Leadholder Mechanics

Leadholder Anatomy

	jaws		barrel
point						end
nose piece grip shoulder shank (with imprint) tail   pushbutton Drafting Leadholder with Spring Clutch

clamping nut

grip

shank

tail

point

end

shoulder

barrel

tailpiece (with lead degree indicator)

Drafting Leadholder with Twist-Lock Clutch

I’ve tried to standardize the terms used throughout the site, but in catalog descriptions and patents the terms vary widely.  Some of the many synonyms and overlapping terms I will mention here:

 

A Word About Grips:

One of the most distinctive features of many drafting leadholders is the grip.  On many, such as the Koh-I-Noor 5611 shown above it resembles the business end of a machinist’s tool, discouraging rather than inviting contact with the fingers.  And indeed, if one were to use such a pencil as many use typical writing instruments—with a firm, unvarying grip—calloused fingers are the inevitable result.

In the hands of an experienced draftsman, however, the utility of the harsh grip is demonstrated.  He holds the pencil with a very light touch.  As he draws, the pencil is rotated continuously to prevent flat spots from forming on the lead.  The sharp knurling of the grip allows the pencil to be controlled with a minimum of finger pressure which lets him draw for hours without fatigue.

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Leadholder Clamping Mechanisms

Unlike mechanical pencils use for writing, drafting leadholders must grip the lead firmly so that it can resist being pushed in, pulled out, or axially rotated.  This is necessary not only for the sake of precision, but also to permit the pointing of the lead which introduces its own set of forces on the lead.  The mechanism used to solve this problem is commonly called the “clutch,” although it is more specifically a jawed pressure clamp.

Prior to the precise mechanical drafting leadholders and consistent lead sizes of the late 19th century, related instruments such as porte-crayons and bow pencils (compasses) used a crude but effective method of securing the marking medium. This was the slide-lock clutch which consists of tapering jaws drawn together by a sliding ring.  This method is well suited to irregularly shaped media and is still used today for artist's charcoal holders.

Porte-crayon with slide-locking clutch.

There have been two primary methods of achieving sufficient pressure on the jaws to grip the pencil lead:  a threaded twist lock clutch and a spring-lock clutch.  The earliest precision drafting leadholders had twist lock clutches.  In the mid-20th century, the spring-lock clutch was adapted for use in drafting pencils and quickly became the norm.

The major clutch mechanisms used for drafting pencils are:

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Twist-Lock Clutch This is the mechanism used in the earliest drafting leadholders.  From what I have observed, it was used on writing pencils prior to being adapted to drafting pencils.

This Koh-I-Noor 1511 is an example of a leadholder with a twist lock clutch.

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Reverse Twist-Lock Clutch This is an evolution of the twist-lock clutch.  Improvements are:  exposed jaws, loosened chuck less likely to be removed entirely, and loosened chuck does not obscure the lead.  These usually have a left-handed thread.

The Eagle Turquoise 3375 is an example of a leadholder with a reverse twist lock clutch.

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Pushbutton Spring Clutch This is the mechanism that has ruled for half a century.  Most recent drafting leadholders use minor variations of this mechanism.  The most notable variation is the location of the spring, which is commonly located at the tail end of the pencil.

The Caran d’Ache Fixpencil was the first precision pushbutton spring clutch drafting leadholder.  The mechanism was in use prior to the Fixpencil in non-drafting pencils such as the Eagle Automatic No. 861 (image courtesy Caran d’Ache)

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Pushbutton Advance Clutch This is the mechanism ubiquitous in thin lead drafting pencils.  There have been attempts to adapt variations of this mechanism to thick lead drafting leadholders with marginal success. The unique components of this mechanism are the friction bushing in the nose that prevents the lead from moving freely, and the clutch ring—shown in black—which engages the collet (jaws) under the pressure of the spring and is released at the forward portion of the pushbutton stroke.

The Koh-I-Noor 5618 is an example of a leadholder with a Pushbutton Advance clutch.