Consiistent-excessive dot gain/TVI on all units.

[Cornishpastythighs]

Do you see this issue more at the leading edge or trailing edge of your plate/blanket. I only ask because in certain extreme cases I have seen dot differences caused by the amount of spray glue used to stick packing together, if you glue your press packings together and then glue them to the cylinder you can create some thickness difference. Only minor I know but worth looking into.
Cheers

 

[CClyde]

Do you see this issue more at the leading edge or trailing edge of your plate/blanket. I only ask because in certain extreme cases I have seen dot differences caused by the amount of spray glue used to stick packing together, if you glue your press packings together and then glue them to the cylinder you can create some thickness difference. Only minor I know but worth looking into.
Cheers

I have seen a good dot with little distortion on the leading edge, then quickly turn to a spray-like dot with no defined edge and a fine spray throughout the sheet.

In the most extreme examples the operator told me he had intentionally rolled the blanket to avoid a small smash, causing the pressure drop where the packing was less/dropping off.
So, we see better dot where the packing is less.

 

[Alois Senefelder]

Hello CClyde,


I'm puzzled re - Blanket Cyl. Packings,,,,,,,,,,,,,, they should extended all the way from the Grip/Lead Edge to the Back/Leave Edge


Regards, Alois

 

[CClyde]

I'm sure the packing extends beyond the plate, I understood they rolled the blanket to avoid a smash and that brought the grip edge of the plate into an area with less blanket packing.

 

[Captain setoff]

Have you checked the thickness of your packing? Your supplier my have given you a dodgy batch. 30% on all units is a bit suss to be a mechanical issue. I had the same kind of issue but with what I thought were roller marks. Turned out my blanket supplier changed the rubber on my blankets and didn't inform me.

 

[Alois Senefelder]

mmmm...............................!




Being a relic from the "Stone Age" with just a modicum of sense .......... I was taught to use a "Micrometer" and not rely ON !!



Regards, Alois

 

[Chris_PTA]

Blanket packing is best checked with a blanket gauge. http://www.roconex.com/1852/24901.html One also on eBay: http://www.ebay.com.au/itm/Roconex-Magnetic-Packing-Gauge-With-Plastic-Case-/152043141985

 

[DeltaE]

No Title

This topic is really interesting! Looking forward to your final result!
Any photos of dots taken by Micro-scope would be very helpful to us.

I just want to share with you some ideas which I read from an instruction of Flint Group for offset troubleshooting (attached photo)
Cause:
1. Improper pressure setting between
plates, blankets and rollers
2. Ink body too long
3. Ink too water-receptive
4. Piling
5. Plate not sharp enough
6. Poorly desensitized plate
7. Poorly ground ink
8. Insufficient fountain solution
9. Excessive ink on roller train
10. Blankets or rollers too soft
11. Improperly packed blankets
Solution:
1. Adjust to proper pressure setting
2. Consult ink manufacturer for stiffer ink
3. Consult ink manufacturer
4. See PILING
5. Coordinate with cameraman and
platemaker for sharper halftones,
negatives, positives and plates
6. Desensitize plate; replace if necessary
7. Consult ink manufacturer
8. Increase fountain solution to cover
plates evenly; check for dirty dampener
cover and replace if necessary
9. Reduce ink; reduce fountain solution
10. Recondition blankets or rollers; replace
if necessary
11. Adjust packing

Hope this help if any!

Regards,
DeltaE

 

[DeltaE]

BTW, if you have tried all things above and no change, in my point of view, I will check mechanical side of the machine. Something like impression mechanism, cylinder baring, connection between unit, even platform! Regards, DeltaE

 

[cementary]

Do you see this issue more at the leading edge or trailing edge of your plate/blanket. I only ask because in certain extreme cases I have seen dot differences caused by the amount of spray glue used to stick packing together, if you glue your press packings together and then glue them to the cylinder you can create some thickness difference. Only minor I know but worth looking into.
Cheers

Mr. CClyde, it's been a while. Did make any progress on your dot gain problem?

 

[CClyde]

Just finished a few hours of testing this morning.

I haven't had time to analyze all the sheets yet. I'll post those results when I finish.

One thing that surprised me, we did the ink test on the bearers and got nothing with impression on.
I would have thought there would be some contact, no?
I thought the bearers were the stop point to prevent destroying plate and blanket and that there would be just the smallest necessary pressure picked up between plate and blanket.
With the gap at 3mil, there was no transfer at all on gear or operator side???

 

[Alois Senefelder]

Cyl. Bearer Contact


Hello CClyde,


ARE you sure the Bearer Ink Dab Test was done correctly ??????????

What do you mean by --- with the Gap at 0.003 thou no transfer onto the Bearers ???

Next.... ARE all the Plate/Blanket Cyl. visually "Bright/Shiny" ??????


Regards, Alois

 

[Cornishpastythighs]

Alois is correct, something does not sound right. If you have a bearer to bearer press then there must be contact.

Pulled this from a website.

Checking Bearer Pressure
If your cylinder bearer pressure is not set correctly the paper, blanket or plate could push the cylinders apart enough to cause a bounce when the blanket and plate gaps meet. The result is gear streaks.

Solution: Have a machinist or a very experienced pressman check the cylinder bearer pressure. There are different three ways that I have heard of doing this and only an experienced person should adjust bearer pressure if required, you can destroy your press if done incorrectly.

• The tin foil method. A thin strip of tin foil is used similar to a stripe gauge. The impression between the bearers will create a strip that when magnified, can serve as a reliable reading to gauge other printing units.
• Prussian blue. This method is used by a maintenance team. It is much like the previous method except that a stripe is made on the bearer using a special blue grease, Cyan ink can be used instead.
• The light method. Using various thicknesses of packing between the blankets, the impression is turned on. A bright light behind where the bearers meet will reveal either a thin crack of light or nothing at all.

 

[CClyde]

The plate/blanket bearers are shiney, like a mirror.
I should have said 3mil pressure - plate, blanket packing minus undercut.

I guess what confuses me (I don't know enough about it) the bearers are not bearing. I thought the bearers were always touching slightly and the plate/blanket presser should be just enough to transfer ink cleanly.

 

[CClyde]

Trust, but verify!
So, it seems the bearers were squeaky, mirror like clean, because apparently they cleaned them when I asked for the ink-transfer test.
Before cleaning they were solid, dry ink on plate and blanket bearers.

 

[CClyde]

No Title

Took a photo of the Cyan unit operator side bearers.

 

[Alois Senefelder]

Hello CClyde,


Disgraceful ! the operators should be ashamed running a press in this condition, obviously they don't

KNOW what the bearers are for.

Are ALL the 4 units Plate/Blanklet Cyl. Bearers like this ??

Next, have the "Felt Pads on the Bearer Wipes" been change ???


Regards, Alois

 

[Alois Senefelder]

Responsibility

Hello CClyde,


You have received many answers to this problem (Dot Gain) - NOW we have the sudden

revelation that the press is poorly maintained.


IS someone responsible for the maintenance of the Presses/Pressroom SOPs ?????


Regards, Alois

 

[CClyde]

Beginning to suspect the operator/s are not as familiar with the press a they claim.
SOPs will have to be discussed and reviewed regularly from now on.

 

[CClyde]

It's possible. You might also consider that while every press has it's own idiosyncrasies, printing in general is very much the same from machine to machine.

Not sure what you mean?