Elongation/shrinkage

Elongation & shrinkage
Elongation & shrinkage
Difficulty	Beginner
Duration	10 min.
Tools	Ruler

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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:

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.
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).

Overview

Calibration can be performed if the dimensions of the printed image do not match the dimensions of the original. 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).

On older and lower model-number machines however, pursuing perfect calibration can be a wild goose chase. It's only really necessary when miscalibration is detected between layers, or when perfect scale to the sheet is needed (to match fold lines, for example—as in a magic zine).

Procedure

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).

Printing and measuring

The means of making a print and measuring it are different depending on whether the calibration is for master making (to calibrate the write roller speed) or scanning (to calibrate the scanner head speed).

Master making

Make a crossed lines test pattern from test mode (with paper in the feed tray and a drum in the riso).

Crossed lines test modes
	RPRN	Z+Any machine released with or after the RZ line, i.e. RZ/RV/EZ/EV/SF/SE and MZ/ME/MF/MH machines.
`119`	`51`	`81`

The resultant grid will either have (relatively) square cels (for machines with square aspect ratio, i.e. 300 × 300 or 600 × 600) or rectangular cels (for machines with RISO's 600e rectangular aspect ratio; 600 × 300).
- For square cels, measure 20 cels across in the feed direction, this is the measured distance. Then measure 20 cels up/down (perpendicular to the feed direction), this is the goal distance.
- For rectangular cels, measure 20 cels across in the feed direction, this is the measured distance. Then measure only 10 cels up/down (perpendicular to the feed direction), this is the goal distance.

Scanning

Make sure to make the scanner bed calibration only after the master making calibration or if the scanner bed is used exclusively.

Scan an original with a lengthwise line or other known distance between points. This is the goal distance.
Measure the distance on the resultant print. This is the measured distance.

Crop marks shortcut

On either of these calibrations, the measurement can be made between crop marks (or any other known distances) on a stencil already made on the drum. It can be done in the middle of a job, just by comparing the original (goal distance) to the print (measured distance).

After the calibration is made, the current stencil should be remade and then printing can continue.

On newer Z+Any machine released with or after the RZ line, i.e. RZ/RV/EZ/EV/SF/SE and MZ/ME/MF/MH machines. machines the actual adjustments are made in test mode, while in older machines they are made with rotary switches on one of the circuit boards in the back of the machine.

Test mode calibration (RP/RN/Z+)

The settings changes are a compensation that's based on the percentage (in thousandths) of scaling desired—with positive values elongating the image and negative value shrinking it. There's a simple formula to determine the adjustment:

({\frac {goal}{measured}}-1)*1000

Rounded to the nearest number.

This is how much the relevant test mode must be changed by—so it's a relative value not an absolute one.

The test modes to be adjusted are:

	RPRN	Z+Any machine released with or after the RZ line, i.e. RZ/RV/EZ/EV/SF/SE and MZ/ME/MF/MH machines.
Write roller speed	`287`	`547`
Scanner head speed	`182`	`382`

The result from the equation should be added to the current value for the new, adjusted value.

For example if the goal is 150 mm and the measured is 152 mm, the calculated change would be -13. If the current value is +5, the new value should be -8.
$({\frac {150}{152}}-1)*1000\approx -13$
$5+(-13)=-8$

Rotary switch calibration (GR/RP)

The technical manuals for and machines have contradictory information in their instructions and circuit board diagrams, so all of these values should be tested to confirm the direction for elongation vs. shrinkage and the +/- sign for the amount of change are correct.

On older machines, the adjustment(s) are made by changing the setting on a small rotary switch on the Image Processing PCBThe circuit board in charge of scanning an image, dithering it, and sending it to the MMU. behind the back panel of the riso. These switches are adjusted with a Phillips #0 screwdriver, changing which value (0–F) that the arrow on the switch points to.

The adjustments are based on the length of elongation/shrinkage in millimeters across the sheet.

GR3770 and FR3950

The 3770 and 3950 machines have the capacity for digital/driver printing—if they are being used for this, then the master making should be calibrated before the scanning.

Calibrate the master making speed with the switch labeled "WPM" (write pulse motor).
Calibrate the flatbed scanning speed with the switch labeled "FB" (flatbed).

These switch values are specified to be:

0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
+8	+7	+6	+5	+4	+3	+2	+1	0	-1	-2	-3	-4	-5	-6	-7
Elongates								Default	Shrinks

Other GR/FR models

For older models which do not have digital printing, only the scanner head speed is adjusted. This is done with a switch labeled "FB" (flatbed) or "SLA" (scanning length adjustment).

These switch values are specified to be:

0–4	5	6	7	8	9	A	B	C	D–F
Do not use	+3	+2	+1	0	-1	-2	-3	-4	Do not use
Do not use	Elongates			Default	Shrinks				Do not use

These are relative adjustments, so in theory if the image needed to be made a millimeter longer, the adjustment would be to turn the dial up one notch. In practice, however, it takes some experimentation to figure out the correct settings to be used—so multiple stencils must often be made and measured to test.

For example, if the scanner head speed is being adjusted on a 3750 with a goal value is 150 mm and a measured value is 148 mm, then the switch should be turned up two notches. If it is currently at 9, it would be changed to B, then another stencil would be made and measured.