8.1 Swappable Nibs

“Is this a fountain pen, which is designed for swapping nibs?” or “Are some brand’s nibs interchangeable?”

In fountain pen forums, I found these and similar questions as well as ongoing debates.  The question does not ask, whether it is possible but whether the pen is constructed for it. This is the better way of asking; the less interesting question would only ask if nibs can be changed. Most can, whether the pen is constructed with this in mind or not.

One can look at this topic in many ways… why would people want to swap their nibs on their fountain pens? … sometimes even frequently? Or one could ask: “If it is possible to swap nibs, why not?”  Hence 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 intended for it.”

As young men, we swapped carburettors on car engines, and we improved the latter’s performance… and we were proud as peacocks. 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 never tread.

Obviously

Sketch 1 — Swapppable Nib Design

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 while others are not?”

Those people assume that a fountain pen is designed for swapping nibs because it can be done easily. They might refer to a fountain pen, which has its nib attached in a way as 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 construction should support this assumption.

Traditionally

Photo 1 — Feed and Section hug the Nib

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

Drawing 1 — Compensating Tolerances

As long as the shank fits in its length, and the front end of feed and nib matches (0.5mm accuracy), there is no problem, technically.  A nib would accommodate the discrepancy in diameter, see Drawing 1.

Feeds of different manufacturers vary much more in their shape; swapping them can be tricky, if not impossible when they have orientation lugs or changes in diameter.

Having said this, producers of custom-made or limited run fountain pens often only construct and produce 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 if one knows where they originate.

Definitely, not

Often nibs have a hook type lug somewhere along the shank that keeps them aligned and positioned with the feed during insertion. Above all, this also prevents the nib from slipping out but also prevents it from being pulled out. If the nib is damaged, feed and nib are somehow extracted from the section together and… this often requires special tools, which are kept by repair shops.

For such a style of design, it is easy to declare: “This fountain pen was not constructed for the 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; consequently making more money. In mass-production, the demand on ingeneers is to construct products and their components for automated or robotised production or at least for assembly. Slipping a nib onto the feed after the feed had been inserted into the section simplifies both assembly steps. The sequential joining of components is simpler than the fitting of subassemblies.

Furthermore, if the nib is the last to be attached to the fountain pen, adjustment to market demand on pens fitted with particular nib sizes and styles can be executed with hardly any delay. Yes, even though the ink demand of a broad nib is about four times more than that of a fine, a well-constructed feed can handle this variation.

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. Don’t overlook, nib and feed also interfere mechanically, which means after fitting the nib onto the feed, the nib will most probably bend a bit and its radius reduces which opens the tines. Therefore they require to be set. I am not sure, if assembly robots can perform this subtle task, today, or is this task merely neglected?

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

This brings us to the finale: “Was the fountain pen’s construction intended for nibs being swapped three times a day?”  Now, with a crescendo: “No! Just simply, no!”  Moreover, sliding on a nib is only one assembly method. There are many others. Either way, I recommend, only confident experts and enthusiasts would try this with a traditional nib mounting.  However, rather than telling you: “Don’t do it!” I keep on feeding you more information so that you can decide for yourself.

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

The Robot’s Way

Returning to sketch 1 we know that the lugs on the nib are bent during the manufacturing of the nib.  they form a small angle α  with the ridge of the nib.  The wedge-shaped recess at the place where the nib fits is marginally larger at an angle α+ forming an increasing profile, as in sketch 2, hence, when pushing the nib onto the wedge, the end of the recess will be slightly deformed.  The joining force can easily reach 10N (1kg ≈ 2.2lbs). In the sketch, both angles are overemphasised to show the function of the wedge.  In reality, it is hardly noticeable.  The holding or clamping force F will develop between green lines, the ridge of the feed and the recess.

Sketch 2 — Ready for robotic Assembly

Instead of wedge, some feeds would have small ridges along the contact side of the recess.  They are squashed to some degree when fitting the nib which provides a certain clamping force. Either deformation also serves as a compensation for nib tolerances.  Injection moulded feeds can be produced at high accuracy, we don’t need to worry about them. And for your consideration: When the nib is pushed on the wedge or ridges on recesses, the nib’s radius will reduce and the tines will open.  In the olden days, this was adjusted during the setting of the tines.

Sketch 3 — Three-pointed Contact

Sketch 3 shows the cross-section of the feed and nib.  In comparison with the curvature of the nib, the shape of the feed is slightly less convex so to assure that the contact between the nib and feed is where you want it.  This is at the ridge, near point 1 which is divided in half by the ink capillary and at the recesses at points 2 and 3.  Eventually, through the creeping of the plastic, all three contacts experience the same load.

Indubitably, one day, this force will be zero, but by then, hopefully, enough ink dye from dried out ink will have settled there which provides some degree of adhesion.  Alas, if someone pulls off the nib, they will have difficulties keeping on the new nib.

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 areas in sketch 3), plastic creeps (changes its shape) in the direction so that the load reduces. And nibs have tolerances. After fitted with a tight nib, when the recesses have crept and adjusted to small dimensions, a marginally larger nib would not hold, perhaps on a feed with a wedge but certainly not one with ridges.  Don’t forget, we talk about tenths of a millimetre, thous of an inch.

Left alone for long enough, all nibs and feeds would reach the same holding force, zero!  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 because I know what you will do and I don’t want to be part of it.

§

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

Sketch 4 — interference

To make use of this behaviour, the two components are Individually dimensioned in a way, so that at worst case tolerance scenario of accumulation of tolerances, they still interfere and push against each other, very gently (a few grams), see sketch 4. Obviously, in the sketch, the interference is highly enlarged.  When brought together initially, the elasticity E of the feed’s plastic and its delicate shape will allow the component to move so that the two parts, feed and nib, find their correct working position.

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 to nothing, eventually, because plastic creeps, at position C.

Here is an example: For the original nib feed combination the interference could have been at the higher end, meaning, the feed would creep more. 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). Plastic feeds don’t like to be under tension, they will always give way to the force impressed by the nib, it’s only a question of time.

Nib and Feed are tuned

If you have forgotten (I know, I have mentioned it innumerous times, but it can’t be said often enough), 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, after altering the nib width, don’t be surprised, when your degree of wetness/dryness changes as well.

Pens designed for swapping Nibs

In the early days, my younger years, drafts-people and artists used dip nibs which came in a large variety, such as different width, thickness and writing angle. The early eyedropper nibs were praised and welcomed, they allowed to write at least one word without interruption, sometimes even an entire line.

For a short time, fountain pens became available on which the total section-feed-nib assembly was swapped (nib and feed are tuned!), but because of the awkwardness, cost and high likelihood of damage, they were given up soon.

Now, one buys one pen per nib style.  That’s what I recommend because there are cheap well-performing fountain pens in the marketplace. If you are a professional or passionate enthusiast, it is well worth the expense, for sure.

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Unfortunate advertisements and photos like the one shown in photo 1 (origin unknown) support people’s erroneous assumption about this fountain pen being constructed for nibs to be swapped.  There were no clarifying comments attached to the photo, for example, that this fountain pen can be purchased equipped with one of the nibs within this range.

Checking on the website of the particular brand, I found their representation in contrast with that in the photo.  There the photographed pen is offered only with nib sizes F, M and LH.  The wider nibs are shown on the site in connection with a calligraphy pen.

Since the two fountain pens present the same nib seat at the tip of the feed, the wider nibs can be attached, but as we said: that it can be done is no verification for a fountain pen being constructed for that purpose.

Photo 1 — False advertising?

On the same website, under the heading FAQ is stated: “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 requires different amounts of ink to be 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/writers (what number?) who would love a fountain pen, which is constructed for nib exchange, and it since 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 to compensate for tolerances and guarantee the contact with the feed… and there is a need for some notch to assure alignment between the feed and nib.

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 6 — Sliding nib – Cross section

Sketch 5 and 6 show the nib with a nice long shaft to sit snugly in the gap between feed and section. And there is a wiggly, springy bit formed at the top of the nib which, when in the right position, will disappear insided the section.  This wiggle matches the groove in the feed and grip-section and aligns the nib with the feed (ink capillary) as well as section.  Further back, inside the section, the same groove (in the feed) could take a protrusion inside the section and further guarantees its alignment.

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

The shoulders of the feed would be shaped (the opposite of drawing 1 further up) so that they facilitate pull and insertion of the nib and to overcome the constant, predetermined friction at the spring (wiggly bit).  It would slide on top of the feed, which has a ridge on either side for initial alignment, which helps to find the groove in the grip-section, even in the dark, just in case.  Since there are hardly any squashing forces applied to the feed or any other plastic part, hardly any creep will be experienced thus, no alterations in fit.

Ideas galore, now an investor is needed.

Above all: Enjoy!

Ω

Amadeus W.
Ingeneer

29 November 2016

This is the first article under this heading.  May I suggest you ask more frequently asked questions and perhaps read about the function of nibs under Nippy Nibs

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