# Lathe Not Cutting Straight



## Coomba (May 31, 2016)

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?


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## kd4gij (May 31, 2016)

Yes your tail stock needs aligned.


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## stupoty (May 31, 2016)

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


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## tq60 (May 31, 2016)

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


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## eeler1 (May 31, 2016)

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.


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## Kernbigo (Jun 1, 2016)

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


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## 4GSR (Jun 1, 2016)

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


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## Low tech (Jun 1, 2016)

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


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## mmcmdl (Jun 1, 2016)

Coomba said:


> 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 .


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## Wreck™Wreck (Jun 1, 2016)

eeler1 said:


> 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?


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## mmcmdl (Jun 1, 2016)

Wreck™Wreck said:


> I am cheating and uncaring so I program the taper out of the part.
> 
> What do you do?



Yesssss.......they were the days !


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## Coomba (Jun 1, 2016)

mmcmdl said:


> 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 .



I tried carbide at higher speeds,lower speeds,then went to HSS,and tried different speeds. 175 was my last cut. If it turns out to be wear in the ways,do I shim the tail stock?


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## mmcmdl (Jun 1, 2016)

Coomba said:


> I tried carbide at higher speeds,lower speeds,then went to HSS,and tried different speeds. 175 was my last cut. If it turns out to be wear in the ways,do I shim the tail stock?



750 rpm would be the minimum rpm I would use with hss cutter . With carbide , go for the limit . Did you pull your tailstock into adjustment ? If so , there are many ways around the taper issue if your ways are worn .


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## 4GSR (Jun 2, 2016)

Wreck™Wreck said:


> I am cheating and uncaring so I program the taper out of the part.
> 
> What do you do?



Reminds me of a place I used to work at. We had a worn out Cincinnati Cinturn, remember them?, that would turn nearly .030" taper that varied on a cut of about 18" in length.  They knew exactly where the taper was and would program for it so the finish part was perfectly straight on the OD.  It's amazing what we will do to obtain perfection in the work we do. Or close to it as we can get it!  Ken


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## Reeltor (Jun 2, 2016)

A lot of good advise and all have merit.  
There are many ways to check for twist in your bed (ie. leveling your lathe).
I came across a new to me way to do it, requires very little investment in materials and you don't need to use a precision level.

I would chuck up a chunk of aluminum, set your compound to 60 degrees and machine a point on it.  Do not remove it from your chuck.  Now put a dead center in your tail stock and slide it up to touch the part you just made.  Make note of what you find but don't make any adjustments to your tailstock yet.
"level" your lathe, here is the link to Tips and Tricks in Metal
after checking the level and/or leveling the lathe, run the tailstock back up to see if the points match






Good luck
Mike


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## eeler1 (Jun 2, 2016)

Wreck™Wreck said:


> I am cheating and uncaring so I program the taper out of the part.
> 
> What do you do?



I take the 5th!!!  (Thought I did the other day! just getting back to the thread).  

Lots of stuff they didn't teach in school, but that works when you just want to make a part.


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## Coomba (Jun 3, 2016)

Thanks for the info. guys I'll give it a try.


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## Paul in OKC (Jun 4, 2016)

eeler1 said:


> 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.



Afraid you lost me on that one! If it makes the part straight, it lines up the tail stock, assuming that is the problem. If it is the head stock that is out, then no, it is a per part remedy. But the OP said he used the tail stock, so....... (Hey Wreck, Programming it out sure is handy, too!)


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## dogma (Jun 5, 2016)

What indicates that this is more likely a tailstock rather than headstock (or both) alignment issue?


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## British Steel (Jun 11, 2016)

dogma said:


> What indicates that this is more likely a tailstock rather than headstock (or both) alignment issue?



Mostly the fact tailstocks are designed to move and be offset, headstocks aren't...

It's _possible_ that it's the headstock, but far more likely that it's either tailstock offset (very few lathes have no adjustment there) or bed twist (I once had a call out to a customer ranting and raving because his brand new lathe (his first full-size machine) cut a 6 thou" taper in 2", he hadn't levelled it so I applied precision level^ to the carriage and some shims under the cabinet - result no measurable taper* in a light 10" cut) - both are a lot easier to sort than a misaligned headstock.

For a headstock check *when the tailstock adjustment and precision levelling have failed *the OP will need a proper test bar (taper to fit his spindle, *clean* spindle taper and test bar, ground test bar extending 8 - 12", DTI checks along its length to check that it runs concentric with the spindle and some easy maths to average out eccentricity if it doesn't) and  good quality DTI - and even that is subject to errors from bed wear which will move the DTI relative to the theoretical axis of the ways.

Hefty "traditional" lathes often have the headstock fitted (machined, ground and usually scraped-in) to the ways on the bed, which doesn't leave much leeway for misalignment (as long as you keep everything scrupulously clean, a piece of grit or swarf's enough to ruin the alignment) - my 50's Holbrook is built that way, there's no measurable shift in headstock alignment when lifting the headstock and replacing it (necessary to get to some of the feed gearing, dammit, especially if you want to see the gears in mesh instead of on the bench!). More recent (and particularly far-eastern) machines may have adjustments either through lockable (I hope!) screws or shims between headstock and bed ways/locating points, usually around the back of the headstock.

Hope that helps,
Dave H. (the other one)

^ my granddad the WW2 ballistician's 10 second-of-angle clinometer, used to set up howitzer sights,  that's about 2" at a thousand yards...
* with a 0.01mm ~1/2 thou" micrometer


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## Rick Leslie (Jun 11, 2016)

Bed twist is probably the most overlooked cause of tapered cuts. I'm neither cheating or uncaring, but I do factor in the precision required on the part being made. If dialing in the tailstock works, then I go with that. I usually do the 'point line up' thingy first to see how bad the tailstock is out. If you can see the misalignment, then it's pretty far out of whack. 

Also, don't overlook vertical tailstock misalignment. My poor old Heavy 10 ha so much bed wear at the chuck that the closer I get the tailstock to the chuck, the more taper I have. But I know it so I adjust for it.

I have chucked a ground and polished bar in the 5C collet and gotten .002" TIR in about 8 inches with the chuck alone, then hung the same bar between centers and tripled the runout.


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## Rick Leslie (Jun 11, 2016)

And thanks for the video Reeltor. Never thought about a plumb bob. Sometimes it's the simplest things...


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