# Is This Thread Possible ?



## BillWood (Oct 3, 2015)

Couldn't sleep, so started pondering what I can and cannot do on my lathe and somehow started wondering if a skilled machinist could cut the nut and bolt shown in the attached sketch.

I have no need to make this, and cannot think why anybody would want to, but I was wondering if it is possible for an experienced machinist to make such a thing.

I can think of a cheat - cut the nut in two parts then screw them both onto the bolt and glue or pin the two parts together, then unscrew the bolt.


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## REdington (Oct 3, 2015)

It would work as long as the threading on both ODs and IDs were done in the same operation.

Rodney


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## JimDawson (Oct 3, 2015)

Yes, it's possible.  What Rodney said


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## Bill Gruby (Oct 3, 2015)

Why not, 20 TPI is 20 TPI regardless of OD or ID. The tricky part would be in making the two diameters in the nut or bolt continuous. You would need to stop the thread and pick it up again for the different diameters. Next time try a sleeping pill, they help to stop the thought process. LOL  Good night Mrs. Callabash, where-ever you are. Now I won't sleep. LOL

"Billy G"


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## GarageGuy (Oct 3, 2015)

I used to wonder about things like this, but it was keeping me up at night... so I stopped  

GG


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## Bill Gruby (Oct 3, 2015)

I just took a good look at your sketch. It calls for a left hand thread. Is that what you are calling for. If so it just got easier because you will be cutting from the chuck end to tail stock. It will take a specially ground tool but I asure you it can be done. Now can I go to sleep or should I cut a set first?  LOL

 "Billy G"


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## BillWood (Oct 3, 2015)

Well ........ thanks - definite agreement here .............the next time I cant sleep I'll go up to the shed and have a go - that was very clever of me to make it an easy to cut left hand thread. Must be some sort of intuitive naturally gifted mechanic somewhere in my family tree.

Why is a LH thread a special tool grind ?

I cut one unintentionally a little while ago using the same tool I'd just used to cut a RH thread .................... thought I was rather clever making things easier by taking the cut towards the tailstock and then wondered why the nut refused to engage with the screw.


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## Bill Gruby (Oct 3, 2015)

A LH is not a special grind per say but to get closer to get that close to the shoulder of the bolt you have to grind one side of the tool so you can run the thread right to the shoulder. It's no biggie.

"Billy G"


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## Tony Wells (Oct 3, 2015)

There is a premium thread with that feature in the oilfield. It was originally patented and named Hydril-cs. Your shop had to be licensed to cut it. There are still a few such protected threads around, but I believe the patents are expiring on many of them.


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## T Bredehoft (Oct 3, 2015)

I've been looking at that monstrosity of a thread,  Its an internal thread on a sleeve, for joining two pieces of (probably) pipe together. It doesn't say so, but I'll bet  one end is left hand the other right hand. It makes my head hurt thinking about it. No. 34 is a compression device to seal the joint.


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## Tony Wells (Oct 3, 2015)

That sleeve is known as a coupling sub, and normally is RH thread on both ends. No need to confuse the roughnecks. There are various drill string components that use this thread, up to and including the bit itself. 

You're right about component 34. This whole thread is complicated to cut because you are making up at torque on more than a single element, as on a standard RSC. Even those you are making up on a tapered thread and a shoulder at the same time.


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## Bill Gruby (Oct 3, 2015)

I don't believe that coupling could not be done with both right and left hand threads. Wouldn't it come apart before the hole was drilled.

 "Billy G"


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## John Hasler (Oct 3, 2015)

Bill Gruby said:


> I don't believe that coupling could not be done with both right and left hand threads. Wouldn't it come apart before the hole was drilled.
> 
> "Billy G"


Clockwise torque at the top of the string will tighten all the threads if they are all RH.  If one set was RH and one LH, torque one way would loosen one set while torque the other way would loosen the other set. 

I don't see the advantage of the design, though.  Presumably it solves some application-specific problem.


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## Tony Wells (Oct 3, 2015)

Not that it couldn't, Bill. There's just little point. At times, the drill string must be reversed anyway, negating any advantage to LHT. The idea is for the assembly torque, which can range into the 100k+ pound/feet on the larger sizes to suffice in holding things together.

There is control on the whole assembly while in the hole through the WOB, and the RT applied torque. There actually is a bit of science behind making holes in the ground several miles deep.


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## Silverbullet (Oct 3, 2015)

Yupp has to do with the rotation of the earth and the moon and tides too.  Ha ha ha . Lol way to serious I think . But has they say there is a way to do everything .


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## Paul in OKC (Oct 3, 2015)

Like said, the oil field thread is a CS Hydril. It is an 8 pitch thread with two diameters. You do have to cut them in the same set up, and the I'd thread in the same set up. To keep the same lead.


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## Wreck™Wreck (Oct 3, 2015)

If you mean something that looks like this 1/2-20 X 1-20, single pointing both threads in the same set up on a manual lathe would work, you would have to do it for both the internal and external threads. The threads do not need to start at the same radial positions (as drawn for simplicity), but the internal and external thread starts must have the same relative radial positions.

An interesting intellectual exercise.


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## Bill Gruby (Oct 3, 2015)

Yes, if the starts on each of the internal threads and each of the external threads are not in the same position , you will not be able to screw them together. That is the tricky part I mentioned earlier on.

"Billy G"


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## Paul in OKC (Oct 3, 2015)

The start position does not need to be in the same 'area'. As long as you run the threads in the same cycle, you will be good. Don't change gears in between running the threads, or they will likely be off.  When we ran the Hydil threads in a CNN lathe, we just left the start position in the same place in front of the part for both diameters.  Not necessary on the manual as to start position, just best to run the threads in the same process.  The hardest part is when the the gage doesn't go on, which one needs tweaked! Unless you have a separate gage for each.


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## Wreck™Wreck (Oct 3, 2015)

A more useful actual product and an excellent challenge would be making a multiple start thread, how is it done?


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## Tony Wells (Oct 4, 2015)

I again fall back to my oilfield experience. There is an adjustable bent housing used in directional drilling that relies on the different effective pitches presented by a single lead on one end of the assembly and a double start thread on the other. IIRC, it was either Sperry-Sun or Dresser Downhole that ran that style of housing. That is the subject is for another thread though. There are a number of approaches to solve the problem unique to locking an adjustable bent housing at  precise angle.


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## 4GSR (Oct 4, 2015)

Just so happens I'm working on a threaded assembly design that is what we refer to as a two step thread like the hydril thread above.  The larger thread is a 8"OD 4-pitch Stub Acme thread and the smaller thread is a 4" OD 4-pitch thread.  Both threads are in timed with each other.  And yes, it goes on a down hole oil tool.  There are many two step threads used in the oilfield industry.  And yes, you can cut them.


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## atunguyd (Oct 4, 2015)

Ok for the folks in the know. We now know that such a thread does exist, but what are it's advantages? I honestly can't see any apart from making a part that will only mate to another the same. 

Sent from my GT-I9505 using Tapatalk


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## 4GSR (Oct 4, 2015)

atunguyd said:


> Ok for the folks in the know. We now know that such a thread does exist, but what are it's advantages? I honestly can't see any apart from making a part that will only mate to another the same.
> 
> Sent from my GT-I9505 using Tapatalk



As for the Hydril thread, CS, PH-4, and PH-6, they incorporate a three point gas tight metal to metal seal for tubular members used down hole.  A two step thread is also a quicker make up when assembled, too.


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## Bill Gruby (Oct 4, 2015)

To 'atunguyd" ----  The initial post asked only if it could be done. There was never any mention of using it. All the other threads only stated that yes it could or had been done. This is a case for my third quote below. It reads, "There are those that see things that are and ask - Why? There are others that see things that have not been and ask - Why not?"

"Billy G"


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## Tony Wells (Oct 4, 2015)

There are many reasons for this type thread, most of which wouldn't be of interest to the hobby machinist. Let's just say that the simplest of them involve OD/ID relationships and strength of the joint. Others involve flow rate and makeup torque. 

If you're really bored, there are some white papers on tool joints that you might enjoy.


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## British Steel (Oct 5, 2015)

Wreck™Wreck said:
			
		

> A more useful actual product and an excellent challenge would be making a multiple start thread, how is it done?



Carefully...
The method needing least tooling is to "walk the spindle", cut the first start to full depth as normal, then mark the spindle, leadscrew and idler gears (chalk or soapstone's traditional), disengage the idler so you can rotate the spindle to the next lead (e.g. 12 teeth round a 48-tooth spindle gear will give the next of a 4-start threading op), reengage the idler (with marks matching on the leadscrew gear) and cut to depth, rinse and repeat.

Otherwise, an indexing plate between chuck and spindle. etc. - more tooling cost, not actually that much faster once you're used to the procedure!


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## 4GSR (Oct 5, 2015)

Dad used to make tool holders that would hold two inserts that were used to single point both threads at the same time on the Hydril two step threads.


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## Paul in OKC (Oct 5, 2015)

You can do multi start threads using the compound. Turn it so it is at zero (parallel) to the X axis. Cut the first thread, then divide the pitch by the number of threads and advance the compound and cut the next.  Could also cut between centers, and use the dog on the jaws to do a 3 or 4 start that way.


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