Fountain Pen Design

Function, Development, Construction and Fabrication

051-7-1 Definitions of Flex – 1-4

1. All Nibs Flex

… more precisely: their tines flex.  Precision and accuracy are of paramount importance for an ingeneer, in particular when he talks shop.  Both dictionaries, the Oxford as well as the Cambridge agree on the meaning of “flex” which amongst other meanings is that of flexing a material: “to be capable of warping or bending and then reverting to an earlier shape.”

In view of preparing the ground for discussion, I add: “When writing with nibs, force is applied to the pen.  In consequence, the vertical component of that force moves the tines apart, the written line, the trace of ink on paper widens, and it narrows when this force is reduced.

This vertical force can vary between 60g to 120g or 0.6N to 1.2N, for regular writing and between 300g to 500g or 3N to 5N to cause the tines of a standard nib to separate by about 1mm.  The latter force (5N) is uncomfortable to maintain, but it can peak at that level when writing one’s signature, for example.

According to ergonomics, a sustainable force applied during controlled action maximises around 100g or 1N.  When this action requires sensitive adjustment (as in writing), the recommended load drops to around 50g or 0.5N.  Since we talk about forces and not weight, I use N, Newton from now on.

2. All Nibs are Preloaded

This may sound like a sidetrack, but you will find it useful later on that you had been introduced this idea at this early stage because it is often overlooked. Instead, I talk about it now, so I don’t need to interrupt the topic to which it is applied.

The preload is the force, which presses the tines against each other.  This force needs to be overcome before the tines can separate.  Why are nibs preloaded?  For non‑flex writers, it has the advantage that the line width remains constant even the writing pressure varies up to the point where the preload is overcompensated.

Graph 1 — Preload

Flex‑nibs have a much smaller preload and therefore respond more readily to variations of pressure.


In Graph 1 the preload is shown as the lines with arrowheads parallel to the Force dimension.  For more information on this go to Stresses and Strains.  The gold nib having a higher preload lifts its force range of operation in the region of the steel nib.  This needs to be considered when a fountain pen, which is offered with a steel and gold nib and it is designed for the same target group.

Photo 1 — Setting of Tines

 How are nibs preloaded?   It happens during the manufacturing process.  After the slit has been cut it is parallel.  It has some capillary characteristics, but when the tines converge, they improve significantly.

The tines move together when they are stamped along their outer edge, noted as the “free sides of the leaves” in Photo 1.  The effect of stamping is increased through an embossed pattern where material is moved.  The embossment also disguises any possible blemishes.

Photo 2 — Reflection on Tines


Better nibs are set (tines brought together), often manually.  In this process, the curvature of the tines is increased by bending them inwards.  Small pliers would grip the tines near the tipped end, and the tines would be turned inwards.  This can be seen through the reflection lines at A and B in Photo 2.


This style of setting also causes the tip to touch in an upside down V shape fashion, a precondition for pressureless writing.  In case you need a refresher on this topic, have a read at Nib Manufacturing.

3. What’s the Difference?

Since all nibs, or more specifically, their tines are flexible, what is the difference between a regular nib (some call it a nail) and a flex‑nib?  All nibs have some proportionality between the applied force and the separation of the tines.

Photo 3 — Ornament

And inevitably, they require different writing pressures; however:  How much? A flex‑nib can write lines as shown in Photo 3.  Did I place the picture in the correct orientation?  I am not a flex writer; I could not tell.

Being an ingeneer, I am in need of a classification based on technical, measurable criteria originating from reproducible tests, which separate standard nibs from flex nibs.  Then I am happy to join discussions.

As a start, I want to set four regular scenarios which apply to both, regular nibs as well as flex‑nibs.  Presenting them in Table 1, I aimed to provide more transparency.  During the analysis, I use ingeneering terminologies.  If you struggle, have a browse through the chapter on Stresses and Strains.

Table 1
scenario 1 2 3 4
defined by the applied force normal writing force more than normal higher force even higher force
when applying a load tines move apart tines move further apart tines move even further apart tines bend, possibly break
after removal of the load tines return to the original position tines return to original position tines stay apart still shapely tines stay apart remain deformed
amount of deformation elastic small plastic more plastic more plastic
preload the same reduced no preload no preload
capillarity as designed as designed reduced disabled
ink flow as designed as designed reduced does not proceed to tip
comment action within designed parameters used to adjust responsiveness (1) some residual deformation remains may still be usable, repairable larger residual deformation, possible break, unusable,beyond repair

(1) Experienced writers and nib artisans use this method to adjust the responsiveness, the sensitivity of the nib (the ratio of force versus tine separation).  Since the preload has been reduced, the tines open now more readily.

Table 1 will apply when we define the Useful Line Width in chapter 6 and the Useful Writing Pressure in chapter 7.  In the next chapter, I have collected some of the commentaries I found on the web.

4. Types of Flex Nibs

Where is the demarcation between flex and nail?  What are the technical definitions for the various kinds of flex nibs I heard being called: “Hard, Semi-Flex, several stages of Superflex and finally the Easy Full Flex?

Some people regard a nib to be a flex‑nib when it can spread its tines repeatedly by one millimetre.  Some others want it to separate by four millimetres.

Some suggest, no-flex and the degree of flex are defined by the ratio between the line width when applying little or no pressure and the line width at a comfortable or maximal (non-destructive) pressure.  A variation from 0.2mm to 1.2mm would result in a ratio of 6, also noted as 6X.  Some flex nibs achieve a ratio of 20X.  Under this method, could we state that a 2X is a standard nib, a 6X is a flex nib and a 20X a soft flex nib?

This suggestion appeals to me because it offers a measurable, repeatable method.  Therefore, I suggested it in the forum.  It did not raise any interest because there was hardly any response.  The replies did not offer any technically useful suggestions.

So that we can move on, I would like to offer my philosophical decision: “A flex‑nib must be designed like one, to be one.”  The designer had the intention to construct a regular nib or a flex nib.  Let us respect the designer and let him decide what he wants to call it.  There are always some who disagree; it is perfectly reasonable.


Amadeus W.

7 December 2017

Continue reading about  C – Quantitative Classification chapt. 5 – 7
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