Lathe Not Cutting Straight

[Coomba]

I have a .375 piece of cold roll, that I need to turn down to .318. It needs to be 3.5" long. I have the lathe turning at 175 Rpm. The piece is supported with a live center. No matter what changes I make,the end closes to the chuck, always comes up .006 larger than the tail stock end. Does this mean the Chuck and the tail stock are out of center?

 

[kd4gij]

Yes your tail stock needs aligned.

 

[stupoty]

I tend to put a dial indicator on he side of the tail stock when i'm adjusting it to watch it moove, somtiMes it shifts quite a lot when first loosened off.

Stuart

 

[tq60]

Make a spool.

Locate anything round and 2 inch diameter is a good size.

Place in chuck and center drill each end.

Face ends if you wish for better look.

CRS works well.

3 inch long works.

Now remove a bit from the center so you have a good spool shape.

Now place 1/2 round in chuck and make a point to hold center.

Make it live so you know perfect.

Place spool between centers and take light cuts.

Skim both ends until clean cut all the way across and do both in one pass...critical you do it that way.

Measure diameter of each end and if tail end larger move toward you and if smaller move away.

Use a dial indicator on carriage to tail stock and move 1/2 the error or less.

Repeat until perfect.

For future alignment just place dial indicator in tool post and check the rims.

This is your first and most important tool.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

 

[eeler1]

Maybe misaligned, even probably. A cheating, uncaring machinist would set up the work piece, then run an indicator along the 3.5"', then adjust the tailstock until the two ends give the same reading. THen try a cut and see what happens. Of course that's not really aligning then tailstock for general use, but might work pretty well for a one-off.

 

[Kernbigo]

put a indicator in the chuck and sweep the tailstock circumference, that is how you align it properly

 

[4GSR]

A lot of good answers. But when you are turning OD's and start getting taper in the part what do you do? I usually wind up messing with the tailstock alignment to get the lathe to make a straight cut. Or at least get it as close as I can get it to cut. My lathe has some bed wear on it. If I know I'm going to do some long turning/boring, I will first re-level my lathe with a precision level. Sometime, that all it takes. Once that is done, start making cuts on the part and if taper exists, start adjusting the tailstock to remove as much of the taper as you can. Just remember, if your lathe has bed wear, you will never remove the taper completely, no manner what you do. I'm not a firm believer in adjusting your bed to remove taper from you part as many will show you to do when doing a two collar test. If not done properly, you can induce "twist" in your lathe bed, which is not good. Ken

 

[Low tech]

My 13" Leblond servo shift cut a .004 taper in 6" , after I leveled it . This was on a piece of 2" aluminum held in a Chuck only . The taper was such that the stock was larger at the Chuck end . I adjusted the leveler at the tailstock end of the lathe on the opposite side of the operator upward about .005 . This pushed the tool bit away from the work slightly . The next cut was within .0002 over 6" . I am happy with that .
I then measured the diameter of the tailstock quill and turned a piece of stock to the same diameter . I left the work piece in the chuck and moved the tailstock , with quill extended , up to the work piece in the chuck . Then using a dial indicator on the carriage I could sweep the quill to the work piece on the top and sides of both . This let me adjust the tailstock for alignment . It turns out I had to shim the tailstock up .012 .
Not sure if any of this is the best way to align a lathe but it worked for my lathe .....Steve

 

[mmcmdl]

I have a .375 piece of cold roll, that I need to turn down to .318. It needs to be 3.5" long. I have the lathe turning at 175 Rpm. The piece is supported with a live center. No matter what changes I make,the end closes to the chuck, always comes up .006 larger than the tail stock end. Does this mean the Chuck and the tail stock are out of center?

First thing I would do is take your rpm's up by at least 1000 , then move your tailstock away from you .003 . Recut till you achieve what is acceptable to you on this piece . After this piece , grab a lathe mandrel or something hardened and ground , put it between a turned center in your chuck and a dead center in your tailstock and indicate the bar true . Turning at 175 rpm on a 3/8 shaft is slow motion , crank it up ( especially if you're using carbide) . I'd start at your machines max rpm and work down if necessary .

 

[Wreck™Wreck]

Maybe misaligned, even probably. A cheating, uncaring machinist would set up the work piece, then run an indicator along the 3.5"', then adjust the tailstock until the two ends give the same reading. THen try a cut and see what happens. Of course that's not really aligning then tailstock for general use, but might work pretty well for a one-off.

I am cheating and uncaring so I program the taper out of the part.

What do you do?