What is an average vector trap/overlap for manuals? How about autos?

[Dottonedan]

Choke, spread, fatting, starving, extending, adding, subtracting, overlap, undercut, etc,  they all mean the same thing. In old school photo stat camera, we called them Fat Matt and skinny Matt as well as choke or spread.

The terms are all different depending on where your from and who told you initially.
How you do them is all the same also. You either add more or take away more. If its an overprint, you add more. Call that what you wish. Same for underbase, but you take away from the sides.

You do this using any measurements you feel comfortable with. Pts, mm, inches, these are all methods or measurements of your choice. The adding or subtracting measurements are any of these. Choke, spread, fatting, starving, extending, adding, subtracting, overlap, undercut, etc,

I assumed everyone would know this general term of choke or spread and to lay out every option possible is not feasible. In your program of choice, stroke something 1pt (or insert your answer) and then change your preferences to Mm or inches and you get your equivalent of choice.

[Rockers]

Depending on the art we choke by anything from 0.17mm to 0.3mm.

Is that about .5 pt to 1pt?

That`s right, we Europeans use different units, sorry about that.

[JBLUE]

zero and zero....just butt registration!

So if you are printing say a yellow on black shirts you do not choke the white underbase at all? If so you have some mad skills!

Its not called mad skills just doing it right...... Trapping is compensation for poor equipment. IE bad exposures, sloppy presses, and just general problems in the process. You can take the same film and get your base screen just right just with exposure alone. Control your dot gain and it is not to difficult to achieve on press. This is one of the times where dot gain can be your friend. The key though is to have your press dialed in. If it is not you wont be able to do it.

[Gilligan]

These brings up a point we avoided the other day.

Light on dark with halftones.  Not semi-process that can hide it but spot color halftones?

Is there anything you can do to keep the white from peaking out? Or do you just roll with it and let it be what it is?

[tancehughes]

In many cases, we do not choke our white underbase at all. Sometimes we may choke it .25 pt, but not usually. It's common for us to use the same film for the underbase and then top color if its just a light on dark print single color.

[Dottonedan]

Butt registration is great. Like he said, if you have everything in check,  you technically shouldn't need to add trap to every job, but we all know that is not the case for all shops and presses.

I would like to say tho, that even for autos and shops that do butt registration, trapping or overlapping is simply a part of the separation process to tackle specific jobs.


Special effect inks for example are better printed when you compensate in the seps for ink that has a tendency to bleed, run, expand. Puff, for example would need a knock out stroke (choke) if it sets butt up next to another color. A clear base glitter is another example of when you would choke a little to allow for some over spreading.

Sometimes, you have a job that has so many colors printing, it helps to build in a gutter ( knock out thin line) to help keep line work sharp.

So my point is, traps, chokes, spreads or what ever you might call them, are a tool to be used based in the art needs (in addition to compensation for registration).

[Dottonedan]

Sim process (multi colors) over top of puff is another example. You need to cut back on the art (tuck the puff under) the sim process a tad (1-2 pt stroke of negative or process white that knocks out of the art... that will knock out a line around the puff screen. This is so that when the puff expands, it does not peak out under your sim process top colors.

[blue moon]

for all of those saying that you should not need to trap, I beg to differ. We were not trapping in the beginning and as a consequence you could see the underbase all the way around the print. It was not visible from above, but when you looked at the side of the print you could see the sandwich effect of the underbase and top color sitting right above it. Since it was exactly the same size as the ubase, if it is sitting right on top of it, side of the ubase will not be covered. Think of it this way, take black piece of paper and put a white piece on top of it. You will be able to see the black sheet even if the top is perfectly aligned.

In the end, we trap the outside color by 0.5 pts just to make our life easier. With the translucent inks we use, it is almost imperceptible and it makes things go smoother.

pierre

[ScreenFoo]

Depends on the art--usually .75pt for athletic style prints.

Thanks JBLUE, was starting to think no one would mention exposure latitude in relation to trapping/choking. 
(I wonder how many people are trapping artwork because they're choking exposures...  )

[blue moon]

I guess what I was trying to say is that if both your top and ubase are exactly the same size, you will see the sandwitch effect. If it is not there, chances are there is more gain on the top screen so it is covering the ubase all the way around . . .

pierre

[tpitman]

On my manual press I generally use .5 points, from the center of the path.
On the auto I run in Daytona, I don't think they use any trap or choke (I don't do the seps, just run the press).

[Dottonedan]

(I wonder how many people are trapping artwork because they're choking exposures...  )

That's actually another method if you forgot to do this in the seps. This is identical to the over and under exposure using a stat camera back in the day.

[tonypep]

And of course if you're set up for it DC colors=no base, no choke, no flash, no hand.......no prob.
Pls don't beat me with the Forum stick