# Internal Threading



## rwm (Nov 29, 2020)

So external threads are easy to set the compound. You want just a half degree or so short of 30 deg.
What about internal threads when you are feeding the compound in reverse? Do you use the same compound setting or do you need to move it 1 degree the other way?
Obviously all of this is for feeding with the compound. If you use the cross slide it is not an issue but I get cleaner threads feeding the compound.

Robert


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## benmychree (Nov 29, 2020)

The compound should be turned to the same angle, but in the opposite direction, that is with the dial end leaning towards the headstock, not away from it.  Personally, I have never subscribed to the half degree business; I was taught to set on 30 degrees, all my associates during apprenticeship did likewise, and to my knowledge, all the journeymen did so too.


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## rwm (Nov 29, 2020)

benmychree said:


> with the dial end leaning towards the headstock, not away from it.



I am not following that part of you explanation? Interesting, I will try just a straight 30 deg.

Robert


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## benmychree (Nov 29, 2020)

rwm said:


> I am not following that part of you explanation? Interesting, I will try just a straight 30 deg.
> 
> Robert


What I am saying is that if the compound is set 30 degrees off zero, set it 30 degrees on the OTHER side of zero, in other words swivel it to the left rather than to the right as is done with external threading, this causes the tool to feed into the cut rather than cutting on the back side as the successive cuts are made.


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## rwm (Nov 29, 2020)

If I swivel the compound to the left it will interfere with the chuck and the workpiece? Do you mean swivel it to the far side of the carriage? That would make some sense? Then I could feed it the same way. The last time I cut internal threads I left the compound the same and fed it in reverse. That worked but not great.
Robert


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## benmychree (Nov 29, 2020)

Leaving the compound in the same position would make the tool cut on the backside as I mentioned above, it indeed does not work well.  I find that with my lathe and its tooling, I can cut threads that way without interfering with the chuck, but there is no reason you could not position it towards the back of the machine, as you suggest.


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## rwm (Nov 29, 2020)

Yes I see. This is what you are suggesting:




One would then back the compound out during cutting.
But wait a minute....wouldn't one really want 31 deg in this picture to keep the heel of the tool from rubbing? 
Robert


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## benmychree (Nov 29, 2020)

Yes, exactly!


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## rwm (Nov 29, 2020)

I edited while you were typing. Sorry.
And while we are at it- is the depth of thread the distance on the compound divided by cos 30? Or in other words, the Depth of thread is 2 times the compound advancement?
R


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## benmychree (Nov 29, 2020)

I did notice the one degree off of 30, but chose not to mention it, as I said before, I chose to use 30 degrees even, and one can, is they want to take final cuts straight in if they think it would make a cleaner thread; another method, taught in school by an excellent teacher, was to slightly drag against the carriage handwheel rotation to clean up the backside of the thread if it looks like it would benefit.


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## rwm (Nov 29, 2020)

I found this diagram:



It confirms the compound orientation and the angles. 
Of course it is completely wrong because the tool orientation has not been adjusted to be square to the work!
Robert


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## rwm (Nov 29, 2020)

I think I am wrong about the Trigonometry. Cos 30 is .866 (not 1/2). So the depth of cut should be compound travel x .866.
I like using 24 TPI since the depth of cut is very close to .024" and that is almost exactly 1/4 of .1" (one handwheel turn on cross slide). Easy to remember without consulting a chart.
Robert


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## benmychree (Nov 29, 2020)

It really does not matter if the tools come to a fine point so far as cutting the threads, the national thread forms allow a flat on the crest and root of threads, and the flat, to specification makes the tool stronger and longer wearing.  I use Aloris HSS threading tools, and come in different sizes for fane and coarse threads; for the finest, I just stone a tiny flat on the point, for the larger ones, I use a larger flat.  Brown & Sharpe made a circular thread tool with vee slots around its circumfrence marked with TPI with the appropriate flats in the root of each thread pitch so that one could, after sharpening the tool to a sharp point, the tool point could be dubbed off to the appropriate width of flat.


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## benmychree (Nov 29, 2020)

Personally, I do not use compound depth in threading, one, because I use tools with a flat at the point, and also because I fit to a gage, or I use a thread mike for fit, which, I think makes for the best possible fit. On the opposite of accurate, years ago, I threaded a lot of square shafts for tillage discs, it was 1 1/8 – 7, and the threads were cut in just five passes; an initial nearly half depth cut was taken, then with the tool set at the same depth, the number on the dial was skipped and the half nuts closed on a line, which took its cut behind the first, the subsequent cuts were taken on a numbered line so that they were only cutting at half the apparent depth you would normally see with the conventional method; I was told that this method was done in the oilfields back in the day. It may not be pretty, but it was quick, and oh! The ODs were turned round and undersize to minimize burrs.


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## mickri (Nov 29, 2020)

In my very limited experience with internal threading I have never been able to have the compound angled towards the headstock due to interference with the chuck.  Also the tool bit has to stick out of the holder by at least double the distance.  So I have had to use the same set up as for external threading.  I can't tell any difference in the threads.   I have often thought about rotating the tool bit 180 degrees and cutting on the far side of the hole.   Are there any problems with doing this?


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## rwm (Nov 29, 2020)

I feel like using the compound is more important on a light lathe because it reduces the cutting force on one side of the tool. I just like to know the thread depth to get in the ballpark.
I'm gonna try the back side of the compound next time. I will report back.
Great-now I need to buy a thread mic...
Robert


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## benmychree (Nov 29, 2020)

mickri said:


> In my very limited experience with internal threading I have never been able to have the compound angled towards the headstock due to interference with the chuck.  Also the tool bit has to stick out of the holder by at least double the distance.  So I have had to use the same set up as for external threading.  I can't tell any difference in the threads.   I have often thought about rotating the tool bit 180 degrees and cutting on the far side of the hole.   Are there any problems with doing this?


Cutting on the backside is a good method, especially if you are working in a blind hole, the tool cutting face is upward and you start in a recess in the bottom of the hole and feed outwards wit reverse rotation; if you have the tool facing down, there is the tendency for the tool to lift in the cut, especially in light machines, another thing is that if cutting with the tool facing up in reverse rotation with a threaded on chuck, it can loosen and start coming off the spindle.


rwm said:


> I feel like using the compound is more important on a light lathe because it reduces the cutting force on one side of the tool. I just like to know the thread depth to get in the ballpark.
> I'm gonna try the back side of the compound next time. I will report back.
> Great-now I need to buy a thread mic...
> Robert


Actually several thread mikes, in zero to one inch, there are three to cover the range of pitches encountered.


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## rwm (Nov 29, 2020)

Sigh...I'll probably just go back to tap and die....
R


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## benmychree (Nov 29, 2020)

rwm said:


> Sigh...I'll probably just go back to tap and die....
> R


Don't let yourself be intimidated, its not all that hard to do; practice makes (almost) perfect.  I see so many on this site acting like everything must be perfect!  Put that aside, there is such a thing as "perfect enough"  That is why on drawings of parts, there are tolerances.


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## mickri (Nov 29, 2020)

I recently made a chuck keeper (wrong terminology) to prevent the chuck from unscrewing if I had to run the lathe in reverse.  Have not tried it yet and am more than a little leery of testing to see if it works.  My thought was to have the threading tool facing down.  My threading bar does flex.  I can see it flex if I take too big of a cut.  I limit my threading cuts to .005.





I'll 2nd not trying for perfection.  I always strive to do absolute best that I can do, not what someone else can do and accept whatever I achieve.  Seems to work for me.


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## Jim F (Nov 29, 2020)

benmychree said:


> Cutting on the backside is a good method, especially if you are working in a blind hole, the tool cutting face is upward and you start in a recess in the bottom of the hole and feed outwards wit reverse rotation; if you have the tool facing down, there is the tendency for the tool to lift in the cut, especially in light machines,* another thing is that if cutting with the tool facing up in reverse rotation with a threaded on chuck, it can loosen and start coming off the spindle.*
> 
> Actually several thread mikes, in zero to one inch, there are three to cover the range of pitches encountered.


With a tight chuck, light cuts and slow speed, it is possible.
Been there, done that.


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## savarin (Nov 29, 2020)

I know all the accepted wisdom is to use the 29.5/30 degree setting on the compound and when I started I also used that method.
I do understand the reasoning behind that system but since I replaced the compound with a solid plinth I have found that threading at 90 degrees is not a problem.
Admittedly I very rarely thread larger than M2.5 but have made a couple of M4 threads both internal and external.
I do hone the bits and ensure they are very sharp and a mere touch to just flatten the tip. Most materials I thread are stainless predominately with some mild steel and heaps of aluminium.


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## benmychree (Nov 29, 2020)

I have always threaded the chuck on my 19" lathe hard up, but still have nearly lost the chuck several times when using reverse as a brake; I quickly went back to forward and screwed it back on; a 10" 3 jaw has quite a bit of inertia!


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## benmychree (Nov 29, 2020)

savarin said:


> I know all the accepted wisdom is to use the 29.5/30 degree setting on the compound and when I started I also used that method.
> I do understand the reasoning behind that system but since I replaced the compound with a solid plinth I have found that threading at 90 degrees is not a problem.
> Admittedly I very rarely thread larger than M2.5 but have made a couple of M4 threads both internal and external.
> I do hone the bits and ensure they are very sharp and a mere touch to just flatten the tip. Most materials I thread are stainless predominately with some mild steel and heaps of aluminium.


I am told that the Germans have their own method of threading, they position the compound at 90 degrees to the cross slide and feed in with the cross slide just so much, and then feed in axially with the compound a certain amount.  BTW, our spell check says that your spelling of (aluminum) is incorrect ---Ha, Ha!


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## BGHansen (Nov 29, 2020)

I set the compound to 60.5 deg. on my Grizzly G0709 for internal threading; compound is flipped 180 from what the diagram above shows.  One issue for me is the knobs on the compound run into the coolant line and carriage light.  Not a big deal to unscrew them and turn the knob by hand.

Bruce


I flip the compound around to the back side and go 1/2 degree past a 30 deg. thread form


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## rwm (Nov 29, 2020)

Everyone knows its much easier to thread aluminium than aluminum...why do you think the Brits and Aussies use it?
Bruce- thanks- that's what I want to try.
Robert


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## savarin (Nov 29, 2020)

benmychree said:


> BTW, our spell check says that your spelling of (aluminum) is incorrect ---Ha, Ha!


That must be why Americans can't spell.  
The correct scientific term over the majority of the planet spells it Aluminium.
Here are some more incorrect spellings you guys get wrong (scroll down)








						American and British English spelling differences - Wikipedia
					






					en.wikipedia.org


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## rwm (Nov 29, 2020)

"Davy's spelling _aluminum_ is consistent with the Latin naming of metals, which end in _-um_, e.g. _aurum_ (gold), _argentum_ (silver), _ferrum_ (iron),[114] naming newly discovered elements by replacing a _-a_ or _-ite_ suffix in the oxide's name with _-um_: lanthanum was named for its oxide lanthana, magnesium for magnesia, tantalum for tantalite, molybdenum for molybdenite (also known as _molybdena_), cerium for ceria, and thorium for thoria, respectively. As aluminium's oxide is called _alumina_, not _aluminia_, the _-ium_ spelling does not follow this pattern. However, other newly discovered elements of the time had names with a _-ium_ suffix, such as potassium, sodium, calcium, and strontium.

In 1812, British scientist Thomas Young[115] wrote an anonymous review of Davy's book, in which he proposed the name _aluminium_ instead of _aluminum_, which he felt had a "less classical sound".[116] This name did catch on: while the _-um_ spelling was occasionally used in Britain, the American scientific language used _-ium_ from the start.[117] Most scientists used _-ium_ throughout the world in the 19th century;[118] it still remains the standard in many other Latin-based languages where the name has the same origin.[113] In 1828, American lexicographer Noah Webster used exclusively the _aluminum_ spelling in his _American Dictionary of the English Language_.[119] In the 1830s, the _-um_ spelling started to gain usage in the United States; by the 1860s, it had become the more common spelling there outside science.[117] In 1892, Hall used the _-um_ spelling in his advertising handbill for his new electrolytic method of producing the metal, despite his constant use of the _-ium_ spelling in all the patents he filed between 1886 and 1903. It was subsequently suggested this was a typo rather than intended.[113] By 1890, both spellings had been common in the U.S. overall, the _-ium_ spelling being slightly more common; by 1895, the situation had reversed; by 1900, _aluminum_ had become twice as common as _aluminium_; during the following decade, the _-um_ spelling dominated American usage.[120] In 1925, the American Chemical Society adopted this spelling.[120]

The International Union of Pure and Applied Chemistry (IUPAC) adopted _aluminium_ as the standard international name for the element in 1990.[121] In 1993, they recognized _aluminum_ as an acceptable variant;[121] the most recent 2005 edition of the IUPAC nomenclature of inorganic chemistry acknowledges this spelling as well.[122] IUPAC official publications use the _-ium_ spelling as primary but list both where appropriate.[h]"

I think since the Americans invented English we should determine these things?
Robert

Damn- Hijacked my own thread again....


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## T Bredehoft (Nov 29, 2020)

Never miond the spelling, I think you're all making too much of tool position. A good threading tool has no back side. Just set the compound as you would for OD threading and without changing it use a boring bar, reverse rotation (if your chuck is locked) and feed out for internal treads. If  you fit the threads to standards, (shop made or otherwise) they'll be fine. The professionals don't switch the compound around for internal threads. I know, I was one for almost 30 years and never even thought about  it. I wasn't trained to do it.


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## rwm (Nov 29, 2020)

Boring bar upside down?
I need to try that also.
Robert

Edit:
NO- boring bar right side up, reverse rotation, feed out. Yes?
R


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## mattthemuppet2 (Nov 29, 2020)

rwm, if you find the compound interferes with the work with the way it's set in the diagram, you can always turn it around 180deg. It helps to visualise which side of the cutter is doing the most work, then you simply angle the compound to feed that edge into the work.


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## NC Rick (Nov 29, 2020)

benmychree said:


> Don't let yourself be intimidated, its not all that hard to do; practice makes (almost) perfect.  I see so many on this site acting like everything must be perfect!  Put that aside, there is such a thing as "perfect enough"  That is why on drawings of parts, there are tolerances.


I got that lecture last week from my good friend who has been running a successful shop for near 40 years. I think for us less experienced it can be hard to know what "perfect enough" is.  It's hard to be sure which details to worry over.  I think he got a little mad at me for checking and complaining about a D1 taper.  He said something about me needing to have someone else check my work to understand how humiliating it can be.  his words also included "that's what tolerances ar for".  I tend to gain my experience from finding out when I'm wrong.  I do get a fair amount of practice.


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## Downunder Bob (Nov 29, 2020)

1. on the point of spelling, the language is English, so therefore, the English spelling should be the preferred method. 

2. Threading, as an apprentice I was taught to keep the compound slide parallel to the bed, and use the cross slide only for infeed, I was also taught about the 29.5 deg method as being useful on small lathes that lack rigidity. As most of our lathes were in the 24 to 20 inch swing rigidity was not a problem. 

Joe Pieczynski Does a very good Youtube video on internal threading. He has also recently done a series on making a model steam engine, in fact it's not quite finished, each part is a separate video. Each segment is presented in a manner that will teach how to set up particular types of parts. The man is a master machinist, and his methods and setups are a pleasure to watch. 

By the way Joe has recently become a member of HM.


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## NC Rick (Nov 29, 2020)

Downunder Bob said:


> 1. on the point of spelling, the language is English, so therefore, the English spelling should be the preferred method.
> 
> 2. Threading, as an apprentice I was taught to keep the compound slide parallel to the bed, and use the cross slide only for infeed, I was also taught about the 29.5 deg method as being useful on small lathes that lack rigidity. As most of our lathes were in the 24 to 20 inch swing rigidity was not a problem.
> 
> ...


Joe's videos are excellent.  I have learned many things from him which I use all the time. The steam engine thing seems weird because of Blondi Hacks, a new hobby machinist who is smart also but without the professional experience.  Quinn did the main casting and Joe did a spectacular job of showing an alternative setup and measuring strategy which was eye opening for me. I was suprised he didn't acknowledge her and provide a little praise in the spirit of camaraderie.  The two videos back to back was fantastic for me because I was trying to mentally solve to problem "with" Quinn and then seeing a pro carefully explain a cool way to do it that I had never considered was wonderful.  Why he just built the whole thing I can understand.  I'm missing something, I am sure but as a result I have lost some interest in watching his videos.  thats a little sad because he is one of the top teachers on YouTube and is very practical.


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## erikmannie (Nov 29, 2020)

rwm said:


> Sigh...I'll probably just go back to tap and die....
> R



I have an economical Shars 0-1” thread micrometer. I have used it a whole lot, and it has never come up short. It comes with 3 tips, so you’re covered there:






						0-1" Screw Thread Micrometer
					

Shars Tool




					www.shars.com
				




FWIW I use the compound handwheel for external threads (I am 29.5° guy) & the cross slide handwheel for internal threads (i.e. I don’t use any compound feeding for internal threads). Disclaimer: I am a noob.


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## mikey (Nov 30, 2020)

erikmannie said:


> FWIW I use the compound handwheel for external threads (I am 29.5° guy) & the cross slide handwheel for internal threads (i.e. I don’t use any compound feeding for internal threads). Disclaimer: I am a noob.



I do it the same way as Erik. I use Micro 100 internal bars for small diameters and inserted carbide for larger ones and it works just fine using the cross slide, including Class 3 threads.


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## T Bredehoft (Nov 30, 2020)

rwm said:


> Boring bar upside down?
> I need to try that also.
> Robert
> 
> ...



Correct. Reverse rotation, boring bar right side up, cuts on top of the tool. Piecea Cake.


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## Jim F (Nov 30, 2020)

NC Rick said:


> Joe's videos are excellent.  I have learned many things from him which I use all the time. The steam engine thing seems weird because of Blondi Hacks, a new hobby machinist who is smart also but without the professional experience.  Quinn did the main casting and Joe did a spectacular job of showing an alternative setup and measuring strategy which was eye opening for me.* I was suprised he didn't acknowledge her and provide a little praise in the spirit of camaraderie. * The two videos back to back was fantastic for me because I was trying to mentally solve to problem "with" Quinn and then seeing a pro carefully explain a cool way to do it that I had never considered was wonderful.  Why he just built the whole thing I can understand.  I'm missing something, I am sure but as a result I have lost some interest in watching his videos.  thats a little sad because he is one of the top teachers on YouTube and is very practical.


If you read the comments on some of his previous videos, he offered her advice on something and she took offense. Even banned him from commenting on her videos.


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## NC Rick (Nov 30, 2020)

Jim F said:


> If you read the comments on some of his previous videos, he offered her advice on something and she took offense. Even banned him from commenting on her videos.


I don't like to focus on Drama but I may have to look into that because there is something going on I don't like.  I'd rather not harbor incorrect bad feelings.  I read something on he Blog asking to not have things "Mansplained" to her.  I really enjoyed watching a novice working through something and particularly when the better way isnt clear to me and then seeing a pro or anyone with a clever different approach show their way.  Super useful.


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## Downunder Bob (Nov 30, 2020)

Jim F said:


> If you read the comments on some of his previous videos, he offered her advice on something and she took offense. Even banned him from commenting on her videos.



Sounds about right. Some women are easily offended. and she is one of them. Puts herself up there as a know it all, but she is really quite an amature. 

I much prefer Joe's style any way, he explains things in  a very natural way and his expertise is without peer on these forums.


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## Mitch Alsup (Nov 30, 2020)

Downunder Bob said:


> 1. on the point of spelling, the language is English, so therefore, the English spelling should be the preferred method.



So color should be spelled colour ??
And liter should be spelled Litre because it was originally French ??


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## Illinoyance (Nov 30, 2020)

Threading RH, LH, internal, external, spindle in reverse, tool inverted, etc, there is one rule that always works: the compound should be parallel with the trailing flank of the tool. Actually the trailing face of the tool  should shave a little off the thread so 1/2* off parallel is the right compound setting.  Those of you that plunge feed can ignore what I wrote.


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