Crooked Bearer Bars

[Red_Right_Arm]

I am wondering if anyone else has encountered this problem.

We use a CTP laser to ablate off a black mask. Our exposure unit is a UV light bank. We use a water washout system. And the exposure unit has two heating racks.

We keep our laser drum clean from residue and we make sure not to tape any plates down to anything other than the bare metal of the vacuum drum.

We make sure that we are wrapping the plate around the drum straight.

We make sure that our heater doesn't get so hot that it will warp the backing material of the plate.

Once the plates are made, they are cut and butted up to each other to verify alignment. In less frequent cases, the bearers look like the attached photo. In most other cases, the plates look fine on our light table, but they look like this photo once they are mounted on a cylinder. And it is always the same one side that is crooked.

We've had the laser checked and had test plates analyzed by our provider.

I've run out of solutions to try or things to look for. Can anyone help?

 

[arossetti]

 

[Red_Right_Arm]

Okay, I actually thought that was kinda funny.

 

[arossetti]

Okay, I actually thought that was kinda funny.

Sorry for derailing the question. Back to CTP's people.

 

[davarino]

I know this is going to sound stupid, but I have to ask: "Have you checked how true the cylinders are?"

Another thing that I would look at would be rotating the plate material 90[SUP]o[/SUP] and 180[SUP]o[/SUP] when making a test plate, just in case.

And the third thing that comes to mind is an observation: it looks like the distance from the middle of the groove to the right hand bearer gradually decreases (as I measure it on my screen: A= 3/4", B= 23/32", C= 11/16"). The distance to the left hand bearer is constant. Why? (Of course that's your question, too.)

Sorry I don't have a solution, but at least you may have some more things to think about.

 

[Bill W]

Where are you building the files? Have you checked the bearers in that application before you rip it to insure they are parallel? Can you check the 1 bit tif in a tif viewer to insure the are still parallel? Basic questions so if you have already run through them, I apoligize.

 

[Red_Right_Arm]

I know this is going to sound stupid, but I have to ask: "Have you checked how true the cylinders are?"

Another thing that I would look at would be rotating the plate material 90[SUP]o[/SUP] and 180[SUP]o[/SUP] when making a test plate, just in case.

And the third thing that comes to mind is an observation: it looks like the distance from the middle of the groove to the right hand bearer gradually decreases (as I measure it on my screen: A= 3/4", B= 23/32", C= 11/16"). The distance to the left hand bearer is constant. Why? (Of course that's your question, too.)

Sorry I don't have a solution, but at least you may have some more things to think about.

Unfortunately the care of the cylinders is outside my department. But I can certainly suggest this to at least eliminate that as a possibility. But one question... how do you check this? I ask because since I never handle the cylinders, I don't know how to do it. And since I'm pretty sure no one at my company has ever thought to do this, they won't know how to do it either.

The orientation of the plate when it is being made does not seem to be a factor.

I think that the distance of the bearer bars that you are seeing is my inaccurate handheld photo taken from my phone. Of course at least one bearer bar goes crooked as it continues its full length. But if it were that bad the alignment marks would be about a half inch off when they meet each other.

 

[Red_Right_Arm]

Where are you building the files? Have you checked the bearers in that application before you rip it to insure they are parallel? Can you check the 1 bit tif in a tif viewer to insure the are still parallel? Basic questions so if you have already run through them, I apoligize.

All good suggestions. But they are items that we've checked and eliminated as a cause. The 1-BIT TIFFs are indeed verified as generated perfectly straight.

 

[Bill W]

What is being used to mount your plates? I have seen two different mounting machines that have caused such problems because they were out of alignment. Usually bad print cylinders point to bad bearings, have someone check the bearings.

 

[Red_Right_Arm]

What is being used to mount your plates? I have seen two different mounting machines that have caused such problems because they were out of alignment. Usually bad print cylinders point to bad bearings, have someone check the bearings.

We have a manual mounter with two cameras to aide with the alignment. The problem that strikes me with the mounting is that it's just the one bearer bar. If the plates were mounted crooked, wouldn't both bearer bars end up crooked? Also, the issue shows up when the plates are mounted by eye as well.

 

[Red_Right_Arm]

I know this is going to sound stupid, but I have to ask: "Have you checked how true the cylinders are?"

Another thing that I would look at would be rotating the plate material 90[SUP]o[/SUP] and 180[SUP]o[/SUP] when making a test plate, just in case.

And the third thing that comes to mind is an observation: it looks like the distance from the middle of the groove to the right hand bearer gradually decreases (as I measure it on my screen: A= 3/4", B= 23/32", C= 11/16"). The distance to the left hand bearer is constant. Why? (Of course that's your question, too.)

Sorry I don't have a solution, but at least you may have some more things to think about.

As far as the cylinders go, we've ruled those out since sometimes the issue goes away and it returns. And it does so on jobs that use the same exact cylinders. Literally the same cylinders. Not just the same size. So if it were the cylinders, the plates would always be crooked on them, right?

 

[Bill W]

I know on the Mark Andy mounter we have there is a parallel relationship between the plate clamp surface and the shaft the cylinder is on. If this relationship is off the plate will be mounted crooked. Could this relationship be off on your mounter? If you flip the plate 180 degrees and mount it does the "off" side bearer stay on the same side of the mounter, or does it follow the bearer?