QM-46 Registration Question

[CSimpson]

First let me say I haven't been running a press very long, so I am not that knowledgeable when it comes to sporadic issues like the one I am having.

I print short run letterhead jobs a lot; most of the requests are for very short runs 500 to 1000 at a time. I have in the past ran a bunch these jobs with the same logo back to back and only changed the plate with the address information as that was the only thing different between the various letterhead jobs. Recently the logo changed and now there are very fine knockouts in the logo, and I am having a problem with the images getting out of register in the print run in the first 500 or so, basically the whole job I am chasing the registration up to 1mm in the first 500. Here is the thing, it doesn't do it all the time, and so I am having a hard time figuring out what is going on. I am not sure if this is because I am not changing the both plates each time, or if the packing is off and that is causing stretch, or if it is because I am using poly plates instead of metal.

 

[Al Ferrari]

I don't run poly, and have no experience with that press. But I would say the poly plates are the problem. Is the miss-register worse in the around the cylinder direction than across the cylinder?

Probably the one you keep changing is stretching a little around the cylinder over those short runs, while the one that stays on for several runs may have stabilized. If the problem is less when both are new but worsens as you keep changing the one color, that would support my guess. When they are both new, they change together, but after that, the new one is changing more than the one that stays on.

Does that explanation fit?

Al

 

[amsman]

QM46-2 Rego

QM46-2 Rego

I run Poly Plates out of a DPX (GTO Size with a Trim and a Punch Down to 505mm x 340mm ).

I have seen this also from time to time and have put it down to the heat generated within the roller system
heating the blanket ( or the plates themselves ) causing a size change.

Check next time you run and you will notice the heat coming out of the top of unit 1.

We run at about 6500 - 8000 per hour.

Hope this helps.

 

[inky]

I have the same press, and could have written your post.

If you do a blanket wash does the register on PU2 seem to ping out about a millimeter and you have to reregister the job again?

 

[CSimpson]

Is the miss-register worse in the around the cylinder direction than across the cylinder?

Yes

I have the same press, and could have written your post.

If you do a blanket wash does the register on PU2 seem to ping out about a millimeter and you have to reregister the job again?

Yes, then I start chasing it again


Guess, I am going to have to live with this. I am not going to be getting a new metal platemaker anytime soon

 

[RGPW17100]

What is your blanket packing? Are you running 8 mil or 5 mil poly? If you imagine a heavy piece of furniture being moved on a carpet you will notice the roll in the carpet. After the heavy piece of furniture is moved the carpet goes back to the normal configuration. We used to have to adjust registration on the fly with poly to counter act this effect. The effect is the plate to blanket pressure making the plates print longer. I have no explination as to why it only affects one unit and not both. My guess is that one unit is chasing the other and that the effect is not as dramatic on the second unit. When we went to metal it went away. Is your press an older QM46 or a printmaster? The older QM had a fit problem where the number one unit prints longer then the number two unit. We have to pack the number one plate with a 3 mm packing in order to get fit across the entire sheet.