Single point threading questions

[zeusrekning]

Cedge and I worked on single point threading with my new lathe yesterday and ran into a few issues that we need help answering.
First off the only manual threading I really have any memory doing in the past was on a Hardinge HLV which was just too sweet. And threading on this machine was just the occasional odd job. So I'm learning how to use this thread dial system.

My first question is what exactly is the thread dial doing. This confuses me b/c the pitch of the lead screw is always the same and the RPM of the chuck and the lead screw are constant but I can't get my head around why I have to wait on the #1 to come around to engage the half nut for a 11tpi thread (just an example) It seems like for an 11 tpi thread that my carriage is traveling at .0909 per rev. no matter what number I am on.But I can see using the same number each cut.

The second question is on a 10tpi my chart says I need to engage at 1,2,3,or4 on the thread dial. Does this mean I can use 1 on the first pass the 3 on the next , and so on as long as I always engage on a whole number? Steve and I tried this with some zero cuts and it seemed to track right but when actually cutting metal I tried a different # and I cut 1/2pitch off.???

The way I am cutting now is to engage the half nut approximately 1/4" in front of the part when my thread dial matches the needed number. Cut to desired depth in Z then disengage half nut. Back out the cross slide, return Z to 1/4" in front of part, return cross slide to zero, then feed the compound in the desired amount for the next cut.(compound set @ 29.5 deg.)

Is the the preferred method?

No matter what, I think both Steve an I had a great time yesterday. It was a little like two deaf guys trying to learn to play a flute :big:.

But we actually got a lot done.
I am surprised he did not start another tool gloat post but you guys should see the toy he picked up yesterday... sweet.
We did get a decent looking thread cut using a 60deg turning tool. I must have bumped the tool a little to much when missing the thread dial because I wound up with about .005" thread missalignment.

Thanks in advance fellas.
Tim

 

[rake60]

No matter what, I think both Steve an I had a great time yesterday. It was a little like two deaf guys trying to learn to play a flute :big:.

LOL
I don't think I've ever heard that line before, but I'll be using it!

On most lathes you can use any number on the dial for an even number pitch. ie. 2, 4, 6,...32
I always use the same number. If my first cut is on 2 on the dial start every cut on the 2.

Odd number pitch threads have to be started on the thread dial number indicated on your machine.

 

[greenie]

Ahh, single point threading, now I'm going to be blasphemous and chuck the cat amongst the pigeons with this lot, but here goes.

The most simple way, to cut any thread, is to forget ALL about that damned thread dial once and far all. Better still, remove the thing from the lathe, chuck it in the cupboard and forget you ever had one.
Then forget about the B#!!$#&T of swapping your compound slide to that stupid 30 degrees, just leave it where it is.

So, there are TWO things that have now been completely eliminated from all the mystery of cutting threads, those that say this way I am about to describe is wrong, well, they should try this way first and then complain that it don't work.

Once you have chosen whatever thread pitch you want to cut, leave the carriage IN GEAR all the time, and at the end of the thread, wind the tool out away from the job, then turn your lathe over to reverse, and reverse the carriage back to the start point.
When the tooltip is back at the start, just wind it in to whatever size cut your game to take.

See, totally eliminated that STUPID idea of the 30 degrees top-slide crud altogether and completely taken out of play that crazy thread dial.

Now somebody is going to say, hey, I aint got no reverse on my lathe, well, what's wrong with winding it back by hand by making a simple handle that fits the end of the spindle. Lot's of designs for these have been produced over the decades, a bonus of using the handle for cutting the thread, is that you can NEVER run the tool into the work-piece/shoulder at the chuck end, absolute perfect control over how the tooltip is cutting, no heart stopping moments ever using the handle.

Now others are going to be downright rude and tell me where to get of with this lot, but, this is the way it's done in industry, has been done this way for decades, so why not get with the times and do it at home this way.

Now how much simpler is that, than what you have been attempting to do?

regards greenie

 

[Cedge]

Awww Greenie... now tell us how you really feel...LOL. If just writing about it gets you in such a lather, then I want to be watching when you actually cut some threads.

What Tim did yesterday appeared to give him a dual start thread. His first cut was engaged on the 4 of the threading dial and then on the next cut he engaged it on 2, which started the cut dead center of the ridge of the first cut. Since I've never cut threads, and Tim is experiencing some early senior moments, his question was one I too was curious about.

We spent part of the day with another machinist who's been at it for 40 years. In discussing threading techniques with him, I don't recall his advice including "chucking the thread dial". He took time to explain the reasons for the 30 degree angle and a 60 degree cutter. His explanations were patient and professional and I'm sure Tim appreciated his taking the time as much as I did. Sadly, the threading dial thing came up after we left the guy's place and had returned to Tims shop.

Tool gloat?... I bought that little sensitive drill /tapping chuck gizmo so cheap that I'm afraid to gloat. I hate it when old guys cry...LOL.

Steve

 

[greenie]

Awww Greenie... now tell us how you really feel...LOL. If just writing about it gets you in such a lather, then I want to be watching when you actually cut some threads.

Steve

OK, I'll say it as I see it. I've been employed as a machinist since the late 60's and was taught to thread, as per the long winded OLD FASHIONED way, it was and still is confusing.
After leaving that first place of employment and when I started the next job, I was laughed at, for going about threading in that stupid longwinded way, and for taking FAR TOO BLOODY LONG to do a very simple job.
Was then shown the EASY WAY TO DO IT, and in a jobbing shop, time is money, so from then on, I do it the easy way. I laugh at these stupid suggestions made by people who should know better, but they still try and confuse the learners. I sometimes wonder if these people who are telling the novice this, are doing it deliberately, to utterly confuse the novice.
As for watching me do a thread, you're welcome to come to Brisbane, Australia and watch me rip of a thread at 500/750 rpm and take a very short time doing it. Now if I have to make a l-l-l-long thread, I'll pump it up to 1200 rpm, no problems at all with these speeds. There is NO thread dial on the machine, I took the thing off and it's in the cupboard where it belongs, just leave the carriage engaged all the time, no problems about cross threading at all, for very obvious reasons.
Now a good machinist is not as fast as a CNC lathe, but he aint far behind either, the fella I work for now is about half my age, he learnt on CNC machines and doesn't like the manual lathes, he just shakes his head when he watches me cut a thread, reckons I'm crazy for getting up it, but hey, the threads are done and the nuts fit, TIME IS MONEY.
You can walk into hundreds of jobbing shops anywhere in Australia and I doubt that you will EVER see, that longwinded confusing way being used anywhere, so why not say it like it is, and tell people how to do it the easy way.
Now what speeds are you threading at and are these threading jobs being done for a jobbing shop or just mucking around at home?
Have you ever given the easy way a go, or are you afraid of taking the mystery out of threading and allowing the masses to do it very easily?

regards greenie

 

[DickDastardly40]

My first question is what exactly is the thread dial doing. This confuses me b/c the pitch of the lead screw is always the same and the RPM of the chuck and the lead screw are constant but I can't get my head around why I have to wait on the #1 to come around to engage the half nut for a 11tpi thread (just an example) It seems like for an 11 tpi thread that my carriage is traveling at .0909 per rev. no matter what number I am on.But I can see using the same number each cut

The thread dial shows the relationship between the chuck and leadscrew, when you have the gears set for a 1mm pitch thread the leadscrew will rotate say for an 4mm pitch leadscrew 4 times per revolution of the chuck. If you cut the first pass at 1 on the dial disengage the half nuts and move the carriage to a slightly different start position and cut the second at 3 the tool will start cutting at a different rotational point on the job and the thread will be (pardon the pun) screwed.

Whilst I agree with Greenie that the threading indicator can be confusing I don't find it long winded per se but recently I was cutting several shortish 6mm blind internal threads on a large imperial machine; the carriage moves very quickly on that pitch even at 40 RPM. You have to be confident that the chuck will stop spinning when you move the lever to stop to avoid a crash!

Al

 

[greenie]

The thread dial shows the relationship between the chuck and leadscrew, when you have the gears set for a 1mm pitch thread the leadscrew will rotate say for an 4mm pitch leadscrew 4 times per revolution of the chuck. If you cut the first pass at 1 on the dial disengage the half nuts and move the carriage to a slightly different start position and cut the second at 3 the tool will start cutting at a different rotational point on the job and the thread will be (pardon the pun) screwed.

Al

Now, if you just left the carriage locked in, do the cut, then moved the carriage in reverse to start the next cut again, you will never need the thread dial. You have taken the thread dial completely out of the equation, never to be needed again.
You can never double thread, or stuff it up, by leaving the carriage locked in either.

regards greenie

 

[Divided He ad]

Now before anyone shouts..... I've never tried to cut a thread.
I just thought I'd ask If you/we want to see Greenie cut a thread then surely with the technology out there it could be recorded and posted?

I know I'd like to see it too ;D


Ralph.

 

[Stan]

Every book on the basics of machining, plus the books published by the makers of school lathes (South Bend and Atlas) describe the theory and method of single point threading. Every beginner should read and understand one of these explanations.

After you become proficient using the book method, you may adapt other methods that you are comfortable using dependent, on the facilities available on your lathe. If high speed production is your object, you are on the wrong bulletin board.

 

[Tin Falcon]

ZK If you have not already done so download a copy of the Army Training circular TC 9-524 and the Navy repairman's manual both offer lots of basic info in a easy to read format. I would offer a CD copy but my burner went belly up do not recall off hand the links.
Back to the question
here are the rules for the thread dial
1 EVEN # threads ANY graduation of the dial
2 ODD # threads any MAIN (numbered) division
3 1/2 threads ie 11 1/2 , 27 1/2 every other main division 1&3 or 2 & 4
4 other fractional threads engage the same division all the time.
5 thread that are a multiple of the lead screw any time the split nut engages. Thread dial not needed. so if the lead screw is an 8 tpi you can do a 10-24,10-32 or a 4-40 with the thread dial missing.

Now that being said if you follow Rick's rule of always use the same even division you will not go wrong just have to wait a little longer for that number to come up.
Hope this helps
Tin

 

[shred]

I've done both the threading dial and reverse things when learning to single-point not long ago. The thread dial tells you when the tip of the tool is in the valley of the thread you just cut and not as Cedge says, somewhere else like on the ridge.

The reverse thing is much simpler mentally, but slower for me, especially on fine-pitch threads. If you have more metal-removal ability (like say a production lathe) you can get by with many fewer passes.

One trick with 'waiting' on the thread dial is you can also move the carriage to catch up with it (just don't hit the thread)

Also, if you have a threading stop, that's worth learning to use since you can do gross cross-slide movements easily and repeatably.

 

[Tin Falcon]

Guys :
It has been a long time since I have had to don my administrators cap and remind you folk to play nice.
so lets all remember to treat others with respect and help one another and answer questions with a helpful attitude. Lets leave the High and migty attitudes to the HIGH AND MIGHTY. To the best of my knowledge God does not post here.
Greenie:
yes there are better methods than the text books teach but do not scold anyone for learning to walk before they run. Or expect them to run before they walk.
Stan : lets also not get into read the book before asking questions mentality and yes you are right this is a hobby forum we are here to have fun an learn an make a few parts and hopefully a running engine or two. this is a fantastic place to hang out and learn lets all do our part to keep it that way!!!!!!!!!
Tin

 

[te_gui]

I use both methods, Greenies way will work and that's what I use especially to cut metric threads on an imperial lathe. However, I would like to hear how he cuts a multistart without the dial, I dunno how too any other way.

 

[Circlip]

Didn't know about keeping the clasp nut closed and driving the lathe backwards till about thirty years AFTER I'd been taught to do it the "Proper" way - on the dial. Only thing for Newbies to be aware of is on lathes with a screwed spindle nose to beware of the chuck unscrewing itself if reversing quickly. Play safe,
Regards Ian.

 

[mklotz]

Some time ago I wrote a brief explanation of the logic behind the thread dial for our club. I've attached it below for those who might find it helpful.

Leaving the half-nuts engaged and reversing the lathe is tedious at best. Worse, I've encountered newbies who, rather than (electrically) reversing the lathe motor, will use the tumbler gears to reverse the lathe, thus completely losing all registration between the spindle and the carriage. Literally thousands of lathes are made and delivered with threading dials installed. Greenie's comments aside, I can't believe that legions of machinists spend time watching their carriage moving ponderously to the right while cutting air.

There is a way to avoid both using the threading dial and reversing. If I move the carriage to the right a distance that is BOTH an integer multiple of the pitch being cut AND the pitch of the lead screw, then the half nuts will reengage and the tool will still be in sync with the thread being cut. This technique is also useful when cutting metric threads on a lathe with an Imperial lead screw. You can learn more about it via the STICK archive on my page.


------------------------------------------------------------------------------------
USING THE THREADING DIAL

Some folks are confused by which marks to use on the threading dial on their
(assumed Imperial) lathe. Of course, you're always safe restarting on the
same dial mark on which you started but that means you'll spend a lot of time
'waiting for your number to come up'.

It's pretty easy to think through. Most dials have four numbered marks
labeled, unsurprisingly, 1-4. Between these marks are smaller, unnumbered
marks.

[Aside: A consequence of the four numbered mark dial is the fact that the
gear that meshes with the feed screw will have a number of teeth which is four
times the tpi of the feed screw, i.e., an 8 tpi lead screw will have a 32
tooth gear on its thread dial. This is worth knowing if you intend to build a
threading dial for a lathe that lacks one. Since there's no load on this
gear, a perfect match to the helix angle of the lead screw is not needed. Any
old gear with the right number of teeth can be pressed into service.]

The numbered marks almost always correspond to a carriage movement of one
inch. (However, you should confirm this by actual measurement on your lathe.)
By deduction, the unnumbered lines must then correspond to a carriage movement
of one-half inch.

Now, suppose I'm cutting an even-numbered thread (e.g., 32 tpi). If I move the
carriage by one-half inch, the tool will reenter the thread perfectly. If I
move the carriage one inch, the tool will also reenter. Therefore, I can
reengage the half-nuts on ANY line on the threading dial.

If I'm cutting an odd-numbered thread (e.g., 13 tpi), the tool will not reenter
the thread if I move one-half inch - I have to move one inch. Therefore, I
must reengage the half-nuts on ANY NUMBERED LINE on the dial. (If I started
the thread on an unnumbered line, I would then reengage on unnumbered lines but
that is generally too difficult to remember in the 'heat' of thread cutting and
should be avoided.)

If I'm cutting a half-fractional thread (e.g., 11-1/2 tpi), the tool will only
reenter the thread every two inches. Therefore I must reengage the half-nuts
on ONLY THE ODD NUMBERS ON THE DIAL (1 and 3) or on the even numbers (2 and
4). It's a good idea to decide on one of these options and always stick with
it. I always start the thread on 1 and then use either 1 or 3 to reengage.

Rarely, a lathe can cut a 1/4 thread (e.g., 1-1/4 tpi). This thread will only
repeat every four inches so, in cutting such a thread, one would reengage the
half-nuts on the same mark one used to start the thread.

 

[Bogstandard]

Because there are so many people on here that have never done single point threading it can be very daunting when faced with, on this type of thread do this, on another do that, very confusing and I am sure offputting to a lot of members that are new to using a lathe.

The information provided is all good info, but for use as experience is gained. I would suggest starting at the very beginning.

For a person that is totally new to the situation, and you have a threading dial, start out with always cutting on the same number with the lathe running as slow as you can get it. Ok, you have to wait a while, but the job isn't going to jump out of the chuck and run away, and you will also be able to see how the threading tool does its job.

If using a smaller lathe, the loading on the cutting tip is reduced by the setover of the compound slide to half the thread angle, and using the compound slide to put feed on, this way the tooling is only cutting on the forwards tool face. On the very last finishing cut, a very small cut is put on using the cross feed (about 0.0005 to 0.001"), to give a two faced cut, just to clean up the rear face of the thread.
With a larger lathe and more rigid setups, full two sided cutting is easily achieved, but on smaller lathes, the finish of the thread is usually a lot worse as the chatter is increased all down the thread, especially as the thread gets deeper.

Take your time, and get starting on one number under your belt, then experiment with starting on other compatible numbers once you are happy. You are not in a production environment making these little engines, just take it steady and calculated. Pretty soon you will be cutting multi start, metric/imperial and left hand threads without any major problems. It all becomes clearer as you gain experience and confidence.

I have in fact modified my screw cutting indicator to show 16 divisions, the little extra ones are not for screwcutting at all, but to make sure that I am not wearing away my half nuts by crashing them into the leadscrew when I want to put a powered cut on. Unlike most people who hold the half nut lever down and wait for them to line up with the leadscrew threads, I can just gently ease them onto the leadscrew at any of the 16 points.

John

 

[bob ward]

With a larger lathe and more rigid setups, full two sided cutting is easily achieved, but on smaller lathes, the finish of the thread is usually a lot worse as the chatter is increased all down the thread, especially as the thread gets deeper.

Sir John, with the small amount of experimental thread cutting I've done so far, up to 2mm pitch in mild steel, I can see little difference in the cutting and in the finished job between setting the compound over and plunging straight in. I'm using a new 14 x 40, is that is a "larger lathe" for threads of this size, or have I just been lucky with plunging straight in?

 

[Cedge]

Shred
I didn't mean to state anything, but to present an observation, which was the reason for the questions. When Tim engaged at the #4, the resulting cut was a nice beginning for an 8TPI thread. When he next engaged, he engaged at #2. This set whole new path for the cutter which, from our OBSERVATION, was apparently dead center of the ridge of the first cut.

The questions we had were basically :
A.... Once you choose a number on the thread dial, should you continue using that number?

B... By engaging at the #2 of the second cut, did we actually begin a multi-start
thread?

Trust me...I'm not even remotely claiming any sort expertise, considering I'm a thread cutting virgin. I just reported the results and asked why.

Jose Rodriguez, who is one of the early converts / advocates for the 7X10 Sieg lathes has a threading instructional CD which describes using the thread dial as well as the technique for not using one. He also briefly mentions the "plunge" method, but advised against it on these smaller lathes due to the almost certain chatter problems.

In anticipation of someday trying threading, I installed a hand wheel on my spindle in order to avoid the anticipated high speed travel of low TPI counts.

I only tugged gently on Greenie's chain, a wee bit, for the "my way is the only proper way of cat skinning" tone. He's welcome in my shop anytime and he's also welcome to give his patented plunge technique a try on my monster 7X14 lathe. It's bound to be a quick lesson in humility and tolerance for those who can't swing it for owning big iron....LOL Apologies to the mods if my tone was possibly a bit off the mark.

I think I got the answer to "A" in "Rick's rule". Use the same number for each cut, once it's been chosen.

Marv...I'll delve into your treatise after I post this. It looks like a pretty fair read. I think I also just won a bet with Tim, due to your post....(grin). I bet him you'd have a prog-lette for the problem...LOL

Steve


Steve

 

[Bogstandard]

Bob,

I wouldn't class a 14x40 lathe as a small modelling lathe, in fact that is the rough size I am upgrading to. So yours definitely has the power to do plunge cutting,

My 10" Atlas just manages, if I keep the cuts to very fine ones. So I tend to stick to a single side, offset cutting method, purely to produce a nice finish, unless it is a quick and dirty job.

John

 

[Mcgyver]

Sir John, with the small amount of experimental thread cutting I've done so far, up to 2mm pitch in mild steel, I can see little difference in the cutting and in the finished job between setting the compound over and plunging straight in. I'm using a new 14 x 40, is that is a "larger lathe" for threads of this size, or have I just been lucky with plunging straight in?

Bob,

you are better off cutting by advancing the compound set at 29.5 until the last pass. These time tested techniques usually have underlying reasons. In this case, the width of the cut as an effect on the cutting force, by plunging you are doubling the width - the tool is cutting on both sides of the V. Many texts advise that the final finish path is done with a 1 or 1/2 thou plunging cut which is correct, but until you get there, it makes sense to avoid the this extra load and only cut on 1/2 of the V.....all things being equal you'll create less cutting force by cutting on 1/2 of the V hence permitting more DOC.