Experiments With Flex

[Plexipens]

Plexipens, great question. Both Synnove and David Nishimura have done studies to quantify flex by amount of pressure.

 

Synnove

https://www.fountainpennetwork.com/forum/topic/320809-my-big-fat-grail-pen/

 

David Nishimura

http://vintagepensblog.blogspot.com/2015/07/measuring-nib-flexibility.html

 

https://www.fountainpennetwork.com/forum/topic/293267-measuring-flexibility-a-proposal/

 

Another, on video

Very interesting and worth the time to read and watch, thanks!

 

I would propose that a fixture to hold the pen and apply a controlled pressure to paper on a digital scale would give the best quantitative measure of force to flex. One could digress into the complexity of finite element analysis would be the purest path for an engineer.

 

Force-to-flex, coefficient of drag for both nib and paper ...... geekdom extraordinaire awaits!!

[Drone]

One could digress into the complexity of finite element analysis would be the purest path for an engineer.

 

Yes, I've been thinking about FEA and fountain pen nibs. Not long ago I ran across an online CFD, FEA, and thermo simulator suite that may have enough CPU time in the free account to model a nib. It's called SimScale:

 

https://www.simscale.com/

 

The limitation in SimScale might be the selection of, or specification of materials. But even with that limitation the exercise would still be helpful by allowing the forces in the nib to be visualized, especially with different breather hole shapes and sizes as well as trimming for added flex.

 

Regards, David

[Mauricio]

Mauricio, I admit that my grasp of physics may be very basic, but what you write about forces and pressure just doesn't seem to make much sense. I guess you take metaphysics for physics.

Birchtine,

 

No. I am not speaking of metaphysics which involves philosophical and unproven matters. I am talking about pure physics, based on facts and hard data. A lot of people do not have a hard grasp of physics. You are not alone on this.

 

If you have interest in knowing more about this please consider finding a good physics study about the basic principles of physics as it relates to forces, radius, angles, movement, torque, pressure, etc. Then try to apply those physics principles to someone attempting to quantify the degree of flex in a nib by writing on top of a digital scale.

[bobje]

This the sixth and final test in this series of flex experiments on no. 6 flex and extra fine nibs from Fountain Pen Revolution. In the next few days, I'll get a chance to summarize my conclusions and recommendations from the overall process.

TEST NO. 6 -- FPR NO. 6 FLEX NIB (SIDE SCALLOPS AND THINNING OF MATERIAL UNDER SHOULDERS)

WRITING RESULTS AFTER MODIFYING NIBS WITH SIDE SCALLOPS, JUST BEHIND THE SHOULDERS, AS WELL AS THINNING OF NIB MATERIAL USING A DREMEL-TYPE GRINDING TOOL

Click pen with side scallops, no. 6 FPR extra fine nib, 6.3 mm standard ebonite feed

In this test, the no. 6 FPR flex nib was modified with angel wing scallops on the sides, just behind the shoulders. Additionally, a Dremel-type spherical grinding tool (Graphic 2, below) was used to thin the steel nib material from approximately the shoulders through the tines. In comparison to the no. 6 FPR flex nib used in Test 2 (side scallops only), this wing-modified and thinned nib provides additional line variation (approximately 3x, from a line width of about 0.6 mm to 2 mm), with more flexibility, and a smooth writing experience (Graphic 1). The nib never railroaded. However, the ink is more difficult to control.

CONCLUSIONS OF TEST NO. 6

Flexibility and line variation are increased, but at the expense of ink control. Additionally, without a micrometer, it's difficult for a layman to control the material-thinning process and to determine exactly how much material is being removed.

 

Graphic 1

 

 

Graphic 2

 

[ReadyFireAim]

 

This the sixth and final test in this series of flex experiments on no. 6 flex and extra fine nibs from Fountain Pen Revolution....

Flexibility and line variation are increased, but at the expense of ink control.

First of all, you appear to be getting much better at modifying nibs.

The work you are doing now looks much cleaner.

 

So far as the thinning the underside, I have a couple of thoughts.

 

I'm curious as to how well a sand paper disk would do on a Dremel tool for that modification.

 

I'm also wondering how the orientation of the scratches effect ink flow.

Would scratches made lengthwise increase the speed of ink flow from the pen while ones made side to side increase flow from slits in the feed???

[bobje]

AFTER SIX TESTS, A COUPLE OF CONCLUSIONS

1. The "angel wings" modification improves flex nib performance, is reliable to match with feed and ink flow, and is fairly easy for a layman to create. I had never used a Dremel before performing this modification. Several companies already offer semi-flex nibs with the angel wing design. According to a July 10, 2017, video by FPN contributor Seele, the Kanwrite company already offers an angel wing flex nib on the Kanwrite Desire model.

https://youtu.be/T_IkURImV80

2. The "vent hole" modification -- similar to the expanded central hole on a dip pen nib -- improves flex. But the modification is difficult to match with feed and ink flow. The mod is easy to create because it just involves drilling a hole. This assembly may be easier for a nib company to implement than for an individual. Once the feed matches the nib, the assembly can be repeated easily. For example, a layman can drill one hole in a no. 6 FPR flex nib, at the base of the slit, and then mate that nib with the stock feed from the Airmail Wality 71j nib/feed assembly. The resulting Airmail Wality 71j combination performs extremely well. But I haven't been able to consistently repeat a nib/feed combinations like this with other pen models and feeds.

3. The "angel wing" modification works well in a nib designed for flex from the beginning -- for example, the FPR no. 6 flex nib. However, in a standard FPR no. 6 extra fine nib, it improves performance and creates a cushioned writing experience, but doesn't really generate a semi-flex nib. There might be a tiny bit more line variation, and the pen is more enjoyable to write with. But it's nothing like a modified flex nib. If a nib is extremely stiff before an angel wing modification, there isn't much of a flex guarantee after the modification, either.

4. The experiments raise other questions beyond the current scope, and certainly beyond the patience of most readers. How might a layman thin the material of a nib reliably? What is the ideal shape and position of the wing scallops? Where should a hole be drilled, how large, in what shape? What are more reliable methods of mating nib and feed? Should the underside of a thinned nib be polished, or would a certain direction in the scratches improve ink flow?

5. In the frequent discussion of why nib companies cannot offer a modern flex nib, observations come up frequently that the tooling is too difficult and expensive to create, and that the metallurgy of the flex nibs of the 1930s is no longer discoverable. I have doubts about both of these observations. Wings could be stamped into the design of a nib, the thickness of the steel can be changed, a different-sized or shaped hole could be drilled in a different location. Materials science has unquestionably advanced in the last eight decades. I'm a rank amateur with no training whatsoever in materials science, but even a duffer like me can improve a nib's performance. Trained engineers can undoubtedly do better, and it's encouraging that Jowo and Kanwrite are introducing new flex nib designs.

Thank you, again, to Kevin Thiemann of Fountain Pen Revolution for supplying materials used in these experiments (oh, the sacrificed nibs and feeds!), and for supporting collaboration on FPN among pen companies and enthusiasts.

[Drone]

In the frequent discussion of why nib companies cannot offer a modern flex nib, observations come up frequently that the tooling is too difficult and expensive to create, and that the metallurgy of the flex nibs of the 1930s is no longer discoverable. I have doubts about both of these observations. Wings could be stamped into the design of a nib, the thickness of the steel can be changed, a different-sized or shaped hole could be drilled in a different location. Materials science has unquestionably advanced in the last eight decades. I'm a rank amateur with no training whatsoever in materials science, but even a duffer like me can improve a nib's performance, Trained engineers can undoubtedly do better, and it's encouraging that Jowo and Kanwrite are introducing new flex nib designs.

 

I agree wholeheartedly with your findings, especially point No.-5.

 

May I boldly suggest adding one more point that addresses the feed:

 

6. A pen with a flexible nib married to a plastic feed is generally a bad idea. A flexible nib needs more ink-flow. Feeds made of Ebonite (hard rubber) provide more ink in a controlled way compared with plastic feeds. Ebonite feeds are relatively simple and inexpensive to manufacture using existing numerically-controlled rotating tools, like a lathe. Proof of this rests with the many inexpensive pens with Ebonite feeds coming out of India and Pakistan today. Despite this, we still see Western and Japanese manufacturers putting out half-hearted attempts to add flexibility with modified nibs married to inadequate plastic feeds.

 

Conclusion: A high quality modern pen with a good durable "semi-flexible" nib and an Ebonite feed is easily manufactured today with relatively little development and almost no retooling required. The added cost would be minimal, basically the cost difference between an injection-molded plastic feed versus an automatically turned Ebonite feed. The demand for such pens exists. But nobody is making them.

[Drone]

Here are two pictures of Pilot's Custom Heritage 743 pen with their No.15 (Pilot proprietary sized) FA "Falcon" nib. Pilot's FA nib is quite flexible for a modern nib, but it is being held back by an inadequate plastic feed. In these photos you can clearly see the very effective scallop-cuts that enhance flexibility.

Putting an Ebonite feed in the CH 743/FA pen would transform this pen into a truly useful writing instrument. But Pilot refuses to do it.

Note: The pictures below are linked from Teoh Yi Chie's excellent Review: "Pilot Custom 743 with Falcon Nib". I encourage you see his entire review which includes many more pictures here:

 

http://www.parkablogs.com/node/11809

 

 

[bobje]

David, I agree with your ultimate conclusion. I am guessing that companies don't believe there's a market. They could create these products with little incremental cost. At least Jowo and Kanwrite are taking small steps.

 

Regarding ebonite feeds -- they're almost too effective. When I muster more time and resources, I look forward to taking advantage of your advice on drill tooling. I still believe a central hole or cutout could improve flex, and it's dependent on feed modification.

[ReadyFireAim]

Regarding ebonite feeds -- they're almost too effective.

I've been wondering if an ebonite feed is really necessary on a non-vent nib.

I'm thinking the vent hole essentially stops capillary flow & forms a puddle right there.

Then the slit takes over and draws from the puddle, "fine tuning" the necessary amount of ink.

It becomes basically a 2 stage delivery.

 

The Zebra-G has always been problems because the ink can't bridge the giant vent hole gap fast enough by taking the detour.

If/when it fills the vent hole the nib is overloaded.

 

I think that is where a monster ebonite feed with a lot of big slits is necessary to bypass the hole and act as a reservoir.

(Kind of like a float bowl in a carburetor)

Then the slit can do its thing.

 

Also there may be a ink stretching/milking action going on when nib flex tries to pull ink away from the feed and then snaps back.

 

There is a lot of stuff going on in what looks like a simple device.

 

BTW...The Pilot FA feed just looks all wrong to me.

The slits are too far apart and the too far behind the vent hole among other things.

(I've been looking at mine)

Edited August 3, 2017 by Bordeaux146

[antoniosz]

Did someone say .. finite element analysis ?
This is from about 7-8 years ago. There is a LOT to learn even from this first order calculation.
There results suggest that there is an optimum (non uniform) thickness variation.

Edited August 3, 2017 by antoniosz

[bobje]

Antonio,

this is a fascinating illustration, but I do not know how to read, interpret, or begin to analyze what's going on. Can you help? I'm guessing that red means there's a lot of stress going on, and blue practically none, and the green area is kind of interesting because that looks like where the pivot is taking place, but there's actually less stress there. But I'm just guessing.

[antoniosz]

Yes, your intuition is correct. Red is high stress, blue is practically no stress. The geometry is close to a Waterman #2 vintage nib (except the thickness that is uniform here - but NOT in many vintage nibs). It is seen at an angle from the top. It shows that the tines bent but the part of the nib above the vent hole does not (as expected) and this creates the maximum stresses in the vent hole (which often drives fatigue cracks). There is also a high stress area closer to the tip which is due to the narrowing of the tines. The old nibs usually have a higher thickness close to the tip which counteracts this effect.

[siamackz]

Yes, your intuition is correct. Red is high stress, blue is practically no stress. The geometry is close to a Waterman #2 vintage nib (except the thickness that is uniform here - but NOT in many vintage nibs). It is seen at an angle from the top. It shows that the tines bent but the part of the nib above the vent hole does not (as expected) and this creates the maximum stresses in the vent hole (which often drives fatigue cracks). There is also a high stress area closer to the tip which is due to the narrowing of the tines. The old nibs usually have a higher thickness close to the tip which counteracts this effect.

 

Now I know why the vintage safety MB with flexi nib that I recently bought has a crack at the vent hole! Someone was pushing it too hard!

[Drone]

Did someone say .. finite element analysis ?

This is from about 7-8 years ago. There is a LOT to learn even from this first order calculation.

There results suggest that there is an optimum (non uniform) thickness variation.

 

Interesting diagram. There is a long running debate as to what the optimum breather hole shape is to best distribute stresses when the nib flexes, a circle or a heart. From the picture, one might conclude that the heart-shaped hole has the lead! Actually this conclusion is somewhat intuitive given the bi-lateral symmetry of the nib.

Edited August 4, 2017 by Drone

[Pen Engineer]

Hi to all.

 

Starting in this topic I sort off skimmed through the very interesting information. It always amazes me what adventures you guys get into. And what I have seen so far, from an ingeneering point of view it makes perfect sense.

 

I have written in my website extensively about the mechanics of nibs and their design criteria, which would assist understanding what is going on. Here, I will address some of the points I have observed.

 

A nib's starting point is a section of a tubular piece, which would be as stiff as... whatever you do, slits at various lengths, "breather holes" of various diameters and cut outs, cut aways on the tines or the side of the nib, this all alters the cross section of this pipe section and when the cross section is reduced then the nib is easier to bend.

 

The cross section, which is the most effective, is the distance and material thickness between the "breather hole" and the side of the nib. Distance and material thickness gives you the area of the cross section. The smaller it is the easier the nib flexes.

 

It also makes the nib more flexible when the cross sectional radius is a large a possible. Some nibs flare out, flatten, quite quickly from where the shaping of the tines starts. That's the reason.

 

Lengthening the slit (or having several slits) cuts the tubular section in half, thus, reduces its stiffness.

 

Changing the cross section will give you a springy characteristic while lengthening the slip would be more sloppy and softer and more responsive to writing pressure variations but the slit would not close as quickly.

 

Finding this topic very exciting I would like to write about it on my site (with reference to this forum) and I wonder if it would be ok with you if I use some of you photos (I will mention the source, of course). Just tell me if you don't want it.

[ReadyFireAim]

Hi to all.

 

Starting in this topic I sort off skimmed through the very interesting information. It always amazes me what adventures you guys get into.

I really liked your article on plastic feeds and feed design.

https://fountainpendesign.wordpress.com/feed-supply-ink-function-foutain-pen/fountain-pen-feed-function/

I noticed this after "reinventing the wheel"

 

I would have liked to design a feed with slits increasing in diameter towards the nib, like a small Christmas tree.

My most successful feed design is kind of pear shaped with the Zebra-G sitting on top (larger on the bottom)

Also, it starts out round where it goes into the section and then gets bigger from there from rear to front.

I'm not sure how easy it would be to make with a machine, I sanded it by hand.

It looks a little like a pregnant guppy wearing a Robin Hood hat (nib)

I'd be very interested to know what you think about the difference between vented and non-vented nibs and how capillary action is effected.

Edited August 4, 2017 by Bordeaux146

[antoniosz]

Hi, maybe, maybe not. I would prefer to do the analysis before I proclaim the heart as the winner.

 

 

Interesting diagram. There is a long running debate as to what the optimum breather hole shape is to best distribute stresses when the nib flexes, a circle or a heart. From the picture, one might conclude that the heart-shaped hole has the lead! Actually this conclusion is somewhat intuitive given the bi-lateral symmetry of the nib.

[antoniosz]

Hi PenIngeneer! I will definitely look into your writings. Please feel free to use the image (just quote my name Antonios Zavaliangos)
I am a mechanical engineer by training and I am a professor of materials science and engineering - mechanical behavior of materials is my "love" (ok, second to pens )

 

Hi to all.

 

Starting in this topic I sort off skimmed through the very interesting information. It always amazes me what adventures you guys get into. And what I have seen so far, from an ingeneering point of view it makes perfect sense.

 

I have written in my website extensively about the mechanics of nibs and their design criteria, which would assist understanding what is going on. Here, I will address some of the points I have observed.

 

A nib's starting point is a section of a tubular piece, which would be as stiff as... whatever you do, slits at various lengths, "breather holes" of various diameters and cut outs, cut aways on the tines or the side of the nib, this all alters the cross section of this pipe section and when the cross section is reduced then the nib is easier to bend.

 

The cross section, which is the most effective, is the distance and material thickness between the "breather hole" and the side of the nib. Distance and material thickness gives you the area of the cross section. The smaller it is the easier the nib flexes.

 

It also makes the nib more flexible when the cross sectional radius is a large a possible. Some nibs flare out, flatten, quite quickly from where the shaping of the tines starts. That's the reason.

 

Lengthening the slit (or having several slits) cuts the tubular section in half, thus, reduces its stiffness.

 

Changing the cross section will give you a springy characteristic while lengthening the slip would be more sloppy and softer and more responsive to writing pressure variations but the slit would not close as quickly.

 

Finding this topic very exciting I would like to write about it on my site (with reference to this forum) and I wonder if it would be ok with you if I use some of you photos (I will mention the source, of course). Just tell me if you don't want it.

[bobje]

I love Fountain Pen Network. I don't know the backgrounds of everyone, but in just this one thread on flexible nibs, we have the following:

 

- the owner of a pen company

- a calligrapher who studied with Lloyd Reynolds

- a professor of materials science

- an expert on Chinese pens

- an engineer in writing instruments

- an expert in vintage flex pens