Super-flexy nib - why not spring steel?

[chud]

It just occurred to me - why not use spring steel as a flex nib material? It would seem that you could get something that would flex much more than you'd ever need (well beyond where you could possibly keep ink between the tines) without being in any danger at all of permanently deforming it.

 

I'm sure people would already have done this if there weren't good reasons not to though... is it too susceptible to corrosion? Too pliable to be wieldy?

 

Just curious.

[J-san]

You know, I had pondered a similar thing myself. I wasn't thinking of spring steel, but Nickel-Titanium or NiTi (I believe the US military has some super flexible memory alloy of NiTi called Nitinol). We use super flexible alloys in endodontic files for cleaning out root canals in dentistry because some people have twisty tortuous roots. You can literally flex NiTi back onto itself and it will spring back to being straight again without any damage. Amazing stuff.

[BillTheEditor]

It just occurred to me - why not use spring steel as a flex nib material? It would seem that you could get something that would flex much more than you'd ever need (well beyond where you could possibly keep ink between the tines) without being in any danger at all of permanently deforming it.

 

I'm sure people would already have done this if there weren't good reasons not to though... is it too susceptible to corrosion? Too pliable to be wieldy?

 

Just curious.

Steel nibs do have a certain amount of yield strength ("springiness"), which is what enables them to return to their shape when pressure is taken off of them. However, the higher the yield strength, the harder it is to work with the steel. In addition, the higher the yield strength, the more pressure it takes to deform the steel. As a result, super-springy steel would be difficult, if not impossible, to form into nibs, and even if this were possible, the amount of pressure you would have to apply to the nib in order to spread the times would be so great that it would result in the paper being pierced or torn.

 

In addition, there is simply no need to have a nib that will open so wide that the ink won't flow.

[trencherman]

I remember Antonioz posting about requirements of flex nib. I think he still includes the link in his signature.

[Possum Hill]

It just occurred to me - why not use spring steel as a flex nib material? It would seem that you could get something that would flex much more than you'd ever need (well beyond where you could possibly keep ink between the tines) without being in any danger at all of permanently deforming it.

 

I'm sure people would already have done this if there weren't good reasons not to though... is it too susceptible to corrosion? Too pliable to be wieldy?

 

Just curious.

Steel nibs do have a certain amount of yield strength ("springiness"), which is what enables them to return to their shape when pressure is taken off of them. However, the higher the yield strength, the harder it is to work with the steel. In addition, the higher the yield strength, the more pressure it takes to deform the steel. As a result, super-springy steel would be difficult, if not impossible, to form into nibs, and even if this were possible, the amount of pressure you would have to apply to the nib in order to spread the times would be so great that it would result in the paper being pierced or torn.

 

In addition, there is simply no need to have a nib that will open so wide that the ink won't flow.

Higher yield strength doesn't change the elastic properties of steel, it just lets you deform it farther before the deformation becomes permanent. So, a nib made out of higher strength steel should feel and act just the same as one made of lower strength steel, except you'd get the "oops - went too far" a little later.

 

A coil spring made out of coat hanger wire would have the same spring rate as a spring made of the same diameter wire of the quality and strength used for engine valve springs. It seems a little counter-intuitive.

[bgray]

I have added flex to standard steel nibs.

 

It's not easy. By grinding very carefully, it can be done.

 

But bottom line, steel is tough, and not bendy. Gold is.

 

It's a lot easier to add flex to a gold nib than a steel one...it's just the nature of the metal.

[Lloyd]

But bottom line, steel is tough, and not bendy. Gold is.

 

It's a lot easier to add flex to a gold nib than a steel one...it's just the nature of the metal.

Then, why are the very flexible dip nibs made of steel?

[KCat]

But bottom line, steel is tough, and not bendy. Gold is.

 

It's a lot easier to add flex to a gold nib than a steel one...it's just the nature of the metal.

Then, why are the very flexible dip nibs made of steel?

 

one distinction made here is "adding" flex v. building it into the nib. Different processes though Antonios or the like would have to explain it 'cause I know nuttin' about metalurgy. I don't even know if I spelled metalurgy right.

[NeoTiger]

The important point to note is that there are many many types of steels out there, which will all have different yield stresses and elastic moduli. It is definitely possible to design a steel with the springy characteristics desired for a full flex nib, although there would be other considerations such as corrosion resistance and durability.

 

Why it hasn't been done, is probably due to cost versus projected sales. Ie, to research, develop, and manufacture such nibs would cost more than the potential interest from customers.

[antoniosz]

Bottom line is that you can make a flex nib out of almost everything.

Steel, titanium, gold, heck you can make a nice flex nib from a turkey feather

 

This is a slightly modified version of an old post on Pentrace:

 

=======================================================

The discussion on best materials for flex nibs is often clouded by a number of misconceptions or unclear use of terms. For example, the stiffness of a nib is confused with its strength. For a flex nib we want:

 

1. Low stiffness, so that a small force can produce large reversible deflections of the tines.

2. High strength, so that after large deflections the tines return to their original shape (i.e. do not deform permanently.

 

The stiffness or the strength of a nib can be adjusted by changing its geometry, e.g., by changing the thickness of the nib. For a fixed geometry, however, the performance of a nib depends on the material. For good flex nib we need a material with:

 

1. Low elastic modulus, to get low stiffness which allows for large tin opening at low force

2. High yield strength and fracture strength: which allows for large openings of the tines without permanent deformation or cracking at the tip of the breather hole.

3. High fatigue resistance: to avoid opening of cracks at the breather hole due to repeated flexing of the pen.

 

Additional criteria that apply to all nibs (flex or not) are:

 

4. Weldability of tip alloy (this essentially excludes plastics, composites and aluminum)

5. Corrosion resistance to inks (this excludes a number of otherwise good materials)

6. Ease of manufacturing.

 

There are steel alloys with excellent strength and fatigue performance but the modulus of steel is 2-3 times that of gold alloys (~200GPa versus 60-100GPa). Therefore any advantage offered by steel due to high strength/fatigue performance is lost due to the high modulus (stiffness) of steel. The strength and fatigue performance of some gold alloys is quite remarkable. The low stiffness of gold is its biggest advantage. In simple words, if you had two nibs of identical dimensions, the gold one would give you opening of the tines at a force which is half or a third of the force needed to flex the steel nib to the same tine opening. As a result, the stresses that may cause fatigue will also be 2-3 lower in the gold than in the steel nib.

 

It is possible to compensate the high modulus of steel by decreasing the thickness of the nib/tines (or other geometric characteristics such as the length of the tines, the curvature of the nib, the width of the shoulders etc). A thinner steel nib can match the opening of a thicker gold nib. Steel nibs with some flex exist (e.g., 9128, 9048 Esterbrooks). In general processing gold sheet is easier than processing steel sheet. Similarly for titanium nibs - in fact the properties of titanium is even better than gold (about the same modulus and high strength/fatigue). The ease of processing is favoring gold.

The advantage of gold is even stronger if you consider the corrosion resistance which excludes some other interesting materials as memory alloys. Stainless is more sensitive than gold to acids and titanium is slightly worse than gold to bases and acids. I would rank the material selection criteria for flex nibs in terms of importance (high first) in the following way:

 

1. Weldability of tip alloy

2. Corrosion resistance to inks

3. Low Modulus

4. Ease of manufacturing

5. Fatigue resistance

6. Strength

 

Therefore gold is better than steel for flex nibs because of the low modulus (stiffness), reasonable strength/fatigue, excellent corrosion resistance and good formability.

 

There are two other facts that also lead to confusion in the discussions on the best material for flex nibs:

 

1. A single material can have a range of properties depending on processing (rolling + heat treatment). In simple words we can change the properties of the metal by rolling the sheet before stamping the nibs or by heating the nibs to a high temperature than induces changes in the internal structure of the alloy.

 

2. Generic materials designations are not enough to specify the material. For example, when we say 14K this includes a very large range of materials. The karat designation only specifies the gold contain. The other elements in the alloy (e.g., silver, copper etc.) can affect the properties and may result in large variation of properties.

 

We say that in general 14K is better that 18K for flex nibs because we can make 14K gold alloys that have lower elastic modulus and higher strength than the 18K alloys. This is shown in the table below that compares some of the common nib materials.

 

 

 

TECHNICAL DETAILS

 

 

MODULUS (GPa) STRENGTH (MPa) FATIGUE LIMIT (MPa) CORROSION TO WATER/ACIDS/BASES FORMABILITY

 

Gold 14K 80-90 200-500* 150-450* Very good/Very Good/Very Good Good

Gold 18K 90-100 150-400* 120-350* Very good/Very Good/Very Good Good

Stainless 302SS 200 750-900 440-750* Very good/Good/Very Good Difficult

Ti-6Al-4V 110 450-750 610-650* Very good/Good/Good Difficult

 

*The wide range of properties indicates variation in composition and processing.

 

Remember we want

 

* low elastic modulus

* high strength/fatigue limit

* good corrosion

* good formability

 

It is interesting to note in the table above that it is possible to get a 14K alloy which is totally inappropriate for flex nibs if its properties (strength and fatigue resistance) correspond to the low end of the range.

 

There is a lot of room to optimize the composition and the processing of gold alloys for flex but the cost of R&D with gold and the small market size for flex nibs are not favorable for such a pursue. I hope to get back to you with a detailed report on the geometry of flex nibs.

We do, however, have to admit that this discussion is academic. Of course in my book there is nothing wrong with academic discussion!..

The answer to the question posted is simple. Chud asked: "why not use spring steel as a flex nib material?" The answer is but they do

Go to any art supply store and you will find that Speedball Art Company produces still the flexible Hunt nibs which are made out of ... steel.

Their price? Few cents, maybe a dollar or two. If they bent or rust, no problem, we get another one.

With fountain pen things are different. Clearly perceptions are much more important than performance because they allow a higher markup.

The fact that most companies are switching to 18K gold or more is a proof

Also modern FP company do not like flex nibs because they give their customer service nightmares. Flex nibs are easy to screw up.

And while bending a few cent Hunt/Speedball nib is not an issue imagine the angry customers who will never admit that they dont know how to handle a flex nib but they will complain about lack of quality

Edited September 17, 2008 by antoniosz

[psfred]

Thank you for that succinct discussion!

 

Spring steel isn't, in the long run, durable enough, I suspect, for the reasons explained above. Gold works well, although I don't know of anyone actually manufacturing fully flexible nibs, though. No market worth the time and money to make one.

 

"spring steel", if by that you mean high carbon differentially tempered steel, won't last long as a pen nib, very very easily corroded.

 

Peter

Edited September 17, 2008 by psfred

[simonrob]

The important point to note is that there are many many types of steels out there, which will all have different yield stresses and elastic moduli. It is definitely possible to design a steel with the springy characteristics desired for a full flex nib, although there would be other considerations such as corrosion resistance and durability.

 

Why it hasn't been done, is probably due to cost versus projected sales. Ie, to research, develop, and manufacture such nibs would cost more than the potential interest from customers.

 

One of the most flexible nibs I've ever encountered (it was marvelous in other ways, too - smooth, excellent flow/wetness, etc.) was in a Soennecken fountain pen from the 1940s (or perhaps earlier); I was quite envious....

 

Simon

[Possum Hill]

The important point to note is that there are many many types of steels out there, which will all have different yield stresses and elastic moduli. It is definitely possible to design a steel with the springy characteristics desired for a full flex nib, although there would be other considerations such as corrosion resistance and durability.

 

Why it hasn't been done, is probably due to cost versus projected sales. Ie, to research, develop, and manufacture such nibs would cost more than the potential interest from customers.

I don't think modulus of elasticity varies much with type of steel, perhaps from 28 x10^6 to 30 x 10^6 psi. Practically, springy-ness in a steel nib will have to depend entirely on its shape and dimensions, with maximum allowable deformation determined by the material's strength.

[NeoTiger]

Actually yeah, you're probably right about the range of elastic moduli for steel not being too large. I was thinking of a more blanket statement for all metal alloys as opposed to just steel.

[Johnny Appleseed]

In addition to the perception issues that Antonios mentioned, fountain pen nibs also have an additional corrosion issue over dip nibs - they are constantly exposed to ink and do not have the opportunity to dry out like a dip pen does. Between uses, a dip pen can be wiped, rinsed or otherwise left to dry out. With careless handling, a dip pen might retain water at the joint with the holder, but usually there is an opportunity to dry out. With fountain pen nibs, the nib is always in contact with fresh, wet ink, and so must have much better corrosion resistance than a dip nib.

 

John

[Robert]

Thanks for the thorough answer, Antoniosz.

As I venture into the world of flex, I've been wondering about the vast differences I encounter. So a related question: why does there seem to be such a pronounced difference in potential for flex between vintage flex 14K nibs and modern 14K nibs. I assume it has something to do with the methods of processing, which have changed. Perhaps the composition of the alloy as well?

Can someone provide a scientifically grounded answer?

[Garageboy]

One would think Titanium would work great, after all it is the memory metal

The problem is welding something to it