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, with quantified data attached to each function.
The Design Brief for a Nib
Here we go. You may have read already the article on How Nibs work; here I just quickly summarise the nib’s essential functions:
- transport of ink
- regulate the amount of ink
- control the start and stop of ink flow
- vary the line width
The brief continues with telling the designer how these functions are to be managed by the user. Here is an example on the steering of a car:
- The vehicle is to be steered by turning a wheel inside the cabin.
- There must be proportionality between the angular rotation and the derivation from projected line of movement.
- The user must receive a sensory feedback from the amount of friction between the wheels of the vehicle and the road surface.
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 with three actions:
- placing the tip of the nib on paper and lifting it
- moving the nib across the paper at varying speed
- spreading the tines in response to 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.
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 come off the nib, unless, it meets the paper.
The fibres of the paper have not only much narrower capillaries and therefore higher capillary forces, causing more attraction; the fibres also have surface characteristics with a higher hygroscopic effect than the nib material.
A refresher on what we know already: Blotting paper can suck up ink, photo 1.
Photo 2 shows a magnified piece of paper. Due to capillary action, the fibres’ suction, as well as their hydrophilic characteristics, is much higher than that of the nib.
Something is written with ink on paper, photo 3.
(Photos 1 -3 I found on the Internet)
Why does increasing writing pressure separate the tines?
Have you ever asked yourself this question? Or have we become so accustomed to this characteristic? It is not as obvious as it appears, initially.
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. A force is applied upwards, and the strip bends upwards, as expected.
In drawing 2, the strip has a slit, like in a nib. As long as the two upward forces are equal, the slit stays closed. Different forces would separate the two flaps, but this is not the separation needed for writing.
In drawing 3, you see the same arrangement as above; however, the strip is slightly bent along the same line of the slit. When you apply a force like in the previous experiment, the loose flaps move apart the more you push upwards. Relating this to the situation of a nib: when the arrangement is pressed against a surface, the slit widens => dimension W.
And in drawing 4, I have attempted to show drawing 3 as it would look like when the flaps are shaped like a nib.
Most nib designs are not flat; Parker had a really flat nib on a slender, elegant pen, which had a very pointy and rigid nib and an untouched iridium bead, I assume, they sacrificed writing quality for appearance. Difficult to write with but it was excellent for drawing and sketching. As I spend now more time with people who write with fountain pens, I am introduced to more flat nibbed fountain pens, and I really like their design.
Photo 4 shows my favourite, the Pilot Falcon with a Namiki nib (not sure why it is called this because PILOT is embossed on it). Beautiful.
As you see, this nib has flat tines, and they are not angled, either. The strong contrast of the shadow line indicates a sharp cross-over from the rounded to the flat part of the nib. 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.
The line of bending was first moved from X-Y to b1 and then angled to follow line b2. This also required the stiffening of area A. Through this, the tines spread as indicated at W. The pink dots in photo 4 demonstrate how this is achieved. The large pink dots show the fixed points for the bending line (dotted pink). The bend lines enclose a small angle; together with the flatness, this nib will be very responsive to writing pressure variations.
Keeping the force/pressure at the front edge constant, the experiment demonstrates, the degree of tine separation depends on several parameters:
- the angle of the longitudinal bent
- the angle between the lines of bending
- the length of the slit
- the modulus of elasticity of the material
- the profile of the tines
- the pre-set force during the setting process
You can see, all dimensions are interdependent and they can and are modified to design a nib with a certain characteristic. I am aware that I have simplified the mechanics. I focused on this topic of bending or flexing, as it is called amongst fountain pen enthusiast, in an article named Flex Nibs, which is still in the process of being edited. It will be published soon, promise!
A nib is not a flat sheet but curved (mostly). This makes it stiffer, and the 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 5.
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 it (2).
Then cut it out (3). If the hole is too complicated, you don’t need it for understanding the mechanics. It does not effect the result much, either.
When you take your mammoth paper nib and place it on the paper with no pressure nothing much happens (4).
When you apply some pressure, the tines will separate (5). You will observe how the widening increases with pressure. As long as you don’t overdo it (like with the real metal nib), it will always return to its original shape.
If you watch closely, you see that the slit does not widen in a straight line but rather in a curve. The reason for that is the consistent material thickness of our paper nib. In the chapter Nib Manufacture, I show, that the material of a real nib is thicker closer to the tip (some of them).
In reality, the amount of deflection of a nib is only a few tenths of a millimetre. In materials physics, this is called a “deformation within the range of elasticity”. After a deflection, the nib returns to its original shape. More about this in the chapter Material Technology.
In the experiment, I exaggerated the pressure so you can see the contour the tines take on. 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 6, 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.
If you haven’t thrown away the other half of the toilet paper roll centre (Germenglish!) glue it on your cardboard nib so that it will be thicker. Then cut out the contour. You will notice that your nib is much, very much stiffer.
This expression indicates that you ought to move the fountain pen across the paper without applying any pressure to the pen, and it would leave a line. This is achieved by bending the tines at the tip so that the slit looks like a turned over V, sketch 1. The following sketches are overemphasised.
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 A in photo 7.
In the chapter on How to…for Nibs I explains this more in depth around photo 5. This process is performed during the setting of the nib, which I describe in the article Nib Manufacturing in more detail.
Due to this geometry (turned over V), there is more ink available at the tip, enough to saturate the paper and leave a trace without applying pressure, sketch 2. It follows that writing is less tiring and provides more comfort to the writer.
The larger amount of ink available at this one part of the tip prolongs the time before the ink dries out.
Once the pre-set pressure is overstepped the tines separate and deliver more ink to the tip. Adding a comment: The width of the line is also influenced by the hygroscopy of the paper if the feed can supply the necessary ink volume.
Sketch 3 shows the disadvantage when a nib is not set in the described way. When the pen is at rest with the slit being parallel, the drying out occurs from both sides and therefore, faster.
When pressure is applied to such a nib, the slit widens on the top side more than on the side contacting the paper; in some designs, it actually closes, sketch 4. This is highly disadvantageous because with more pressure more ink needed and not less.
More about the Slit
When you look at the slit in our paper roll nib, you will notice that the slit does not widen linear, in a V shape but rather curved. Very pronounced it is in this photo 6, which I have shown already above for a different reason.
This is significant, because the capillary force, which pulls the ink towards the tip needs the slit to narrow towards the tip. In the old ingeneering days, we had special drawing nibs, where the width of the slit was adjustable with a knurled nut.
If the nib was not clean or the gap too wide this would happen: Then ink would not progress to the tip, photo 8. The photo shows the tip of a pair of tweezers, however, the circumstances is the same.
In the case of fountain pens, we are luckier. As shown in sketch 5, you see the starting situation:
The slit is filled with ink, and the narrowing increases the capillary force towards the tip, and the ink is pulled forward. It crosses over to the paper because its absorption is even higher than the narrow capillary 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.
Sketch 6 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 5. However, the capillary attraction of paper is generally much higher than that of any metal (nib material); therefore, the ink does not retract. There is more to it, and I wrote about it in the article about Flex Nibs (not published, yet but soon!).
The ink contact can be broken, and the ink flow interrupted, if the nib is tilted or when the nib is widened extensively, like in photo 6. But such distortion would also damage the nib.
I have advertised my Flex Nib article already several times. Technically, it belongs here, but it would require rewriting of both topics, and I rather write about something else or go to the beach.
The next chapter is on Stresses and Strains