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Threading dial dumb question...

N

ng19delta

Aluminum
Joined
Jun 24, 2014
Location
Merchantville, NJ
I have a simple question regarding the threading dial on my South Bend 9A... I understand how to use it, but this is about how it operates... I have tried experimentally cutting threads so far, but am still in the learning/practice phase.

What I have noticed is that when I set the thread gauge, it engages the screw drive thread and starts turning- This is normal... Then, when I engage the half-nuts (when it reaches the prescribed index)it kicks back out of the threads, and while the cut takes place it is disengaged, and I have to re-engage it when I go for my next pass. Is this normal?

I haven't found reference to this particular question in HTRAL, so I figured I'd better ask here, as I am trying to learn how my lathe operates and how to use it well...

Thanks!
Scott

(Here's a pic- I restored her a year or two ago... I'm waiting for the plate to do the reverse lever quick-change conversion- should be here tomorrow!)
 
When you engage the half-nuts, the dial will stop turning because the carriage is moving with the lead-screw. This is normal. The thread dial should be tight against the carriage when engaged, but mesh with the leadscrew without binding. The thread dial should not disengage from the lead-screw until it is untightend from the carriage. Hope this helps.

Best Regards,
Bob
 
If the half nut is not fully engaged it might have some pressure from the gears lead bevel and so wish to pop out.

So badly wore the mesh might act like a bevel.

Agree it should not disengage..

Nice job.. nice looking lathe
 
No a SB guy so not sure but on many lathes the thread dial can be swung out of the way so that it's disengaged entirely. You might need to swing the dial in a little more if possible so that the worm is better engaged with the half nut.
 
michiganbuck said:
Nice job.. nice looking lathe
Click to expand...

Thanks!

I seem to remember it kicking out even when I tried holding it in place... It appears mounted by a single pin: I've tried tightening the pin set screws on both the carriage and the counter, but it still occurs. I'll have to take a look & see if I put the pin in wrong- maybe there were flats I missed to keep it from rotating out.

Thanks again,
Scott
 
i am not the south bend guy .. it seems the guys who know the machine are not replying
Perhaps delete this thread and title a proper title.

South Bend 9 half nut pop out. or something that describes the problem as you think best
 
There is a setscrew on the front of the apron to apply pressure to the thread dial mounting stud. Tighten that screw after you swing the thread dial gear into contact. If that does not do it, the pin is likely spinning in the thread dial body.

allan
 
car2 said:
Make sure the shaft/gear in the dial is not bound up with old oil, etc, or the gear butted tight against the casting (there's a set-screw holding the gear to the shaft); the dial/shaft/gear should turn with virtually no resistance. Also, make sure the gear meshes with the leadscrew. Cheers.
Click to expand...

The dial was completely taken apart, cleaned, relubricated, etc. when I rebuilt the lathe...
Scott
 
No offence, but is the gear on the right way? I had a similar problem with my 10L until I found a picture showing the correct orientation. The gear was not meshing on the centerline of the leadscrew and would ride up and out of the thread. Jim
 
jmm03 said:
No offence, but is the gear on the right way? I had a similar problem with my 10L until I found a picture showing the correct orientation. The gear was not meshing on the centerline of the leadscrew and would ride up and out of the thread. Jim
Click to expand...

Well, actually... lol... Found out the lathe and all are FINE... It was the PERCEPTION which was out of whack... While playing with the lathe tonight, I decided to check into the issue... Well... Seems I forgot something I learned about flying aircraft... When you are on the ground, the air moves around the aircraft... It only moves when commanded to move. Once you take off- even just have wheels off the ground- you are PART of the airflow, and your movement is now different... Well, Here's what is happening- Just what should: It is NOT that it has been kicking out, but rather the dial STOPS when the carriage starts moving with the half nuts! Because it is traveling at the same speed, and along the helically wrapped inclined plane of the lead screw- thus, as it is moving with the drive of the screw, it is no longer operating from a fixed point, and thus being driven...

Well, stupid me for not figuring this out earlier, and wasting a thread...

Scott, the embarrassed...
 
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