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Threading on a South Bend 9A

Hey all,

I'm looking for someone who can help me troubleshoot a South Bend 9A. I have read the "How to operate a South Bend lathe" book, but doesn't have the specific info I'm looking for. When I set the gears to cut a 20 tpi thread it is real slow and looks to be cutting something like 40 or 60 tpi. I made sure the 20 tooth stud gear was on there, it is, and that's all the farther I can get with the book. I was thinking someone at some point switched a gear somewhere, but I don't even know where to start.

BTW, it's the same with all the settings, they all move the carriage too slow. Even at the 4 tpi setting it cuts a smidge slower than 20 tpi.

Thanks,

Eide

Reply to
Eide
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Perhaps you are engaging the longitudinal feed and not the half nuts. ?????

In any case I found a wealth of info by using google to search on "South Bend 9A gear train"

Reply to
Allen Parks

You *are* using the half nuts and not the X powerfeed, right?

GWE

Reply to
Grant Erwin

As the others said... make sure you're using the half nuts and not the power feed. I went through conniptions with SB 11" until I realized that the two produce different rates of feed...

Peter

Reply to
Peter Grey

What grant said!

The ultimate tip-off in a questionable case like this is to set the QC gearbox to thread the same pitch as the lathe's leadscrew. Which in this case for a model A, I *think* is

8 tpi.

Then put a masking tape 'flag' on the leadscrew, and one on the spindle as well.

If the geartrain is set up properly, when you turn the spindle by hand, the spindle and leadscrew will turn at the same speed.

If not then there's something out of kilter in the QC box or on the banjo.

Jim

Reply to
jim rozen

Thanks all,

I think the half nut might be the (my) problem. I know squat about lathes, and this one is in the shop at work where no one knows anything about them either. Good tip Jim about setting the gearbox to the leadscrew pitch and checking that out. Thanks again everyone!

Eide

Reply to
Eide

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