Chuck Misalignment?

[draculon]

I've had my Harbor Freight 7x10 Mini Lathe for about 7months now. I haven't really been able to do precision work on it for a lack of tools, but I notice that when I turn my parts down, they're not concentric with each other. It's to the point where you can tell that the centers of the unturned and the turned peice aren't on the same axis. Is there any way I could fix this? I've had a headache trying to figure out what was wrong. :bangin:

[tp555]

What do you mean not concentric? Details, its all in the details.Give us more info. What chuck are you using? 3jaw? What are you doing? Boring a hole or turning outside dia or both? Most 3jaw chucks have about .003" accuracy when
holding a round bar.If you remove the piece and place it back in the chuck the
outside dia could be out of round the .003" or whatever your chuck is unless you dial it in.Could you post a pic? regards.

[draculon]

" What do you mean not concentric? Details, its all in the details.Give us more info. What chuck are you using? 3jaw? What are you doing? Boring a hole or turning outside dia or both? Most 3jaw chucks have about .003" accuracy when
holding a round bar.If you remove the piece and place it back in the chuck the
outside dia could be out of round the .003" or whatever your chuck is unless you dial it in.Could you post a pic? regards."

I'm using the standard 3inch 3 jaw chuck that came with it. It happens both when I'm turning the outside diameter and boring it out. I'll try and post a picture of something to show the misalignment as soon as I can get it back up and running (took it apart to clean everything up and relube it).

There's a paint picture here (not drawn accurately) but it gives an idea as to what's going on.

[tp555]

Looks like sloppy chuck holding your work. Chuck is probably screwed on the lathe spindale, maybe 1 1/2 x8 thread. If this is tight then what happens when you place a round piece of material in and tighten up the chuck? the work piece
is supposed to be centered within a few thousands of an inch.If you have an indicator see how much runout your chuck has or start the motor and look at the work piece. It should be spinning with very little wobble.A 3 inch small chuck
should have less then .003" runout probably .001" if its made properly.If your chuck is holding the work way off center try removing the jaws and replacing them back in order.You may have one of the jaws out of order. Jaws are usually
numbered 1,2,3 and go into the grooves in order.If the groves do not have marks that correspond to the 1,2,3 numbers mark them.Remove jaws. Look in the grove at the scroll that moves the jaw. Its spiral shaped.Drop n1 jaw in and turn the key until jaw 1 catches and you can't pull it out. Then do n2 and n3.
Only turn key enough so the jaw catch do not over turn.When all 3 are in close the jaws.Should be in the center . If one jaw is out it should be at least 1/4 " different then the others.Hope this helps. regards.

[DonT]

One other item to look at... Is the chuck attached to a mounting plate? Typically on smaller lathes the three (and four) jaw chucks are screwed to a mounting plate that is threaded to go on the spindle. Ideally you want to take this mounting plate, mount it to the spindle (screw it on) turn it true to the spindle, clamp the chuck to it and indicate it to get it centered on the plate and running true on the spindle then take the whole unit off and drill your mounting screws.

IF it were mine I would but a drill bit in the chuck backwards so most of the shank is pointing out, use a 3/8" or bigger if you have it. Indicate off this. This should tell you, as others have indicated, if you have run out (the chuck is not true to the spindle). If this is the case and it, the chuck, has a mounting plate you should be able to remove the screws, follow the procedure outlined above and rotate the chuck on the plate to allow you to redrill and tap the holes. I have had to do this on a couple of 3 jaw chucks over the years cause I bought them after getting the lathe and they did not run true.

Just a thought...
DonT:wink: