Help Best way to fix.

[kvt]

Help, Need to know how to fix a problem. Have just redone the lathe. The seals and bearings were bad, Replaced all of them The when Trying to align things back up, Though I had it good, then chucked up a long piece (4 jaw chuck) to start a job and found that although I could get it set at the chuck it was way out at the other end, Though it was a bent piece of metal, Tried another few and got the same results on all of them, Then did a bit more checking and testing and found that it was always off at the same spot.
Even pulled the chuck off and checked the back pate, It was a little off on the face but not much but trued it up just in the same. the put he chuck back on, and indicated it. Seems fine when indicating it. But chuck up a long piece and it is still way out on the other end. It is almost as if the jaws are ground at an angle or something. Do not have another backing plate, to put another chuck on. Due have a 3 jaw not sure what shape the jaws are in. So what is the best way for me to get the jaws fixed to where I can get hold a piece properly. without needed about 0.100 of extra to material to get it cut properly. Oh, when I set and aligned up did get it to where I have it aligned to less than a thou over 10 inches.
any suggestions would be appreciated.

 

[Silverbullet]

Is the head mounted in the right spot aligned , you may have to loosen the head and move it a few thousandth.

 

[Joncooey]

Is your tailstock aligned correctly? If not check out Tubal Cain and see if he has a procedure. I find his tutorials the most helpful.

 

[joshua43214]

Sounds like your headstock is out of alignment.

 

[Ulma Doctor]

10" is a lot of stick out, the part should be supported by either a steady rest or the tail stock.
unless you are turning something that has already been precision ground, it is very likely that you'll have runout.
the compounding factor of long stick out, combined with the runout in the piece you are trying to turn- is most likely causing the problem
it would not hurt to indicate the spindle and test the chuck/spindle deflection
the next step is to make a test bar, if the other 2 above checks were inconclusive

 

[markba633csi]

KVT: Need more info. How much error are you seeing with a 10" piece? Is this a new chuck or a used one? Several thou runout with a 3-jaw on a piece
that long is perfectly normal, and it will change every time you chuck it up.
Mark S.

 

[jim18655]

Old computer scanners have a guide bar inside that makes a pretty good test bar. Also, try find a file called "Rollie's Dad's alignment" , or something similar, and try that.

 

[RJSakowski]

You didn't say in your "way out" if problem was runout in the mounted workpiece or the workpiece was just closer or further away at the tailstock, If it is runout, the problem is in the chuck or in its mounting. Four jaw chucks can be adjusted for zero runout at the chuck but still exhibit runout nearer the tailstock. My new Grizzly four jaw had this problem which I determined was caused in part by jaws which had an excessive taper which caused contact on a single ring around the mounted part. I ground my jaws to remove most of that taper and improved the far end runout significantly.

If you are experiencing a tapered cut as evidenced be the two collar test or the RDM, you have either a headstock misalignment or a bed twist.

Lastly, have you checked your bearings for play? A loose spindle bearing could give acceptable runout when measured at the chuck but 10 inches out, the play would be more noticeable.

 

[4GSR]

KVT,

4-jaw chucks are notorious for not holding stock true from end to end, when indicated true at the chuck. And I do this all the time, get you a piece of brass and bump the bar at the far end to get it running true. May have to go back and re-true the material at the chuck and again at the far end. But with a little patience, you can get running true. OH MY!!! you and every else saying, reading this! You going to damage the spindle bearings! No you won't as long as you are not using a sledge hammer. And the blows you are giving it are small, more or a "bump" that a "bam".

Ken

 

[owl]

Is your problem that it simply doesn't point at the tailstock, but runs true, or is it that the end, when the lathe is turning, describes an O shape? If the former, you probably need to align the headstock, if the latter, you need to track down the out of alignment part.