The increment of the raster point is different.

[Andrei83]

Hello dear specialists. On 135 coated paper, I placed a scale with a gradation of 0-5-10-20.....80-90-90-100%.I performed measurements of the scale compared according to the ISO standard, all the gains are normal, just wonderful.I decided to observe the increase for two shifts. We printed a book with a volume of 15 paper sheets. And I found that the increase of the raster point on different paper sheets is different, both plus and minus, in addition, some on the reverse side are normal, but not on the front. I wanted to make corrections on the rip for an increase and realized that there is no point, since there is no stable same value. Why is this happening? And in this case, how to standardize offset printing? Machine Speedmaster sm 102-5+lac. 70,000,000 sheets mileage.

 

[gordo]

I think you're talking about dot gain? When you say "And I found that the increase of the raster point on different paper sheets is different, both plus and minus," - what is the actual amount of change from your standard?

 

[Andrei83]

If after the first measurements it was within +-3% on all scales. I took measurements on other pages of the book with different illustrations, but on the same scales. And already, in some colors, I went beyond the limits of the point growth rate. Let's say the yellow paint has a 10% deviation. Or by blue paint 8% in some gradations.

 

[Andrei83]

I think there is a dependence on the area of the printed element. In large illustrations, the increase was also higher.The slur scale was out of order visually visible in the direction of printing a strong slip.

 

[gordo]

To avoid confusion, what are the actual numbers. For example, at what % are you measuring? When you say an 8% deviation do you mean that if your target is 71% measured at the 50% you are actually getting 79% or are you getting 76%. Also can you graph your dot gain curves - target vs actual?