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  #21  
Old 01-31-2021, 03:36 PM
ShawnR ShawnR is offline
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Originally Posted by Ironman View Post
I can't see anything odd with your process. Maybe try to start on the same number on the dial each time. You shouldn't have to, but it eliminates one thing that way.

You are certain the shear pin is intact? A visual inspection won't do. You should be able to tap it out with a pin punch. If it won't drive out, it has been sheared and rotated.

reversing and not disengaging the half nut will probably break the insert as it won't follow the cut, in my opinion.
I definitely was trying to hit the same number each time. I checked the pin, even knocked it out. It is good. I tried rotating the lead screw 180 cause several years back, I think I had it out so wondered if it could have went in wrong but the pin is tapered, as is the hole so only goes one way.
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  #22  
Old 01-31-2021, 03:37 PM
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I have cut threads on many different lathes over the years and, for whatever reason, I've never trusted
the thread dials--my current lathe doesn't even have one. I always thread by selecting the correct pitch
in the gearbox, engaging the leadscrew, making a pass, stopping the lathe, backing the tool out a bit
and reversing direction without disengaging the leadscrew. It really doesn't take any more time and it
ensures that you get accurate threads every time. Give it a try and see what happens...
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  #23  
Old 01-31-2021, 03:54 PM
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check the pitch of the lead screw maybe its metric, and you are trying to cut US threads.

we had one member with a Jet lathe that had the wrong gear on the thread dial.


place a travel dial on the carriage and rotate the spindle by hand and count the spindle rotations within 1" of travel.
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  #24  
Old 01-31-2021, 04:02 PM
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Originally Posted by GWIZ View Post
...place a travel dial on the carriage and rotate the spindle by hand and count the spindle rotations within 1" of travel...
Leadscrew pitches are generally coarse enough that even if you don't have an acme pitch guage an ordinary 60 degree guage should enable you to figure out what your pitch is...
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  #25  
Old 01-31-2021, 04:06 PM
ShawnR ShawnR is offline
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GWIZ, I do believe I have a metric leadscrew. Everything on the machine is metric but the charts give gear combinations for imperial threads. At this point, I don't care what the thread is. I think the procedure would be the same and I think my main problem is the inconsistency of the tool hitting the work piece. I will try to shoot some over head video tomorrow. Maybe I will catch myself doing something that I don't think I am doing....

Keith, I have seen postings on that procedure. I have been avoiding it just cause I wanted to be able to do it the "usual" way, but no one can argue that it would ensure accuracy. I may need to go that route. Probably not as bad as I think.

Thanks for the input
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  #26  
Old 01-31-2021, 06:24 PM
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Quote:
Originally Posted by ShawnR View Post
GWIZ, I do believe I have a metric leadscrew. Everything on the machine is metric but the charts give gear combinations for imperial threads. At this point, I don't care what the thread is. I think the procedure would be the same and I think my main problem is the inconsistency of the tool hitting the work piece. I will try to shoot some over head video tomorrow. Maybe I will catch myself doing something that I don't think I am doing....

Keith, I have seen postings on that procedure. I have been avoiding it just cause I wanted to be able to do it the "usual" way, but no one can argue that it would ensure accuracy. I may need to go that route. Probably not as bad as I think.

Thanks for the input
Hi Shawn. If you are sure you have a metric lead screw, are you cutting an inch based thread? If so, the thread dial will not work and you will be forced to follow Kieth's suggestion to do multipass/single point threading.

The other clue as to whether you are mixing thread systems between the work and the lead screw is to look carefully at the gear train at the end of the headstock. If there is a 127/120 gear pair in the train, you are mixing metric with inch and your thread dial is useless. The 127 tooth gear is the translation gear between metric and inch. I understand some lathes use 63 tooth gears to save space, but those would likely include more error to the thread pitch on the work.

IIRC, the parts list in the manual you posted does include a 127 tooth gear.
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  #27  
Old 01-31-2021, 06:40 PM
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Originally Posted by ShawnR View Post
...I think my main problem is the inconsistency of the tool hitting the work piece...
Exactly, whether your leadscrew is metric or inch has nothing to do the inconsistency of your thread starts.

Quote:
...I wanted to be able to do it the "usual" way, but no one can argue that it would ensure accuracy. I may need to go that route. Probably not as bad as I think...
I'm not sure if I would characterize it as the "usual" way. I know lots of "professional" machinists who won't use a thread dial--it certainly opens the door to possible mistakes. A "good" dial on a "good" lathe is OK but on a lot of cheaper lathes there is enough play that it's quite easy to miss and pick up the thread on the wrong number--do it once or twice and ruin a part that you've got a bunch of time in and you'll think twice about it.

As I said before I've never used a thread dial on any lathe I've ever run. The old fellow who showed me how to thread 40+ years ago did it by reversing direction--I picked up that method and have never used anything else. Threading by reversing is not a "compromise" but a good alternate method. For example, if you're cutting metric threads on an imperial lathe you have to leave the leadscrew engaged since there's no way to consistently pick up the threads...
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  #28  
Old 01-31-2021, 06:49 PM
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Quote:
Originally Posted by camdigger View Post

The other clue as to whether you are mixing thread systems between the work and the lead screw is to look carefully at the gear train at the end of the headstock. If there is a 127/120 gear pair in the train, you are mixing metric with inch and your thread dial is useless. The 127 tooth gear is the translation gear between metric and inch. I understand some lathes use 63 tooth gears to save space, but those would likely include more error to the thread pitch on the work.

IIRC, the parts list in the manual you posted does include a 127 tooth gear.
His picture shows a 127/120
I'm guessing his machine will track metric (metric lead screw)

But he will have Issues with US threads not tracking as I recall some will, some will not.
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Last edited by GWIZ; 01-31-2021 at 07:05 PM.
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  #29  
Old 01-31-2021, 06:59 PM
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Forgive me if I am stating the obvious. There are two ways to move the carriage with the gear train. One way is to engage the half nut below the cross slide, the other way is to engage the threading lever towards the tailstock end of the carriage. Only the threading lever synchronized with the threading dial will pick up the correct start point.



Don't ask me how I know this.
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  #30  
Old 01-31-2021, 08:16 PM
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Originally Posted by arizonian View Post
Forgive me if I am stating the obvious. There are two ways to move the carriage with the gear train. One way is to engage the half nut below the cross slide, the other way is to engage the threading lever towards the tailstock end of the carriage. Only the threading lever synchronized with the threading dial will pick up the correct start point.

Don't ask me how I know this.
Bill, didn't your machine have an interlock? I couldn't do that with mine, because the feed lever is locked solid when the half nut is used.
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