I've been asked countless times what the stroke length is on my machines, if I can do custom strokes for someone who currently uses a 3.5mm and loves it and ultimately, why I don't do custom stroke lengths on my machines. In short, the stroke length on my machines are right about 4.5mm, I don't manipulate this because it is directly responsible for the tune and stroke characteristics that I've designed into my machines. Let me explain.
Many people are mistaken that a shorter cam offset on a rotary makes for a faster machine. For example a 3-3.5mm stroke is meant for lining and anything above that is meant for shading. Because liners traditionally run faster than shaders, when not aware of the actual dynamics of the mechanism that logic may make sense. A smaller cam offset does not make the machine cycle faster however. The cam is not a gear, in that one rotation of the spindle will always equal one rotation of the cam, which will in turn one full stroke of the needle. So a machine that has a 3mm stroke running at 6v’s for instance will be running the same speed as the same machine with a 4mm stroke at the same voltage. That being said, cam offset does manipulate needle speed. This may seem confusing at first but think of it this way. A machine that is set up with a 4mm stroke running at the same voltage/ speed as a machine that is set up with a 3mm stroke the needle is cycling at the same speed as the 3mm, but traveling a greater distance in the same amount of time. So the needles are traveling faster but the machine is not cycling faster. This needle speed creates a snappy, punchy feel to the machine. A characteristic I like in my liners, and not as much in my shaders. In the same respects, a 3.5mm stroke will feel completely different on different machines. If you love your 3.5mm on your Neotat you wouldn't necessarily love a 3.5mm on my machines, There are too many factors to account for to make this generalization.
To break down stroke characteristics even further lets discuss responsiveness. Take into account that the cam is essentially a lever. The longer the lever extends from the center the harder the machine will have to work to move it against resistance. So a motor with a 3.5mm cam won’t be working as hard pushing a needle in to the skin as a machine with a 4mm cam. A DC motor unlike a coil machine however will always finish it’s stroke. Meaning it will always either go all the way around to complete a cycle or stall completely. A coil machine doesn’t have to finish a stroke. The magnets pull down on the armature bar, the needles engage the skin, when the resistance gets too great the downward motion stops and the springs pull the armature bar back up. When a coil machine is tuned and ran properly in the skin the armature bar won’t even reach the front coil on it’s cycle. The machine is being responsive to the skin, or the skin is telling the needles how deep to go, rather than vice versa. This is paramount in a well tuned machine, whether coil or rotary. This stroke characteristic allows the absolute most skin saturation, the least skin trauma and the fastest heal times. I use the coil machine example to describe a stroke characteristic that many rotary machine builders try to replicate with adjustable give. The way I allow for this with my machines is by pairing the ideal cam offset to the right motor. Every DC motor has a set torque rating at a set voltage/ speed. By pairing just the right offset cam to the right motor I manipulate the motor to slow down when meeting the resistance of the skin. By allowing the needles to slow down in the skin you allow the needles to open up the skin more. This allows for greater saturation, and a more efficient stroke with shading and lining. So without any adjustments, the machine is already set up and tuned to respond to the skin and to have the best stroke characteristics. Rotaries with a shorter cam offset often spend just as much time out of the skin as in the skin. This 50/50 stroke creates turbulence in the ink well of your tube rather than creating a nice flow of ink down to the skin.
The last topic I will discuss here is needle setup. So many artists I’ve talked to set up their machines how they were taught to do so by their mentors. A slight bend in the needle bar and adjust the tube tip to be even with the needle tip when the needles are fully retracted. This is absurd to use this as the rule of thumb for every machine you set up. Let me explain. If a machine only has a 3 or 3.5mm throw then this makes more sense, but I’ve seen so many people use this setup on a 4.5 - 4.6mm stroke machine. I only hang out the amount of needle I plan on using, I don’t care where the needles are in relation to the tube tip when retracted. Let me break this down. The further the needles are reaching out from the tube tip the further the ink has to travel to reach the skin, and the harder it is create a positive ink flow. This is even made worse when you consider that in this needle setup the solder band on the needle grouping never travels outside the tube tip, all but blocking ink flow completely. I like a longer stroke on my machines, not just because of the tuning it allows but because I can set up the tube to reveal as much needle as I want and the rest of the stroke travels in to the ink reservoir of the tube, and back out again picking up all that ink on it’s way down, creating a positive ink flow down to the skin.
I hope this information is helpful, useful or at the very least inspires a new perspective when thinking about tattoo machines, more specifically rotary tattoo machines.