Fountain Pen Design

Function, Development, Construction and Fabrication

57-5 Caps – The Clip

Early in the nineteenth century, pocket clips appeared for men’s pens, originally as optional extras. Ladies often opted for smaller pens without a clip but having a ring at the cap’s top for attachment to chains. Some men used the same design and linked them to their watch chains and wore them in vest pockets.

Obviously, a good reason for a clip on a cap is that it causes the user to store the pen in a nib upwards position. (This permits the possible air pressure increase in the reservoir to escape without pushing out any ink.)

Styles of Clips

1.)  Stiff Metal Clip, hinged, springloaded

Photo 1 — Lamy cp1

Clips come in many versions. A good clip would be stiff within itself, be mounted on a pivot pin or pivotable edge and be pushed against the cap body with a return spring, a compression spring of some sort. See Photo 1. These clips move relatively easy and can open up to five millimetres with the force hardly increasing. 

Photo 2 — TWSBI

An example of a well-ingeneered clip is shown in Photo 2. Here, the clip is hinged on an actual hinge pin while in other design solutions the clip hinges on a sharp edge.

You may think that these are quite a few components to simply achieve a moveable clip.  However, it is here where quality shows.  Keeping the cost down depends on the skills of the manufacturing ingeneers.  “Good quality does not have to cost one cent more,” is one of my favourite sayings.

In Photo 1 and 2, the clips are solid but the stiffness can also be created through the clip having a U, V or box-shaped cross-section.

Photo 3 — Parker 65

Photo 3 shows an example of this well-known construction.  Where the clip is attached to the cap body the highest moment occurs.  There the V-shaped feathers cause the strongest stiffness.  The shaft and point are tubular.  The ring is embedded in an elastic mounting, which supplies the pre-load.

Disappointed I must add that a deceptively similar clip is used on Parker ballpoint pens where it is immovably connected with the pen body.

Photo 4 — Penn State Industries

In such a situation a clip’s purpose is reduced to that of a mere ornamental logo to entice customers.

A similar example is shown in Photo 4.  Through profiling the cross-section, the clip is very stiff and neither does the mounting provide any elasticity.  I marked the area of possible flexibility with a blue line.  The same applies to the clip in Photo 3.

Internet

Photo 5 — Elastic Hinge

2.)  Stiff Metal Clip, flat spring/hinge

In the version of clip shown in Photo 5 the stiffness of the clip is created through a U-shaped cross-section.  The clamping force between the clip and the cap body is caused by a blade spring, which also acts as the hinge.

Photo 6 shows a style of clip, which lifts off the barrel when one pushes down on the extended end of the clip.

Photo 6 — Rocker or Conklin Clip

This helps the clip to slip on and off any thicker material.  I have seen such a clip on a ball-pen where it is used to retract the refill.  The same idea could be applied to a fountain pen cap to disengage the cap from the fountain pen. That would be something novel.

However, the screw-on and clip-on cap can cause enough confusion about the way to remove them from the fountain pen, this style would add the third version still not offering any visible distinction for separation.  Let’s keep on thinking!

3.)  Elastic Clips, flat spring

Elastic clips are called this way because they are flexible within themselves.  Often they are flat and this way they offer the best elastic characteristics and range.

Photo 7 — Uniball Micro Deluxe

The mounting with the cap body is stiff and the curved part is inflexible because of work-hardening. See Photo 7.  With this kind of clip, a preload can be created through the assembly with the cap body where the two shapes have some interference. The clip is held in place by the red coloured component, which acts like a wedge.  It further indicates the colour of the ink in the pen.

The clip in Photo 8 has a curved cross-section which makes it stiffer along its shank.

Photo 8 — Jinhao 599

Through the nature of a leave spring, the resistance against a bending force increases rapidly with the reduction of the radius and the widening of the gap between the clip and the cap body.

Therefore, the range of gentle flexibility of these clips is narrow and forcing them on thick material may result in plastic deformation, and they may not return to the clip surface.  I have talked about this principle in the chapter about Nib Mechanics.

Photo 9 — Fisher Space Pen Bullet

Since their clamping force is quite high when pushed on thicker material, they often mark or even damage the material.

In Photo 9 I show an example of a flat spring clip.  The pressure point is formed through folding back the metal strip.  Often such components are formed while the material is in its malleable state and they are hardened afterwards.

4.)  Elastic Clips, Wire

Photo 10 — Montblanc Turbo

The only difference between this style and the one in paragraph 3.) is that the clip is made of a piece of elastic wire.  Generally, they are not as functional like the flat spring clips because wires have a smaller elastic range and therefore tend to deform plastically more easily.  In my opinion, wire clips are more a styling feature rather than good ingeneering design.  It is the element of function, which draws the line between lasting pristine simplicity and fashionable decor.

Photo 11 — Lamy Safari

Photo 10 shows the gap between the cap body and the pressure point after plastic deformation of an ill-designed clip. Further, it shows that a reputable brand name does not always stand for good design.  The Lamy clip in Photo 11 is very stiff in the section of the wire but at least has some inbuilt elasticity in the clip mounting.

Photo 12 — Clip by Schaeffertec

An example similar to the Lamy design is shown in Photo 12.  Here the elasticity is created by a (hopefully) elastic enough small leave spring on the mounting ring, which also serves to hold the wires in their position, rather than relying on the strength of the clip screw.

5.)  Elastic Clips made of Plastic, two Parts

Photo 13 — Pilot Petit 1

The construction principle is the same as described in paragraph 3.), however, the clip is made from plastic with an elastic range of deformation.  The cap body and the clip are two separate components often made of different materials of which the clip material is more flexible.  See Photo 13.

The preload is achieved during assembly through the dimensional interference of the two components.

This elasticity range of plastic is considerably less than that of metal.  The plastic reaches plastic deformation at smaller openings between clip and cap body.

6.)  Elastic Clips made of Plastic, one Part

Photo 14 — Paper Mate Kilometrico

The simplest and cheapest version to produce a clip is to injection mould the clip with the cap as one part, see Photo 14.  I have shown this construction for the sake of completeness.  I have not seen it applied in fountain pens.

These arrangements have no preload, there is a gap between clip and cap body and this type of clip deforms very easily.  They are suitable to hook onto a sash or the like but only provide some holding force when deformed by the material they are clipped onto.

Photo 15 — Uniball Signo

There are designs where the pressure point workes together with the pen body, Photo 15.  Initially, when the pen is inserted into the cap, they don’t line up, which they will when completely engaged.  This causes a pre-load.

There is a constant battle between the force that keeps the cap on the pen and the force between the clip and whatever it is holding onto.

The shape shown in Photo 14 has a long lead-in before the pressure point comes into action which I consider an advantage when engaging the clip with some material.

Ingeneering Commentary

It amazes me that some upper-end brands squeeze the last cent out of their products and sacrifice function and durability and still charge exorbitant prices, while moderately priced pens, even cheap pens offer well-designed solutions.

Furthermore, a good clip would have a “smooth” pressure point (contact with the cap body) so it can glide on most surfaces with a predetermined, designed range of friction.

In most clip designs the pressure point is shaped through a small, fixed protrusion on the clip.  And then we find even cheap pens’ clips with a free spinning roller or ball at the tip of the clip. So even if the clip is heavily preloaded, it will still slide well.  The ultimate design would offer free moving pressure surfaces on both sides.  This way, the friction can be determined independent of the surface of the material the clip is engaged with.

Opposing Forces can cause some dilemma when a fountain pen is kept in a tight fitting pocket or a tie in a bag or briefcase and the cap is kept on the pen with a slip-on mechanism.  When taken the pen out of that tight pocket the pen is pulled by the cap. It has happened that the friction force between pocket and barrel is higher than the force between the slip-on cap and the section.

Do I need to describe the mess? A screw-on cap would certainly have prevented it.

Whatever clip design, when the cap is on the pen, it prevents the pen from rolling off the desk.  For some designs, it is the only function.

Testing

Here are some comparative data of pens I found in my drawer. I held the cap horizontal and applied a load near the clip (a hinged clip) contact point with the cap (see Photo 16).

Photo 16 — Force measured near Contact on a hinged Clip

Three measurements were taken; the preload just at lift-off, then at 0.7mm (thickness of a credit card) and at 2mm.

I have chosen three styles of clips.  The selection criteria?  Anything I found in my drawer and what I could have coped with if damaged, perhaps not the Montblanc because it has some sentimental value.

Hinged-metal has a stiff clip which is hinged and includes a spring to cause the closing force like described in paragraph 1.

The spring-metal style has a stiff clip made of one material, often a die-cast, while the hinge is made of a blade spring, which in this version is attached to a mounting ring as shown in Photo 5 in paragraph 2.

The clip of the spring-plastic style as described in paragraph 5.  The clip and the cap are two components and the preload is caused by an interference during assembly.  Unfortunately, after time, plastic creeps and the preload is reduced to basically null.

Table 1 Style Clip Length
[mm]
Preload
[N]
Load at 0.7mm
[N]
Load at 2mm
[N]
Spring constant
[N/mm]
Lamy cp1 Hinged metal 36 1.4 1.7 2.4 0.5
Lamy 2000 Hinged metal 30 0.7 0.9 1.2 0.25
Shorty Hinged metal 20 0 0.8 2.2 c 1.1
Montblanc 22 Spring metal 32 2.5 4.6 8.5 c 3
Curved wire Spring metal 50 0 1.1 3.2 1.6
Sharpie Spring plastic 35 0.5 2 4.6 c 2.1

The red c indicates that I calculated the value to avoid damage to the clip.  And remember: 1N (Newton) ≈ 100 grams.

Discussion: Indubitably, the hinged and spring-loaded metal clips perform the best and I like to recommend the Lamy cp1 as a benchmark. You can see the small spring constant, which indicates their softness. Combined with a preload, their clamping force does not change much (≈ 30%) when increasing the gap.

The Lamy 2000 is a bit too soft.

The Shorty having no preload has a strong increase of force, from 0.7mm up to 2mm almost threefold.  I found this clip useless, merely ornamental.

All spring clips did not close, leaving gaps of 0.4mm up to 1mm. The curved wire clip performed reasonably well and had the lowest spring constant in this group. Sharpie’s clip was too stiff for the 2mm gap to be practical.

Montblanc offered a gold-plated ornament and not a clip.  With its high spring constant takes it outside the practical range; to serve as a useful clip it is far too stiff. I didn’t dare open it to 2mm because I worried it would deform permanently or even break.

Above all: Enjoy!

Ω

Amadeus W.
Ingeneer

16 January 2019

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