4.2 Nib Mechanics

At the beginning of a structured ingeneering approach to any product stands the design brief.  It is a list of tasks a product has to fulfil, ideally, but hardly ever, including the quantified data attached to each function.

The Design Brief for a Nib

Here we go.  You may have jumped ahead and read already the article on Design of Fountain Pen Nibs; here I quickly summarise the nib’s essential functions so that you won’t need to interrupt your reading:

1. transport of ink
2. regulate the amount of ink in accordance with the requirement 
3. start and stop of ink flow as demanded
4. vary the line width in reference with writing action

The brief continues by telling the designer how these functions are to be managed by the user.  Not all readers are avid fountain pen writers; therefore, here is an example of the steering of a car:

• The vehicle is to be steered by operating a suitable implement inside the cabin such as turning a wheel.  (There are different suitable steering methods but user expectation biased on tradition is a powerful criterion for design decision-making.)
• There must be noticeable proportionality between the operation of this implement (angular rotation of the wheel) and the deviation from the original line of travel. 
• The user must receive sensory feedback from the amount of friction between the wheels of the vehicle and the road surface. (This is a historical criterion. Power steering has obliterated this useful feedback, replacing it with comfort for the unskilled driver. A bit like hard nibs for unskilled fountain pen writers.)

Aren’t we glad, we don’t have to design a car?  Returning to fountain pens: The four topics in the list of nib functions are to be controlled by three actions:

1. placing the tip of the nib on paper and lifting it
2. moving the nib across the paper at a varying speed
3. spreading the tines with varying writing pressure

Imagine, you have never seen a fountain pen or a nib.  Then try to visualise a device, which is able to satisfy this design brief.  No, it is not done with a microprocessor, not even with a miniature tap and a micrometre screw.  Mind you, while researching this topic, I found a fountain pen in which a valve is operated by removing and replacing the cap.

Why does placing the tip of the nib on paper start the ink flow?

The capillary forces around the nib and the slit are high enough to hold the weight of the hydrostatic column of ink, which is determined by the height from the level in the reservoir to the tip of the nib.  You can hold the fountain pen in whichever way you want, no ink would (should) come off the nib, unless, it meets the paper.

Photo 1 – A piece of magnified paper (free from Internet)

The fibres of the paper have not only much narrower capillaries and therefore a higher capillarity, causing more attraction; the fibres also have surface characteristics with a higher hygroscopic effect than the nib material. These combined forces overcome the capillarity in the slit and the ink flows on the paper.

Photo 1 shows a magnified piece of paper.  The amount of capillary action between the fibres determines the paper’s suction which is promoted by the paper’s hydrophilic characteristic which is defined by the composition of the paper (fibre, coating, additives and binder).

Photo 2 — Blotting paper sucking up ink

Saturated paper is less hygroscopic, hence, demands less ink but still adjusts to the writing speed or the width of the tines. It’s fantastic when the contributing characteristics work in harmony, generally unconscious to the writer. It makes things easier. Remember this, next time when you write.

A refresher on what we know already: as shown in photo 2, blotting paper (left image in photo 3) can suck up ink better than other types of paper.

Photo 3 — Pilot ink on various papers

Photo 3 shows in two different magnifications lines drawn with Pilot ink on different kinds of paper.  Blotting paper we all know, Rhodia is a writing and calligraphy paper, Maruman is a Japanese paper manufacturer; both pride themselves for producing top-class fountain pen writing paper. 

The amount of capillary action between the fibres determines the paper’s suction which is promoted by the paper’s hydrophilic characteristic which is defined by the composition of the paper, (fibre, coating, additives and binder).

Paper, next to ink and the nib, is the third member in the thousands of years old alliance of writing. It certainly has fascinated me, however, focused on constructing fountain pens, I only touched its surface… never in much depth. Sure, I could have studied it now but there is so much to write on nib and pen, things, I have an understanding for. Having said this, if one of my readers is a paper person, I would like to invite you to publish on my site.

Why does increasing writing pressure separate the tines?

Have you ever asked yourself this question? Or have we become so accustomed to this characteristic behaviour of the nib? It may not be as obvious as it appears, initially.

Drawing 1 — A force applied to a piece of sheet metal

Have a look at drawing 1.  There is a flat strip of material (we won’t need to waste gold for this experiment) firmly held along the X-Y axis (like in a brick wall).  When a force F is applied upwards, the strip bends upwards, as expected.

Drawing 2 — The sheet metal is divided

In drawing 2, the strip has a slit, like in a nib.  Again, as expected, as long as the two upward forces F are equal on both flaps, the slit stays closed.  If the forces in drawing 2 are half of the force in drawing 1, the deflection is the same in both arrangements.  Different forces would separate the two flaps but not open the slit, the separation needed for writing.

Drawing 3 — The sheet has been bent downwards from the slit

In drawing 3, you see the same arrangement as above; however, the metal strip is slightly bent along the same line of the slit.  When you apply the forces like in the previous experiment, drawing 2, the loose flaps move apart the more you push them upwards. Relating this to the situation of a nib: when the tip of the nib is pressed against a surface, the slit widens → dimension W.

Drawing 4 — Now, shaped more like a nib

 

And in drawing 4, I modified drawing 3 to show what it would look like when the flaps are shaped like a nib.  I have not considered the bending of the tines within themselves.

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Photo 4 — Parker 180

Most nib designs are not flat; Parker 180 had a really flat nib on a slender, elegant pen, which had a very pointy and rigid nib with an untouched iridium bead at its tip.  I assume, they sacrificed writing quality for appearance. Difficult to write with, it was excellent for drawing and sketching, see photo 4. 

Since I started writing this website, I spend more time than ever with people who write with fountain pens, and I am introduced to many fountain pens, including more with flat nibs, and I really like their design. I may have mentioned it before, a good nib does not need to be rounded in profile. They are because we are used to it, it is our expectation, and we don’t like change.

Photo 5 shows my favourite, the Pilot Falcon with a Namiki nib.  Beautiful.  Originally, the nib is covered with embossing (see photo 6) which I find superfluous and a gross disturbance of the clean aesthetic design, so much so, that I photoshopped it away.

Photo 5 – Pilot Falcon with a Namiki nib

As you see, this nib has flat tines, and above all, they are not angled, either.  How can this possibly work after all that has been said before?  Superb artisans and ingeneers, who mostly are artistically talented, always find ways around standard solutions.  That’s why.  The telltale in photo 5 shows is the strong contrast of the shadow line which indicates a sharp cross-over from the rounded, traditional section of the nib to the flat part of the tines.  How do they spread?  It has to do with the line or area of bending.  I explain this in drawing 5, a modification of drawing 2.

Drawing 5 — Modification of drawing 2

Photo 6

The line of bending was first moved from X-Y to b1 and then angled to follow line b2.  The larger the enclosed angle between  b1 and b2, the more the tines spread as indicated at W.  For this to be possible the area A must be solid stiff which is achieved through the knuckle or dome just upwards from the breather hole, forming a much smaller radius than the radius of the nib’s shaft.  

The pink dots in photo 6 demonstrate how this is achieved. The large pink dots show the position of the outer fixed points where the bending lines (small dots) start.  They continue inwards to the common end being the hole.   The bend lines enclose an angle with the imaginary line b1 which corresponds with the angle between b1 and b2 in drawing 5.  In photo 6 the enclosed angle is much larger, hence, together with the flatness of the tines, the nib is very responsive to writing pressure variations. The very quality we expect from a flex-nib.

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Keeping the force/pressure at the front edge constant as well as the dimensions and the material, the experiments demonstrate, the degree of tine separation depends on several parameters:

• the angle of the longitudinal bend (along the axis) of the nib
• the angle between the lines of bending
• the length of the slit within the area where the tines are able to bend
• the profile of the tines (thickness and curvature)
• the pre-set force during the setting process, see Fountain Pen Nib Manufacturing

You can see, all dimensions are interdependent, and they are modified to develop a nib with certain characteristics.  Being aware that I have simplified the mechanics of the nib, I focused on the topic of bending or flexing, as it is called amongst fountain pen enthusiasts, in a separate article named Fountain Pen Flex Nibs.

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Let’s play for a while and find a feel for what all the above means.  We know, a nib is not a flat sheet of metal but curved (mostly).  This makes it stiffer, and the mechanics of movements of the tines become rather complicated. Instead of using more words, I would like to invite you to undertake another experiment, yourself.  There are easy to follow instructions in photo 7.

Photo 7 — Toiletpaperroll experiment

Begin with the cardboard centre of a toilet paper roll (1).  After you slit it into two halves along its length, you end up with blanks for two nibs. I marked the shape of a nib on one of them (2).

Then cut out (3) the shape of the nib without cutting the slit.  If the hole is too complicated, you don’t need it for understanding the mechanics. It hardly affects the result much, either. I marked the approximate line of bending.

Take your mammoth paper nib and hold it like in (4) with the tip placed on a flat surface. When gradually increasing the pressure you can feel how stiff, stable the construction of the nib is without the slit, as expected, nothing much happens.

Then cut the slit. When you now hold the nib like in (4) and apply some pressure, the tines will separate (5) as expected, and you will observe how the widening alters due to variation of pressure.  You can see the flexing of the tines along the line (area) of bending.  As long as you don’t overdo it, the nib will always return to its original shape.

If you watch closely, you notice that the slit opening is curved, rather than straight.  This can be prevented.  If you haven’t thrown away the other half of the toiletpaperrollcentre (Germenglish!) glue some of it onto your cardboard nib along to the slit (either top or bottom) for its entire length so that the tines will be thicker. 

Then cut out the contour and the slit.  You will notice that your nib is much, very much stiffer.  The tines will remain straight when pressure is applied and therefore provide a straight opening because the area of bending is more confined to the space around the scallop, where I marked it.

Sketch 1 — Rolled nib blank

In a good nib construction, this is achieved by leaving the metal thicker closer to the nib (some of them) when the profile is rolled, see sketch 1. More about this in chapter Nib Manufacturing.

In reality, a standard nib deflects under normal writing pressure for only a few tenths of a millimetre.  In materials physics, this is called a “deformation within the range of elasticity”.  After the load is taken off the nib, it returns to its original shape. More about this is in the chapter Fountain Pen Nib Technology.

Back to the experiment in photo 5 (image 5), where I exaggerated the pressure so you can see the contour the tines take on when abused.  

Photo 8 — Overstreched tines

In the real world, a deflection to such proportions would bend the nib beyond its elastic range.  One would end up with a permanent distortion, and the nib would be rendered useless.

Here, in photo 8, is an example of what not to do with a nib, especially not when it is a gold nib.  This gold nib will plastically deform.  If you tried this with a steel nib, you would end up with a hole in the paper.

Pressureless Writing

Sketch 2  — Front view of nib tip

Using this expression indicates that you could move the fountain pen across the paper without the need of applying any pressure to the pen, and still, it would leave a line. I won’t say anything about the quality of this line.   This function is achieved by bending the tines at the tip so that the slit looks like a turned over V, sketch 2 where I have overemphasised the angle.

Photo 9 — Shadow lines of inward bent tines

The tines are bent inwards ever so slightly; you can notice this through the shadow lines radiating out from the breather hole towards the tip marked as B in photo 9.  The lines marked A show shadow lines of the normal curvature of the tines and nib.

In the chapter on Design of Fountain Pen Nibs, I explain this more in-depth around photo 5.  This process, the inward bending, is performed during the setting of the nib, which I describe in the article Nib Manufacturing in more detail.

Sketch 3 — Nib tip on paper

Explanation? Due to this geometry (turned over V), the slit capillary is kept open (against the pressure of presetting) hence, there is more ink available at the tip. Because the slit capillary is wider, its smaller capillarity facilitates the ink crossing over to the paper. It goes without saying, there must be enough ink to leave a trace without applying pressure, sketch 3. This pressureless writing is promoted by telling the user that it is less tiring and provides more comfort to the writer. Ask yourself: “What writer would use a fountain pen if they would want to write like this? Any old ball pen would do.”

A more useful effect of the inward bent tines is that the time before the ink dries out is prolonged by a larger amount of ink available at this one part of the tip.

Once the pre-set pressure is overstepped the tines separate and deliver more ink to the tip. For sure, the width of the line is also influenced by the hygroscopy of the paper if the feed can supply the necessary ink volume.

Sketch 4 — Nib tip before setting

Sketch 4 shows a nib which is not set in the described way. Assumable, it would write normally, but when the pen is at rest the drying out occurs from both sides and therefore, faster.

Sketch 5 — Nib tip opening on top

When pressure is applied to such a nib, sketch 5, the slit widens on the top side more than on the side contacting the paper; in some designs, it actually closes.  This is highly disadvantageous because with more pressure the writer wants to draw a wider line which requires more ink and not less. This is one reason for “railroading” meaning, for a short distance, the nib draws two parallel, thin lines using up the tiny bit of ink on the tip.

More about the Slit

Photo 6 — Overstreched tines

Let me refer back to our toilet paper roll nib where we noticed that the slit did not widen straight, in a V shape but rather curved.  Very pronounced it is in the real-life photo 6, which I have shown already above for a different reason.  Exploring this situation is significant, because preferably, the capillary force, which pulls the ink towards the tip needs the slit to narrow towards the tip. 

Photo 10 — Waterdrop between tongs of tweezers

 In the old ingeneering days, we had special drawing nibs, where the width of the slit was adjustable with a knurled nut.  The ink was inserted with an eyedropper.  This particular draw nib had a marking on the nut which permitted to adjust the width to preset values.  In addition, the lower tine could be turned to the side to permit cleaning the inside of the tines without changing the spacing.

Photo 10 — Waterdrop between tongs of tweezers

If the nib was not clean inside the gap or the gap too wide the ink would not progress to the tip, photo 10.  The photo shows the tip of a pair of tweezers, however, the circumstances is the same.  You can see the concave meniscus which indicates a small contact angle, hence a low surface tension and good capillarity.  How to bring the ink to the tip?  By gradually adding more ink at the upper end with an eyedropper.

Sketch 6 — Position of tines during start and with low-pressure writing

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In the case of fountain pen nibs, we are luckier.  In sketch 6, you see the starting situation, when the tip of the nib just touched the paper:

The slit is filled with ink; since its narrowing increases the capillarity towards the tip, and the ink is pulled forward.  Then the ink crosses over to the paper because its absorption presents an even higher capillarity than the narrow slit of the nib.

The ink is absorbed by the paper.  The compression of the paper fibres by the tip increases the capillary action and spreads the ink out, just a bit beyond the width of the tip, depending on the ink supply and more.

Sketch 7 — Tines under pressure

Sketch 7 shows what happens when the slit widens extensively in a standard nib.  As the tines open they bend and the opening of the slit curves.

Technically speaking the ink should retract like in photo 9.  However, the capillary attraction of paper is generally much higher than that of any metal (nib material); therefore, the ink does not retract.  An explanation for this behaviour can be visualised by looking at the scenario from a bird’s-eye view when we see a triangle-shaped membrane with two sides being formed by the tines and the third by the paper.

Since the pull of the paper is so strong the membrane will remain as long as there is enough ink supplied by the feed and the geometry does not extend beyond certain limits or the nib is tilted.  If the ink retracts while moving the nib across the paper, you end up with two parallel lines, an effect also known as “railroading”.

I have advertised my Flex Nib section already several times.  Some of the technicalities also belong here, but it would require rewriting, and I rather write about something else or go to the beach.

The next chapter is on Fountain Pen Nib Technology where I introduce you to the principle of elasticity, deformation and work hardening.

Above all: Enjoy!

Ω

Amadeus W.
Ingeneer

26 May 2016

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