Fountain Pen Design

Function, Development, Construction and Fabrication

4.15 Modifications

17. Real-Life Testing

17. A – Increasing the Breather Hole

As a way of applying what we have learned so far, let us look at some of the experiments and results posted at the forum Experiments With Flex on the Fountain Pen Network website.  In the descriptions, I use the usernames in the forum.

Photo 8Oval Breather Hole

In one test Bobje widened the breather hole of an FPR flex steel nib extra fin no. 6 to a 3.5mm oval, as shown in photo 8.  He stated: “After adding the hole much less pressure is required to make the tines separate easily. During writing, the line width varies from about 0.6 mm to 1.2 mm.  Another nib with the same modification gave a line width variation from about 0.4 mm to 1.1mm — about 3X.”

In the photo, I drew two combinations of dimensional arrangements. The l1b1 scheme refers to the variation with the oval hole.  The original shape (without a hole I assume) is marked as l2b2.  One would expect that after adding the oval hole, the nib would flex more easily.  Calculating an estimation of the tine separation with our well-known formula provided very similar results.

Drawing 11 — Increasing of Breather Hole

In drawing 11 the original profile is shown in black colour.  The section taken away by the hole is blue O, and the segment lengths responsible for resisting bending are both shown in pink.  Adding the hole shortens the original segment length from b2 to b1.  As a consequence, the initial bending axis distance y2 shortens to y1.

From drawing 7 in the previous chapter More Technical, we discovered the significant impact the cambering of the flat strip had on its resistance to flexing, the profile turned out to be much stiffer.  The opposite happened here: the shortening of the distance y1 and the profile segment b1 reduces the bending resistance significantly thus cause the tines to be more flexible.  Assuming that b1 is half of b2 the tines would open four times wider.

Photo 9 — Intricate Hole – Joseph Gillott#1

Whether the hole merely is oval or as intricate as in photo 9, is irrelevant for determining the efficacious breadth.  The pink dotted line shows the location of the very short breadth.  I believe the sanding marks are the residue from removing the burs from stamping the shape.  The marks would influence the surface reaction between ink and metal; however, the marks perpendicular to the slit do not promote the ink flow but rather hold it in place or even draw it away from the slit.

Used as a dip-nib an ornamented shape would help to hold more ink to prolong writing between dipping.  Regrettably, the design in Photo 9, would hold the ink in the upper part of the ornament because its shape widens before entering into the slit which severely interrupts the capillary draft.

17. B – Wing Scallops

Next, let’s look at another modification which is referred to as wing scallopsBobje started this topic, with Bordeaux146 being another major contributor to technical aspects.  The nib in question is: “FPR no.6 flex extra-fine” nib as shown in photo 10.

Photo 10 FPR no.6 flex nib

My comments on the nib variation shown in photo 10: “The reason for the softening of the tines is the same as above, which was the shortening of the profile segment b (pink dotted line).    The difference is that here the scallops reduce the width of the effective section of the profile from the outer edge rather than the addition of the oval hole which reduces the width from the inside. Since the bending of the nib is radial in opposite to oval or elliptical, the layout is different only in principle but this would show only marginally when applied.  The effective length l is determined by the location of the scallop, the extension of the slit beyond that point is unnecessary.”

Further down I wrote a chapter titled Hole versus Scallops where I look into the difference between the two modifications in more detail.

Photo 11FPR no.6 extra fine nib

Photo 11 shows the alteration to the standard FPR no.6 extra-fine nib.  In this case, the modification causes a second breadth b2 whereby the two breadths b1 and b2 compete with each other. Originally the combination b1l1 determines the flexibility.  I tend to say that the b2l2 combination hardly contributes toward the flexibility if at all.

In agreement with my observation, here is Bobje’s comment: “However, in a standard FPR no.6 extra-fine nib (photo 11), it improves performance and creates a cushioned writing experience, but doesn’t actually generate a semi-flex nib. There might be a tiny bit more line variation, and the pen is more enjoyable to write with. But it’s nothing like a modified flex nib.”

17. C – Long Slit and Breather Hole

Photo 12 shows another test undertaken by Bobje.  The test object was an FPR no.6 flex nib to which a hole of 5/64″ – 2mm diameter was added at the end of the slit. Bobje’s comment: “The lines varied 3X, from approximately 0.5 mm to 1.6 mm, and the nib rarely railroads.”

Photo 12Long Slit and Breather Hole

He also reported that initially the nibs flooded, which I assume was caused by the combination with a feed whose air canal ran along the top (underneath the nib).  The problem subsided after matching the nib with a feed where the air canal is located on the underside of the feed.

The location of the effective breadth is approximately somewhere above the middle of the slit’s length, at b1 (7mm), which would mean that adding the hole would not change anything. Even if the effective width would be a b2 (15mm) adding a hole of 2mm would reduce b2 from originally 16mm by only 1mm.  We know that a change in width impacts only linearly on tine spreading.  In this case, it would increase by just 6%, a hardly noticeable amount.

Photo 13Flex Nib with Breather Hole

Hypothetically, moving b1 to b2 would lengthen the effective length hence would have no effect because the softer profile at b1 would respond before.

Furthermore, (this is about photo 13) one could consider b3 as the effective breadth; however, the radius of curvature at this location is much smaller, and therefore, the profile is much stiffer than at the b1 position.  This is another reason for suggesting b1 as the effective breadth.

17. D – Radius of Nib Curvature

And since the topic is curvature, let me comment on a stack of questions by Bobje, starting with: “Where should a hole be drilled, how large, and in what shape?”

The most efficient position of the hole is near the end of the slit for reasons discussed in this chapter.  This gives rise to the question: “How long should the slit be?”  Sensibly, it can reach up to the point where the nib protrudes from the section.  However, such a long slit would have no impact on the flexibility of the tines because of the stiffness of the nib in that area.  (Referring to drawing 12, now.)

Drawing 12Curvature and Stiffness

When the slit is combined with a profile of high curvature, like when the nib hugs the feed (see c), then the flexibility is reduced so far and the slit may not even be there.  To be there or not makes a difference, but in either case, it is of no use for a nib, because the stiffness is beyond any usefulness for a nib. The reason for this is the increase of y1 to y2.  A useful length of the slit is determined by the curvature, or in another way: A shallow curvature is necessary to benefit from the advantage of a long slit.  That’s why most nibs are designed with a shallow radius b at the front and sensibly, the slit has not much reason to extend beyond this region.

Drawing 11 Increasing of Breather Hole

Considering the size of the hole, I repeat drawing 11 from further up, which demonstrates that enlarging the hole diameter increases flexibility.  The required stability of the nib in this portion, as well as the tines, sets the limit of the shortening of length b1. which equals the increase of the dimension of the opening O.

Photo 9 Intricate Hole

Finally, the shape of the opening O can be whatever you like, except, it should not include any sharp corners which would cause high-stress points and subsequent fatigue cracking.  Also, consider the capillary forces; otherwise, the ink does not empty from the opening because of ink sticking in corners.  I have repeated photo 9 as a reminder.  Like when constructing the ink path in a feed, also here applies the rule:

The ink always flows towards and keeps on flowing areas of increasing capillarity. 

This is important when the opening has the function of a breather hole because if it does not open, the pen can’t breathe.

17. E – Thinning Nib

“How might a layman thin the material of a nib reliably?”

This is a difficult enterprise even during manufacturing, requiring much skill, big machines and precision.  For example, the precision required to control flexibility predictively is below a tenth of a millimetre, demanding a high amount of accuracy.  Every new batch of material requires new testing and tuning of the machining process.  Remember, the thickness of the material impacts the area moment of inertia (responsible for the resistance to bending) by the power of three.  During nib manufacturing, the accurate thickness is achieved mostly through roll-forming with the added benefit of work hardening.

Frankly, if you want to experiment, enjoy yourself.  Thinning the material reliably – as a layman, I would not go where even angels tread softly.

17. F – Shape and Position of Scallops

“What is the ideal shape and position of the wing scallops?”

Photo 14 Intricate Scallops

The form of the scallops is an artistic, visual matter, technically, they can have any shape.  The sample in photo 14 shows an intricate design; however, it is merely the length of solid material, the distance along the dotted line which causes the effective breadth when determining the bending of the tines.  The rest is there to impress.

Photo 15Scallop near Grip Section

Photo 15 shows the scallops at the very end.  They are too far back to have any function.  My point is, the scallops as well as the previously mentioned openings, only work within the vicinity of the slit, as close as possible towards its end as well as within the area of the shallow curvature.

Photo 16Long Open Scallops

Since I like simplicity, the nib shown in photo 16 is my preferred style.  It is a modification of an Ahab flex nib performed Bordeaux146, Fountain Pen Network. This kind of transition would result in a smooth opening of the tines.

17. G – Matting Nibs and Feeds

“What are more reliable methods of matting nib and feed?”

The main production method for matting the nib is tumbling.  It is performed after the forming of the nib but before tipping (welding on the bead) and slitting.  During the process, the burrs are removed and the edges are slightly rounded.  As a consequence, the initial sheen of the surface turns matte, somewhat.  A tumbler is like a cement mixer, even with ribs on the inside, but generally, it has a tight lid.  Together with the components, particular types of aggregate are added, sometimes also with some fluid such as water, soapy water and all kinds of oils.

The aggregate comes in various sizes and shapes as well as the oddest kinds of material, pebbles, hardwood, apricot kernels only to mention a few and any blend.  A further parameter is the speed of rotation and the time.  There are no rules, but once you have worked out the cocktail of additives and the actual component it must be kept absolutely constant.

Every component, even though it is made of the same material as another, will have to undergo a trial and error process.  However, once it’s done, it is very reliable and cost-efficient.  A small tumbler is quite easy to make a tumbler for anyone skilled enough to experiment with fountain pens.

Another method would be sandblasting.  It is not difficult to build a box but it requires much skill to achieve a constant result.  It is also possible to use chemicals, however, as you know already, unless it is ABS plastic, I am not good with chemistry, you will need to experiment to find out.

Matte plastic components are the result of an unpolished cavity in the injection mould.  Complicated shapes are electro eroded whereby the surface roughness of the mould, which determines the “roughness” of the component, is regulated by the current used during eroding.   In addition, the matte surface of the mould cavity rubs off along the surfaces of the component’s ejection, which leads to undesirable abrasion marks.

However, one needs to consider that such mattness wears off through handling a plastic component, which may be desired because the component develops the worn look.  In addition, the matte surface of the mould cavity rubs off along the surfaces of a component’s ejection, which leads to undesirable abrasion marks on the component.  If this component forms part of the outer contour of a product, it is time to rework the mould cavity.

17. H – Underside of the Nib

“Should the underside of a thinned nib be polished, or would a certain direction in the scratches improve ink flow?”

In my experience of nib production, all nibs came with a smooth surface finish as it was caused by roll-forming and subsequent tumbling.  No extra effort was made to alter the surface finish on either, the inside or the outside, the latter except for decorative reasons.  Often one sees grain lines on nibs which in my opinion are caused by de-burring after slitting (demonstrating a lack of skill) or stamping of holes and ornaments.

Ink acceptance of metal surfaces can be promoted by the cleanliness of the surface rather than by the scratches.  They cause some changes in surface reaction, but they lose effectiveness for promoting ink flow after progression of ink of 1‑2mm up the scratch; they rather hold the ink than promote its flow, where it dries and leaves unsightly marks.

I have written about scratches and roughing under the topic: Feeds made of Plastic.  In the case of plastics, a (microscopically) rough surface decreases the contact angle and makes the surface more accepting of water (ink) significantly because without this “roughness” plastics repel water (ink).

18. Hole versus Scallops

You may have already wondered about this: “If both modifications soften the flex, what is the difference?”  Rather than debating, ingeneers like to reply: “A drawing says more than a thousand words.”

Drawing 16— Holes versus Scallops

The two modifications are shown in drawing 16 where half of a nib is displayed; that’s why F/2 … while F would be the total force applied to separate the tines. The blue and the pink segments indicate where some material has been taken away from the breadth of the tine.  Blue is the opening and red is the scallop.  The blue markings relate to the opening near the slit, the pink to material being taken away from the outer edge such as ornaments or scallops.  The difference shown in the drawing lays in the variation of the force applied to the tine.  The forces Fs and Fo act onto the remaining, solid section of the nib.

The effective forces are

Fs = F/2×cosαs and Fo = F/2×cosαo .

The value of cos α reduces with the increase of angle α – meaning cosαs is larger than cosαo – the force F/2 required to spread the tines by the same amount increases with an increase of angle α, alone.  Moreover, the moment of inertia adds to the same result in the same manner, see Fountain Pen Flex Nibs -Technology drawing 5.  Hence, a scallop is more effective than an opening.

Oh, and there is always a, however: as long as this happens in a position where the curvature of the tine profile is flat or flattish, there is no problem.  Going further back towards a smaller radius the nib with the opening would show some sidewards instability; something we want to avoid.

19. Flat Tines

Further up, near the start of the paper — not this page but on the bottom of the page Flex Nibs Technology –, I commented on a particular nib, which was shown there in photo 12 and promised to return to it.  It’s late (11:30pm as I am writing), but here the photo is again, and I will be commenting on it.  Earlier on, I also noted that hardly any nibs/tines are flat. By now we have learned that: “The flatter the tines, the easier they bend.”

Photo 4 — Flat Tines

Generally, the two tines are tilted towards each other and they are curved in profile, see drawing 16.  How can tines separate if they are not?

Photo 18 — Flat Tines Bending

In photo 18 (same pen as in photo 4) the abrupt and significant change of shape from the rounded to the flat part of the nib is highlighted by a stark contrasting shadow line.  This kink in the material makes this edge structurally stable, like a cantilever.  We had talked about kinks before (somewhere).

This means that the corners, marked with large pink dots, are fixed in their position and thus define one end of the bending axes. The other end is given by the location of the hole at the end of the slit.  And since the bending axes are angled towards each other, the tines separate when bent upwards.  Now you know why/how tines can separate on a flat nib portion.

I also said before that there are other good things about the design of this fountain pen section.  They have nothing to do with flex‑nibs, but I like to mention them because for me they are signs of good fountain pen design.

One is the metal ring, which could include several functions.  Firstly, it prevents the section from splitting.  It also appears to me that the narrow edge is used as the counterpart for the inner cap to produce a reliable and durable seal as well as provide an exact position for the cap to sit.  This fountain pen, a Pilot Falcon, uses a thread to hold the cap.  In the case of a clip‑on cap, the metal ring could serve as a definite stop rather than relying on the elasticity of the clip mechanism, worst case: the inner cap.

Photo 19 — No Add

Why did I add photo 19? It is the same fountain pen and nib as in photos 4 and 18…  Forgive a designer but I photoshopped the embossments away!  Does this not look so much better?  The type of nib can still be recognised by the tiny number 1013, located where the nib progresses out from the section.  However, now the beautiful line of the nib is clean and uncluttered.

Besides, I don’t like advertising at all, especially not on items I have paid for.  I don’t buy things with logos and prints, and I remove even the inner labels off garments.  It interferes with my sense of aesthetics, and when writing, any label disturbs my area of vision and distracts me.  Does this nib in its purity not look so much better?  Perhaps, the reason for my reaction is that I am a designer and ingeneer whose “formative” years of ingeneering were during the sixties, a time of clean and simple design, the time of the Bauhaus design.

Photo 20 — Elegance

I like this style of nibs, and therefore, I add photo 20. It is a Namiki nib, super fine.  Its design correlates with that nib shown in photo 19 whereby its tine portion has been extended, narrowed and elongated.  This is a superb example of nib craftsmanship where functions and elegance (Form and Function) have been united brilliantly, rather than one following the other.  Flex writers sing about this nib in their highest notes. However, here again, I just could not resist Photoshop away the embossing, and a few sputters of ink that showed on the original photo.


Photo 21 — A Really Flat Nib

Lastly, let me show another sample of a fountain pen with a flat nib but this time with its tines tilted towards each other, very much like the hypothetical model for our early calculations.  It is a Parker 180, shown in photo 21.  Somewhat unusual is the almost spherical tip.

Some may say: “What has this nib to do with flex-nibs?”  Nothing really, but I like it, and it certainly makes a point about flat nibs.

Some suggested that this nib can also be used in its turned‑over position.  Then it should be possible to write lines of two different widths as well as to achieve two different stiffnesses.  During the days when I was drawing pictures, I thought it was a brilliant idea, moreover, the fountain pen was slim and very light, ideal for drawing and sketching.  I had the opportunity to use such a fountain pen, but alas, disappointing, it did not work.  To top it all, Parker Germany had not been helpful.  Later, I also realised that almost all other nibs produce a fine line when used upside down.

The metal cover on top of the nib was there for strengthening the construction; without this support, the tines would bend easily into plastic deformation too easily.  Much fatigue cracking happened at the end of the slit, and later a tiny cross slit was added to distribute the stress over a larger area and, most likely, to soften the tines.

Most excitingly, with the feed, a novel idea had been realised whereby the ink was fed to the nib through the centre of the feed.  Working in the field of fountain pens at the time, I was keen on the individual idea, but the overall performance was disappointing to me. What a waste of two advances because one of them was insufficiently thought through.

19. In Summary

Since I know the painstaking effort invested in designing a writing aggregate and seeing to it being finely tuned, I would not recommend mixing nibs and feeds.  However, I know it is done.  Here are some recommendations:

1.)  Adding a hole to a nib, which sits on a feed with the air canal on its upper side causes such a nib‑feed combination to leak.  The control of airflow into the ink reservoir is the presence or lack of ink in the top end of the slit or a hole if the pair was designed for it.  This membrane of ink is ruptured by the lack of ink caused by the increasing vacuum in the reservoir and allowing air to enter.

Drilling a hole or enlarging one at this position either makes the membrane less stable and more reluctant to form or not to establish at all.  This depends on the size of the opening and the width of the air canal.  A less stable membrane allows more ink to be released per gulp, which may not be absorbed by the feed.  In the worst case when the membrane does not form at all the ink just runs out.

I would only consider adding a hole if the feed has its air canal at the lower side, opposite the nib as well as the ink canal. It is also against my design principles to combine more than one function with one feature.  Why?  That’s another topic; I will write about it, one day.

Feeds with their air canal at the bottom do not rely on a “breather hole” since their breathing control facility lays further back near the opening of the ink reservoir.  Its shape is intricate, and one finds such designs in feeds manufactured in an injection moulding process.  Since Ebonite feeds are machined, I wonder if they ever come with the air canal at the bottom.

Photo 17Flex Nib in Action

2.)  One can often observe that flex nibs lift off the feed when writing a broader line.  It is at this moment when more ink is required.  This sounds like a contradictory request because, as Photo 17 shows, there is no ink in the slit.  One can’t write without ink, so, what’s the point of spreading the tines apart this far?

Drawing 13Ink Crossover

Unless the feed has a cross-over design (Drawing 13) that is far enough back and the nib has enough capillary force in its slit, the ink flow will be interrupted.  This is demonstrated in Photo 17.  So, how can it work?

Indubitably, the Noodler nib is capable to perform, meaning, its tines are elastic enough so that they can spread and return and ink is/can be transported in the slit.  How?  Here we go: “When the nib is at rest (no force applied), the nib sits snug on the feed.  The ink cross‑over to the slit is uninterrupted.  As the tines widen the ink meniscus between the feed and the underside of the nib draws back, upwards.  Since the air canal is on top of the feed, it opens more and more as the nib lifts off the feed along the area of ink crossover.

Therefore, if the air canal is next to the ink canal, more air can get into the reservoir, in consequence, more ink is supplied to the nib‑feed interface.  It is the amount, the weight of ink which pushes the ink into the widening slit against the reduction of capillarity.  Therefore, the nib can write a succulent line.  At the end of the line, writing pressure reduces, the nib starts hugging the feed, and the air canal closes, and the flow of ink seizes.  All good, aren’t we lucky?  Otherwise, we would need to tell Mr Noodler that the nibs cannot work.”

PS:  This only works if the ink canal runs along the top of the feed, where the nib is positioned.  I have been told, there are feeds with their ink canal running along the opposing side.  In that case, my explanation does not apply.  Are there fountain pen designs that combine a flex nib and a feed with the canal opposite the nib?

One more point: The user must be skilled in writing with a flex nib. When the tines are spread too harshly, suddenly, the ink will withdraw up the slit. In return, the end of the widening must occur gradually, otherwise, the surplus of ink hanging behind the nib will end in a puddle.

I remember as a student reading a paper on the mechanical design of insect wings, and it demonstrated that insects could not fly.  Academia has not changed.  The explanation I offer may be somewhat complicated, and if the need exists, I will add a few drawings.

Drawing 14Capillary and Hygroscopy

Back to nibs and wide slits.  You could raise one more question: “Why does the ink not retract in the slit when it widens?  According to the laws of physics, it should, shouldn’t it?”  (If you are not sure about this, read about Capillaries on this website.)

If the written line widens gradually while the tip remains in contact with the paper, the superior capillary attraction of the paper, as well as the above mentioned hydrostatic pressure of the ink column acting onto the ink in the slit, prevents the ink from retracting.  See Drawing 14.  Hydrostatic pressure in fountain pens?  The free-hanging column of ink inside the fountain pen.  Additionally, this topic is covered more extensively in the article on the principle design of the feed, called Bubbles and Bottles, here, on this website.


The above demonstrates the importance of considering writing with a flex nib as a form of art.  It needs to be learned through practising for hours, days and years and may need to be repeated when one uses a new style of nib or another fountain pen.

Drawing 15 — Radii Variation of a Nib

3.)  The difference between the nib radius and the diameter of the feed may ask for some consideration; however, I would not regard it critical as long as one observes a few aspects.  For this I show one of my favourite drawings again, drawing 15.  It is essential that the nib stays in contact with the top perimeter of the feed because that is the location of the feed capillary and the longer the length of contact, the easier the ink can transverse from the ink canal to the nib and its slit progressively.  See also above, ink crossover in drawing 13.

In drawing 15 I show the flattening of the nib as increasing radii; however, they can be parts of ellipses or any other artistic curve.  The criterion is the increasing distance d3 and d2 from the original centre, which varies the flexing characteristics of the tines and assures the contact between nib and feed.


It seems this paper has come to an end.  I hope it provided some clarity about the flexing of nibs and other few odds and ends.

Furthermore, I had expected that during writing some clarity would have occurred allowing to set suitable technical criteria providing final demarcations between standard nibs and the different characters amongst the flex‑nibs.

At least, we have worked out a test method.  The execution and collating of data I would like to leave someone else or a group, who has a considerable collection of fountain pens, sufficient technical interest and a passion for the job.  If needed, I would be available for some guidance.

You have been reading this paper (I can tell), and I can hear you say: “…and what about this, and what about that?”  Let me know your questions, I will add them to this paper and answer your questions to my best knowledge and ability.

Finally, I would like to thank the members of the forum Experiments With Flex at the website Fountain Pen Network. Without their stimulating, thought-provoking contributions, this paper would not have come into existence.  They gave me permission to use the information and display their photos.  My gratitude extends to members of forums of other sites, and I want to acknowledge the usage of the information and many photos, freely and anonymously available on the internet.


Amadeus W.

21 December 2017

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