Screenprint white overprint problem

[Akuma]

I have been fighting with this screenprinting job all night !!! A white base needs to go down first behind all graphics and needs to trap back behind the graphics by .12mm. Is there a easy way of doing this in illustrator.

Everything overprints white

btw all that was supplied was pdfs, cruel mofos

[Sparky]

I think the answer can be obvious, don't make it White. you can use any color you want for your background (we use a light yellow to represent a varnish plate) This will allow you to manipulate the color in Illustrator as something other than white. when the plates (or screens) are made they don't care what color they are just make sure the printer uses the correct color ink. :?

[Akuma]

Sorry maybe i was not clear enough. My spot colour "White" is custom Spot colour mixed from c=5 m=2 y=2 k=0 and set to overprint. This part works fine... The problem I have is getting the white to trap back .12mm in illustrator

[almaink]

Trap back .12mm in illustrator to what? White has no trapping properties. You could make a stroke of .12mm and set it to overprint I guess or like Sparky suggested use another color to represent white in the file.

[Akuma]

Originally Posted by almaink

Trap back .12mm in illustrator to what? White has no trapping properties. You could make a stroke of .12mm and set it to overprint I guess or like Sparky suggested use another color to represent white in the file.

Ok lets say I am trapping the White (which I have said is not really "white", it is a custom spot colour I have mixed to represent white) to shrink behind a square shape. So the "white" square goes down first then the cmyk square goes down over the top. The white spot square must trap back behind the cmyk square by .12 mm.
If you stoke the white and set it to overprint it would spread out from behind the square the wrong way. I want the white to choke behind the cmyk square by .12 mm

[DCurry]

What if you give the white shape a .24mm stroke that knocks out? I say .24mm because strokes in Illustrator straddle the line, so .12mm will be on either side of the line. If you knock out the stroke rather than overprint it, it should reduce your white shape .12mm.

[Akuma]

if you stroke it by 0.24 then set to knockout the line sort of cancells itself out leaving you with the original square size

[DCurry]

Originally Posted by Akuma

if you stroke it by 0.24 then set to knockout the line sort of cancells itself out leaving you with the original square size

No, it will only cancel itself out if you set the stroke to Overprint.

Here's another method: Do like I said about adding the .24mm stroke, got to Object>Path>Outline stroke. Click and drag to select the outlined stroke and the white-filled shape, use the Pathfinder to Divide. Ungroup, then delete the 2 outermost shapes.

[Akuma]

Originally Posted by DCurry

No, it will only cancel itself out if you set the stroke to Overprint.

Here's another method: Do like I said about adding the .24mm stroke, got to Object>Path>Outline stroke. Click and drag to select the outlined stroke and the white-filled shape, use the Pathfinder to Divide. Ungroup, then delete the 2 outermost shapes.

If you set the stroke to overprint it would spread wouldn't it??

[DCurry]

Originally Posted by Akuma

If you set the stroke to overprint it would spread wouldn't it??

Unless I'm misunderstanding whay you are trying to do, the bottom line is that you want to reduce your white ink shape by .12mm all the way around, right? An overprinted stroke will be the plain stroke color to the outside of the line, and your fill color + stroke color to the inside of the line. Print a sep to your laser (or place your file into InDesign and use its awesome Separations Preview) and you will see that nothing has changed regarding the size of your white ink shape. If you don't overprint the stroke, then your white fill doesn't begin until the stroke color ends, which will be .12mm inside of the line that defines the overall shape, thereby resulting in a .12mm keepaway.

Have you tried either of my suggestions, cause I tested them before suggesting them and they work. Try experimenting with a much fatter stroke just to see the results more clearly. You can also use the Overprint Preview to get a better picture of what is happening.