South Bend 9a new gap between chuck plate and spindle

[dansawyer]

The machine is a 1945 South Bend 9a. I recently removed the chuck for some 4 jaw work. When I replace the 3 jaw I noticed a gap between the chuck and the spindle ridge. It was an real drill to remove the 3 jaw so I spend a lot of time looking at it, I do not recall the gap.
Now there is a 1/8 inch gap between the 3 jaw plate and the spindle ridge. The chuck 'clicks' upon seating so I am reasonably confident it is on. But I do not remember the gap.

 

[DavidR8]

Can you shoot us a photo?

 

[dansawyer]

Pictures attached. Thank you in advance. Dan

 

[DavidR8]

Has there been any increased run-out in chucked up stock?

 

[benmychree]

Look for chips stuck in the threads inside the chuck backplate.

 

[Low tech]

Look for chips stuck in the threads inside the chuck backplate.

Exactly
Two chucks for my Logan lathe had that problem . I cleaned out the chips from the chucks and they both ran right up to the spindle register .

 

[ericc]

Get a strong light and take a really good look. Are you sure that that gap was never there? I have that problem with a lot of my faceplates and backplates...from an old Atlas lathe. None of them fit my South Bend 9. When I get tired, I will sell one on Ebay or skim one so it fits. I am very aware of any gap. The tiniest of a gap can lead to a stuck chuck in the future. It must seat tight against the shoulder without getting too tight on the threads.

 

[dansawyer]

Thank you all
First, I measured the runout at the chuck, it was about .001 at the chuck. I then measured the runout at 4 inches from the chuck, it was about .004. My take away is the chuck is not perpendicular with the spindle. That would map with the back plate not seating squarely.
Second, I have a face plate. It appears to sit squarely on the spindle. As a note I can thread the face plate in reverse, I cannot thread the chuck back plate in reverse.
I will check for chips.

 

[dansawyer]

It was chips in the threads. The chuck back plate now sits squarely on the spindle. The runout is about 2 thousands at the chuck. (It must have been a lucky fluke for the one thou reading).
(The chuck jaws do not square with the spindle, there is now about 6 thou runout at 4 inches. )

 

[graham-xrf]

Yes yes. Thanks much for this. I lurked, because I will be critically checking out my 9A soon.

From what I gather so far, chips in the threads stopped the chuck from seating home, but the alignment was better when it was stuck on the chips compared to when cleaned up so that the back face mated.

When we say "runout". Several kinds I read about.

1. There is runout, axial and radial, from when you put a dial indicator to the face and the radius of the chuck itself.

2. There is runout on a drill rod, or some other rod known to be accurately ground, put in the chuck, and you try the dial indicator close to the chuck, and also some inches away.

3. There is runout from a MT3 test bar put into the taper of the spindle. Checked first if you want to diagnose the chuck.

I have to check what might be a typical norm for a SB9A in reasonable condition, but I am pretty sure numbers like 6 thou means it is not yet right. I think the threads are supposed to be regular symmetrical. If you can't put the chuck back plate on in reverse, look hard at the threads of both spindle and chuck. Something is biased to one side.

Short of taking a damaging whack, it might be that using the chuck under load, when it was not fully home, locked up onto chips in the threads, may have had it doing a little high force axial banging wobble, impacting on the chips, and "modifying" the chuck somewhat. A pure speculation on my part - but you got me thinking!