Atlas-craftsman 101.07301 Chuck Wobble

Round, The spindle threads look great but the chuck threads were messed up when I got the lathe. I chased the threads with a tap just to get them on the spindle more than about a 1/2". I am beginning to think I need to do that again, maybe I did not go far enough? Lot of questions in my head. Wondering if the threads are so messed up that that is what is causing the problem. Thanks Ed
 
The chuck stops 3/16" away from the spindle collar? This is not right, the chuck must lock up against the collar on the spindle to register. Otherwise you are relying only on the threads themselves to keep things on spot, and they never will.

-frank
 
sounds like the spindle is fine. Now you need to get that backing plate threaded on ALL the way so that it sits flush on the spindle register (flat part perpendicular to the threads, closest to the headstock) before doing anything else. Then, once you've done that, face the backplate and recut the chuck register. The chuck "registers" to the back plate in 2 ways. The end of the chuck, where the bolts go, sits flat on the outside portion of the backplate - this is the bit that reduces runout or wobble that increases with distance from the chuck. The inside lip of the chuck sits against the ledge sticking out from the backplate - this is the bit that makes the chuck run perfectly inline with the spindle. If it's off, then the tip of a point held in the chuck with scribe a circle, instead of rotating in place.

Most likely you'll need to recut both. The flat register is pretty easy, the inside register (the last one above) is trickier and takes a lot of care. Also make sure that the bolt holes or even the countersunk holes are not interfering with the chuck bolts as that can throw the chuck off too.

I had to do all of the above with the chuck that came with my 6 x 18, now it shows ~0.001in runout and no wobble. Before it was in the 0.01+ range. Also, even once you've made those changes, you can often lightly tap the chuck while it's loosely screwed to the backplate to get rid of the last couple thou runout (I got mine from 0.004 to 0.001 that way).

If you do all of that and it's not fixed (unlikely from what you've described so far), then the chuck may be shot, but that's the very last thing you should worry about.
 
For the time being, ignore the 3MT taper inside the spindle nose. Although important, it has nothing to do with chucks, backing plates or face plates. The register actually consists of two parts. The cylindrical unthreaded area to the left of the threads, and the face of the flange to the left of that. Unless it is oversize, which is unlikely, you can only make matters worse. Measure the runout on the cylindrical part. That controls chuck runout (if the chuck is otherwise perfect). And measure the axial variation in the face of the flange. That affects wobble.
 
CONFUSED The spindle is threaded to within 3/16" or so of the flange BUT the chuck is threaded all the way so that it has to stop app. 3/16" from the flange. Am I missing something? Is there a part I don't have? ?????? Is this the wrong chuck for my lathe? It is an Atlas chuck.
 
The back of the chuck (or if it has a separate one the back plate) should be counterbored to a depth of about 3/16" (just slightly greater than the length of the unthreaded register on the spindle) and a diameter of at a guess 1.0006"/1.0001". The spindle register diameter is probably 1.0000"/.9995". That's based on the register dimension on the larger spindle in the 10" and 12" machines. If it isn't counterbored, that is why the chuck won't screw all the way onto the spindle and probably accounts for most of the horrendous runout you reported. Note that it is not unusual to see just the very tip of the thread cutting across the surface of the counterbore. Because the major diameter of the female thread must be larger than the major diameter of the male thread or it would be an interference fit.

FWIW, few if any of the original 3" through 8" chucks sold by Atlas (or Sears) had separate back plates.
 
You might want to check the size and tread count on that Atlas lathe. I just made a 4th axes and removed my 3 jaw chuck from my atlas lathe to be used on it, and it had 1" 10 tread count which is not standard size with any of my taps & dies sets. When I made my new spindle i just threaded to fit the chuck 1" 10 tread. The run out is okay for what I want to do with it. The new setup has a stepper NEMA 23 motor with a 4 to 1 ratio.
 
If the machine is a 101.07301, as the first post says, it will have 1"-8 spindle nose threads.
 
It has 1"-8 threads on the spindle and the same on the chuck, the problem is the unthreaded part of the spindle and a fully threaded chuck won't allow the chuck to go all the way on to the spindle.
Wa5cab so I need to take my chuck to a machine shop and have 3/16 or so of the threads cut out?
 
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You have a faceplate, yes? You could mount the backing plate backwards on your faceplate, mount faceplate to lathe, and then take the offending threads out yourself. Just a thought until Robert replies.

-frank

Sorry, thought the "faceplate" referred to earlier was an actual faceplate and not the back of the chuck. Could you do the same process though but with the chuck back?

-frank
 
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