Fountain Pen Design

Function, Development, Construction and Fabrication

My Classification Proposal – chapt. 8

Let’s get our hands dirty, load up some fountain pens and perform some investigational testing.

The fountain pens tested were:

Parker 105 Flighter, Lamy Safari, Sheaffer Targa 1001XG, Lamy 2000.  Except for the Safari, they all have gold nibs.

The method:  I drew six lines at loads starting at 0.5N increasing the load at increments of 0.5N up to 3N.  I held the fountain pen at a 45° angle and pulled it in the direction of the line.

Observations:

•  Initial trials demonstrated that the speed of writing influenced the line width. I drew the lines 100mm length in approximately one second.
•  I measured the line width at three places, after 30mm, 60mm and 90mm.
•  The variation of the line width was up to 20% in lines drawn at low loads, while the accuracy improved to 8% at higher loads.
•  Instead, then the separation of the tines causing the widening of the lines it was the deeper impression of the nib into the paper at higher loads. Then the tip was more enclosed by the paper, and therefore the lines were broader.
•  Except for the Parker, no separation of the tines was noticed. I assume that none of the tested fountain pens had flex‑nibs.
•  Impression marks on the paper were left by the tines were noticeable.

Conclusion: Paper and ink influence the test too much, and therefore the results are inconclusive.  I believe a direct measurement of the line separation as proposed by Senior Campos is more useful.

Therefore I suggest a static method.  The easiest way to measure the load is using one of those electronic scales with a tare function and an accuracy of a tenth of a gram.  The nib merely is pressed against the scale’s surface at a 45° angle.

Photo 6 — Measuring Loupe

How to measure the spread of the tines?  The simplest way is with a measuring loupe as shown in Photo 6.  This one has a magnification of 10, you can see the ruler between the two support arms.  You hold the tip of the nib against it, apply a comfortable load and read the tine separation.

You would need a second person to take the reading of the display of the scale while you look through the loupe.  Sure, you could construct a mirror contraption, then, you could read both values at the same time.

§

Having moved these obstacles out of the way let us return the preload of the tines, which I will include in this method since it impacts on the value of the spring constant σ.

Graph 3 — Determine Preload

I demonstrate this in Graph 3 with a hypothetical nib.  The blue line is determined through only one measurement where the tine separation of 2.2mm requires a load of 2.2N.  Calculating σ = 2.2mm ÷ 2.2N = 1mm/N.

The red line is determined by the additional measurement at 0.5mm tine separation, which required a load of 0.8N.  Here σ is determined through the differentials 2.2mm – 0.5mm = 1.7mm and 2.2N – 0.8N = 1.4N from which σ = 1.7mm ÷ 1.4N = 1.2mm/N.  You may consider this not a great difference, however, with increasing preload the spring rate increases, too.

Therefore, the procedure involves two measurements of loads at two different amounts of tine spread.  Preferably the first load measurement should be at a point when the tines just start to separate, somewhere around 0.2‑0.5mm.  For accuracy, the second load measurement should be at least 0.5mm further than the first measurement or more, as long as the writing pressure does not exceed 3N.

With this method, the preload can be determined as being 0.5N.  If in another hypothetical example the preload were 1N, σ would be around 1.7mm/N.

The more significant the tine separation per load, (the softer the nib is,) the higher the value of the spring constant σ.

The advantages of the suggested method are:

  • The points of measurement can be adjusted to the type and design of the nib.
  • The value of σ will not be influenced by the choice of measurement points.
  • σ is a standard value and permits comparison across any nib data.
  • It allows the determination of the preload.

§

Now we have two technical ways of describing a nib’s characteristic, determined by its shape and material:

  1. The spring constant σ, which gives a measure for the softness of a nib or more technically speaking: It tells how readily the line width responds to a variation of pressure.
  2. The preload tell us about the amount of writing pressure needs to be applied to a nib before the line begins to widen or point when the tines start to separate.
  3. There is a third characteristic I would like to add. How far can the tines spread?  For this, we need to know what the useful line width (chapter 6) is.  Put a sheet of paper on the scale.  Draw a line with increasing pressure.  When the line is interrupted, you have determined the Useful Line Width of this nib.  Read the load value.

Graph 4 — Useful Tine Separation

Knowing σ, you can calculate the tine separation, the Useful Tine Separation.  You can also determine it graphically following Graph 4.  I used the same sample nib as in Graph 3.

There is a close correlation between the tip width, tine separation and the written line. The tip with can be measured and then add the Useful Tine Separation and you are close to the Useful Line Width.

§

Now we have three technical characteristics, which (in my point of view) describe the properties of a nib in a standardised way, which permits comparison and classification.

§

From here, where to next? Now we need data obtained from a selection of fountain pens with all kind of nibs.  After they are grouped, a correlation between the data and writers’ experience must be established.  This will provide a classification based on measurable, technical terms.

I hope there will be several enthusiastic collectors with a range of fountain pens which would perform the test and collect the data.  Then this job will be completed.

Eventually, I envisage someone completing a table like Table 6 containing the agreed titles of nib styles, may they be as romantic as we like, as long as we agree.  Then there is a column for the spring constant, the preload and the max. Tine spread.

The values in the table are sort of sensible suggestions, but they don’t originate from performed tests.

Nib Style                [Table 6] Spring Constant
[mm/N]
Preload
[N]
Max.Tine Spread
[mm]
Hard, Nail 1.2 2 0.5
Semi-Flex 1.6 1 1
Superflex 2 0.8 1.5
moderate Superflex (noodle) 2.5 0.6 2
soft Superflex (soft noodle) 3.2 0.4 3
Easy Full Flex 4 0.2 4

This brings the excursion through the classification of flex‑nibs to an end.  Now I begin with delving into their technology.

Ω

Amadeus W.
Ingeneer

19 December 2017
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Continue reading about D – The Technical Side – chapt. 9 – 12
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