Questions You Should Know about steel rod threading machine

I have a project where the client needs to tap their own solid material to form a nut and then thread their own rods to go into these tapped nuts. The material we are using is A304 stainless steel. I am wondering how one would go about making sure these items are capable of resisting the design loads imposed by them? ie, if the thread on the rod will be long enough/strong enough/not eat into the rod to reduce the tensile capacity of the member with the same questions for the tapped material. To preserve 100% of the tension capacity, I'd think that you'd need upset threads or tapered threads similar to some rebar splicing products. The folks at Portland Bolt may be a good resource.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it. The bar is 1" dia ASTM A304. The length varies but is 10'-14' in length (it's part of a bracing system for a tower).

I'm thinking that maybe we should just increase the size of the rods by 1/4" across the board and not have to worry about it. Then again, I was a bit nervous about the project so these bracing members are only 40% stressed.... but I wouldn't be too enthused with cutting into my design FOS. SteelPE:
You really should give some more detail, maybe some sketches, to explain what you are trying to do. You say you have a 1" dia., A304 stainless steel bar, which is part of a bracing system, but it is only stressed at about .4Fy. You should have no problem putting an adequate threading on a rod with a load of .4Fy, although SS can sometimes be tough to thread. Also, there can be galling problems with SS threaded parts. Then, the question becomes, what does the rod thread into, is this pl. A304 also, or mild steel? You may have to adjust the thickness of this plate to get enough female thread. Do you need a turnbuckle in the system to make up the final connection? As mentioned above various Machine Design texts and Machinery’s Handbook should show you how to do the analysis. This will not really be covered by one of our normal bldg. codes, the design is a matter of some engineering experience and judgement.
dhengr,

This project is a 100' tall tower in a coastal area. The owner originally wanted to build it out of mild steel (or carbon steel, I don't know the correct term) and after the bids came in they decided they wanted to switch it to stainless steel. The tower has 4 legs with bracing that runs in-between the legs. The SS fabricator switched every detail we gave them on the drawing in favor of details that were easy for them to construct. They also seem more focused on the aesthetics of the tower with the structural stability playing second fiddle. Some of the questions you asked are the same questions I sent back during their first submittal It has been a fight over the past 1.5 months that I did not anticipate when I put my proposal together.

Attached you will find a partial elevation of the tower. The X rods you can see are the bracing members I am talking about. In the specific elevation shown, the rods are 1/2" diameter. Also, my stresses are not 0.4Fy my unity equation is 0.4..... or I guess you could say 0.4Fy/omega.  http://files.engineering.com/getfile.aspx?folder=9f177f2c-9d4f---a04c29f2b717&file=Partial_Tower_Elevation.pdf
Carbon steel - rusts until failure, Alloy Steel - doesn't rust, Weathering Steel - forms coating of rust for protection. Mild steel refers to steel that hasn't been worked (OK, a little working) and treated to increase it's structural properties.

Structural stability never plays second fiddle and no one in their right mind would promote that. Take this as meaning the client has full faith in the structural engineer in making sure the final structure is stable.

How are you going to adjust the length of the threaded rod so that it fits the field conditions? If you have tapered threads on both ends of the rod, then you will have no adjustment = super bad idea. You also need to account for offsetting the rods (can't tell if you have or not). Just cut standard threads into both ends and design for the reduced section - KISS.

The simplest approach, in my mind, will be to provide clevises (with just a hole and no threads) at both ends (offset the holes for geometry) provide a jamb nut on the outside of the clevis and double nut the inside so the rods are tight. If they really want pretty, then they should get those gussets normal to the angle of the rods and line the rods up with the panel points, but alas, I am not an architect.

You might look at rigging used for sail boats. Also I would check the connections for fatigue. Once had a 60 foot tower with a detail similar to yours but not as sophisticated where one of the tie rods failed and stabbed the deck of a bridge that the tower was cantilevered off the floor beam outriggers. Your tower is surely going to be resisting a lot of windage with the canvas infills. I imagine there will be a lot of shaking from the turbulence. Might be noisy as well. What if I had them fabricate a connection and had them send it out for testing. I assume that would be acceptable? This fabricator is just plain useless when it comes to answering my questions in regards to this item (which is quite important).

My other option is to look at similar items (carbon bolts) and mimic what I see in terms of material sizes and thread lengths (and just be conservative) as stated above. Hi SteelPE

I think stainless threads on stainless threads is not a good idea, mainly because of galling as others have mentioned.

Regarding analysing the joint you need to check that your external force does not cause the screw threads to strip internally before the bolt physically breaks in tension, this condition shows you have enough thread engagement. If you have a fatigue situation then clearly the bolt needs to be checked for failure in fatigue as well as the joint.

One point about thread engagement, following the formula for thread engagement either on the Roy mech site and/or machinery's handbook will lead you to believe that the shear stress can be reduced indefinitely by increasing thread engagement which is not so, there is no benefit increasing thread engagement beyond a length of 1 to 2 times bolt diameter.


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

A list of the 13 most important types of threads you should know

Today we would like to provide you with an overview of the most important types of threads that you should know. But first we would like to give you a short introduction to threads and explain important terms.

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What exactly is a thread?

A thread is, simply explained, a profiled notch that runs in a wave-like and continuous manner around a cylindrical bolt.

As already described in our articles from the section History of Threads, threads are thousands of years old. Threads accompany us in our everyday life. Not always visible. We are not really aware of the benefits they have for us. But they are used everywhere. For example, in our motor vehicles, right up to when we put on our reading glasses. The connectors make our lives easier and literally hold everything together.

As versatile as they are in use, there are very special requirements and loads on the threaded parts. A fundamental distinction is made between:

1. Mounting thread
2. Transmission thread
3. Transport thread

Fastening thread is probably the type of thread that most of you think of first. They are tight threads, as we find in nuts and bolts.

Movement threads, on the other hand, are thread types that convert rotary motion into linear motion.

Nowadays, we find transport threads in agricultural machines and in water conveyance in the form of screws.

Right-hand thread (RH) and left-hand thread (LH)

Usually clockwise threads (right-hand threads) are threads that can be fastened by turning them clockwise. Less common are left-handed threads (left-handed threads), which can be screwed together counterclockwise. This connection is always used if it is to be avoided that the thread could loosen due to the self-movement. As for example with the left-hand bicycle pedal. The left-hand thread can be recognized by the abbreviation LH, while the right-hand thread has the abbreviation RH.

Pipe thread

Pipe threads are threads that are used in water and gas installations. The ends of the pipes can have internal and external threads. On the one hand, a distinction is made between tapered and conical pipe threads, which are self-sealing. On the other hand, there are cylindrical pipe threads which are not self-sealing and require sealing agents such as hemp. The most important pipe threads are dealt with in more detail in our list

Why the different thread types?

The different types of threads result from historical developments and cultural preferences. In addition, there are different thread standards due to special requirements on the load-bearing capacity. The thread form is a decisive factor here.

What are the 13 most important thread types?

Here we want to give you an overview of the 13 most important thread types. The thread types are sorted according to country-specific types. Our list is by no means to be understood chronologically according to importance. Among the most important threads are:

ISO thread types

For the metric ISO thread types, the dimensions are always given in millimetres. The pitch is calculated by measuring the distance between the first and second tooth.

1 .  ISO metric thread (M)

The ISO metric thread is a worldwide standardized thread and is probably the best known and most used in Europe. It is also known as a standard thread. Pitch and diameter are measured in millimetres. The code letter for the metric thread is M. The flank angle is 60 degrees. Furthermore, this type of thread is precisely defined in DIN 13 and DIN 14. DIN is the German Institute for Standardization.

2 .  ISO metric fine thread (MF)

The ISO Metric Fine Thread is similar to the bigger brother of the ISO Metric Thread. Here the code letters are MF and the flank angle is 60 degrees. However, both differ in the pitch.  The metric fine thread is used for example for watches.

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3 .  Steel conduit thread (Pg)

The steel armoured pipe thread or armoured thread (Pg) is a historical thread that was used in electrical engineering and is defined in DIN . It is increasingly being replaced by metric threads (DIN EN ). The flank angle of the armoured pipe thread is 80 degrees.

4 .  Trapezoidal thread (Tr)

The trapezoidal thread owes its name to the profile of the threads, which have the shape of a symmetrical trapezoid. The trapezoidal thread bears the identification letters Tr and has a flank angle of 30 degrees. There are three different standards. DIN 103 defines the ISO metric trapezoidal thread. In DIN 380 the flatter trapezoidal thread. And finally in DIN the rounded trapezoidal thread. Further information can be found in this article: Trapezoidal thread spindle.Beitrag: Trapezgewindespindel.

American thread types

For the American thread types, the dimensions are always given in inches (1 inch = 25.4 mm). The flank angle is always 60 degrees. The main difference between the various American unified threads is the pitch of the threads. These are also indicated in threads per inch. To determine the pitch, the number of threads is counted in one inch.

5 .  Unified National Coarse Thread (UNC)

The Unified screw thread is a standard thread, which is mainly used in the USA and is the American equivalent of the Metric ISO thread. Only the unit of measurement inch instead of centimeter is used. The flank angle is – as with the ISO thread – 60 degrees.

6 .  Unified National Fine Thread (UNF)

The same applies to the Unified National Fine thread type, which is the American fine thread to the ISO metric fine thread. As with the UNC, the flank angle is 60 degrees.

7 .  Unified National Special Thread (UNS)

The thread type UNS is a special thread, which differs from the other Unified-threads in the pitch. Here, too, the flank angle is 60 degrees. This thread type is used for microphone stands, among other things.

8 .  National Taper Pipe (NPT)

The thread type National Taper Pipe (NPT) is a tapered or conical pipe thread which is used for pipe fittings. The flank angle here is 60 degrees. Unlike NPTF, it is only self-sealing at low pressure.

9 .  National Taper Pipe Dryseal (NPTF)

The NPTF is a tapered or conical pipe thread, which is self-sealing and has a flank angle of 60 degrees. The main difference to the NPT thread is that the internal and external threads overlap and can therefore be self-sealing without the use of sealant.

British Whitworth threads

The Whitworth thread is named after its inventor Sir Josep Whitworth. The British engineer introduced the world’s first thread standardization in and thus influenced the mass production of threads. The Whitworth thread is specified in inches and has a flank angle of 55 degrees. This type of thread is mainly used in the British Kingdom.

10 .  British Standard Whitworth Coarse (BSW/ WW)

The British Standard Whitworth is on the one hand a standard thread and on the other hand a screw thread. It is often abbreviated with the abbreviation W or WW. In terms of meaning and use, it is equivalent to the ISO metric thread. It is specified in inches and has a flank angle of 55 degrees.

11 .  British Standard Fine (BSF)

The British Standard Fine is the English variant of the fine thread. The meaning and use corresponds to that of metric fine thread. The thread is also specified in inches for the BSF and has a 55 degree flank angle.

12 .  British Standard Pipe (BSP/ G)

The British Standard Pipe is a Whitworth pipe thread. It is a cylindrical thread and therefore not self-sealing. It is abbreviated with the abbreviation G. A small special feature is that the inch specification does not correspond to the inch diameter. For example: BSP 1″ = approx. 33.25 mm.

13 .  British Standard Pipe Taper (BSPT/ R)

Whereas the British Standard Pipe Taper has a tapered external thread and a cylindrical internal thread. It is often abbreviated as R (tapered male thread) and Rp (cylindrical female thread). It is self-sealing in itself.

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