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Old 08-31-2023, 07:43 PM
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arizonian arizonian is offline
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Default Single point pipe threads on a lathe

Once again I have a project where I need to single point pipe threads 'cause I'm too cheap to by a 2" pipe die. Tapered threads can't be cut single point without a taper attachment, so let's get that out of the way and concentrate on a straight thread. Sealing is not really an issue with this project. Pipe threads between and including 1" and 2" are 11-1/2 TPI, as are garden hose threads.

The Grizzly QC gear box has a 10, 11 and 12 TPI but no 11-1/2. It also has a means to cut metric threads with the change out of a couple of gears in the gear train feeding the QC and re-arranging the gear train to use the 127/120 tooth conversion. A multiple of 25.4 is required so that is where the 127 comes in. Using the metric gears, the closest I can come is a 2.25mm pitch, which is 11.29 TPI.

The gear train consists of a 40 tooth on the headstock driving a 127/120 tooth conversion, which drives either a 30, 32 or 40 tooth on the QC. For imperial threading, the 40 drives the 127, which in turn drives the other 40 at the QC.

Any body have any similar experience?
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Last edited by arizonian; 09-03-2023 at 12:09 AM.
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  #2  
Old 09-01-2023, 12:51 AM
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Quote:
Originally Posted by arizonian View Post
Tapered threads can't be cut single point without a taper attachment, so let's get that out of the way and concentrate on a straight thread.

Any body have any similar experience?
How long is the part?

You need too do your homework,
I would consider off setting the tail-stock.

I have not tried threading a taper between centers but it should work.

IIRC: if the offset is too much you may need to use a Bell center drill.
https://www.shopfloortalk.com/forums...highlight=bell
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Old 09-01-2023, 02:35 AM
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Quote:
Originally Posted by arizonian View Post

The gear train consists of a 40 tooth on the headstock driving a 127/120 tooth conversion, which drives either a 30, 32 or 40 tooth on the QC. For imperial threading, the 40 drives the 127, which in turn drives the other 40 at the QC.

Any body have any similar experience?
There is not a lot of info on your lathe on the net.
post pictures of the thread charts.......... hoping for a list of all gears.

What is the pitch of the lead screw? if it is 16tpi you maybe in luck?
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Old 09-02-2023, 08:54 PM
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I have mounted a single pipe thread chaser into a quick change tool holder and cut a thread into PVC. Have not had to try metal yet, so do not know if it will work, just wanted to pass on the hint.Click image for larger version

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  #5  
Old 09-02-2023, 11:57 PM
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Quote:
Originally Posted by GWIZ View Post
There is not a lot of info on your lathe on the net.
post pictures of the thread charts.......... hoping for a list of all gears.

What is the pitch of the lead screw? if it is 16tpi you maybe in luck?
How does that compute? Pipe thread from 1" to 2" is 11-1/2 TPI. Pitch of the lead screw is 8 TPI.

Quote:
Originally Posted by mcostello View Post
I have mounted a single pipe thread chaser into a quick change tool holder and cut a thread into PVC. Have not had to try metal yet, so do not know if it will work, just wanted to pass on the hint.Attachment 168955
How did you advance the tool post/apron to keep the teeth properly engaged?
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Last edited by arizonian; 09-03-2023 at 12:11 AM.
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  #6  
Old 09-03-2023, 06:11 AM
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Quote:
Originally Posted by mcostello View Post
I have mounted a single pipe thread chaser into a quick change tool holder and cut a thread into PVC. Have not had to try metal yet, so do not know if it will work, just wanted to pass on the hint.Attachment 168955

If you can time your hand to advance the carriage exactly 1 thread (11-1/2TPI) per revolution of the spindle, that might work.

Or possibly turn your compound 180 degrees or parallel with the spindle. Set the thread chaser up in the tool post. Set Carriage to cut 11 TPI. Now you only need to advance your compound .003952” every 1 revolution of the spindle to equal 11 1/2 TPI.

Even if you cut your threads at 11TPI, if you over cut them, the parts will screw together. But if you are needing them to be air tight seal/ water tight sealed, it may not work well. Not sure if pipe dope would seal it enough.

I guess it depends on what you are making, as to how accurate you need to get them.


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  #7  
Old 09-03-2023, 10:22 AM
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Originally Posted by toprecycler View Post
If you can time your hand to advance the carriage exactly 1 thread (11-1/2TPI) per revolution of the spindle, that might work.

Or possibly turn your compound 180 degrees or parallel with the spindle. Set the thread chaser up in the tool post. Set Carriage to cut 11 TPI. Now you only need to advance your compound .003952” every 1 revolution of the spindle to equal 11 1/2 TPI.

Even if you cut your threads at 11TPI, if you over cut them, the parts will screw together. But if you are needing them to be air tight seal/ water tight sealed, it may not work well. Not sure if pipe dope would seal it enough.

I guess it depends on what you are making, as to how accurate you need to get them.


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You're backwards. An 11-1/2 TPI is a slower feed than 11 TPI.
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  #8  
Old 09-03-2023, 08:21 PM
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Hand feed, very slow spindle speed.
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Old 09-03-2023, 10:18 PM
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Quote:
Originally Posted by arizonian View Post
You're backwards. An 11-1/2 TPI is a slower feed than 11 TPI.

I stand corrected. Thanks. I guess you could set the TPI to 12, and still feed the same. That way you can always keep the compound screw in tension as the carriage is feeding forward.


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  #10  
Old 09-04-2023, 08:05 AM
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Quote:
Originally Posted by arizonian View Post
How does that compute? Pipe thread from 1" to 2" is 11-1/2 TPI. Pitch of the lead screw is 8 TPI.
Way back, quite a few import lathes only listed SAE or Metric threading
with the right combination of gears an SAE only lathe is able to cut Metric threads.

IIRC: 127T gear was a key size to get SAE to metric cutting but 127T gear were not available or too large.

programs starting to show up that would try different gear combinations from a list of gears that one would have.
the issue is the calculations are based on a 16tip lead screw, quite a few import lathes have 16tpi lead screws.

I was hoping you had a better selection of drive gears to use one of the programs to figure out 11.5tpi.

If you scroll down you will find some programs and links to software but 16tpi lead screw.
http://www.varmintal.com/alath.htm#Cutting_Odd_Threads

Bear in mind the programs do not check if the gears can physically mate or clear obstacles/mounts in a lathe.
so a gear in the list may be to big or to small.
Idea would be once you figure out what gear you need, have one 3D printed.


When I first got my mini lathe I purchased a few sets of gears so the software would have a better chance of finding a closer metric match for cutting metric threads. but that was when a set of gears cost $12.00.
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