Re: Home Made Registration Punch and Carrier?

On 6/2/2008 8:15 PM gr spake thus:

David Nebenzahl wrote:

Contrary to what Nicholas said, there's no reason to use anything but regular round pins. Two pins will keep the sheets in exact alignment no matter what their shape, so long as the holes are sized exactly to the pins.

The reason that a round hole is paired with slotted holes (on larger punches it is one round hole and several slotted holes) is that the polyester film base expands and contracts in size with temperature and humidity changes (approx 0.001" change in 10" for every 10% humidity change). With round pins a size expansion is trapped and causes the film to bow, preventing good contact and registration. A slotted pin allows the film to slide in the expansion direction but prevents rotation and maintains registration.

That makes sense, and it's true I've never worked in a shop that handled really big film (for big presses). But in this case, the expansion factor is probably minimal, since the O.P. is dealing with 8x10 film.


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