Need Help! Lathe Cutting A Taper!!!

Realistically I am not expecting 0 but 1 thou over 2 inches an inch out from the headstock when added in a linear way adds up to a lot more than 1 thou over the length of my bed 22" .
There is a grinder in your future.
I suspect that the set up and material are causing problems, a machine of that size with a collet chuck can't hold over a 1" bar I imagine. As a rule of thumb do not extend a piece of stock more then 3 diameters from the collet or chuck face.
If using a tailstock then just move it over until the taper is acceptable, done deal.

I often run a 24" X 100" lathe that will sometimes taper yet not every time, I can turn a 60" long part within .002" on the diameter other times it will be all over the place depending on the stock and setup.

Again, Good luck
 
Yes I do agree, there is a grinder in my hopefully not too distant future!
 
Aside from my PITA inaccessibility of 1 hold-down bolt to loosen (which is located behind my gears) the actual headstock re-alignment on my Asian lathe was nothing more than tweak of 2 adjusting screws while watching the dial movement. Then you're back in the game & will wonder what all the fuss was about. Now that I know what its all about, seriously, it takes me as long to dial in stock on a 4-jaw chuck.

Tonight my level arrived, a Starrett 98-12 good for 0.005" per foot. Not over the top precision but good enough for now & price was right. Turns out my guess & by golly foot setting was within a half division so call it 0.003"/ft twist difference between headstock & tailstock over nominal 40" bed. Then I installed my MT3 test bar + MT5/MT3 socket assembly into the headstock. Chuck is completely removed & no tail stock involved. This parallel stub section is only 5" long, but I measured exactly the same headstock rotation direction & amount as my last recorded coupon cutting test when prorated to this length (0.0010" over 5"). This tells me I was chasing my tail on the lathe levelling as suspected.

As mentioned, I'm not suggesting this MT bar as a replacement for test bar cutting method, but its convinced me of the ease & reliability of spot checking this way. My preference would have been this longer bar (ebay 49$U, same MT3 section but a 245mm = 9.6" straight section) for same price. It would be the exact same procedure but even more accurate because its over double length. Theoretically you could probably go longer yet but a) haven't seen one longer b) its ~1" steel but might start seeing cantilever droop issues towards tailstock so DTI off-centering? c) does it really matter at this point relative to cutting things even tool post grinding because you way past what should be tailstock domain & now that dominates alignment?

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With any lathe, the answer is to make sure the bed is not twisted, and I suggest that a .005 level is not really up to the job, then adjust the headstock so as to get the lathe to cut straight; I make a mandrel that is about 4;1 diameter to length, and relieve it between a narrow band on each end; this eliminates tool wear as a factor in the readings taken on each end to determine if the cut is tapered. I have never worked on a lathe that does not have at least one prismatic way under the head/tailstocks, so I will address that situation; a rebuilder would determine where material would be removed by re scraping the prismatic way surface of the headstock, so much at one side, and so much at the opposite side on the other end; a quick and dirty way to achieve the same result is by putting shims between the bed surface and the headstock surfaces at opposite sides at opposite ends; usually this does not take much of a shim to cure the taper problem. I have a 19" Regal Leblond that cuts with virtually no taper by this method.
 
I need some input and or suggestions. I have a 10x22 king lathe, ( I know , sorry for your luck) all kidding aside. It seems that all of a sudden I am cutting a taper .002" over about an inch, two inches out from the headstock. I am using an ER 40 collet chuck that I built. The work is slender so I am expecting some deflection, but even with spring passes the taper continues. I have made a test bar and re adjusted my tailstock to less that .001 run out turning between centers. I checked for chips under the mounting register and face of the chuck, re adjusted the headstock bearing tightness and can see no appreciable movement there I have done the compound hold down mod for added rigidity, any suggestions where I should be looking. The only thing that I haven't looked into is leveling the lathe bed, and do not know if it can even be done as the lathe is in my basement and not anchored to the concrete ( yet ). As I had mentioned this is a new problem to this machine and I have been running it for 3 years with very little in the way of issues. Any help is greatly appreciated and thanks in advance.
I had a very similar problem on a 1979 Harrison M300 lathe (.001 every inch). Turns out, there were tw0 problems that were not immediately discernible. 1 - the four adjustment screws on the cross slide corners were out of whack; not obvious at first, but it created some slack as it moved across the ways. 2 - the split lead screw nut was very worn; turns out the lead screw itself was on the way out, also. Was able to buy the nut and have made a new lead screw.
Had a couple of seasoned machinists look at the lathe, and it took even them a while to zero in on it. (They both initially thought headstock/tailstock as well.)
Another possibility, but not likely, is wear on the ways. This kind of issue develops SLOWLY, but if your lathe is older and has seen a lot of heavy use in a particular range, it may have developed a sweet spot. Not likely, though, because you would probably have noticed it before. Also, I suspect the taper would be in the other direction.
This kind of problem is no fun (I feel your pain). Hope you get it resolved.
 
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