Coil, rotary and pen: comparing architectures

Coil and rotary are distinguished by their working principle: in the first the movement comes from electromagnets, in the second from a rotating motor. Pen, instead, indicates the format, that is, the cylindrical body held like a pen. A pen is almost always a rotary that uses cartridges, but the name alone does not guarantee it.

To compare in an orderly way it is therefore useful to keep two questions apart: how is the movement produced? and how is the machine made in the hand?

A coil machine uses two electromagnetic coils that attract a metal bar (the armature bar). When the bar moves, it opens an electrical contact: the coils switch off, a spring pulls the bar back, the contact closes again and the cycle restarts. The frame, coils, capacitor, springs and contact screws are the main components.

The needle's movement therefore depends on all of these elements together: length and stiffness of the springs, distance between components, voltage and characteristics of the coils. The adjustments are mechanical and the result also depends on the hand that makes them and the needles used.

A rotary machine starts from an electric motor that spins. A mechanism, usually an eccentric, turns the rotation into the needle's back-and-forth movement. In so-called direct drive systems the motor acts on the needle without intermediate arms; other systems use levers or arms that add elasticity or change the stroke. The term direct drive is used by manufacturers with slightly different meanings.

The stroke is often defined by the machine's design, and on some models it is adjustable or interchangeable. Speed depends on voltage and the motor.

The pen format gives the machine a cylindrical, elongated body in which the motor and mechanism are placed along the axis. It can be powered by cable or battery (in the latter case it is called a wireless pen) and usually uses cartridges. There are also machines of other shapes that use the same rotary principle.

The table summarises how the main characteristics change. They are general tendencies: every manufacturer and model can make different choices.

A coil can be adjusted from the outside and in depth: springs, contacts and coils make it possible to change the stroke, speed and character of the machine. This makes it very flexible, but it takes time and familiarity, and the setup is largely subjective. A rotary generally offers fewer adjustments, but more repeatable ones: the machine behaves more consistently from one session to the next.

A coil concentrates mass in the frame and coils; a pen distributes it along an elongated body, and in a wireless pen the battery moves the centre of mass further. Total weight, therefore, does not tell the whole story: two machines of the same weight can balance very differently.

In coils many components (springs, contact screws, capacitor) are accessible and replaceable, but they wear and need checking. In rotaries maintenance mostly concerns the motor, bearings and mechanism, and is often left to the manufacturer or handled by replacement. Cleaning and replacement procedures depend on the model and are to be read in the instructions.

The architectures did not clearly replace one another: they added up.

• Electromagnetic machines. The first tattoo machines derive from an electric engraving device adapted to tattooing in the late nineteenth century. From there comes the coil family, which for decades remained the reference.
• Rotary. Machines with a rotating motor spread later and offer more constant operation and usually more silent running.
• Direct drive and other systems. Designers refine the transmission: eccentrics, arms, systems with more or less elasticity.
• Cartridges. Needle, tip and membrane become a single sterile, single-use element, and machines are designed around this system.
• Pens. The cylindrical body accompanies cartridges and changes ergonomics.
• Batteries and wireless. With more compact batteries, cordless pens appear, often with removable or replaceable batteries.
• Modular machines. Some recent models make it possible to change the stroke or other parameters without changing machine.

Exact dates and the boundaries between one phase and another are debated: the history of manufacturers and inventions should be checked against specialist sources.

There is no system that is best in absolute terms. Those who want very fine control and like to work on the machine may find coils a familiar tool. Those who prefer constant behaviour and little maintenance may lean towards rotaries. Those who work with cartridges or place great importance on ergonomics and freedom from the cord may find a pen format consistent with their way of working. These are preferences tied to hand, style and habit, not technical verdicts.