Fountain Pen Design

Function, Development, Construction and Fabrication

Swappable Nibs

In fountain pen forum I found this question and an ongoing debate on it: “Is this a fountain pen, which is designed for swapping nibs?” or “Are “some brand’s” nibs interchangeable?” The question does not ask, whether it is possible but whether the pen is designed for it.

One can look at this topic in many ways… why would people frequently want to swap their nibs on their fountain pens? Or one could ask: “If it is possible to swap nibs, why not?”  As all matter is grey, so it is with this question; there is no black and white answer.  My philosophical first response is: “When something is possible, it does not necessarily mean, it is designed for it.”

As young men, we swapped carburettors on car engines, and we improved their performance… and we were proud. The car ingeneers did not design motors for the carburettors to be exchanged by the drivers… for car mechanics, for sure.  And then there is a special breed of enthusiasts, who can do anything, where car mechanics would not tread.

Obviously

feed-nib-assembly

Sketch 1

After it is established that some people love swapping nibs, the next question is: “Why would they assume that some fountain pens are designed for swapping nibs and others not?”

Those people assume that a fountain pen is designed for swapping nibs might refer to a fountain pen, which has its nib attached in a way, like shown in Sketch 1: two bent lugs L to fit around a recess R on the feed. (The very front end of the feed I have chopped off; too difficult to draw!)  This design could support this assumption.

Traditionally

Feeds have a diameter of 1/4 inch or 6,35 mm, the raw standard size of the old Ebonite rod.  During my time most feeds had this diameter (ranging between 6.35 and 6 mm).  Nibs hug the feed with their shank for 7 to 15 mm;  across that distance, both fit firmly into the section.

As long as the shank fits in length and the front end of feed and nib matches, there is no problem, technically.  A nib would accommodate the variation in diameter.  Feeds of different manufacturers vary much more in construction; swapping them is tricky, if not impossible.

Having said this, producers of custom-made fountain pens often only construct the outer shape components of the fountain pen but employ feeds and nibs from specialist suppliers.  For sure, in this case, swapping is definitely possible.  Nibs, feeds and all.

Definitely, not

Often nibs have a hook type shape somewhere along the shank that keeps them aligned and in position during insertion.  It also prevents the nib from slipping out or being pulled out. If the nib is damaged, feed and nib are somehow extracted from the section and… this often requires special tools, which are kept by repair shops.

For such style of construction, it is easy to declare: “This fountain pen was not designed for nib and/or feed to be swapped by the (ordinary) user.”

Production

Manufacturers’ first concern is making money, obviously; secondarily, about manufacturing… in particular, to cut cost, thereof. In mass-production, the demand on ingeneers is to design products and their components for automated or robotised production or assembly, at least. Slipping a nib onto the feed after the feed had been inserted into the section simplifies both assembly steps.

Being able to change a damaged nib in this way, makes life easier for the repairer at customer service.  In my opinion, the customer was considered in regards to keeping repair cost down but not to do the exchange themselves.

Whether the assembly is put together in a traditional or robot way, for either manufacture the focus is on joining nib and feed, not on simplifying the exchange during repair and even less on swapping by the user.

This brings us to the finale: “Was the design intended for nibs being swapped three times a day?”  Now, with a crescendo: “No! Just simply, no!”  Sliding a nib on is only another assembly method.  Only confident experts and enthusiasts would try this with a traditional nib mounting.

That it can be done does neither confirm nor deny intentions.

The Robot’s Way

The lugs on the nib are bent during the manufacturing of the nib. The cross-section of the feed at the place where the nib fits is marginally larger and wedge-shaped (increasing in cross-section) at an angle α, as in Sketch 2.  The angle α is overemphasised to show its function.  In reality it is hardly noticeable.  The green line shows where the holding or clamping force F will develop.

feed-nib-wedge

Sketch 2

When the nib is pushed on, the two plastic recesses (either side) deform slightly.  Instead of wedges, some feeds would have a small ridge along the contact side of the recess, see Sketch 1.  They are squashed to some degree when the nib is fitted.

This deformation also works as a compensation for nib tolerances.  Injection moulded feeds can come with high accuracy.

feed-nib-3-point-copy

Sketch 3 — three pointed contact

Sketch 3 shows the cross-section.  In comparison with the curvature of the nib, the shape of the feed is slightly more convex so to assure that the contact between the nib and feed is where you want it.  Eventually, a three-pointed contact always causes all three to have contact (under the same pressure).

Some feeds have a cutaway section under the nib (the curved dotted line), which permits the plastic to creep more easily.

Each and every time when the nib is pulled off/ pushed on, the friction between the lugs and the recess abrades some plastic and the recess gets thinner, until one day…

Creeping

There is another point to consider: When under load (green) above a certain level for some time, plastic creeps (changes its shape) in the direction so that the load reduces, the direction of the green markings. And nibs have tolerances. After a tight nib, when the recesses have crept and adjusted to a small dimension, a marginally larger nib would sit loosely, but it should not fall off.

However, more wear, more tear… who knows?  Don’t forget, we talk about tenths of a millimetre, thou of an inch.

Left alone, nibs and feeds would reach almost the same holding force.  That’s theoretical, in real life, the gap between nib and feed will be filled with ink residue and stick together.  No, I won’t tell you what to do.

§

Creeping of plastics plays another intended role. Where the ink capillary, -ies end and the tines touch the feed, their contact is crucial for the cross-over of the ink. The smallest gap can prevent it.

feed-nib-compensation

Sketch 4 — interference

Individually, the two components are dimensioned in a way, so that at worst case tolerance scenario they still interfere, see Sketch 4. When brought together initially, the elasticity E of the plastic will allow the plastic of the feed to move and have the two parts find their correct working position.  The two components will always push against each other, very gently (a few grams).

The pressure at this point varies proportionally with the interference of dimensions, or rather their tolerances. After a while, one or two weeks this pressure reduces even more, because plastic creeps, at position C.

Here is an example: For one nib feed combination the interference could have been at the higher end. If the nib is replaced by, swapped with one with a lesser interference, one could end up with a gap. There are ways of compensating for it; however, the number of times they can be applied is limited (3 – 5 times).

Nib and Feed are tuned

If you have forgotten, nib and feed are tuned and designed to work together optimally.  If you change one of the two, this tuning is lost.  It may not show much, however, if you alter the nib width, don’t be surprised, when your degree if wetness/dryness changes as well.

Pens designed for swapping Nibs

There used to be pens for drafts-people and artists, which were designed for changing nibs of different width, thickness and angle. Initially, they were dip-pens and eyedropper pens. For a short time the section-feed-nib assembly was swapped, but because of the awkwardness and high likelihood of damage, this was given up soon.

Now, one buys one pen per nib style.  That’s what I recommend. If you are a professional or passionate enthusiast, it is well worth the expense.

§

Unfortunate advertisements and photos like the one shown in Photo 1 (origin unknown) support people’s assumption.  Checking on the website of the particular brand I found their representation in contrast to the photo.  The photographed pen comes only with nibs F, M and LH.  The wider nibs are intended for calligraphy pens.

lamy_nibs__lamy_nexx

Photo 1 — false advertising?

On the same website, under the heading FAQ is stated: Nib Change:  “All steel nibs can be changed by specialised retailers in authorised Lamy shops. Gold nibs should be changed by the LAMY Repair Centre only.”

And one more aspect to consider:  the width of an EF nib is around 0.5 mm, the broadest nib on the photo is 1.9 mm, almost 4 times more.  Writing with these nibs would require different amounts of ink supplied by the feed.  Can one expect a feed to cope with such variation?

Innovation

Having arrived at this point, where we know that there is a number of people (what number?) who would love a fountain pen, which is designed for a swappable nib and it seems there is none, the true ingeneer starts pondering.

Why not a bit of technology transfer?  From the old nib-holder, which was designed for swappable nibs and apply it to a fountain pen?  There is a need for some springy element on the nib, feed or section… and there is the extra requirement of nib-feed alignment.

feed-nib-slding

Sketch 5 — sliding nib

Just a first flash… it can be done and would work, no doubt.  And, no doubt, there are many other solutions to this challenge, which would work as well, or, even better.

Sketch 5 shows the nib with a nice long shaft with a wiggly, springy bit formed at the top.  This tongue matches the groove in the grip-section and is responsible for alignment, near the opening for the nib. Further back inside the section, the same groove could take a protrusion of the feed and guarantee its alignment.

Having them both lined up with the same functional element (the groove) assure alignment of all three components.

The shoulders of the nib would be shaped so that they facilitate pull and insertion of the nib and to overcome the constant, predetermined friction at the spring.  It would slide on top of the feed, which has a ridge either side for initial alignment, which helps to find the groove in the grip-section, even in the dark.

Ideas galore, now an investor is needed.

Ω

Amadeus W.
Ingeneer

29 November 2016
cropped-cropped-ink-pen-writing_wide113.jpg

This is the first article under this heading.  May I suggest reading about the function of nibs under Nippy Nibs

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One thought on “Swappable Nibs

  1. Thank you for the research you publish. Is is very interesting for this growing business.

    Like

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