Elongation shrinkage

Elongation shrinkage
Difficulty	Beginner
Duration	10 min.

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Based on the way stencils are made in the risograph, if certain test modes are not properly calibrated, printed images can be elongated or shrunk by 0–3 mm. This comes from two places:

1. The speed of the write roller when making a stencil—if it is faster than it should be, the image will be elongated; if it is slower, it will be shrunk. This is a physical property of the changing properties of the depleting stencil roll (so it changes over time, based on how many stencils remain on the roll). On two-drum machines and full-featured one-drum machines, compensation for this often happens automatically, but on older and lower model-number machines, this will regularly need to be calibrated for 1:1 printing.

1. The speed of the scanner head (when scanning)—if the head moves too fast, the image will be shrunk; if it is too slow, it will be elongated. This is a more stable setting, so it rarely needs calibration (and should only be calibrated after correcting elongation/shrinkage in the write roller).

Both calibrations can be made by comparing a measured (printed) distance against a goal (original) distance, along the left/right axis of printing (along the feed direction of the paper).

Calibration procedure

Calibration can be performed if the dimensions of the printed image do not match the dimensions of the original (this is often measured between registration or crop marks). What needs to be calibrated depends on how the machine is used on a regular basis.

• If the stencils are made both from the scanner bed and sending files from a computer then both the write roller speed and scanner head need to be calibrated.

• If either the scanner bed is used exclusively or files are sent from a computer exclusively, then only the write roller speed needs calibration (though both can be calibrated if desired).