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Offline pspdfppdfxhd

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press calibration
« on: August 10, 2017, 11:35:58 AM »
Well, the management finally decided to calibrate our plates to the presses.

Our Komori 5 colour was measured and calibration curves were input to the rip for each of CMYK.

Our Komori 4 color pressman was away on holidays and his press did not get calibrated, he's been running linear plates for years with no big complaints. Boss says give him the same curves for the plates as the 5 colour but he is having a hell of a time making his work look good now. We have had to bump up his calibration curves a lot for him to get good colour. We're still trying..... next trial is a dot gain in the 50 percent area of about 8 percent. The other press is about 18 percent which seems about normal. Both guys are running the same Agfa Azura plates. They are running up the proper ink densities on the color bars....up to spec.

Question is.... could 2 presses be so far apart in the calibration curves they require?

Offline pspdfppdfxhd

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Re: press calibration
« Reply #1 on: August 10, 2017, 11:47:16 AM »
Even a simple yep or nope would help. Providing you know what you're talking about. :banana:  :drunk3:

Offline david

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Re: press calibration
« Reply #2 on: August 10, 2017, 12:38:22 PM »
short answer is yes.
2 presses, even if they are identical and the same age, will print different. You will need to calibrate each press to a standard, and yes, they will probably need different curves.
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Offline pspdfppdfxhd

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Re: press calibration
« Reply #3 on: August 10, 2017, 01:08:22 PM »
I can understand how they could each need separate curves, but such a big difference? Doesn't seem to make sense somehow.

(one dot gain at 50 about 18 percent, one about 8? This guy used to run plates with no calibration on them at all and made it look good. Never used color bars like the other pressman).

Maybe we should just give him the plates with no calibration applied.

Offline Joe

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Re: press calibration
« Reply #4 on: August 10, 2017, 02:02:31 PM »
Ahhhh...the old calibrate one press and use those settings for every press to save money trick. Never has worked. Never will work.
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Offline pspdfppdfxhd

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Re: press calibration
« Reply #5 on: August 10, 2017, 02:11:57 PM »
Yeah, I figured as much.

Can't say I am not suprised. :banghead:

Offline david

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Re: press calibration
« Reply #6 on: August 10, 2017, 02:35:09 PM »
Quote from: pspdfppdfxhd link=msg=293299 date=1502384902

I can understand how they could each need separate curves, but such a big difference? Doesn't seem to make sense somehow.

(one dot gain at 50 about 18 percent, one about 8? This guy used to run plates with no calibration on them at all and made it look good. Never used color bars like the other pressman).

Maybe we should just give him the plates with no calibration applied.



when is the last time he checked his blankets?
is the press maintained to specs?
checked the ph?
The fact that he runs "without colorbars" means you have no idea what the press gain is even on a good day. It's a crap shoot.
Prepress guy - doin' jobs one at a time
www.texasgraphics.com

Offline pspdfppdfxhd

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Re: press calibration
« Reply #7 on: August 10, 2017, 02:45:27 PM »
Yes, I am not the guy to ask these questions, there are much smarter people around here than me about such things.... :drunk3:

Question: Does anyone on here run linear plates? (like the 50 coming out 50)..... AGFA Azura plates.


Offline Marktonk

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Re: press calibration
« Reply #8 on: August 10, 2017, 03:42:20 PM »
It really depends on what your standard is. It could be an  in house standard/target or Gracol or ISO or SWOP or other. This will direct what the dot gain is based on the paper and ink combination along with the many other variables. A linear plate will print with the adherent dot gain but will that meet the target? If not, then you need a curve to achieve it.

Best,

Mark
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Offline pspdfppdfxhd

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Re: press calibration
« Reply #9 on: August 11, 2017, 07:31:50 AM »
Yes, the one press that was calibrated correctly was done with the G7 method. Basically it was balancing out the greys on the press. For a simplified example, printing a 50 percent black circle on top of a 50 cyan, 40 magenta, 40 yellow square and making them look grey like the black circle.


Offline johnny_jay

Re: press calibration
« Reply #10 on: August 11, 2017, 08:54:08 AM »
We have 2 nearly identical presses that are just 2 years apart in age and we have found that they will drift apart. Maintenance is key.
We need to run one curve for these because work will often bounce from press to press after jobs are plated. The two presses can also run in tandem.

We have another press that has had an aggressive curve in the yellow for years. We were pulling 15 points out of the yellow in the 50 and sometimes they needed to lower density to match a proof. They went through the unit and replaced almost all rollers, we fingerprinted again and now we are adding slightly in the yellow at the 50.

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Offline pspdfppdfxhd

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Re: press calibration
« Reply #11 on: August 11, 2017, 12:04:58 PM »
Well that pretty well says it all.

Thanks.

Offline Farabomb

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Re: press calibration
« Reply #12 on: August 14, 2017, 08:15:12 AM »
Quote from: Joe link=msg=293300 date=1502388151

Ahhhh...the old calibrate one press and use those settings for every press to save money trick. Never has worked. Never will work.

Yet it worked well enough in the place I used to work. There was a single curve for all 6 presses and we didn't change a damn thing when they bought 4 new ones.

Not saying it was right but having curves for each press would never work there. They would hop jobs around from press to press constantly.

They also caved in to their salesmen when they insisted they needed a dot accurate proof. Much $$$ later we had a Creo specturm. Few months later as we were using it for basically just dielines. 
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Offline pspdfppdfxhd

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Re: press calibration
« Reply #13 on: August 14, 2017, 08:41:46 AM »
Through trial and error, we've ALMOST gone back to linear and the 2nd press.

Cyan linear, MYK just a small cutback, about 45 percent at 50 like a rubber band going from 1 to 100.

Doesn't make too much sense to me but it's working ok.


Offline Joe

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Re: press calibration
« Reply #14 on: August 14, 2017, 08:47:08 AM »
Quote from: Farabomb date=1502712912 link=msg=293340

Quote from: Joe date=1502388151 link=msg=293300

Ahhhh...the old calibrate one press and use those settings for every press to save money trick. Never has worked. Never will work.

Yet it worked well enough in the place I used to work. There was a single curve for all 6 presses and we didn't change a damn thing when they bought 4 new ones.

Not saying it was right but having curves for each press would never work there. They would hop jobs around from press to press constantly.

They also caved in to their salesmen when they insisted they needed a dot accurate proof. Much $$$ later we had a Creo specturm. Few months later as we were using it for basically just dielines.


Hey we do it here with 4 out of 5 web presses. Still doesn't make it right. :rotf:

We have a "new to us" ManRoland web press being installed right now. They say they are going to be G7 certified on this press.

Me:  :lmao:
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