As I mentioned in the previous post , the bladder is both the core and the Achilles heel of the early twist-fill fountain pens, at least from the perspective of today. The rubber tube or sack was not sufficiently robust to withstand the repeated stresses of being twisted and untwisted. The problem was compounded by the fact that the rubber would become stiff and embrittled over time.
Twist-fillers were not the only fountain pens that suffered from the failure of ageing rubber. Replacement of the rubber bladders, tubes, or diaphragms is an everyday occurrence for collectors of vintage fountain pens. Sometimes the replacement is easy (as I found with the bladders of old Conway Stewart pens), but sometimes it is very difficult (as with the Vacumatic Parker 51 that I broke…).
A Platypus Model 20 bladder being displayed by an expensive hand model. Notice the built-in flexure zones that minimise the stresses imposed on the bladder during use.
The Platypus Model 20 bladder
The bladder of the Platypus Model 20 will quite likely never need to be replaced. The material is very robust and strong.
The picture here shows a Platypus Model 20 bladder stretched by a dumbbell weighing nearly 10Kg. The bladder was stretched to nearly four times its normal length, and even though it did not return all the way to its initial length after the weight was removed it continued to spring back after being twisted.
A Platypus Model 20 bladder supporting nearly 10Kg (22lb)
A bladder undergoing a stress-test of 100,000 actuations.
The bladder shown in the video was actuated with a stepper motor (driven by a 3D printer control board) repeatedly for more than a day. After 100,000 actuations the bladder was still intact, still moved water in and out when twisted, and was totally undamaged by the experience.
It seems likely that the bladder would withstand far more than 100,000 actuations, but that is far more than any bladder would see in even a lifetime of continuous use.
Polyurethane (TPU)
The Platypus Model 20 bladder is made of polyurethane, a type of plastic that is often called TPU in the context of 3D-printing. Polyurethane is remarkably robust, chemically stable, and resistant to many solvents. Polyurethane’s flexibility and stability make it remarkably useful. It is widely used in many different roles, from stretch fabrics (Spandex, Lycra) to components of car suspension and skateboard wheels.
Polyurethane comes in many variants and different degrees of hardness. The TPU filament used for printing the Platypus Model 20 bladders is softer than many TPU filaments, with a technical Shore hardness rating of 82A, as compared to the most common 95A. The particular filament used is Filaflex 82A, made by Recreus in Spain.
In contrast to rubber, polyurethane does not suffer from embrittlement much at all. It has even been reported that polyurethane becomes less brittle over time [1], albeit at elevated temperatures. It has also been reported that the presence of water hinders embrittlement from developing with ageing [2], a finding that might be relevant to polyurethane ink bladders.
I do have some limited long-term experience of 3D-printed polyurethane. I still have the tree frog that is the first ‘flexible’ print that I ever made. You can see in the photo that it is not a great print (I like to think that I could do much better now), but it sat on a windowsill for about 7 years and has proved itself both stable and an excellent dust collector.
The 3D-printed polyurethane tree frog is looking at some of the data collected to determine the rate of water loss through the walls of various bladders. Those data will be the subject of the next blog post in this series.
Polyurethane is not perfect
Not every property of polyurethane is perfect for its role as the bladder for the Platypus Model 20 fountain pen. Unfortunately polyurethane is slightly permeable to water. Not disastrously so, but even a little can lead to drying out of ink if it is left in the pen for long enough. The next blog post in this series will detail my studies of water loss from various bladder constructions and the ways that I have made the problem minor enough to be unproblematical for normal fountain pen use.
References
Abbas Tcharkhtchi, Sedigheh Farzaneh, Sofiane Abdallah-Elhirtsi, B Esmaeillou, F Nony, et al.. Thermal Aging Effect on Mechanical Properties of Polyurethane. International Journal of Polymer Analysis and Characterization, 2014, 19 (7), pp.571-584. ff10.1080/1023666X.2014.932644ff. ffhal-01191410f
Possart, W., Zimmer, B. Water in polyurethane networks: physical and chemical ageing effects and mechanical parameters. Continuum Mech. Thermodyn. (2022). https://doi.org/10.1007/s00161-022-01082-y
I have been working on a totally new fountain pen model that differs in major ways from the exisiting models 1 and 10. It will be called the Platypus Model 20.
A clutter of Model 20 prototypes
The Model 20 is not yet available, and the last details of its design are not yet final, so this announcement runs the risk of inducing the Osborne effect. The Osborne effect is a lesson for marketers where customers hold off on buying existing models in the expectation of buying a newer model. Legend has it that the pioneering Osborne computer company went bust in the early 1980’s because people stopped buying the existing stock after more advanced models were shown in prototype form (https://en.wikipedia.org/wiki/Osborne_effect). I’m prepared to wear that possibility, but really, if you like everything about the Model 1 or Model 10 then buy one. The new model will be different in just about every way, and is ‘better’ only if you prefer the differences. It will also be a little more expensive.
The newest prototype Model 20. The final version will almost certainly look like this.
First thoughts
The Model 20 was initially going to be a simple flat-top version of the current Model 10, with a Jowo or Bock nib unit and a cartridge converter. I won’t say that it would be boring (particularly as a Model 30 might be just like that!) but it promised to be a relatively simple task for me to re-shape an already well worked design. Gradually the brief for the new model expanded into a totally new pen that differs in lots of important ways.
An early prototype for Model 20 alongside a Model 10.
One way to make the new pen stand out a bit from the current Model 10 —and from most other cartridge converter pens— was to utilise the large volume cartridge converter that TWSBI sell for their Swipe pen. (If I recall correctly, the idea was originally Michael Lampard’s. Certainly it came up in a conversation with him.)
The Swipe converter has a larger ink capacity than the standard international (about 1.3ml compared to 0.75ml) but nonetheless fits onto any nib unit that expects to be mated to a standard international converter. The Swipe converter is fatter than the standard and so it does not necessarily fit into the body or section of your conventional cartridge converter pens. It does not fit into the Platypus Model 1 and Model 10. Of course it would be an easy matter for me to make the inner dimensions of a new pen big enough. I could supply the pen with a Swipe converter inside and with an accessory adaptor collar to allow standard international converters (or cartridges) to also fit snugly.
I made a few prototypes of that pen, both with my standard patterns and a couple of new ones. A new pen, based on the Model 10, but a bit thicker to accept a slightly larger cartridge converter and with nearly flat ends. Same nib units as the Model 10, but maybe some new patterns… On second thoughts, that doesn’t sound very challenging for me. And, for my customers, it might even exacerbate the difficulty of choosing models, patterns can colours. Hmm. Maybe I can do something a bit more interesting, and something more challenging from the design and manufacturing point of view.
Second thoughts
How about a pen that does not take a cartridge converter, a pen that has an ebonite feed? That sounds better. How about one that uses a filling system different to any currently offered by other pen makers? Interesting.
Ebonite feed
People like ebonite feeds for their excellent flow characteristics, and I can put one of them in if I move away from cartridges and converters.
To use a cartridge you need a nipple at the back of the feed that mates to the cartridge. The Jowo and Bock nib units that I have been using feature such a nipple and a corresponding extension at the end of their plastic feeds to reach up into the nipple. Ebonite feeds typically do not have such a feature and so ebonite feeds are mostly seen on pens that do not use cartridges.
A plastic feed from a #6 nib unit and a 6.35mm ebonite feed. (With a lovely Platypus Pens sticker.) Notice the part of the plastic feed that protrudes into the cartridge.
I’m not saying that every ebonite feed is incompatible with a cartridge, as there are some counter-examples. The Flexible Nib Factory offers ebonite feeds that would work with a standard cartridge (e.g. this one). Such an ebonite feed and nib housing might make a nice upgrade for a Model 1 or Model 10, but they are a bit on the pricey side given that they cost more than the whole Jowo #6 nib unit with a plastic feed and the nib. I did not consider them for the new Model 20 because I was already enthralled with the idea of a novel (sort of…) unique (sort of…) filling system that would work with a plain ebonite feed.
A novel(ish) and nearly unique filling system
Novel(ish)? Nearly unique? Well, the truth is that when I first designed the system I thought that I was inventing it. Turns out that I was re-inventing an old system, a system that appears to have died out. That makes it novel(ish) and nearly unique. (No matter what sticklers for the rules of grammar might say!)
The basic idea of this filling system is that it has a deformable portion that is compressed to blow out air and then rebounds to make a vacuum to suck up ink. Yep, like the bladder of a vintage lever-fill pen. But not exactly like that. The bladder of the Model 20 is compressed by being twisted and wrung out. It is a twist-fill system.
Detail from a diagram in the 1903 patent for a twist-fill system for a fountain pen.
A prototype Platypus bladder being twisted.
As I’ve said, the twist-fill mechanism is not a new invention. There are many patents from early in the twentieth century relating to twist-fill mechanisms. Twist-fill fountain pens were sold by A.A. Waterman as “The Pen with the Magic Button” and versions of it were sold for several decades. Other pen makers offered their own take on the twist-fill mechanism, including Sheaffer with their 1930’s Wasp twist-fillers. An explanation of the many variations on twist-filling pens can be had at the Vintage Fountain Pen Doctor and Home of Paul E. Wirt pens & the Museum of Fountain Pen Filling Systems.
Twist-filler pens appear to have been quite popular early in the last century, but you cannot buy a new one now. Why? Well, the twist-filler mechanism offer fast and easy filling, but with an Achilles’ heel: the rubber bladders used in the twist-fill pens would eventually fail as a result of either the stresses of being wrung out, or because natural rubber bladders eventually go hard and crack. The Platypus Model 20 bladder should never crack because it is made of a very robust and stable plastic, polyurethane, and it is designed with pre-programmed flexures that minimise the stresses imposed on the material as it is being operated.
I have tested the bladder of a prototype pen by twisting and untwisting it 100,000 times over two days using a stepper motor. At the end of the test the bladder looked and felt no different. That number of actuations is more than anyone should expect in a lifetime of regular use of a Model 20 but, nonetheless, I intend to re-run that test with even more actuations as soon as I have finalised the design of the Model 20 and its bladder.
The Platypus Model 20
The Model 20 takes a #6 sized nib and has an ebonite feed that offers excellent ink flow. It’s a twist-filler where a half turn and release of the knob will suck ink into the pen. Repeating that 4 or 5 times takes a couple of seconds and fills the pen with over 2ml of ink: more than most piston filler pens and far more than a cartridge converter holds. Like the Model 10, the new pen is middling to large in size (by modern standards: vintage pens tend to be smaller than current pens) and is fairly light and exceedingly comfortable to use. (All details are subject to arbitrary change!)
Future posts of this blog will show and discuss a range of issues relating to the choices of design and materials of the Model 20.
A pocket-sized fountain pen: small in the pocket and full sized in the hand.
Quokka Model 1: full sized for writing
A new pocket pen from Platypus Pens: the Quokka.
Quokka pens are small and cute and turn into full-sized pens when in use. Less than 10 cm long (less than 4 inches), they can slip easily into a pocket or purse and, when posted, they become full-sized pens for writing.
A mob of quokkas: small in the hand, comfortable in the pocket. Left to right: Quokka model 10 pattern 1 in onyx and aquamarine; Quokka model 1 pattern 2 in bronze and alpha brass; Quokka model 1 pattern 3 in night sky and aquamarine.
The Quokka pen grip sections are identical to those of the original Platypus Models 1 and 10, so the small size does not come at the cost of writing comfort.
These pictures show the Quokkas alongside a Kaweco Sport, possibly the most popular pocket-sized pen. The Quokkas are shorter than the Sport when closed and slightly longer when posted. The nibs are larger than that of the Sport as well, with a #5 nib in the Quokka Model 1 and a #6 nib in the Quokka Model 10.
Quokka and Kaweko Sport
Cartridges
The short bodied Quokkas take standard short international ink cartridges like those from Kaweco, Pelikan, Diamine, and others. A huge range of ink colours is available (see those at Jet Pens, Pulp Addiction, or your favourite ink retailer), and empty cartridges can be filled with your favourite bottled inks using a pipette or needle and syringe.
The short cartridges are short, but they fit almost as much ink as an average cartridge converter fill, so you should not worry about running out of ink too often. Anyway, spare cartridges are easier than ink bottles to carry.
Quokka and original Model 1 pens.
Marks and scratches
Pockets and purses can sometimes be fairly rough environments. Pocket pens have to contend with rubbing up against other contents like coins and car keys. The Quokkas are relatively resistant to abrasion as the PLA plastic is fairly hard (harder than, for example, ABS) and the textured surfaces of the pens means that any scratches that do happen will typically be hard to see.
Why ‘quokka’?
The Australian quokka (Setonix brachyurus) is one of the smallest members of the wallaby family, and ‘wallaby’ is what we call smaller species of kangaroo. That means that the quokka is a pocket-sized kangaroo. It’s a marsupial and so the female quokkas have a pocket! What’s more, the other standard name of the quokka is ‘short tailed brush wallaby’ and the Platypus Pens Quokkas certainly have short tails.
A quokka family on Rottnest Island, Western Australia (photo by Hesperian https://en.wikipedia.org/wiki/Quokka#/media/File:Quokka_family.jpg). The mother quokka (left) has a Platypus Pens Quokka Model 1 in her pocket, and the father (right) has a full-sized Model 10 on his desk. They are discussing when it will be best to give their daughter her first Platypus pen. (She would prefer to have a surfboard.)
Platypus pens is now offering its pens constructed from a PLA filament that contains 50% terracotta (by weight). The pens look like they are made from terracotta, and feel like it too.
Platypus Pens Model 1 and Model 10 in their natural habitat
Terracotta infused PLA filament makes a truly lovely pen, but it also offers a few disadvantages for the user and for the penmaker.
For the user
The surface of pens made from the terracotta filament is slightly rough and that means that ink cannot be simply wiped away with a tissue. A wet cloth is usually sufficient to clean the pen after filling, and an occasional purposeful cleaning may be necessary. What’s more, the rough surface is relatively prone to marking when scraped against hard edges, and when scraped against soft surfaces it is slightly abrasive. Cap posting is not recommended for terracotta pens.
Terracotta pens are likely to develop a patina after long use, something that some people might not like, but others will certainly enjoy.
For the designer
Terracotta filled PLA has a matt finish with no sheen or shine. Just like a terracotta pot. The patterns originally developed for Platypus Pens exploit the shininess of some PLA filaments to exhibit sparkles and play with light reflection. They do not work so well with terracotta. Therefore a new pattern has been designed, cleverly called ‘Pattern 4’, a pattern that uses shadows instead of reflections. I call the pattern ‘dimples’ for reasons that may already be apparent. (Dimples works pretty well with the shiny filaments as well and so it is being offered for all pens.)
A Model 10 pattern 4 (‘dimples’) Platypus pen showing its rustic charm on an old sawhorse outside the Platypus Pens factory (shed)
For the maker
The terracotta filament comes out of the extruder differently from other PLA filaments. It seems more fluid than normal PLA at the optimal printing temperatures and it’s heavy and so it sags during printing when given half a chance. What’s more, it doesn’t weld as well to the non-terracotta filaments used for the contrast bands and so each of the bicoloured components has a weak point. That is not at all a problem for the completed pen because the weak joint is reinforced in the epoxy-glued sandwich of inner and outer parts, but I suffer a much higher failure rate among the components made from terracotta. The component rejection rate is probably about double that of components made of normal PLA.
Why use terracotta at all?
So if terracotta has all of those disadvantages, why bother making (or buying) a terracotta pen? Simple: the terracotta pens feel GREAT!
The micro texture and slightly porous nature of the terracotta feels distinctly different from the ordinary PLA Platypus pens of otherwise identical design—different in a way that many people find to be better. It’s hard to describe the feel, so perhaps I can just say that it is less ‘plasticy’. I’ve never held a Visconti Homo Sapiens pen, but I suspect that the feel of their lava powder-infused resin might be similar to the terracotta powder infused PLA.
Should you choose a terracotta pen? Not if you would find the extra care needed to keep it free of ink stains, or if you do not like a pen to shows signs of its long use. However, if you want a pen that feels wonderful in the hand and that is unlike any other that you will see then, yes, give it a go.
A pre-review on YouTube
Mick L (Michael Lampard) has just released a YouTube video where he talks about his terracotta Platypus pen (prototype).
Platypus Model 1 and Model 10 pens have a shared distinctively elegant and simple shape. This blog post describes the shapes of those pen models and explains why they were chosen.
The body and cap of both models have outlines that are formed almost entirely on the intersection between two circles. They consist of a symmetrical pair of arcs truncated at the top and bottom (see the diagram below). Once that form was chosen the technical design is based on the diameters of the circles, how far apart the circles lie, and where the arcs start and end relative to the centre-line of the circles.
Apart from looking good, the smoothly curved shape of the body allows the cap to be posted relatively deeply and securely. The end of the body is naturally narrower than the inside of the cap and the smooth taper fits well within the tapered bore of the cap liner.
The shape of the cap and body are both formed from the intersection of two circles
The cap liner obviously has to be tapered to fit inside the outer shell of the cap, but its taper is straight and slightly narrower than necessary simply to fit within the cap. Its shape is deliberately arranged such that while you are capping the pen the cap threads become aligned with the body threads before they engage. That eliminates the possibility of cross-threading, which could damage the threads in the softer cap liner material.
Model 1 Pattern 2 pen being used with the cap posted
The cap liner also has a small step inwards about half way up. That step acts as a stopper for the widest part of the bulge at the end of the grip, and effectively seals the nib into a small volume to minimise nib drying.
The grip section of the pen has a straight taper for comfort and to give the writer plenty of options as to how to hold the pen. For the Model 1 pens the grip ends with a bulge and then a narrow portion right at the base of the nib. The bulge is what seals inside the cap, and it is set back from the nib so that the writer’s fingers are comfortably held back from the relatively short nib. The nib of the Model 10 pens is longer and so it is not desirable to move the user’s grip so far back from the nib, and thus the Model 10 grip ends very conventionally with a slight flare. Of course, that flare is what engages with the sealing step within the cap.
There is only a very slight step between the threads and the patterned body and the step is smoothly tapered. That means that the pen can be held far from the nib, if desired, without the threads and step being very noticeable. The body’s coloured band is placed between the threads and the step in order that it is neatly covered by the cap band when the cap is in place.
The cap band of Platypus pens are quite wide compared to the standard steel bands on most fountain pens. They might remind you of the wide bands on some classic models of Sheaffer pens, but the wide band is not entirely aesthetic for the Platypus pens. The inside diameter of the plain band is larger than the inside diameter of the patterned wall of the cap because the pattern thickens the wall, and because the outer diameter of the band extends just a little beyond the patterned wall. That extra diameter allows space for the cap threads and therefore minimises the extent to which the cap has to be wider than the pen body. That improves the look of the pen overall, in my opinion.
All in all, the shape of Platypus fountain pens is determined by a mixture of functional considerations and aesthetics. I like how they look and I hope that you do too.
In some previous posts I have discussed the pros of 3D printing of fountain pens, but alongside those advantages there are some important downsides. This post discusses them and the strategies to mitigate them that have been used in the design and manufacture of Platypus pens.
In order to understand the difficulties for fountain pen making that come with the pen being predominantly 3D-printed, we need to have a clear idea of the 3D printing process.
Platypus fountain pens are made using a type of 3D printer that extrudes a thin stream of molten plastic—a type of printer that is usually described as FDM for ‘fused deposition modelling’. The extrusion head of the printer moves around in a programmed manner in a 2D plane to deposit a thin pattern of molten plastic which rapidly cools and solidifies. Layers of plastic are built up one upon the other to form a 3D shape from 2D layers.
My 3D printer, a modified Voron V0, printing a test cube accompanied by backyard birds
If you are interested in learning more about 3D printing then you can read some of my other blog posts, and I recommend the video series about the basics of 3D printing created by YouTuber Tom Sanladerer.
The layer by layer process intrinsic to 3D printers allows for a remarkable range of object shapes and designs to be formed, but that flexibility comes with a downside: 3D printers are quite slow. The components for one Patypus fountain pen take about four hours to print altogether. (And then more time is taken to assemble and finish the pen, but that is not the topic of this blog post.)
Rapid prototyping and development
Despite their slowness 3D printers are widely used in the process called ‘rapid prototyping and design’. A 3D print might takes hours to complete which stands in contrast to a few seconds to injection mould an object from plastic, but the 3D printer is ‘rapid’ because the tooling for the injection moulding process might take weeks or months to make or procure. It’s the total turnaround time from design to inspection and testing that is rapid with a 3D printer, and that short turnaround facilitates design iteration and optimisation prior to the product being manufactured by more conventional methods.
The 3D printers that sparked the development of consumer-level 3D printers were called RepRap in recognition of that role: the “Rap” part is short for rapid prototyping. The “Rep” part of RepRap is short for self-replicating. The first RepRap machine was able to print many of the components of itself, which were then used to make a second RepRap machine which printed the parts for a third, and so on. My second 3D printer—the one on which I print the Platypus pens—is constructed with parts printed by my first, and the first was repaired and improved with new parts printed by the second: a nice RepRap circle.
It may not need to be said, but Platypus pens are the product of rapid prototyping and iterative design.
Limitations of FDM printing for pen production
The layer by layer process of FDM 3D printing brings some important limitations to the objects that can be printed, and those limitations are relevant to fountain pen production. Here is a list of some. Each will be dealt with in turn below.
• Surfaces are not smooth
• The dreaded seam and pimples
• Weakness at the layer lines
• Threads are difficult
Surfaces are not smooth
The surface of an object printed with a 3D printer will display some sort of evidence of the layer by layer printing. With the FDM printing used for Platypus pens the layers present as crests separated by valleys as a result of how the filament is extruded from the printing nozzle onto the layer below. Using finer layers (i.e. layers that are less thick) gives a smoother finish because the crests and valleys are small, but there are more of them. The diagram here represents cross-sections through a wall of an object printed with thick layers (say, 0.3mm) and with finer layers (0.15mm).
Finer layers give smoother surface
The roughness of layers is often considered to be a limitation of 3D printing and a deficiency in the finished objects. However, Platypus pens are designed so that the layer lines contribute positively to the quality of the resulting pens: the pens would not be produced with completely smooth surfaces even if it was possible. To a large extent, the unusual and eye-catching character of Platypus fountain pens comes from the layer lines. See the blog post Layers of Sheen.
Even the un-patterned grip section of these pens benefits from the layer lines as they make the grip more ‘grippy’ and mean that even sweaty hands can hold a Platypus fountain pen without slipperiness.
The dreaded seams and pimples
Any time an object is being printed layer after layer the printer nozzle has to move from the end of one layer to the beginning of the next. Sometimes that movement is a simple vertical jump, but most often it involves horizontal movement as well. The hot nozzle contains molten plastic and so inevitably some plastic leaks out during that movement and is deposited into and onto the object being printed.
Closeup of an FDM 3D-printed object showing clear layer lines and defects that arise during the transition between layers.
That problem is typically combatted by having the filament retract suddenly just before the layer change and then un-retract when the nozzle reaches the start of the next layer. The retractions and un-retractions almost always leave visible defects on the surface of the object, defects that are called seams where they are vertically aligned and pimples where they are randomly scattered over the surface.
Platypus pens are designed to almost entirely eliminate this problem. Most of the components are printed in a single layer and so there is no seam or pimples. Well, not exactly one layer, but the extrusion path is a single helix. Single wall helical printing is often called ‘vase mode’ printing, and it eliminates seams and pimples by removing the need for filament retractions and un-retractions.
There is one component in the Platypus pens that is printed in the conventional layer after layer mode: the section inner. It does have a seam at the thread that connects to the pen body. You may need a magnifying glass to see it because the part was printed with a high quality printer fitted with a direct drive extruder and the printing settings are optimised to minimise the seam.
Weakness at layer lines
The layer by layer nature of 3D printing usually leads to uneven strength. The plastic is strong in the direction of its layer plane because it consists of a continuous strand of extruded plastic, but the object can be weak at the layer junctions because the plastic of adjacent layers is incompletely welded together.
That inter-layer weakness is not much of a problem for thick-walled objects and for solid objects, but for a long thin-walled thing like a fountain pen it can be critical. Furthermore any weakness is especially problematical when the object is printed with a single wall, as are most parts of a Platypus pen! What to do? Well, the solution to this problem is conceptually easy: make an epoxy-bonded sandwich of nested components. The strength of the sandwich is much, much higher than the strength of the two printed layers.
The cap of a Platypus pen has an outer layer made with shiny, colourful filament and has an interesting surface pattern and the plastic. That layer, by itself, is pretty weak, but that doesn’t matter because it is sandwiched together with a liner made of a different plastic selected to suit its structural and functional roles.
The body is made of three parts glued together with epoxy: the outer thread and band which slip into the end of the body proper, and the inner threaded liner that extends almost to the end of the body. After being sandwiched together those components make structures that are much stronger than the sum of their individual properties would suggest.
The section has a single wall helically printed coloured grip on the outside and a conventionally printed inner. The only part of the pen that is entirely one piece is the section thread that goes into the body. It is made of a modified PLA that has strong inter-layer adhesion and is not brittle. It is relatively thick wall where it meets the grip and is more than strong enough when the pen is fully assembled.
Threads are Difficult
A process of rapid prototyping and iterative design was used to come up with the several strategies employed to help make robust and effective threads for the Platypus pens.
Strategy 1: the male and female parts of the thread have different layer heights. That reduces the possibility of the threads interlocking on the layer lines and improves the feel of the threads in use as well as reducing wear.
Strategy 2: use a thread cross section that ‘knows’ that the thread is being 3D printed. My usual 3D model design software is the open-source CAD program OpenSCAD, and there is a very useful thread library available for it that includes a huge range of official thread designs. They work well as long as the thread size is large relative to the layer height and precision of the 3D printer. Unfortunately the threads of standard nib units are very fine and so I had to develop my own software for threads. (Yes, it involved a process of rapid prototyping and iterative design!) On a platypus pen only the male section to body thread is a standard design (M10x1 for Model 1 and M10.5×1 for Model 10).
Strategy 3: reduce thread wear by ensuring that the male and female thread parts are made of different plastics. The layer by layer construction of 3D printed threads means that they are never perfectly smooth and so a thread with close tolerance is going to the prone to both galling (where two surfaces freeze together from friction induced ‘cold welding’) and wear. In the Platypus pens the threads are made of dissimilar plastics, one harder and one softer. In use the harder plastic distorts the softer during the initial running in of the thread and the result is a good fit with minimal ongoing wear. Using a softer PLA in the cap liner not only helps prevent cap thread wear, but also minimises the possibility of the cap scratching the body surface when the cap is posted and un-posted.
Strategy 4: minimise the risk of thread damage from cross-threading. The cap liner is shaped with an inner taper that guides the section during capping so that the cap and body threads are aligned before they come together. It is only possible to cross thread the cap and body if you cap the pen without the section installed, and why would you do that? The body to section thread can be cross threaded if you are inattentive—as could that thread on any pen—but it’s a fairly hard to do because the section has an unthreaded lead-in that goes into the body before the thread engages.
Perfection!
So, given how effectively the difficulties and disadvantages of 3D printing have been overcome or minimised, Platypus pens mut be perfect, right? No, not right. If you look closely enough you will be able to see some minor flaws in any Platypus fountain pen. Those flaws come from the nature of 3D printing which cannot compete with the perfection of computer-controlled lathes and modern injection moulding for precision and repeatability. Squeezing molten plastic out of a nozzle like toothpaste out of a tube necessarily involves some imprecision and the occasional minor glitch.
Platypus pens are skilfully designed and carefully hand made to a high standard and you can expect them to be very comfortable, eye-catching, unusual, and, above all, to write well.
When I started making 3D-printed fountain pens, initially for myself, I was intent on making a pen with a piston filling system. A noble objective. After all, piston filling systems are the acme of filling systems, aren’t they? The most expensive models from famous pen companies such as Pilot, Pelikan and Montblanc always have piston fillers. Surely that’s because they are better.
Well, piston filling systems are better than the bladders in my vintage Parker English Duofolds and Sheaffer Imperials. At least they’re better in some ways. Somehow. Pistons do not perish with age (or do they?), and they are not adversely affected by ‘difficult’ or ‘dangerous’ inks. Those things are either true or mostly true. However, in my opinion the push-button filling of the older of my Duofolds is less fiddly than a piston and the ‘Touchdown’ system of the Sheaffer is pretty cool. Probably the piston filler pens are more easily cleaned for ink colour changes, but they are certainly not superior in all ways.
I eventually gave up on the idea of making a 3D-printed piston filler because I was unable to make the inside of the ink cylinder smooth enough for a piston to seal (see my previous blog in praise of layer lines). I then fiddled around with printing ink bladders of various designs out of flexible TPE filament. They worked variably well but I never got them into a pen, for a variety of reasons that don’t matter here. (I may return to the printed bladder for a future series of pens. We’ll see.)
A pen with a cartridge converter (Model 1 pattern 3 in ‘alpha brass’ and ‘copper’, since you asked!). That converter looks just like a piston, don’t you think? The ink is Van Dieman’s Ink Harvest series Eggplant.
I gave up on pistons and printed bladders and bought some cartridge converters. Hey, hang on, this cartridge converter is a piston filling system!
(That might not be an entirely accurate account of the history, but it carries a good deal of verisimilitude.)
It turns out that, for me, cartridge converters are an optimal ink filling system. Optimal for me as a pen maker in the sense that it is easy for me to pair a converter with a converter-ready nib unit and get a pen that fills, empties, and writes reliably. And optimal for me as a pen user because cartridge converters facilitate ink changes. Changes of ink colour.
Coloured inks: the secret to fountain pen joy!
When I first used a fountain pen (don’t ask how long ago that was—I was in primary school) No-one I knew ever thought much about ink as we all used blue ink. I might have been forgiven if I had spelled the word ink with a Q because my dad was a Parker man (I wish I knew where his 51 went…) and so our house used Quink blue-black.
My first fountain pen in front of my father’s last box of Quink blue-black (with Solv-X). The tiny nib is marked “Platignum 1st quality M” and has no tipping per se, but the tips are bent around to serve as tipping. It is worn, dirty, the cap has shrunk and won’t fit the threads, but the pen still fills and writes (scratchy!) and I’m pleased to have it.
It turns out that whereas a fountain pen with one ink is a tool for writing, a fountain pen with its choice of many colours is a joy!
I have a collection of inks including the old Quink blue-black from my dad; that box is not empty. Most come from Australian ink makers. I’ve just counted the bottles and I’m a little embarrassed but the numbers. Fouteen from Van Dieman’s Ink, eight from Blackstone, a handful of sample vials from Robert Oster, but I also have inks from Waterman, Fountain Pen Revolution and Diamine. That’s a lot of ink, but I’m sure that I’ll buy more before too long. (Please don’t tell my family!)
With the large capacity of a piston filler I would have to hand write a novel each month to get more than a couple of inks into rotation, and that’s where cartridge converter comes into its own. The Standard International converters that I use hold just on 0.8ml if you get all the air out. It’s not difficult to write one dry, particularly with a broad and wet nib. It’s also easy to get a partial fill into the cartridge so that ink changes can be even more frequent. Lovely.
And to top it off, a cartridge converter is relatively easy to clean. If the ink is not readily rinsed out with a couple of fills and empties of the pen you can be remove the cartridge converter from the nib unit to allow flushing of the nib and feed under the tap or with a bulb. The converter can be flushed easily with a syringe and blunt needle and then you’re good to fill with the new ink in just a minute or two. Compare that to the sometimes tedious precess of cleaning out an ink bladder or fixed piston and I think you’ll see what I mean about the optimality of the cartridge converter.
All in all I am happy to make, use, and sell pens that come equipped with the ‘lowly’ cartridge converter.
The sparkle and glitter and gleam of platypus pens comes from the shininess of the plastic used and the interplay of light and their layer lines.
So many fountain pens have a smooth polished surface that it is surely the default surface. Platypus 3D printed pens come in surface patterns that are much more intricate and interesting than the default. A smooth finish _could_ be achieved by sanding and polishing away the layer lines, by filling the lines, or with some types of plastic by solvent smoothing. However, why fight against the layer by layer nature of 3D printing with complicated post-print processing when a far better result is had by taking advantage of it?
Pens in their natural habitat: under the lamp on my desk. Top: Model 1 Pattern 3 in ‘alpha brass’ with ‘copper’ bands. Centre: my vintage Parker English Duofold senior in shiny black. Bottom: Model 1 Pattern 2 in ‘onyx’ with ‘merlot’ bands.
Compare the bright reflections of a classic smooth polished pen, the Parker English Duofold, with a couple of 3D-printed Platypus pens. The Parker pen is shiny, certainly (well, apart from my finger prints!), and you might say it ‘catches the light’. But the reflection is minimal and almost static. When the pen is rotated along its long axis the reflection stays almost exactly the same in intensity and shape (run the short movie). Contrast that with a Platypus pens. Each layer has multiple places at which the angle exactly right to reflect into your eye and so you see a glittering array of reflections. Move the pen in any direction and the pattern changes, with bright spots fading and growing: the pen sparkles and the reflections move. The 3D-printed pens play with the light brilliantly!
Short movie of the pens being rotated outside under a light overcast sky.
…and that’s not all!
The layers of a 3D-printed fountain pen also hide fingerprints—something that’s quite useful in an object that is held in the hand during use!—as well as scratches. Not that a Platypus pen is easily scratched: the PLA they are made from is harder than, for example, ABS plastic and so they are naturally scratch resistant.
There’s a long answer and a short answer to that question. The short answer is that by 3D printing fountain pens I am able to combine two of my hobbies: 3D printing and fountain pens!
The longer answer is, I hope, more interesting. By 3D printing my pens I am able to make a product that is beautiful, functional, and interesting.
I suppose that I might be able to achieve at least a coupe of those virtues when making fountain pens by other methods, in particular by turning acrylic or wood in a lathe. (I’d love to have a lathe…). However, I think that no matter how beautiful and functional a pen I could make that way it would be difficult for me to achieve ‘interesting’. After all, there are so many beautiful and functional fountain pens already available from large and small pen makers that my efforts would be largely superfluous.
What makes a 3D printed pen interesting?
Well, that depends on who we might be thinking about. Many people find 3D printing and 3D printed objects interesting simply because they don’t often see them. (I’ve been exploiting that by giving 3D printed gifts to friends and family. Please don’t tell them!) That probably counts here because very few fountain pens are 3D printed. If you are ‘into’ fountain pens then a 3D printed fountain pen is intersting, and if you are ‘into’ 3D printing then a fountain pen is an interesting thing to print.
There’s another important way that 3D printing allows the manufacture pens of more than usual interest: 3D printing allows the pens to be intricate in ways that are not easily (or cheaply) achieved with other manufacturing methods. Consider the surface texture of my Pattern 3 pens. Is that not interesting?
Pattern 3 plays with the light every time it moves
The layer by layer nature of the 3D printing process allows repeating spaces in the surfaces of varying depth and widths that give the surface an apparent depth and hand-feel that is unlike all others. Even completely the completely uniform layers of the grip sections get a peculiar sheen from the 3D printed layer lines.
Why 3D print fountain pens? Look at the results and you will see.
Other 3D printed fountain pens
My pens are by no means the first to be 3D printed. The pen company Additive specialises in 3D printed fountain pens that are very different from mine in looks and in the construction methods used. Perhaps I shouldn’t, but I will suggest that the Additive pens achieve only two of the three virtues mentioned above. Check them out here.
I have seen a few high-end ornate metal 3D printed fountain pens that achieve amazing levels of intricacy… at amazing prices. For example, see the pen reviewed here.
Finally, if you have a 3D printer and you would like to print your own pens then look at this project on Thingiverse for an open-source fountain pen.
There are two main categories of 3D printers for home users: FDM and SLA. Those acronyms might not tell you anything, and their expansions are probably just as arcane. FDM stands for fused deposition manufacturing and SLA is stereolithography. (Why is it not just SL? I don’t know.) But don’t worry about “deposition” and “lithography” just know that an FMD printer melts a rod of plastic and extrudes it as a fine stream into a pattern or shape and an SLA printer projects an image onto a light-setting resin to make it set into a shape. Both types make a 3D object one thin layer atop another.
SLA printers offer high resolution and so can make highly detailed prints. They are the printer of choice for people who make miniature figurines, for example, where the high resolution enables the production of wonderfully detailed objects. See here for examples. Usually SLA printers can only make relatively small objects, but fountain pens are made of small objects and so that limitation is not important. What’s more important is the types of plastic that can be printed by SLA.
SLA printers have to use photopolymerising resins which are basically liquid acrylics or epoxies (and maybe others too—I’m not an expert on SLA). I may be asking for trouble here, but judging from a DuckDuckGo image search, the number of different resin types and colours is tiny compared to the range of plastic types and colours for FDM printers. And for my purposes, the limited palette of plastics of SLA printers is a problem and so I use an FDM printer.
The level of detail possible with an FDM printer depends on the quality of the printer, the size of the nozzle through which the plastic is extruded, and the properties of the molten plastic. Happily, a good printer has a high enough resolution to make a lovely fountain pen out of PLA (poly-lactic acid), the plastic that is the easiest of all to print. And equally happily, there are more colours and styles of PLA than there are of any other 3D printing filament! One of the companies that I buy from offers 25 different brands or types of PLA filament, and each of them comes in many colours. Yummy!
A bundle of filament about to become a pen.
PLA is made from plant-derived starch and so it’s a ‘bio-plastic’ and is, allegedly, compostable and biodegradable. In practice PLA does not break down even after years of exposure outside. The compostability refers to high temperature industrial composting and so there is probably no environmental benefit to the PLA beyond it being made from plant-derived starch rather than fossil oil.
3D printer nozzle extruding the green filament. Plastic is heated inside the orange heater block and squeezed out the small nozzle onto the previous layer of the pen. (The tapered bit at the bottom of the pen is a disposable support structure.)
There are three important types of 3D printers that I have not yet mentioned, powdered bed fusion, wire welding, and concrete extrusion.
Powdered bed printers work by fusing together a layer of fine powder which is then covered by another fine layer of powder to be fused, and so on. How the powder is fused depends on the nature of the powder. Some home experimenters made 3D printers that fused baking powder or talcum powder with super glue fired out of an inkjet printer nozzle, but industrial powdered bed printers can use metal powders and they are fused (sintered) by heating with high power lasers. 3D printing can make parts that have shaped and voids that would be difficult or even impossible to form using conventional machining from chunks of metal, and so 3D printing has great potential for aerospace components such as jet engine parts. In fact, you might already have flown in a plane powered by engines with 3D printed parts.
Rocket parts have been made with powdered bed fusion printers, but at least one company is making rockets virtually ENTIRELY with 3D printers. They are using a welding-like 3D printing method that fuses metallic wire in a manner quite similar to the way that FDM printers fuse plastic filaments.
At least one bridge has been made using fused wire 3D printing, and 3D printed concrete is being touted as a material for rapid production of cheap and safe housing on earth, and on other planets!
Even though those uses of 3D printing might sound exciting, the most important use of 3D printing is the production of fountain pens!
