled and ways wiped down over the years. Oh, you also have the issue of wear of the tailstock barrel or spindle wear and tear, too! Don't forget...
That's why God developed the Cylindrical Grinding Machines. Or was that Brown & Sharpe? He knew the lathe would not cut exactly straight as the customer wanted it. They were made to grind to exact OD's with near zero taper from end to end on a shaft with the correct setup. Ken