Coil Binders -- Punching for Plastic Coil
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.
Simply pull your outside pins like double loop wire and center your sheet prior to punching. If you have a machine that can spread the coil during insertion to jump the wider margin, this is no problem. Once again, most machines cannot.
Therefore the margin cannot exceed the bridge (the distance between two holes). The coil spinning in may not spread. The distance between the leading edge of the book and the first hole cannot be longer than the distance between the pitch or any two holes. It is impossible to pull pins and center the sheet prior to punching. It is then necessary to punch a full 44 holes on an 11˝ (279mm) sheet.
This led to another problem: 44 round 11⁄64˝ holes will not fit attractively on an 11˝ (or A4) sheet. It will leave you with a razor thin margin, totally unacceptable to the customer.
What many manufacturers did was devise a new die pattern—the .2475˝ pitch die. This means one hole for each .2475˝. But the problem was that the hole was still too small to accommodate many automated coil binders. If the hole was made any bigger, it would punch a partial hole off the edge of the sheet.
The solution was to make the die an oval die. Not your grandfather’s oval die, but a new, oversized oval die 11⁄64˝ (4.365mm) wide and 7⁄32˝ (5.5mm) high. This allowed for a bigger hole without causing to punch too close to the edge of the sheet. It also forced customers to purchase brand new dies for their punching machines with this pitch.