Chuck asks,
My question, is there a formula that determines how long of a print area (thru the machine) can be printed without being printed a second time when running skip feed. We have a 66” rotary diecutter with skip feed. We did a test on a sheet size of 79-1/4, mounted a 28″ plate, centered and it did not reprint.
I reached out to a few of my industry contacts. My colleague Dwayne Shrader put together some info for this post.
Max Sheet Length Before Print Repeat
On a 66 inch machine the print is going to repeat every 66 inches from the lead edge of the plate. That’s the key to determining the length of the sheet before repeat… ‘from the lead edge of the plate’.
To determine the maximum sheet before print repeat where …
Cylinder Circumference with plate installed = CC
Lead Edge Offset = LEO
Max sheet Before print Repeat = MBR
Then…CC + LEO = MBR
You say you mounted it in the center, I assume you mean you centered it around the cylinder. So the lead edge of the plate would have been at 19 inches behind zero register… (66 – 28)/2=19. This being true, then CC + LEO = MBR, or 66 + 19 = 85. Therefore, you could run a sheet just under 85 inches before the print would repeat.
Maximum Print Length
Now, determining the maximum print length, is just a little different because the cylinder circumference is not the maximum machine print length. Keep in mind that the lead and trail edge lockup takes up some of the circumference (or print area). On the typical 66 inch cylinder your maximum machine print length is going to be between 61 and 64 inches depending on machine design, lockup type, etc. Your machine manufacturer should be able to provide the maximum through machine print length.
To determine the maximum print length where …
Maximum Machine Print Length = MMPL
Lead Edge Offset of printing plate = LEO
Maximum Printable Length through machine = MPL
Then… MMPL – LEO = MPL.
For example, let’s say the maximum machine print length is 62 inches and the lead edge is offset by 5 inches… 62 – 5 = 57 inches of available print length. Consequently the maximum sheet before repeat would be 71 inches in this case.
Sometimes a converter may have a plate that is made for a normal feed job, but they want to use it to print a larger skip feed job. In this case the plate is mounted in the normal position and then the register is retarded to offset the distance from the lead edge to the start of the print. The same formula for maximum print length is used here as well just substituting the register offset from zero register.
To determine the maximum print length where …
Maximum Machine Print Length = MMPL
Register Offset from Zero = ROZ
Maximum Printable Length through machine = MPL
Then… MMPL – ROZ = MPL.
Hope this is helpful.
askralph 