Steps for HOWTO Make a CNC pickup winder
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Step 2: Winding pattern
Another consideration is the desired winding pattern, as this affects the mechanics of the machine. Most ideas about winding patterns for machine wound coils come from the manufacturers of motor or solenoid coils. Traditionally guitar pickups have been hand wound (with acceptable results) and the reguality of the winding pattern is probably not an important consideration. Consistency is desirable, if you stumble across a good sounding design you want to be able to reproduce it reliably.
Helical winding
To produce helical winding the wire traverses across the bobbin smoothly as the bobbin rotates. With each rotation of the coil, the wire criss-crosses the layer below, as consecutive layers have opposite helical lay. The resulting effect is like trying to force a left handed-thread nut onto a right-hand thread screw. The wire tries to follow the groove between two turns beneath it, but that groove is slanted in the opposite direction, and before one full turn is completed, pressure from preceding turns forces the wire to jump to the adjacent groove. This process repeats for every turn of every layer after the first one.The wire is should be plastic enough to lie on top of the previous layer as if it were flat. If each successive layer rests directly on the turns of the layer below it, copper density would be around 79 percent. This compares with copper density of approximatly 84 percent for a more or less random winding pattern.
Perfect layer (orthocyclic) winding
The bobbin rotates laying the wires parallel to one another and there is only a small traverse during rotations (this appears as the kink in the wire in the picture). For most of the rotation the traverse mechanism is stationary. This requires precision control over the movement of the bobbin and traversing mechanism. The key to a successful perfect layer winding is in positively securing the turns of the first layer in position, so that the second and succeeding layers have a form foundation to wind upon. The bobbin might require the application of an adhesive to the winding surface to supply the necessary friction for the first layer. Another alternative is to cut (or mold) grooves into the bobbin so that the first winding of copper wire to creates a base for the initial stages of winding. In theory perfect layer winding yields a higher copper density than any other method, approaching a theoretical 91 percent for a large number of turns. It allows for a smaller coil size for a given number of turns, with less microphonic feedback . Perfect layer winding, however, may ultimately prove too difficult to achieve in practice in a home made machine and might not contribute to the sound of the pickup.
Irregularities
Irregularities in the wire or the bobbin will mean succesive layer’s transitionscould be in different locations. Under these conditions, the wire applies a ”crossed turn”. Winding additional layers propagates this inconsistency from layer to layer, ultimately creating a randomly wound pattern. For the purposes of guitar pickups, howere, this probably acceptable. The position of the start lead (where the wire first enters the coil) prevents a perfect helical path by producing small bump which will propage through sucessive layers. If attempting perfect layer winding the start wire should enter the coil through a slot in the bobbin flange, or a groove milled into the end plate, positioned so as to cause a minimum disruption of the winding pattern. Ideally the start wire should enter at a transition point, and at the same angle the wire makes when jumping from one groove to the next.
The current machine design should allow helical winding. Perfect layer winding might also be possible depending on the characteristics of the wire and bobbin.
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