What is a Frequency Waveform/Stroke Profile and why is it relevant to tattooing?
Frequency, related to tattoo needles, is how frequent a needle is oscillating in a given second. Generally a tattoo machine will oscillate a needle at a frequency of between 60-150 hz (pokes per second). A Frequency Waveform or Stroke Profile is the pattern created when a needle is graphed by its position over time. Below, you will see an example of a waveform of a needle while used with a traditional coil machine. This graph represents the total duration of one cycle, or one needle poke. Notice how the needle is in contact with the skin for roughly 10% of its total cycle duration. This means that the needles get in and out of the skin very quickly, and therefore do not dwell inside the skin for very long.
A Standard or Traditional Rotary tattoo machine has a very different stroke profile than a Traditional Coil tattoo machine. Since the mechanism and geometry is different, the Wave Form or Stroke Profile is different, as illustrated in the graph below. Notice that the needle, in this configuration, is in contact with the skin for roughly 35% of its total stroke cycle. The result of this is a dragging sensation, as the artist is moving his or her hand forward, yet the needle has not yet been given sufficient time to retract. This can also result in unnecessary skin tissue trauma/damage.
Additionally, many Rotary machine manufacturers have implemented a type of cushioning system into their machines, to allow for a cam to complete a cycle without the need for the needle(s) to completely extend to the farthest part of the stroke. While this does seem to achieve the benefit of a softer hitting machine, in reality these cushions flatten the extended-most portion of their waveforms (the portion in which the needles are interacting with skin), thereby extending the amount of time a needle will dwell inside the skin. This can result in an even more traumatic effect on the skin. Notice in the graph below how the waveform (at the top of the curve) has a flat spot, widening the amount of time per cycle a needle spends inside the skin.
The Neuma FOUR, although it is a Rotary tattoo machine, does not have the same stroke profile as a Traditional Rotary tattoo machine. The mechanism is designed such that the needle has a dwell in the fully retracted position of the needle, which results in the needle getting in and out of the skin much faster that a Standard Rotary tattoo machine, and more similar to a Traditional Coil tattoo machine. The result of this is dramatically reduced drag on the skin while an artist is moving their hand across it, which equates to substantially reduced trauma to the skin. Notice in the graph below, in this configuration and with this cam (.20 cam), the needle is in contact with the skin for roughly only 20% of its total cycle. In effect, this is a best-of-both-worlds scenario, wherein you have the benefits of both Coil and Rotary style tattoo machines. Also note that these cams are variable, so that an artist can experiment with what percentage of a cycle they prefer the needle to be in contact with the skin.