Moire' Pattern Trouble

[mike carlisle]

We bought a larger press, and so had to buy a larger CtP. Our older CtP was a ECRM Mako 4 - we bought a ECRM Mako 8.
The Moire' is showing up consistently on the lead edge & drive side of press (only first 25 - 30 mm from lead edge).
Haven't had to deal with a Moire' for years, in the past it was always camera man error (wrong screen angle).
Any suggestions on where to begin to resolve problem?

 

[BeauchampT]

When you say a larger press, how much larger? What size are we talking? Is it possible that this is moire showing because of a registration issue on press?

 

[gordo]

Can you describe the moiré? What do you actually see that you think is moiré?

 

[mike carlisle]

When you say a larger press, how much larger? What size are we talking? Is it possible that this is moire showing because of a registration issue on press?

We had a 2-color 26" x 20" Hashimoto - doing 4 over 4 work. On 18.5" x 24" 80lb matte text. We print the same jobs over and over changing the language (340 +) Check us out at WMPRESS.org
The ECRM Mako 4 CtP gave us many years of dependable & consistent plates. We were able to purchase a ManRolland 306 29"x23". So we went with the ECRM Mako 8 to accommodate larger plate size.
We are printing from the same files, using the same plates (larger), and the same sheet.
The Moire' only appears on the lead edge (for 25 - 30 mm) and drive side.
How ever the Moire' does not appear on EVERY job. Only on certain color combinations.
Back in the days of film - a moire' was the result of a incorrect screen angle in the camera. We had before the CtP a film imagesetter - no moire' (with the same files). The previous owner of the ManRolland did not have moire' problems. Would moving the press give a probable (not barely possible) cause for registration issue?
I suspect the problem is in the CtP.

 

[maxon]

Easy fix, replace the input drive motor.

 

[BeauchampT]

Dumb question, but, have you tried running the image in different position? What I mean is if the image is from the same file that was run on your smaller press, it seems you have registered it to the lead/drive side. Why not shift it to register to the tail/operator side and see what happens to the moire?

 

[gordo]

Can you describe the moiré? What do you actually see that you think is moiré?

Still haven't answered the above question.
Moiré is a secondary pattern resulting from two or more patterns harmonically beating with one another.

 

[BeauchampT]

And good point to Gordo as always....
A picture would be helfpul

 

[gordo]

And good point to Gordo as always....
A picture would be helfpul

I just think it would be a good idea to understand the problem before throwing solutions at it.

 

[MacTwidget]

Are you using polymer plates or metal plates?

 

[Rover]

I don't know if you got this sorted, but the earlier post about the input motor faulty normally gives a circa 1mm "beat" pattern - lines across the plate width.

You can check this by swapping the input and output drive motors, they are identical, and the fault should move to the trailing end of the plate.