Offset trap size (Industry standard)

[dgraves8rd]

Stupid question: One of our salesreps is upset with the width of our traps. What is the industry standard for offset traps? I have done google searches and can not find anything.....


Thanks

 

[Prepress_Parasite]

What are you using for your traps? We use .002".

 

[dgraves8rd]

.003" - we are sheetfed and web

 

[gordo]

Stupid question: One of our salesreps is upset with the width of our traps. What is the industry standard for offset traps?

There are no stupid question - but there might be stupid answers

Trap amount depends on many factors, printing process, substrate, lpi, etc. The classic rule of thumb is to calculate from the line count of the halftone screen and be equal to half the diameter of a halftone dot.
For example, for a 133 lpi screen. Divide 133 into 1 inch to get the diameter of the dot. In this case 1 divided by 133 = .0075". Divide that by 2 to get the suggested trap diameter. In this case it would be .004". While an 85 lpi screen would end up with: 1 divided by 85 = 0.012 divided by 2 = 0.006" and so on.

best gordo

 

[dgraves8rd]

Wouldn't the age of presses and paper being used also be a factor?

 

[gordo]

Yes, maybe you missed my post:

Trap amount depends on many factors, printing process, substrate, lpi, etc. The classic rule of thumb is to calculate from the line count of the halftone screen and be equal to half the diameter of a halftone dot.
For example, for a 133 lpi screen. Divide 133 into 1 inch to get the diameter of the dot. In this case 1 divided by 133 = .0075". Divide that by 2 to get the suggested trap diameter. In this case it would be .004". While an 85 lpi screen would end up with: 1 divided by 85 = 0.012 divided by 2 = 0.006" and so on.

best gordo

 

[RGPW17100]

If my math is still correct and I use the ancient term of 1/4 point trap that would be using gordos number .004 x 72 =.288. Is this correct thinking?

 

[gordo]

If my math is still correct and I use the ancient term of 1/4 point trap that would be using gordos number .004 x 72 =.288. Is this correct thinking?

Errr, I hope your math class teacher is not reading this thread

Taking the 1/4 point trap idea:
72 points = 1 inch
so 1 point = 1 divided by 72 or:
0.013888888888888888

which rounds to:
0.014" = 1pt

so 1/4 point equals .014 x .25
which equals:
.0035

which rounds off to:
.004"

Which is one of the values already quoted for 133 lpi. Which may be where this notion came from - SWOPland back in the day.
So the 1/4 idea gives you a value that works, however it does not accommodate changes in lpi which the method I posted does.

best, gordo

 

[Joe]

We use .004 for newsprint.

And .003 for coated stock.

 

[DavidMa]

We use .002" for our sheetfed and web presses, and even smaller sometimes depending on the paper.

 

[longlimb]

Same here.

.002" most of the time. Sometimes smaller.

 

[wkrepsig]

We used .004" in our film days but when we switched to CTP we went to .002". Heidelberg sheetfed shop.

 

[blkczar217]

We use .003 for board(10pt) and .005 for label(70-80lb) stock.

 

[khasmir]

There are no stupid question - but there might be stupid answers

Trap amount depends on many factors, printing process, substrate, lpi, etc. The classic rule of thumb is to calculate from the line count of the halftone screen and be equal to half the diameter of a halftone dot.
For example, for a 133 lpi screen. Divide 133 into 1 inch to get the diameter of the dot. In this case 1 divided by 133 = .0075". Divide that by 2 to get the suggested trap diameter. In this case it would be .004". While an 85 lpi screen would end up with: 1 divided by 85 = 0.012 divided by 2 = 0.006" and so on.

best gordo

I do not agree that the trapping distance has anything to do with the screenruling, this is completely unrelated. Trapping is to disguise printing registration errors and this depends on the printing technique, press, substrate, temprature, humidity, ... but not the screenruling.

With a higher or lower screenruling there will not be a bigger or smaller registration error, hence...

For offset this will ususally be between 0.002 and 0.004" or between 0.05 and 0.1 mm.
For flexo this is quite a bit higher and can easily go up to 0.02" or 0.5 mm. or sometimes even higher.

 

[T]

Sheetfed
We use .003 for small presses
and
.006 for large format (64 - 81")

 

[svharter]

We're still film based.

.003 for Our Flexo Presses
.006 for Our Screen Presses

Scott