Parameterizing Flex Nibs

[Arnav]

Good evening!

 

I've been trying to synthesize much of what's been said about flexible nibs. Here's my attempt. Please correct me if I've bolixed it up!

 

It sounds like there are 3 separate (potentially quantifiable) parameters of a nib's flexibility:

• Flexiness: How far can the tines spread while maintaining ink flow, and without damaging the nib. More flexiness means the tines can spread wider.
  
• Yieldiness: How little force is needed to spread the tines? More yieldiness means less force is needed.
  
• Responsiveness or "springiness": How quickly does the tine flex track the applied force? More responsiveness means the tine flex responds more quickly to change of force.
  

Are there well-accepted terms for these parameters? Have I missed any parameters?

 

Is it true that more "responsiveness" is always better, but not necessarily more "flexiness" or more "yieldiness"?

 

Could other FPNers post these types of descriptions of some of their better and worse flex nibs, and what makes them good or bad for which purposes?

 

For me, at least, this would be immensely fascinating and educational.

 

Thanks in advance! -Arnav

[Guest Denis Richard]

Hi Arnav,

 

I don't know if there are any accepted classifications or definitions, but 2 and 3 seem to me to be equivalent.

 

1 and 2 are truly properties of the nib, but 3 is force/user dependent, and the less force is needed (2), the more responsive will be the nib.

 

Denis.

[Titivillus]

Hi Arnav,

 

I don't know if there are any accepted classifications or definitions, but 2 and 3 seem to me to be equivalent.

 

1 and 2 are truly properties of the nib, but 3 is force/user dependent, and the less force is needed (2), the more responsive will be the nib.

 

Denis.

 

 

Nope I think that the second two are opposite and they should be equivalent in opposite directions but a nib has a bit of hysteresis and so you can have a pen that wil spread at the slightest but the response in returning to the base position is different. Or the other way around.

 

Kurt H

[Arnav]

Thanks, Denis.

 

I included #3 ("responsiveness"/"springiness") because I had read (somewhere here on FPN) that some nibs don't "close" right away when force is removed, and that this is a problem for Spencerian script -- the thick-to-thin transitions become muddied.

[Arnav]

F.Y.I., #3 ("responsiveness"/"springiness") was my attempt to summarize some of what Antoniosz wrote about here.

[Titivillus]

Thanks, Denis.

 

I included #3 ("responsiveness"/"springiness") because I had read (somewhere here on FPN) that some nibs don't "close" right away when force is removed, and that this is a problem for Spencerian script -- the thick-to-thin transitions become muddied.

yep that is the metal's hysteresis!

[Guest Denis Richard]

I see... I did not think about that.

[Arnav]

I'll stir the pot a bit more...

 

Are there inherent tradeoffs in a flex nib's design parameters? For example (I don't know this to be true!), does thinning the tines increase the "flexiness", but decrease its "responsiveness" (or, alternatively, increase the hysteresis).

 

-Arnav

[antoniosz]

All parameters for a flex nib are "clear" except one.

 

1. The maximum safe opening and the maximum safe force that do not produce permanent deformation anywhere in the nib. Maybe this should be called flexing limit . This parameter depends on nib material, nib geometry, and pen holding position.

 

2. The amount of tine opening achieved by a given force. This is perhaps the best place to use the term flex.

 

3. The amount of vertical deflection of the nib with respect to tine opening soft-to-flex ratio. No they are not the same. There are nibs that can take significant deflection with little tine opening (soft but not flex).

 

4. There is one more possible flex nib parameter which is the maximum thin-thick contrast (thin-to-thick ratio). I.e., it is not (1) above alone that defines a good flex nib but rather the ratio of the thinnest to thicknest possible lines. I beleive this is true but (1) is related to the safe usage of the nib. For a nib that writes very fine at low pressure I can get a good effect without having to push close to the flexing limit.

 

5. The most difficult parameter is the fast return from thick to thin lines.

I do not want to use the term hysteresis because hysteresis is connected to energy dissipation** (for the chemical engineers in the discussion ... these are not polymers ... ). This performance metric is not 100% clear (at least in my head). Possible factors are:

 

a) How well the feed and the nib "cooperate". I.e., although we need a generous feed to coop with the high ink requirements when flexing, the feed should not flood the nib during thick-to-thin returns.

 

There is a theory that upon release the return of the nib to the initial configuration is not instantaneous because of inertia. This argument has been put forward because some practitioners praised (modified - no Levenger) titanium nibs (low density - higher stiffness than gold) - even steel flex nibs over gold. If this argument is true then there is coupling between fast return performance and flex (No 2). In other words a semiflex nib has a better return performance than a flex one....

 

I sincerely hope that these are not intimidating to the non-technical person. On the other the beauty of physics and math is that all these can be expressed very naturally and very precisely mathematically. But I will spare you the details.

 

AZ

 

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** There is no hysteresis is a flex that is safely and slowly flexed.

If hysteresis occurs, i.e. if there is a residual tine opening upon force removal - this would be a (bad) sign of permanent deformation somewhere in the nib.

This means that the road to a fatigue crack has started...

[Guest Denis Richard]

Antonios,

 

I'm sure you thought about that already, but considering that their are little chances that a mechanical study of flexible FP nibs exists or would be conducted, can you think of any other similar mechanical system that could have been the subject of some more extensive studies ?

 

Denis.

[wimg]

Hi Arnav,

 

I just would like to add a note on springiness. This is not necessarily related or bound to flex.

 

F.e., modern Stipula nibs are very springy, they have a bouncy behaviour, almost like a shock absorber, which, IMO, makes for a very pleasant writing experience.

 

Essentially, rather than the tines spreading sideways, both tines bend upward slightly (ok, the tines may spread a little, but it certainly isn´t flex), and back again quickly, without compromising ink flow. So, the paper contact is maintained in a very pleasant way; it allows for good "road holding", and good feed back from writing.

 

Just my 2c.

 

Kind regards, Wim

[antoniosz]

Antonios,

 

I'm sure you thought about that already, but considering that their are little chances that a mechanical study of flexible FP nibs exists or would be conducted, can you think of any other similar mechanical system that could have been the subject of some more extensive studies ?

 

Denis.

Denis,

 

The only study of flex that I know is on my ... hard drive.

I have analytical mechanics solutions for the flexing of nibs for simple shapes, and numerical integrations for more complicated one.

I need to complete some FEM simulations to examine the methodologies of improving the flex in an existing nib.

I need also to work on the inertia argument. Of course eveything has to be double check.

 

It is just too bad that this is ... unfunded research, and I have to put some time on the funded one

So it will finish eventually some time in the ... future.

Unless I find a student flexohilic to do a senior design/thesis on it.

 

AZ

[Guest Denis Richard]

It is just too bad that this is ... unfunded research, and I have to put some time on the funded one   

So it will finish eventually some time in the ... future.

Unless I find a student flexohilic to do a senior design/thesis on it.

 

AZ

I hear your pain.... In the good old FP days, you may have been able to find funding from on of the big companies... But of course, in the same good old days, you did not need to hunt for funds... <_<

 

Great to hear that you are working on it though.

Edited March 23, 2005 by Denis Richard

[Titivillus]

** There is no hysteresis is a flex that is safely and slowly flexed.

If hysteresis occurs, i.e. if there is a residual tine opening upon force removal - this would be a (bad) sign of permanent deformation somewhere in the nib.

This means that the road to a fatigue crack has started...

Maybe I was using the term incorrectly but I had though that hysteresis was the change in a force vs. distance curve such that the release of a force does not line up with the initial force applied line.

 

If the force applied causes a specific change in tine distance and the release of pressure causes a opposite but not quite exact change then there is some hysteresis.

 

 

Kurt H

[Guest Denis Richard]

If the force applied causes a specific change in tine distance and the release of pressure causes a opposite but not quite exact change then there is some hysteresis.

I would say that the forces acting during the spreading and the closing of the tines are different. Hence the term hysteresis might be improper.

[Stylo]

There is a theory that upon release the return of the nib to the initial configuration is not instantaneous because of inertia. This argument has been put forward because some practitioners praised (modified - no Levenger) titanium nibs (low density - higher stiffness than gold) - even steel flex nibs over gold. If this argument is true then there is coupling between fast return performance and flex (No 2). In other words a semiflex nib has a better return performance than a flex one....

That seems pretty obvious. The return speed seems to be a function of the modulus of elasticity, which in turn determines how flexible the nib is. Antonio, do you think there may be any appreciable non-elastic effects with common nib materials, especially gold? Do you think there might be some amount of plasticity here?

 

On the other the beauty of physics and math is that all these can be expressed very naturally and very precisely mathematically.

 

Nothing like a nice little tensor to sum it up, eh?

[Guest Denis Richard]

Nothing like a nice little tensor to sum it up, eh?

Sheeez... I'll trade you my tensors for a system of differential equations anytime. Tensors are nasty. Never got to get a feel of them.

[Stylo]

Unless I find a student flexohilic to do a senior design/thesis on it.

Sounds like a neat idea. You could even get them to do a very idealized analysis. For example, you could have them represent the nib as just a stick with density and stiffness variation along the axis that would approximate the 3D nature (or 2D triangle for simplicity) of the actual nib (is that what you would call lumped density and stiffness?), then get the student to compute eigenvalues of the problem to come up with the stick response. If you think there might be any non-elastic effects, you can make them include it in the model and force them to solve the problem numerically if it can't be done analytically. Make them sweat a little

[Stylo]

Sheeez... I'll trade you my tensors for a system of differential equations anytime. Tensors are nasty. Never got to get a feel of them.

Need the right teacher/book for it Was clobbered with them in fluids and solids. Often you are better off without them, but sometimes they are much more convenient. I suspect someone like Antonio would use them at least for the constitutive equations, especially with composites.

[Guest Denis Richard]

I could give a hand if you can fit a nib into the hydrodynamic approximation...

 

I can provide computing power if needed, but I'm guessing you have waht you need.