Lathe/Jacob chuck alignment questions.

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Fish30114

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Well I have been chasing around a problem for a while with my Jet 1221 VS lathe and the Nova supernova 2 chuck I have had. One thing I resolved with the help of Ken here, is that I had a wrong insert in my chuck, I've since got that sorted but I have a remaining issue that I thought I would ask you folks for some help with.

If I put a live center in the tailstock, and a spur drive(with point) in the headstock, and slid the tailstock all the way up to the headstock, and lock the tailstock down, the points meet pretty damn precisely.
My issue is if I take a pen blank and chuck it up in my pen jaws, after marking center on the blank, and confirming it is definitely square, when I put my Jacobs chuck in the tailstock and put a drill bit in it, when I bring it up to the pen blank it is consistently slightly low and very slightly left of center.

I don't know how to check where the error is occurring, and what I might do to correct it.

Help!

Thanks for any ideas feedback or suggestions.
 
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Don; My first suggestion is not to use a pen blank, but a transfer punch or other metal rod in the head stock. It is possible the head stock isn't aligned. Check out the Lathe Alignment page in the Wiki.

The lathe head stock and tail stock may not be coaxial / concentric.
 
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I'm not familiar with the supernova chuck and it's pen jaws, but I would be suspicious of four things:
1. The alignment of bits in a jacobs chuck can be affected by debris inside the chuck. Make sure there is no dust or other crap inside. Also, make sure that the bit is correctly held between noses of the three dogs, and not jammed between the sides of two jaws. Use a center bit or brad point bit when checking alignment - other bits can be misleading. Finally, make sure you are looking at the alignment properly - this may be an issue that applies only to me because I have vision problem with one eye.
2. When I think 'pen jaws' I think of a pair of jaws that mount on opposite sliders (1 and 3, or 2 and 4) on a scroll chuck. Have you tried switching the pen jaws to the other pair of sliders to see if that makes a difference? For most chucks, its important that the jaws be mounted on the correct sliders (they are usually numbered). I don't own pen jaws, but it seems to me that the alignment of pen jaws could be dependent on the pair of sliders they are mounted on.
3. When I first put my new lathe together, I did the 'nose to nose' test and everything seemed ok. But later I found that there was a very slight misalignment, and the error was amplified when it was transferred through a blank.
4. Are you locking down the tailstock before checking alignment? On some lathes there is a very small wobble in the tailstock when it is loosened for movement that can lead to to suspect misalignment when there is actually not a problem.
 
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are you locking down the tailstock with the Jacobs chuck in it? Is your Jacob's chuck firmly seated in the quill? is the MT on the Jacobs chuck smooth and free of any galling? are both morse tapers CLEAN?
 
As I age, I would do this a different way!:eek: I would put my lathe and all the pieces in my truck or trunk and go to the nearest machine shop, explain the problem in person, and ask them if you can afford to have them solve your problem so you don't grow old chasing solutions to problems!:tongue:

But before you do that, make sure that your lathe bed is level. If it is mounted on a bench, make sure the bench is level first. Be Bold, Be Safe, Have Fun in the World of Woodturning!!!:biggrin:
 
Yes, my Morse tapers are clean, yes the chuck is seated firmly in the taper, there is no debris in the chuck, bit is centered between all 3 dogs, for the pen blank chuck, I have tried the jaws in different position--same result. When I am checking the headstock-tailstock alignment I lock the tailstock down and run the quill out the last 3/4" or so--and the points line up well. I can actually move my tailstock a goodly amount up, away from the bed when it isn't locked down, but I have never thought of this as unusual. Is there a simple way to adjust the tailstock so that the drill bit hits center before I drill my blanks?
 
If the issue was with the Jacobs chuck the centering would change if you took it out, rotated it a fraction of a turn and reseated it. The fact that it stays the same tells you the tailstock itself is misaligning with the headstock. My old Excelsior lathe has to have the tailstock held against the front edge of the bed as it's tightened to get alignment as there is slop between the stocks bottom form and the bed channel. If you can twist the tailstock off alignment while it is not locked down you might have the source of your problem there.
 
Don, I would suspect that Gary's point about movement of the tailstock is valid and should be checked.
Something else to check is this. Run the test you do with the points lining up and take note of the tailstock position when you lock it down. Did you push it or pull it or just tighten the lever. The simple act of pushing the lever can actually be moving the tailstock a few thousandths and you would not know it. Mine is like Gary's in that I push it back before locking the lever, it has become an automatic thing now. Also, I finally decided that it is why the lever is in the back of the tailstock casting, because you are pushing the tailstock toward the headstock when you are locking the lever.
Anyway, after you get the points to line up, move the tailstock back and install the chuck and drill bit and see if the end of the bit meets the point of the spur center. That may tell you if the chuck and bit are still in line after bringing them that much further away from the headstock.
It occured to me that there may also be a variance in the ways from one end to the other or a burr from the casting. Slide the tailstock back and forth and see if you can detect any such variance.
Also, maybe some closeup images of your setup and tests would help.
Finally, something that I check often is to use a dial indicator to check the runout of various tools. Putting the drill chuck in the headstock and checking it for runout at different points on the chuck and with a known good bit in it can tell a lot about the setup and how things will run.
 
Wood lathe chucks are not accurate like metal lathe chucks. With wood lathe chucks, close is considered good enough when you crank down on a piece of wood it gives, if you clamp down on a piece of metal, it clamps and the jaws do not dig into the metal.

Try this, find a 3/4" steel rod about 5" long, chuck it up, and see if it turns true in the pen jaws.
 
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