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(Oli?), Germany

lead diameter
production date
2 mm
twist-lock clutch
machined plastic barrel, metal mechanism
none known
    Oli-Rotomin instruction sheet

I do not spreken zee doytch, but I swear to kittens these instructions recommend gasoline as a lubricant for the bearings.
special features ball-bearing lead spinning mechanism
Oli-Rotomin package
  Oli-Rotomin box

edge roller

  nose clamp collet grip barrel tail

detail diagram:  The nose clamp, collet grip, and tailpiece are rigidly connected via the lead tube (not visible) which runs through the barrel.  The barrel is connected to that assembly by ball bearings.

The idea behind the Rotomin is a pencil with a constantly rotating lead.  In principle such a thing is useful in that a rotating lead wears evenly and requires less dressing (sharpening) than one worn flat by the drawing surface.  It is a standard technique when drafting with a leadholder to spin the pencil as a line is drawn, but when drawing a long stroke it can be tricky to keep the pencil turning throughout.

To achieve its automatic rotation, the Rotomin is constructed with its barrel isolated from the lead holding assembly save for two bearing points.  To achieve the low friction necessary for the lead holding assembly to rotate while drawing pressure is being applied via the barrel is no simple trick.  The Rotomin is equipped with tiny ball bearings that look no bigger than 0.25 mm. 

The engineering of the Rotomin is peerless, but the design does have serious shortcomings, the most serious of which is the tedious process of pointing the lead as discussed on the Keuffel & Esser Speedraft patent page, a pencil which shares this difficulty.  Another serious problem is damage caused by the Rotomin’s grooved roller tip to the straightedge or template.  For pencil rotation to have any benefit, the lead must be oblique to the drawing surface, otherwise the wear pattern is identical to a stationary lead. When held obliquely to the surface and rolled against the typically plastic edge of a drawing aid, the serrations on the Rotomin’s nose have a shearing effect which degrades the edge.

How do you spell “not drawing with a full range of degrees” in German?