# threading problems.....



## Bob Kelly III (Oct 21, 2019)

(I looked for a threading thread but didn't see any so I figured it was Ok to put it here <GRIN>)

    Today I did a little practice on the Logan 922 lathe.
but it didn't turn out worth a darn ...I wiped out the threads because of hitting the half nut too late I think....
but regardless of the results  i am not sure if I can cure the mistake... as I was extremely careful to engage the half nut on the same line every time
 and i'm not sure why it wiped out my threads  !!!!!  it shouldn't have ! for all I know I did everything right ....obviously I didn't or the threads would be good ! LOL....
the thing is.... that threading dial is small and the enguagement of the half nut seams to take some time it's not like it is instantaneous !... and I think that is my problem
 I  have read where you need "Cat like reflexes" in order to thread on some machines..... is that true ? is the Logan 922 one of these things ?
.... I don't have a reverse switch hooked up yet on the lathe but I will get to that soon  I hope.  if I did I could just leave the half nut engaged and stop  back out the threading tool and reverse the motor and then do another pass.... this may well be my last option because that thread dial is far from accurate...or so it seams !
......
do you guys engage just before the line? or right on it ?
I could slow the lathe down alot more, and probably should to some degree.... as my results were so poor !
do you have any suggestions ?
 I was trying to cut 1/2" x 12 TPI threads  on fairly soft  1/2" steel Rod.
it should be easy... I don't understand why I keep wiping out the threads about half way through the thread depth ! 
thanks....
Bob........


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## brino (Oct 21, 2019)

Bob Kelly III said:


> do you have any suggestions ?





Bob Kelly III said:


> I could slow the lathe down alot more


Yup, that ^^^.

I would check carefully the threading dial gear engagement with the lead screw.
If you have any slip/skip that's your problem.

You could also run some practice on a piece of plastic pipe, or even with a sharpie marker, rather than a real tool.

Good Luck!, and please keep us posted.
-brino


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## RJSakowski (Oct 21, 2019)

Check to see that your thread dial is exactly on the mark when the half nuts are engaged.  There are multiple intermediate positions between the marks.  If the dial is slightly off, you may be engaging a half tooth before on one pass and a half tooth after on the next.  The thread dial can be adjusted be loosening the screw and rotating the dial to correct alignment.

Re: engaging the half nuts. As the mark on the thread dial approaches the index mark, you start to engage the half nuts so they fully engage as the dial mark passes the index mark. Once the half nuts are engaged the dial no longer moves.  If the dial isn't lined up exactly with the index mark, disengage the half nuts and move the carriage back and give it another go.

You also didn't say what thread you were cutting.  You can't use a thread dial to cut metric threads on an imperial lathe and vice versa.


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## eugene13 (Oct 21, 2019)

brino said:


> You could also run some practice on a piece of plastic pipe, or even with a sharpie marker, rather than a real tool.


Using a sharpie marker is probably the best way to practice threading, also, if your machine is new the half nut may be tight or filled with shipping grease and need "working in" until you get the "feel" of engagement.  Keep practicing and you'll get it.


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## Bob Kelly III (Oct 21, 2019)

RJSakowski said:


> Check to see that your thread dial is exactly on the mark when the half nuts are engaged.  There are multiple intermediate positions between the marks.  If the dial is slightly off, you may be engaging a half tooth before on one pass and a half tooth after on the next.  The thread dial can be adjusted be loosening the screw and rotating the dial to correct alignment.
> 
> Re: engaging the half nuts. As the mark on the thread dial approaches the index mark, you start to engage the half nuts so they fully engage as the dial mark passes the index mark. Once the half nuts are engaged the dial no longer moves.  If the dial isn't lined up exactly with the index mark, disengage the half nuts and move the carriage back and give it another go.
> 
> You also didn't say what thread you were cutting.  You can't use a thread dial to cut metric threads on an imperial lathe and vice versa.



I am Sure that is the case... but I thought that was normal so yah I will fix that imediately !  thank you !!!!!!!
and I thought I did say ...it was 1/2"x12 TPI ....


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## Joeman77 (Oct 21, 2019)

Hate to be the elephant in the room, but are you sure you're set at 59-1/2 degrees and not 29-1/2? I've had trouble with that if it was a machine I wasn't too familiar with in the past. Some of the newer lathes aren't marked in a "user friendly" manner, the older ones were consistently marked, not so these days.


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## MontanaLon (Oct 21, 2019)

The cutter matters too. HSS is the way to go for cutting threads at low RPM. It will cut much better than carbide when it is turning at a speed where catlike reflexes aren't required. Carbide will work fine when you get practiced with threading and can run the higher speeds, but at low speeds I have found it will tear up the threads instead of cutting them sharp.


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## MontanaLon (Oct 21, 2019)

And for practicing start with a piece of stock, cut a thread into it and then turn the threads off and do it again. You can cut threads 6-8 times on a piece of stock before it is all chips and a tiny bolt. Rarely is it a good idea to try to cut threads into something that matters for the first time.


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## higgite (Oct 21, 2019)

Joeman77 said:


> Hate to be the elephant in the room, but are you sure you're set at 59-1/2 degrees and not 29-1/2? I've had trouble with that if it was a machine I wasn't too familiar with in the past. Some of the newer lathes aren't marked in a "user friendly" manner, the older ones were consistently marked, not so these days.


I think you mean 60-1/2 degrees from spindle axis. That would be 29-1/2 degrees from perpendicular to spindle axis.

Tom


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## Bob Kelly III (Oct 21, 2019)

Joeman77 said:


> Hate to be the elephant in the room, but are you sure you're set at 59-1/2 degrees and not 29-1/2? I've had trouble with that if it was a machine I wasn't too familiar with in the past. Some of the newer lathes aren't marked in a "user friendly" manner, the older ones were consistently marked, not so these days.


the compound does have degree markings on the back side and I have it set at 29.5deg....   are you saying it should be 59.5 deg ????
never heard that before  !
.........
Um.... I am set at 29.5 degrees on the compound..... but it hasn't moved in 3 days ( blush !) i forgot and just used the cross slide ! DUH !!!!!  would that contribute to taking out the threads ?  because I just finished another practice run and although the threads are there they are the worst looking threads I've ever seen !  hunks of metal hanging off them  even after I made a few passes with the file....
I guess for the last 3 days I've been teaching myself bad habits !  LOL.....
 " no more cross feed BOB !!!!!..... just in and out and reset to zero and advance the compound ! geez Bob ! what a dummy !!!!" 
.... I guess sense I've neglected to advance the compound and not the cross feed I should have no complaints ! LOL 
oh well live and learn ! 
thank you for pointing that out ! 
...Bob.........


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## mikey (Oct 21, 2019)

Bob, don't beat yourself up. Lots of folks thread with the cross slide and have no issues doing so. It would really help if you showed us some pics of your set up and your tool.


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## T Bredehoft (Oct 21, 2019)

The reading on the compound is not cast in iron, it could be off by 90º. Many manufacturers don't take into account the "real" angle. Draw a line 30º on a piece of card stock, cut it out and use it to set the compound to that angle relative to the face of the chuck. In this case 30 is less than 45. 

Yeah, use the compound to move the tool.


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## Bob Kelly III (Oct 21, 2019)

MontanaLon said:


> The cutter matters too. HSS is the way to go for cutting threads at low RPM. It will cut much better than carbide when it is turning at a speed where catlike reflexes aren't required. Carbide will work fine when you get practiced with threading and can run the higher speeds, but at low speeds I have found it will tear up the threads instead of cutting them sharp.



well cutters have been a problem but I think I cured it a bit ago.... I made up a holder a long time ago for the 3 in 1 lathe that holds a piece of broken file with a 1/4"x 20 bolt ao I used a piece of broken file and made my thread cutter out of it and that seamed to work fairly well  I don't have any HSS cutter stock( yet)  but I will have eventually !
not using the compound to advance onto the threads i am sure is 90% of my problem !  that just slipped my mind !
..... all my threading up to now has been done with taps and dies  and yes I've even resorted to making my own threaded rod before under duress !
 but I have a lathe now and I want to make my own threaded rod on demand so far I've had no luck at all !
HAHAHAHHAHA
Bob.....


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## Bob Kelly III (Oct 21, 2019)

I am wondering now if that "not using the compound " is the biggest issue here now......
that and my tool was ground by hand and may very well be too wide......

I'll try to snag the wife's cell phone and take a few pictures of the setup
.....
the thread dial :
I took it off and discovered I could hold the gear in my left hand and turn the dial easily with my right hand !
but it did take some force, so it's not very likely to have been the problem sense air is the only thing that would be trying to turn it !( or vibration)<grin>  but I tightened it up anyway re set it and made sure it was point at a mark ( all I had to do was move the cross slide up or down the bed to do that ....so I don't think that is the issue, I engaged the half nuts this time exactly on the mark and it fell into gear just after the  mark.... every time .
I was going at about half the speed I was before    ( 15 on my VFD! ) which proved to be so slow the motor didn't have any power  so if I do it again I will put it in back gears and slow it way down......
lots of little nuances in threading !
......
here I thought threading would be easy sense I have watched every threading video on Youtube a dozen times or more ! LOL !
but it's giving me hell !
.... tomorrow I will try it with a fresh grind on the cutter and Use the compound to advance the tool and see if I can get some decent threads or not !
thank you for the help guys !
.....
I think the addition of a reverse switch would cure all my problems in one fell swoop !  and just leave that half nut engaged during threading.
i think that is the easiest cure...
....
Bob........


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## ttabbal (Oct 22, 2019)

Any idea what RPM you're running at? I usually thread pretty slow, about 100 RPM. Definitely try the back gear. If nothing else, timing for engaging the half nuts is much easier. For that, try starting at about half way between the two lines. Just get the lever moving and looser. Just before the line, add pressure and it will drop in at the right time. 

You might try not using the compound. Set it for 90 degrees (perpendicular to the work) and use the cross feed. Just use lighter passes as you are engaging more of the cutter. Sharp HSS helps. I do it like this all the time as I usually don't have the compound installed, and I'm too lazy to get it set up for a quick thread. It's one less thing to remember as well. 

If you suspect that the thread dial is not clocking properly, leaving the nut engaged is a good test. You do need reverse though. Can you enable it on the VFD directly? Good for testing anyway.


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## mikey (Oct 22, 2019)

Bob Kelly III said:


> well cutters have been a problem but I think I cured it a bit ago.... I made up a holder a long time ago for the 3 in 1 lathe that holds a piece of broken file with a 1/4"x 20 bolt ao *I used a piece of broken file and made my thread cutter out of it* and that seamed to work fairly well  I don't have any HSS cutter stock( yet)  but I will have eventually !





Bob Kelly III said:


> I am wondering now if that "not using the compound " is the biggest issue here now......
> that and *my tool was ground by hand and may very well be too wide*......



In my experience, faults in thread form are usually from the compound being at the wrong angle or engaging the half nuts at the wrong time or the tool is not ground at a 60 degree angle. *Burrs* are due to the tool and typically if the relief angles are too low or uneven or if the tool is dull.

Thread cutting is one of the simplest of lathe operations, Bob. Not much to it but your set up needs to be good and your tool must be ground correctly. You stand a much better chance if you grind a square HSS tool bit into a 60 degree threading tool and toss out the piece of old broken file.


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## Joeman77 (Oct 22, 2019)

higgite said:


> I think you mean 60-1/2 degrees from spindle axis. That would be 29-1/2 degrees from perpendicular to spindle axis.
> 
> Tom


59, 60, 61 I could be off a bit, like T Bredehoft said it's not set in iron, as long as you're close it should cut threads. But yeah it needs to be relative to the actual angle of the threads & I've noticed some of the newer lathe compounds just aren't marked correctly.


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## Bob Kelly III (Oct 22, 2019)

RPM ? probably about 40 or 50 RPM..... definitely less than 100 RPM
but no, the VFD does not give me any indication of RPM at all just percentage of power for motor speed, I try to run it at 60 sense I have it to where it can go 2 times that  
..... Yes the forward reverse switch can be very simple to hook up...all I need is a 3 way switch but it is between paydays and I gott'a wait for the funds to get a switch ! it may be a switch or brazing rod but not both LOL...we'll see !  but a $5.00 switch shouldn't mean not eating ...Right ? LOL....
.....
60 degrees eh ?for the threading tool point ? well I went way past that to a needle point a few days ago  that doesn't seam to last very long ! LOL
yah.... I know toss the crap and use good stuff, but when crap is all you have to work with , well you work with crap !
 broken bits of files or busted drill bits are the only HSS stuff I have, I bought a box of carbide 1/2" shank cutters when I got the 3 in 1 about 15 years ago and still have about 3 left but they have a half moon of carbide brazed onto the tip and they are extremely hard to grind.... they eat my grinding wheels very fast ! LOL..... I don't have one for carbide.
but I have one that I took down to a center point a few years back I may well make it into a 60 deg point and use that !
I always put a healthy undercut on the lathe tools I make,......  maybe too much but they usually cut real good
the file does by the way.... it looks like I just put it in !   I hate chatter ! and discovered it was my grinding of the cutters with not much undercut or relief now I am very careful about that.
the more I play with this Logan the more impressed I am with that old 3 in 1  although I have to tighten every gib on it to get it to stop chattering even at slow speeds it does take deep cuts that gives the Logan a run for the money !
.....
 OK one more question..... how deep of cuts should you take when threading ? I've been taking 10 thow to 15 thow for the first few passes then back off to no more than 10 thow then go to depth..... problem is it never seams to reach depth ! I thought I had a deep enough thread on a rod a bit ago but it would not go on the nut !  and that is the only thing I can think that it is .....
...... I watched a video where a guy took 5 thow cuts when threading ....is that NORMAL ???? my god, that will take you an hour to make a thread !!!
......it's possible I am hogging out too much at a pass ! LOL...maybe that is why their so ragged ! ripping them to pieces
....
Obviously I got a lot to learn with this thing!
.... 
I hear the raggedness is in the cutter !  I concur with that assessment !  I shall work on that !!!!! 
maybe ordering some HSS  tool stock is the best option here !
....
Thanks to all of you ! I appreciate the help !
I'll let ya know what I discover and learn in the process !
C ya !
Bob.......


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## mikey (Oct 22, 2019)

Bob, the cutting tool used to cut threads on a lathe is essentially a form tool. That is, it has a 60 degree point that cuts a 60 degree thread. If the tool tip is not at 60 degrees then your threads will also not be at 60 degrees and your nuts or parts (that do have 60 degree threads) will not fit onto your part. Now, when I say it has to be 60 degrees, I mean 60 degrees, not 58 or 61. In order to grind a tool to a precise 60 degree angle you should use a template like the common Starrett C391 or the Mitutoyo 950-201. You grind the tool to match the fishtail shape of the gauge. 

Alternatively, you can use inserted carbide threading tools (Carmex is good) or even inserted HSS threading tools from AR Warner.

You can have the lathe set up right and do everything else right but if the tool is wrong then you cannot cut threads on the lathe. I suggest you fix this first.


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## Bob Kelly III (Oct 22, 2019)

Will do thank you !


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## savarin (Oct 22, 2019)

What about setting it to cut at 90' its not a problem on small threads.
Slow the speed right down, make the cut but stop the machine at the end.
back out the tool a bit so it doesnt rub, disengage the half nuts and move back to one or two threads from the start,
engage the half nuts and set the tool bit into the thread jiggle the feed to remove the backlash, then hand wind in reverse along a bit further out so the tool bit isnt touching the thread any more, increase the feed into the next cut and turn on.
Rinse and repeat.
This should tell you if its a machine problem.
Once you get the reverse working just keep the half nut engaged and reverse back to the start.
With a bit of care and taking regard of the backlash in the feed screw its very easy to pick up a thread.


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## Bob Kelly III (Oct 22, 2019)

well I just came in from the shop I went out there to practice threading again.... wound up pulling the spindle completely out again because of that darn Bull pin....it came out too far again even with my indent !!!!!! so this time I fixed it ! I put a bevel on the end of the pin so I can get it back in even if I do pull it out too far ! that'll learn it !!!!! LOL.....( now I won't have to pull the spindle if the pin comes out too far I can just push it back in because of the bevel as it will raise the spring itself NOW !)
anyway  got it back together and did some attempts at threading and had a good thread forming and that darn half nut skipped a tooth again and just wiped out the threads AGAIN ! .... so I am going to pull the apron , something I haven't done yet and have a look see  and see if that half nut is buggered up or not....  I kind of doubt it because if I use the half nut for longitudinal feed it works great ! but who knows their may only be one tooth left on it ! LOL  something ain't right  !   maybe the mechanism is not sliding smoothly..... that would do it too I think ! 
when I tried it tonight I had it turning about 5 RPM  really slow..... and it still did it !!!!!!  something is borked ! it's gott'a be 
going that slow I had time to stop it and only have a ring around the threads but at that point I said fooie on it 40 trys and 39 fails  I don't think it is me anymore ! so the apron comes off tomorrow !
the one thing all the attempts have in common is the half nut, speeds were different, cutters were different , fingers were crossed , fingers uncrossed !
i used the cross slide only, I used the compound for thread depth only, yet they all failed and I used the half nut on all of them....
and they all failed for the same reason jumping out of sync ! 
....... I already know what I'll find.... "nothing wrong"  the best possibility I can see is the mechanism that moves the half nut is locking up at times and I can't tell .... if so that should be repairable !  so wish me luck ! LOL.....
but at least that Bull pin is finally ,Finally Fixed ...I shouldn't have to pull the spindle again for that !....( I am getting good at it though ! )
HAHAHAHA
I was thinking of making a handle so I could wind the lathe backwards easy( a.k.a Steve Jorden)... but what's the point ? I'll get the 3 way switch soon I am sure !
but in back gears that beast does not want to turn easy !  I'ed have to raise that lid to take the tension off the belt each time.... that's no good !
.....i'll just get the stupid switch ! LOL....... I want to wire it properly anyway and take off the big clunky push to stop switch the last owner put on it
it just controls power to the VFD anyway.... i can't use it to stop the machine !
.....the stop button for the motor must be wired to the VFD and the VFD's power put on another toggle switch.
....
Also.....I used the tail stock when doing all my attempts by the way,  and had it supporting the long rod about 8" of it sticking out of the chuck.....just to give me plenty of room sense the carriage was going toward the chuck !....call me chicken ! LOL.....
 and the carriage stop was in place too  !
.....
all in all it was a frustrating evening ! but clean living and perseverance prevailed ! HAHAHAHAHAH
we'll see what exploring that apron shows us tomorrow !
.....
Later !
Bob..........


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## higgite (Oct 22, 2019)

Joeman77 said:


> 59, 60, 61 I could be off a bit, like T Bredehoft said it's not set in iron, as long as you're close it should cut threads. But yeah it needs to be relative to the actual angle of the threads & I've noticed some of the newer lathe compounds just aren't marked correctly.


Just to avoid confusing newbies, I don’t think that’s what T Bredehoft meant. I believe he was referring to the protractor markings on the compound, which can be off by 90 degrees, depending on the particular lathe manufacturer’s way of marking their compound. 

If you’re cutting threads with the compound, close is not always good enough if you want to cut good 60 degree threads. There have been a multitude of posts on here about folks cutting screwed up threads (pardon the pun) because they set their compound more than 30 degrees from perpendicular to the spindle axis, or less than 60 degrees from parallel to the spindle axis if you prefer. But, like others have pointed out, if you use the cross slide to advance the cutter, the compound angle is irrelevant. Hope this clears up more confusion than it causes.

Tom


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## Choiliefan (Oct 22, 2019)

Lately I've been threading without the use of power.
Setting everything up as usual but am now turning the spindle by hand without disengaging the half-nuts between passes.
I started this technique using the Sherline threading attachment and have now transferred the same method to the Maximat 10p and my threads have improved (especially when threading up to a shoulder) and the process is far less stressful.
Every one should try this at least once.


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## ttabbal (Oct 22, 2019)

If your chuck is not threaded on, Joe Pieczynski's reverse threading trick is nice. Thread away from the chuck, no stress about hitting the shoulder on the work or the chuck. 

Of course, if you have the tailstock out, you can still hit that. I find I generally have more room even then though.


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## Bob Kelly III (Oct 22, 2019)

I do have a threaded on chuck ! and it comes loose fairly easy  ....I'll probably make a chuck lockdown arbor for it if I find it'a a problem
..... no confusion here about the compound protractors being off it's not a problem with this machine I don't think.....
it's gott'a be the machine somewhere ..... probably that half nut jamming on me ! I'ed just about bet on it !
.....when I get my act together I hope to produce good clean threads on demand from single point threading..... one of the main reasons I bought the lathe ! .... so I'll get there it's just a matter of time and money !( money being the hard part to come by ! )
..... there is a million opinions on threading do's and don't  ....and I do appreciate the help ! 
I've tried cutting threads with the cross slide and with the compound, both ended up the same way wiped out because of the half nut skipping a tooth
..... it's gott'a be in that thing ! 
....
we'll see ( i wann'a pull it apart anyway and check it out !)
later Guys !
Bob.....


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## brino (Oct 22, 2019)

Bob Kelly III said:


> I do have a threaded on chuck ! and it comes loose fairly easy ....I'll probably make a chuck lockdown arbor for it if I find it'a a problem



Bob,
Then you should beware that the chuck may try to un-thread itself from the spindle if you do wire up that reversing switch!
I have never seen it happen, but because I also have a thread-on chuck I do NOT run in reverse.
A chuck lock is a very good idea!
-brino


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## RJSakowski (Oct 22, 2019)

It's time to approach the problem systematically.  

As has been said, advancing the feed using the cross feed eliminates a compound angle error.  You have played around with the form of the cutting tool, with rpm, and depth of cut without any improvement.  That leaves loss of sync. between the carriage and the spindle.  The half nut doesn't have teeth.  It is a nut that is split in two.  Disengaging the half nut pulls the two halves apart and away from the lead screw.  Engaging the half nuts brings them together on the lead screw.  

You can check if the half nuts are not engaging properly by closing them with the lathe stopped and trying to move the carriage.  You should not be able to move the carriage except for a small amount of backlash. If you can move the carriage, you have to remove the half nuts and inspect them for wear and/or dirt.  It is also possible that they are not adjusted properly.  They should clamp down fairly tightly on the lead screw.

If the lead screw passes the test, then you need to look elsewhere for a loss of sync.  One possibility would be a sheared drive pin.  There may be enough resistance to drive the lead screw but under load it slips. Another would be one of the gears in the gear train is jumping teeth.  This should be fairly obvious to spot  but if you have an enclosed gear box, one of the internal gears may be slipping due to a sheared key. You might try another thread pitch  to see if you can isolate the problem to a particular gear.

If the gear train passes muster, I would turn to the thread dial mechanism.  A piece of crud in the thread dial gear could cause the gear to jump a tooth.  Not having the gear fully engaged with the lead screw could also cause it to jump a tooth. 

It appears that the 922 has an 8 tpi lead screw and that the thread dial gear has 16 teeth.  This would mean there are four teeth between marks on the thread dial.  jumping one tooth on the thread dial gear would advance or retard the half nut by 1/4 of the thread pitch causing you to cut a new track in your screw as you have observed.


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## Bob Kelly III (Oct 22, 2019)

RJSakowski said:


> It's time to approach the problem systematically.
> 
> As has been said, advancing the feed using the cross feed eliminates a compound angle error.  You have played around with the form of the cutting tool, with rpm, and depth of cut without any improvement.  That leaves loss of sync. between the carriage and the spindle.  The half nut doesn't have teeth.  It is a nut that is split in two.  Disengaging the half nut pulls the two halves apart and away from the lead screw.  Engaging the half nuts brings them together on the lead screw.
> 
> ...


very astute observations ! .... I do have one questionable gear in the gear train and it IS in use threading toward the chuck ( it''s the upper idler gear on the logan 922 a 34 tooth'er....  and I have thought about the shear pin, on the lead screw ( if this thing actually has one)  ....
i did turn out one rough but viable thread about 6" long when I first started this a left handed thread.....  but the thing never skipped a tooth on me doing the left handed threads ! ...... I have a feeling you just found the culprit ! 
I have been gearing up to braze up that gear sense I got the machine !
it has been repaired by the screw /file method but it is a very crummy job way too much open spaces in that gear....
...... I looked at the half nut when I thad the thing all apart and the cross slide/apron  on the floor it looked fine to me.
with the machine not turning I can move the half nut in and out of engagement easily...no binding at all but it may not be clamping tight on the leadscrew ! ( no, the carriage is locked to the lead screw when the half nut is closed it does not move hardly at all!)
....
I think I will swap idler gears.....and see if that cures the problem temporarily...
I have 2 more idler gears that came with the lathe but they are 36 tooth..... I could elongate the hole in the bracket and get one to fit to replace the bad gear..... but I thought that would screw up the thread count for the QCGB.... any thoughts on that ?
.....
I'll just fix the  chewed up gear like I had planned..... and hopefully that will cure the jumping out of sync....
I think you hit the nail on the head ! ..... after looking at all the other possibilities that is the only weak link in the chain that I know of....
.......
before I forget.... what is the depth of cut when threading ?
I've seen a thousand threading videos and enjoyed all of them, but no one has ever said the depth of cut you should be taking....
This old Tony showed his dials and he took 10 thow  but he's got a monster of a lathe and proper cutters
I don't .... steve Jorden mentioned 5 thow on his mini lathe....

thank you very much ! .....  I hadn't thought of that bad gear if any more consequence than Just looks bad.... but evidently it is much more serious than that !

time to FIX THAT !!!!! 
LOL
Bob..........


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## RJSakowski (Oct 22, 2019)

Bob Kelly III said:


> very astute observations ! .... I do have one questionable gear in the gear train and it IS in use threading toward the chuck ( it''s the upper idler gear on the logan 922 a 34 tooth'er....  and I have thought about the shear pin, on the lead screw ( if this thing actually has one)  ....
> i did turn out one rough but viable thread about 6" long when I first started this a left handed thread.....  but the thing never skipped a tooth on me doing the left handed threads ! ...... I have a feeling you just found the culprit !
> I have been gearing up to braze up that gear sense I got the machine !
> it has been repaired by the screw /file method but it is a very crummy job way too much open spaces in that gear....
> ...


If it is an idler gear, the tooth count shouldn't matter.  It only counts when the gear is the driving another gear on the same shaft or it is the first or last gear in the chain.  

Generally, you can start out with a heavier cut but once you are starting to remove a fair amount of material, you back off on the depth of cut.  The actual depth of cut will depend on the lathe, the material, and the thread being cut.  Advancing the cut with the cross slide rather than the compound set at 29.5º will require a shallower cut to prevent chatter.  

I use the compound to advance the feed and after the first light pass to verify the thread pitch, I would start with a depth of cut between .006" and .010" depending on the thread pitch and reduce the depth of cut with each successive pass.  As I approach the final cut, my depth of cut would be around .001".


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## Bob Kelly III (Oct 22, 2019)

thank you for the detailed depth of cut ! that helps alot ! I think I have been cutting way too much and tearing up the thread !
......
well the idler gears on this lathe  are twins on a shifting lever for forward and reverse, so you might call them the forward/reverse tumbler set
but when it is in reverse ( cutting toward the chuck) it is the 2nd gear from the spindle gear....(counting the spindle gear as ONE).when it is in Forward, the gear just spins with the other one and serves no purpose (other than to make some noise ! )
the Bad gear drives the other idler gear and then that goes into the gear reduction chain for the lead screw , it is an ingenious setup I must admit !
...if it doesn't matter about the gear size I can simply replace the gear that is bad with a 36 tooth instead of the 34 tooth !
and that is a real good gear hardly any wear on it at all .  .... all I would have to do Is mill or file a elongated hole in the bracket that swaps the 2 gears in and out.....
  I even have the bracket they came on but it will not fit this lathe .
if you're sure it won't matter my problems are cured !  I'll just put in the 36 tooth gear !
.....
Bob......


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## RJSakowski (Oct 22, 2019)

Bob Kelly III said:


> thank you for the detailed depth of cut ! that helps alot ! I think I have been cutting way too much and tearing up the thread !
> ......
> well the idler gears on this lathe  are twins on a shifting lever for forward and reverse, so you might call them the forward/reverse tumbler set
> but when it is in reverse ( cutting toward the chuck) it is the 2nd gear from the spindle gear....(counting the spindle gear as ONE).when it is in Forward, the gear just spins with the other one and serves no purpose (other than to make some noise ! )
> ...


While changing the size of an idler gear won't affect to final gear ratio, it will affect the position of the forward/neutral/reverse detents.  It may also create interference issues.  Check everything carefully before making any modifications that can't be undone.


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## Bob Kelly III (Oct 22, 2019)

OH yah ! your right  ! so , not so simple a fix..... 
that definitely will effect at least one indent....maybe 2 

I gott'a go and think on this a bit, might just be easier to braze the old gear and re cut it ! 
thanks again for all your help !!!!!!
Bob....


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## brino (Oct 22, 2019)

Hey Bob,

Some may call me a stickler (or worse) but I'd like to get a few things cleared up for anyone learning threading from this thread......

1) in terms of the out-of-sync (wiping out the threads during the next pass) it does NOT matter if you advance the cut by either the cross-slide or the top-slide. Both are fixed to the carriage and the carriage is driven by the lead-screw. It must be a problem "upstream" of this.....the same list Bob (@RJSakowski) mentioned (half-nut, sheared pin, gears, etc.)

2) the big difference between advancing the cut with the cross-slide vs. the top-slide is the how the tool is presented to the cut on successive cuts.

When feeding with the cross-slide, the 60 degree tool tries to cut equal chips on both sides of the tool.

When feeding with the top slide (set to the proper angle) the tool cuts mainly on its' left edge, and just barely scrapes on the right side.

On some small, less rigid lathes cutting on both sides of the tool at the same time can cause chatter.
I typically feed with the top-slide for that reason......less forces on the tool, post, carriage, etc.

Keep going, I know you'll get there!

-brino


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## Bob Kelly III (Oct 22, 2019)

yes indeed !
Well I went out to the shop this afternoon and "thought about it" while ripping apart an old bed frame for the scrap steel.
and I got to thinking that if it was that gear causing most of my problems ( granted Far from all!) then cutting threads on the other gear...( going in the other direction)  should go alot better.... so I put the lathe in back gears and ran it at about 50 RPM and  gave it another try....
it seamed odd at first but that soon disappeared ... as the threads grew using the cross slide to bring it in and out only and the compound for the thread depth.... they started looking quite substantial and good threads !  then I blew it, and hit the half nut too late ..but unlocked the half nut before it moved more than 1/16" ... backed up the carriage and tried it again.... on every half nut locking in, I was dead on the money except 2 times in over 30 to 45 minutes of cutting this left handed thread ! and the threads were forming very nicely I was taking .005" cuts and then they started looking a bit ragged..... so I dropped it back to .002" in cut depth increases.....  but once the damage was done there is no going back right....! the old saying " it's too late when you've gone too far comes to mind !  So Bob's wisdom in his cutting method is very apparent to me !!!!!
threading this slow makes it allot easier on the nerves and is much easier to stop the cutter fast if you screw up and miss your mark ! 
I continued on for a while but didn't like the way the threads were looking as they had a big slope on one side and a little slope on the other...
so I stopped and tried  adjusting the piece of file I ground into a 60 degree point and moved it slightly.... Wrong move ! the next pass took out the threads completely.... but it was kind'a expected, I was just farting around at that point because it already told me what I needed to know
 I also cut a different thread this time  a 10 TPI instead of 12 TPI .... figured I'ed see if that made any difference at the same time.....
so apparently what has been happening is the bad idler gear can skip a tooth on occasion when it comes around just right and I hit the half nut and put a load on it, it can skip.... threading in the other direction didn't do that ... it was me that screwed up 2 times... so it's something I will really have to watch when threading ! ......( there is about 1/16" window on that thread dial !!! I think I will make a larger dial so I can see it better ! it is about the size of a quarter ! I think I will make a 2" dial and just make a off set bracket for the thread dial !  having a 3/16" to 1/4" window would be so much easier for me to do !  LOL......)
......  
Now I know why this old tony always makes such large gutters for his threading videos ...... ! LOL
.... I think a big part of it is just getting to know the machine..... I've never had a REAL lathe before just a 3 in 1 from Harbor freight and it has no threading ability at all.... but I am a Mechanical appratious lover ! the more bells and whistles on it the more I like it ! 
I've been a motorcycle mechanic 90% of my life and there were times when I would have given my left leg for a lathe like this....  it is as old as I am
it was manufactured in 1952.... the same year I was born !  how is that for irony ? HAHAHAHHA
.....
I am leaning toward brazing the old gear rather than using the other gears that are slightly larger... I don't want to modify this Old iron....its too good for that ! although I am not real happy with the Metal-flake green paint job..... eventually I think I will paint it grey 
a good grey will hide the oil and mess.... as I oil that thing every time I use it !  and it's starting to drip everywhere ! LOL.......
that reminds me I'm getting quite a pile of shavings behind the lathe now I should clean it up !
LOL !
......so... braze the gear and make a larger threading dial ..... easy peezy !  
later all !
Bob.........


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## savarin (Oct 22, 2019)

Just a check, you do use a fishtail gauge to ensure the tool bit is exactly at 90' to the work?




__





						Center gauge - Wikipedia
					






					en.wikipedia.org
				



And I have had threads that tear when cutting when the steel rod was a bit suspect ie, reo bar or similar.


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## rock_breaker (Oct 23, 2019)

I probably missed some things so I will relate some of my threading problems that I "missed" here. The first is my Armstrong tool holder being tightened in the lantern tool post so it cannot turn horizontally as the cut gets deeper. Second is the regular cutting engagement lever interfering with the engagement of the half nuts? Third in your first thread you said you were going to cut  a 1/2" x 12 TPI thread then later you said the nut would not start; correct me if I am wrong but I believe the TPI for 1/2" National course threads is 13.  YOU HAVE LISTED EVERY PROBLEM I've  had in threading and I have done what the guys here have suggested to improve my threads;  use the back gears, keep the spindle speed slow. a really sharp 60` cutting tool set at the center of the work. and shallow cuts   
Have a good day
Ray


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## Bob Kelly III (Oct 23, 2019)

Howdy guys  !
Savarin......  well no i don't use a fish tail gauge.....don't have one !
and I ground the cutter by guess and by golly but I am sure it is very close( famous last words right ?) 

Ray.......  HAHAHAHA well you know....that may well be why the nut don't fit on the thread I made !!!!!!
I'll try it again with 13 TPI thanks ! ( very tactfully stated I must say .... I'm thinking..... hay stupid your trying to put the wrong nut on there that's why it don't fit !  HAHAHAHHAHA

My Machinery's hand book burned up in the Ranch fire darn it... and I have not had the funds to buy a new one yet.... i can't check those things very easily..... it would make a dandy locking nut on that rod ! for a one time use ! LOL......thanks Ray !

later guys !
Bob......


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## RJSakowski (Oct 23, 2019)

Once thread cutting is started do not take the lathe out of gear, remount the work, or make any changes to the cutting tool.  You will lose synchronization.  

If you do have to make a change, it is possible to resync the lathe.  To do so, I engage the half nut  and run to the previous cut with the cutter backed away.  Stop the lathe and move the cutter into the groove using the compound and the cross slide to position it.  When you are satisfied with the fit, make a trial pass with the cutting tool just touching the work to verify the fit.  Reset your cross feed and compound dials and continue to cut the thread.

I had noticed the 12 tpi but there actually is a 1/2-12tpi  BSW (British Whitworth) thread.  I cut some very nice 3/8-18 threads in stainless instead of the required 3/8-16 tpi one time (I attributed it to my momentary loss of sanity  ).  

If you peruse eBay, you will find perfectly usable used Machinery's Handbook's for less than $20.00.


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## Bob Kelly III (Oct 23, 2019)

LOL Yah I learned that real quick..... if you take the part out of the lathe you'ed best call it done !!!!!
I discovered that the steel I was practicing on was very very soft almost pot metal ...and it's ripping out the threads ...so I need a different practice hunk of steel.... 
the plastic PVC pipe idea works good for 3 or 4 passes.... but when you get close to crowning the thread it seams **** happens ! dunno what's up with that......  I think I was only using the cross feed on that and that may well be why..... I have stopped doing that and use the compound to advance the thread depth.
I turned out some fairly decent looking threads last night ( left handed threads) ..... the secret I think is going extremely SLOW ! at least for this old man anyway !
.....
yah I'll get a machinery's handbook soon I hope.... but keeping warm is more important right now !  being poor sux ! 
later !
Bob......


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## Joeman77 (Oct 23, 2019)

higgite said:


> If you’re cutting threads with the compound, close is not always good enough if you want to cut good 60 degree threads. There have been a multitude of posts on here about folks cutting screwed up threads (pardon the pun) because they set their compound more than 30 degrees from perpendicular to the spindle axis, or less than 60 degrees from parallel to the spindle axis if you prefer. But, like others have pointed out, if you use the cross slide to advance the cutter, the compound angle is irrelevant. Hope this clears up more confusion than it causes.
> 
> Tom


Thanks Tom, that's where I was headed, just couldn't get it in print. 
 But, if you're tool is ground with a good edge & angle and the tip set right with your work the angle of your compound can be off a bit (plus or minus a degree) and you'll cut good threads. 
 Like Tom said though if you use the cross feed it'll work.


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## rock_breaker (Oct 24, 2019)

Bob Kelly III said:


> Howdy guys  !
> Savarin......  well no i don't use a fish tail gauge.....don't have one !
> and I ground the cutter by guess and by golly but I am sure it is very close( famous last words right ?)
> 
> ...


Sorry about the ranch fire Bob, building a library takes a long time. The text book "_Machine Shop Operations and Setups" 4th edition _ is my goto book in addition to this website and a loose leaf note book full of downloads are my trusted sources of information. I hope you have been able to get your thread cutting problem corrected. Having a tool that needs repair is personally very frustrating If your Logan lathe is like my Clausing you will be making new things for a long time, but at the lathe's speed and capability. Threading is fun but time consuming and I go at it some what differently. The 60` threads mean each side is the same length so I use my cross slide set at 29.5` to cut the depth equal to the pitch.  When I get close to depth I start trying the nut, again time consuming but keeps you from having loose nuts.
Have a good day
Ray


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## Latinrascalrg1 (Oct 24, 2019)

I come across this simple graphic that i thought might be helpful but it also leads me to ask about the "Alternating flank infeed" approach, how exactly is that done?


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## Bob Kelly III (Nov 20, 2019)

I've had good luck with the 29.5deg. infeed  if that means anything...( good graphics !)
.....
I tried a test threading today, sense I have a reverse switch now on the lathe....
 WHAT A DIFFERENCE ! 
I was only cutting PVC plastic pipe 1" in diam. but it went so easily that it was hard to believe I was threading !
....  I got everything set up and then just locked the half nut and left it locked throughout the whole threading practice
I was doing 13 TPI as that seems to be very common....  but the operation was so easy... I didn't even bother to use the compound
just the cross slide and although the scratch pass was fairly deep  I had fully formed threads in about 6 or 8 passes ! so it didn't take all that long at all
.... towards the end I only gave it 5 thow increments on the depth of cut and it worked real good on the PVC.
you need to pay attention to the depth of cut in threading I have found.... but being able to reverse the motor sure made the process much, MUCH easier..... i think I will be using this method from now on, as even a kid could do it... the only thing you have to remember is to back out the cross slide before you reverse...... and if I made up one of the Aussie's flip up threading tools I wouldn't have to do that....
...... just add depth and reverse.....add depth and reverse ! do that a few times and your done ! LOL
 I was quite impressed ! 
it was taking my lathe about 3/16" to 1/4" to stop in cutter movement and I wasn't in back gears ....i just slowed the VFD down to 20%
.....
I finished the re make of the Expanding mandrel for the Lathe indexer ,and bored the 5/8" hole through the 3" wide flat pulley that I have yet to drill any locating holes into ....so I am still stuck with saw blades for the time being.
.....the aluminum gear I made for replacing the chewed up idler gear is working great... no signs of ware at all.
....
so the next project is probably going to be a hand crank for the spindle....i could use one of those ! <grin>
later !
Bob..........


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## rock_breaker (Nov 20, 2019)

Congrates on making threads! Doing the movements in a routine order is most important. If you will cut some more threads using your cross slide only you will see the cutting tool is probably cutting on both sides of the point. If at some time your threads are ragged this may possibly be corrected by adjusting the cut depth with the compound rest where the left side of the cutter is removing the material. You have crossed a major hurdle by producing good looking threads.
Have a good day
Ray


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## Bob Kelly III (Nov 21, 2019)

Rock_Breaker:
 The help I received here made all the difference in the world....
the things that made the biggest difference on my machine and on me  were....
1. Super Sharp tool.....(a piece of old file works but not for long soon you will be ripping the threads out when it dulls)
2. finding the slop in the lead screw was a major changer ,hitting the mark on the thread dial is much easier when the tooth is actually there !
3. getting the Routine down.... so you don't have to think about it.... and remembering where you were on the depth of cut.
4. Several types of threads being practiced HELPS !   from 28 t.p.i. to 10 t.p.i   the finer the thread the  sharper your tool needs to be !
5. practicing on everything I can find helped allot ! it mainly reinforces the routine, but it IS NECESSARY !

With the addition of the reversing switch on my Logan lathe I can now put the lathe in reverse.... so I can leave the half nut locked
and I was really surprised at how much that helped ! all your left with then is In and Out and reversing and thread depth which really uncomplicated the single point threading for me  ! 
......
thread cutting is using a forming tool ! if your not dead on with the point of that threading tool your threads will show it ! 
...
Bob.....


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## rock_breaker (Nov 21, 2019)

BOB,

You hit on some things I missed. IMHO threading is one tool a hobby machinist must be familiar with. Being able to cut threads has given me more confidence to make tools  and do repairs. Another threading capability is being able to reset the lathe to repair worn or damaged threads. In my case it starts with measuring (identifying) the thread, then setting each function as if starting a new thread after putting the old threaded piece back in the lathe.  It is called "serious concentration" here. 
Enjoy your shop
Rock_breaker


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## Bob Kelly III (Nov 22, 2019)

I'm wondering if a Special threading tool just for the repair of damaged threads would be worth considering one that doesn't cut away the bent over porton but pushes it back into shape..... a simple bevel on a HHS threading cutter on both sides to "DULL IT "  and go in till the threads are pushed back into shape but no further....
   I wonder if that would work or not ..... obviously the severity of the damage would vari  but for light stuff that a nut will go over but not easily
this may well be the better action than cutting off the dents and leaving holes..... though in my experience I've never had a problem with doing that
when I discovered my first thread file I went around on the ranch and repaired every damaged thread I could find !  especially on the tractor
as everything that had exposed threads had massive dents in the threads..... but cleaning them off sure made it operate good again !
 ..... I however would be reluctant to use a good HSS thread cutter to this task..... one you were considering tossing is a real good candidate for the experiment !     just round the cutting edge over .... oil real good and see if the idea works !.....you'ed be chasing the threads.... so after everything is all set up and ready to go  hand placing the cutter / deformer into a area with no damage  then tightening down the cutter should get you there for repeatable passes  right ?
any opinions on that idea ?  is it worth the bother ?
.....
Bob.......


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## rock_breaker (Nov 22, 2019)

An interesting idea Bob!

My first thought is that this tool would be pushing material back into a stronger material mass which would take a lot of energy. Heating it would also affect the larger mass (bolt)  and possibly twisting it. PM me as I have an Idea.
Have a good day 
Ray


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