lathe setup dilema ?

[coldte]

hi every one,
After trying to turn a shaft 6 inches long and 1 inch diameter i measured it and found the tail stock end bigger than the headstock end so in my usual cavalier fashion thought i can fix that just set over the tail stock hmm!
So off i went and after 3+ hours and lots off tea gave up with an error of 0.0025mm over 5 inches.The adjustments were done between centres and a new cut(.003) after each.
Question - what is an acceptable error and how do you get to it with out hassle ?
thank you
coldte

 

[CrewCab]

Mmmm ............ that's a run out of less than a 1/10 of a thou, I'd be happy with that degree of accuracy coldte.

CC

 

[tornitore45]

0.0025mm is 1 tenth and that is good enough for me.

 

[starbolin]

That's a bit closer than is usually needed ( and a lot closer than my poor old lathe could ever do. ) When turning shafts you do whatever you have to do to get the taper out. Whether that be shim the legs, set over the tail stock or whatever. I usually try to avoid fussing with the tailstock once I'm happy with it's setting ( it does usually take some time to get it set ) preferring instead to shim the the right front (tail end) leg.

0.005mm ( about two tenths for those of us who aren't bi-lingual ) is the closest that I usually need to do and that's on short pieces. Any closer than that and it's going to be easier to lap it. Long pieces usually only need to be accurate on the ends. When doing shafts you cut from the tail stock into the middle then flip the piece and repeat. This cuts your windage in half.

 

[CrewCab]

Long pieces usually only need to be accurate on the ends. When doing shafts you cut from the tail stock into the middle then flip the piece and repeat. This cuts your windage in half.

And that's a first class tip 8)

CC

 

[chillybilly]

Sounds pretty good to me that ,i would make a setting piece while i had the set that good ,may prove a useful addition should you ever have reason to need it .
Good job

 

[charlesfitton]

One of the lads wrote:

...preferring instead to shim the the right front (tail end) leg.


All I can add here are question marks?????????????????????????????

 

[mu38&Bg#]

That refers to my question here.

http://www.homemodelenginemachinist.com/index.php?topic=4919

I setup up my lathe this way and stopped at .0005 over 2". The trouble is that my bed drops ~.003 at 18" from the headstock and I can't seem to remedy that.

 

[starbolin]

One of the lads wrote:

...preferring instead to shim the the right front (tail end) leg.


All I can add here are question marks?????????????????????????????

Raising the right front leg of the lathe makes the tailstock end of the piece smaller. Lowering it makes the end larger. This is assuming a long enough bed that the lathes own weight makes a difference. This also assumes the headstock and tailstock are otherwise in line. On my old sebastian often the only way I can cut a shaft free of taper is to have one leg hanging in the air :-[ My bed is also a little sway-backed like an old nag but there is little help for that other than a complete bed referb'.

 

[ieezitin]

Hi people.

In my humble opinion. People seem to think accuracy is the first thing they must achieve before they start to make there pieces, people go nuts trying to achieve perfection.

The machines we use are not intended for finite accuracy but tweaked in certain ways and through knowledge of them measurements of high accuracy can be achieved.

I do it this way. What ever I am trying to make I have in my minds eye what tolerances are needed and what can I get away with, I always build in cheats and ways out incase something happens. Once I decide on what’s needed I check to see if my lathe/ mill is achieving this at that time, all our small machines are quirky and move around every time we use them so a wise thing is to survey what you are dealing with.

Its more important to know what’s going on and why rather than shaving that tolerance to sometimes unachievable goals. Switching the shaft around between centers as mentioned is a classic example of knowing what’s going on and cutting your odds down by half, it works and saves a lot of headaches.

1/10 of a thou is outstanding I would take that to the bank everyday.

All the best. Anthony.