Threading Issues

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vair8
Posts: 12
Joined: Thu Nov 12, 2020 12:16 am
Location: Ogden, UT

Threading Issues

Post by vair8 » Tue Feb 16, 2021 12:43 am

Hey guys, posted here a few months back about an awesome deal I picked up. Its this carrol Jamieson 16" lathe. Well I'm finally getting around to trying to learn and operate it, and my first thing I'm trying to do is cut some pipe threads. I got the taper set right to 3/4" per foot, but when I set the gear box to cut 11 1/2 TPI I'm getting double that. I tried quite a few and they're all doubled. If I had 5 1/4 as an option I'd just say who cares and run it, but I don't, I thought maybe I just needed to swap it out to the smaller gear but after cutting a few threads with it it seems to be metric. anyone have any Idea why it's doubled? I know I can just grab a die but the main point for doing it this way was to learn.
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Harold_V
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Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Threading Issues

Post by Harold_V » Tue Feb 16, 2021 2:52 am

vair8 wrote:
Tue Feb 16, 2021 12:43 am
If I had 5 1/4 as an option I'd just say who cares and run it, but I don't,
That wouldn't work, as the yield would be 10½ pitch, assuming it's actually doubling. If so, you'd need to be able to dial a 5-3/4 pitch.
I thought maybe I just needed to swap it out to the smaller gear but after cutting a few threads with it it seems to be metric.
Hmmmm. I'm not sure that makes any sense. The typical metric thread can not be discerned from an imperial thread except by its lead. If you are truly getting a doubling of the thread, I strongly suspect that it has nothing to do with metric. If, by chance, you are getting close, but not exactly half, you may be right. Check your gearing to see if you have a 127 tooth gear installed. It's part of a conversion for an imperial machine so it can generate metric pitches.
anyone have any Idea why it's doubled?
It's possible that the previous owner changed the gearing on the headstock end, the gears that power the quick change. I did that with my Sag 12 Graziano when I was not pleased with the finest feeds at my disposal. I specialized in small work, which requires fine feeds, so I used the additional gears that came with the lathe and changed the ratio, cutting it in half. I chose halving so I didn't lose the ability to dial threads, but I had to dial a 10 pitch in order for the lathe to generate a 20 pitch thread. Sounds very much like the same thing you're facing. You might take a look at the manual (assuming you have one) and compare the gears that are installed against it to see if they are as they should be.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

vair8
Posts: 12
Joined: Thu Nov 12, 2020 12:16 am
Location: Ogden, UT

Re: Threading Issues

Post by vair8 » Tue Feb 16, 2021 3:00 am

You’re right about that, must’ve not been thinking. I’m going to be at the shop again tomorrow, so I’ll run a few scratch passes again and verify what I think it’s doing.

I really don’t know much about any of this, just learning. All I did was put an inch pitch gauge up against a thread I cut with the second gear and nothing matched it. But my metric one did line up.

Can’t seem to find a manual anywhere only thing I can find is one of the sales brochures. Apparently they weren’t too common.

Thanks for the help!

Harold_V
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Re: Threading Issues

Post by Harold_V » Tue Feb 16, 2021 4:16 am

What pitch metric lined up? Was it 1¼mm? If so, it would be close to 22 tpi .

What would help immensely is if you'd take a long shallow threading pass, so you leave a light line. Make it at least three inches long. With that done, you could accurately measure the generated thread with a ruler. You'd want to see if you got a reading that makes sense. At some point you should be able to get the lines to line up at an inch (or fractions thereof) interval (if you generate 11½ tpi, you'd find the lines matched every two inches). See if you can develop some kind of repeatability. If you find that the lines line up at some interval, define the interval and count the number of threads within. That will give you the pitch you're generating. It might start making some sense at that point.

I just noticed you're in Ogden. I used to live in the Salt Lake Valley. Born and raised in Utah, but moved to Western Washington back in '96. I don't miss the Utah winters.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

vair8
Posts: 12
Joined: Thu Nov 12, 2020 12:16 am
Location: Ogden, UT

Re: Threading Issues

Post by vair8 » Tue Feb 16, 2021 10:20 am

Harold_V wrote:
Tue Feb 16, 2021 4:16 am

I just noticed you're in Ogden. I used to live in the Salt Lake Valley. Born and raised in Utah, but moved to Western Washington back in '96. I don't miss the Utah winters.

H
Speaking of those winters just had a storm last night!

I'll definitely give that a shot today. I should probably go ahead and disengage the taper so I can get that long pass then. Thanks for the advice!

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BadDog
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Re: Threading Issues

Post by BadDog » Tue Feb 16, 2021 6:58 pm

Definitely take a look at the gear train feeding the threading/feed gear box. I expect someone has swapped them to get ranges not otherwise available. Lots of lathes come with one or more configs to swap out if you need specific ranges. And metric transposing gears are a completely different matter, those will be a stacked/locked pair, usually somewhat large depending on accuracy expected..
Russ
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NP317
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Location: Northern Oregon

Re: Threading Issues

Post by NP317 » Tue Feb 16, 2021 10:21 pm

My Grizzly 14-40 geared lathe has transposing gears, and a front-panel label specifying which gear combinations are required to achieve specified thread pitches.
And there is a 127 tooth gear involved.
That fits with Harold's post above.
RussN

vair8
Posts: 12
Joined: Thu Nov 12, 2020 12:16 am
Location: Ogden, UT

Re: Threading Issues

Post by vair8 » Wed Feb 17, 2021 10:23 am

Got stuck late at work yesterday, I'll see if I can get it in and take some pictures and count teeth after work today.

LIALLEGHENY
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Re: Threading Issues

Post by LIALLEGHENY » Mon Feb 22, 2021 9:11 pm

Many of the older lathes had a lever that would select feeds in inches, versus feeds for threading. A Leblond Dual drive I used to own had that, and if you weren't paying attention and had the lever set for feed in inches, when you were threading you could come up with all sorts of different thread pitches.

Nyle

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