I know your misery. I've got a Logan 820 lathe (quick change gear box, does 8-224 threads per inch; change one gear and you can do 4 threads per inch). The ways are worn so to hold a 10 thousands over 5 inches I have to twist the bed. I twist it with a level like this on the carriage:
I didn't get that one, $863 is spendy. I got a Russian copy for $150.
Anyhoo, you put that level on the carriage and then crank the carriage back and forth over the range you want straight, adjust the levelers on the legs.
I can turn mild (cold rolled) steel and hold a 10,000 of an inch for almost 5 inches and then it goes to hell. And the head stock bearing is crap, the originals had some preload but the replacements do not so I have to use a live center in the tailstock to put some load on them or it doesn't work.
http://www.starrett.com/metrology/product-detail/Precision-M...
I didn't get that one, $863 is spendy. I got a Russian copy for $150.
Anyhoo, you put that level on the carriage and then crank the carriage back and forth over the range you want straight, adjust the levelers on the legs.
I can turn mild (cold rolled) steel and hold a 10,000 of an inch for almost 5 inches and then it goes to hell. And the head stock bearing is crap, the originals had some preload but the replacements do not so I have to use a live center in the tailstock to put some load on them or it doesn't work.
Watching that video? I'm in awe.