Plating fine strokes, Vert & Horz - LPI Degrees, Frequency

[pdan]

Whilst I ponder wasting some plates - I could use some techy help.
A 3x5 pocket card, for sketching, is composed of a graph, off the press, the lines appear uneven. I had a 50/50 chance this would happen.

I set strokes, .5pt, 20% tint (black)

Stepped at .10487 inch (near as I can tell. To match a previous sample, 27 steps worked out to 3 inches. I stepped 28 strokes total, and used distribute)

Plated at 150 lpi/2400dpi, 45 degrees, there is unacceptable dot pattern of strokes two dots & single dot (due to the angles involved(?))

Is there some long math to handle thin strokes, at right angles?

Perhaps 0 degree angle...30 degree change of frequency/lpi...

The imagesetter is not driven by any external RIP. The ppd allowed me AS, BAL, STD (Agfa - Accuarate Sceening, Balanced Screening, STD unknown)

scan attached shows previous sample (not mine), proof and press sheet area in that order

[DavidMa]

increase the line screen to something higher (175, 200, or 250) to get more dots in the stroke and/or change the angle to run parallel to the stroke if possible.

not much you can do with a screened stroke that thin.

[gordo]

DavidMa is correct, and his suggestions might help.

or you could use an FM screen which will eliminate the problem entirely.

best, gordo

[pdan]

Will try that route
I read about 1/2 of the moire thread, was looking forward to some spot on techie advice, Gordo must be a real hoot at parties...the guy's a walking encyclopedia reference set...

[brent]

How bout making them solid lines and run light grey ink?

[gordo]

Will try that route
I read about 1/2 of the moire thread, was looking forward to some spot on techie advice, Gordo must be a real hoot at parties...the guy's a walking encyclopedia reference set...

Of course that depends on the frequency of the parties as well as the shape of the guests - typically some what round and at a slight angle. Keep in mind that the higher the frequency of parties the rounder the shape of the guest. That is usually accompanied with a change in guest angle from vertical (0°) to horizontal (90°) - especially after midnight. ;-D

best, gordo

[pdan]

and he's got a great smile

[pdan]

0 angle sure messed it up, there is a more pronounced pattern...
Lucas ? !
Ponder, the rule frequency is at .1114in, I might need a lpi at a consistant repeat...

[gordo]

0 angle sure messed it up, there is a more pronounced pattern...
Lucas ? !
Ponder, the rule frequency is at .1114in, I might need a lpi at a consistant repeat...

To get the halftone dots to land on top of the grid the halftone lpi needs to be an even divisor of the grid line distance. Otherwise the halftone dots will sometimes land on a rule line and sometimes not. The chances of you figuring that out and the halftone screen being applied by the RIP so that occurs is pretty remote.

So you'll end up with this effect (KCMY are the screen angles used):

K (45°) is your best bet.
Y (0°) might have worked - but didn't.

Upping the lpi helps by packing more dots into the same area as DavidMa said.

FM would be best because there's no screen angle to conflict with the grid lines.

best, gordo

[DCurry]

If printing them as solid lines with a light gray ink is not an option, maybe change the stroke's color to 100K and make it a dotted line.