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Coil Binders -- Punching for Plastic Coil

February 2005
By David Spiel

Punching for spiral binding of any kind is a tricky matter—and even trickier for plastic coil. Punching for double-loop wire has always been a snap: Merely open your die, place your sheet against the pins and pull the pins nearest the edges of the sheet. This way there is no chance of punching a partial hole. You have the luxury of centering your sheet and producing a generous, attractive margin (the distance between the first or last hole and the head or foot of the book).

Punching for spiral is not always so easy. If you have a plastic coil machine that can manipulate the spiral prior to insertion, consider yourself lucky; most cannot. Therefore you are stuck with whatever pitch the spiral may be. Let's use the industry standard of the 4:1 pitch.

In days gone by metal spiral binding used a 4:1 (or in Europe a 6mm center-to-center) pitch. But back in those halcyon days, the holes were small, 9⁄64˝ (3.5mm). They only needed to accommodate a very thin gauge of wire. Plastic coil gauges are much thicker, some as thick as 1⁄8˝ (3mm) and 9⁄64˝ holes just won't do. Standard plastic coil gauges range from .063˝ to .085˝ (1.5-2mm).

Some had turned to oval holes. Oval holes were, for many years, the accepted way to battle thicker books with spiral wire and, even for a time, plastic coil. The old standard was a double "D" die. Why is it called double "D"? Imagine two Ds mirrored against each other and turned counter-clockwise 90 degrees. It is actually a round hole with its sides sliced off. A double "D" die used to be 9⁄64˝ (3.5mm) wide and 11⁄64˝ (4.365mm) tall.

This, obviously, helped with insertion of spiral wire and hand-held plastic coil books. However, oval dies are much more expensive than round hole dies since they have to be EDM'd (laser burned). They can cost up to $2,500 more than a round hole die.

These holes proved too tight when automatic plastic coil machines came into the fore. While the holes are tall enough, automatic machines, which drive the coil horizontally, need more "wiggle" room from side to side. Hence, a new standard was born: The 11⁄64˝ (4.365mm) round hole. This is now the standard round hole for plastic coil within the industry.

However, this wider hole led to a problem: If you attempt to fit 43 11⁄64˝ round holes on a sheet there is no problem.
 

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