Calculating Distortion - HELP

[Brad38CMU]

Need an answer with a little 'Show your work' math to back this question up.

I have artwork that has a 10.42" repeat that is going to be mounted on a 10.5" cylinder. PLEASE show me the math to figure out the correct distortion.

Thanks!!

 

[meddington]

determine print diameter by dividing cylinder circumference by Pi. 10.5/Pi = 3.34225"

subtract 2x soft plate thickness (typically .067 plate thickness minus .05 for hard base of plate = .062" x 2 = .124

divide by print diameter (again, cylinder circumference divided by Pi).

(3.34225-.124)/3.34225 = 0.96289 or 96.289% distortion

This method matches the results I get from my calculator:
Flexographic Pre-Press: Calculating Distortion Factors Without a Chart!

 

[Bill W]

Years ago, 1981, I was taught this simple distortion formula for 1/8 pitch presses:

repeat - .39 = X
X divided by repeat = Y
Y x 100 = distortion factor

10.5 - .39 = 10.11
10.11 / 10.5 = .962857
.9628 x 100 = 96.2857

I have been using this formula for, WOW, 30 years without any problems.

 

[Bill W]

No I am not living in 2011, meant to write 32 years - just a bit tired tonight

 

[meddington]

And we're to trust your math Bill?

Seems to correlate quite close to my method, but without the use of pi.
Everything's better with pi.

 

[Stephen Marsh]

Being mathematically challenged, I am not sure if the attached extract document is of help or not!