Calculating cutting positions w. bleed etc

[bcr]

Hi all,

This may sound like a bit of a dumb question but I am still very ignorant about how to calculate cutting points for imposed/ganged up items onto larger sheets.

When doing something straightforward like a single image on a larger sheet not ganged up then I will do the following:

• First/bottom cut lengthways = (Half of substrate length + half of the (trimmed) length of the image)
• Second/top cut lengthways = (trimmed) length of the image
• ... and then the same for the width.

But I'm not sure how best to do this for more complicated gangup imposition, particularly when using bleeds.

Are there any useful guides out there on this, or programs which will generate a list of cutting points for me? I don't like cutting by eye as I tend to mess that up. I want to know to the milimetre where I should cut using the measurement gauge and in what order.

Currently I'm using Ricoh TF Prep for imposition and CWS (without Impose).

I could be persuaded to try different imposition software if it would also give me the cutting measurements when producing the job..

 

[kslight]

Are you asking for the software to just arbitrarily tell you what numbers to plug into the cutter? I’m afraid it’s not that simple in my experience. To be accurate you often need to use a ruler, set your gutters the same, etc and eventually if you make a lot of the same cuts you’ll “know” what the right number is. But your cutter, printer, paper stock, etc all vary in their own tolerances.

Usually I set .25” gutters as most of my equipment isn’t set to millimeters. If I print on a 18x12” sheet I first cut in half lengthwise, minus half of the gutter, so my first cut should be 8.875”. But I know that between the above tolerances, 8.9” is a more accurate cut, so I cut there. Then I rotate the other half of that stack and cut the rest of the gutter, which is now 8.85”. Then I cut the net length of the piece…that is easy, if the printer isn’t stretching then if my piece is 8.5x11” then I cut at 8.5”. Then I cut top and bottom…1” off each; unless the print / cutter isn’t quite centered then adjust. But I follow these same principles no matter what the finished size or sheet size.

 

[bcr]

Are you asking for the software to just arbitrarily tell you what numbers to plug into the cutter? I’m afraid it’s not that simple in my experience. To be accurate you often need to use a ruler, set your gutters the same, etc and eventually if you make a lot of the same cuts you’ll “know” what the right number is. But your cutter, printer, paper stock, etc all vary in their own tolerances.

Usually I set .25” gutters as most of my equipment isn’t set to millimeters. If I print on a 18x12” sheet I first cut in half lengthwise, minus half of the gutter, so my first cut should be 8.875”. But I know that between the above tolerances, 8.9” is a more accurate cut, so I cut there. Then I rotate the other half of that stack and cut the rest of the gutter, which is now 8.85”. Then I cut the net length of the piece…that is easy, if the printer isn’t stretching then if my piece is 8.5x11” then I cut at 8.5”. Then I cut top and bottom…1” off each; unless the print / cutter isn’t quite centered then adjust. But I follow these same principles no matter what the finished size or sheet size.

yeah i was hoping that if the imposition software knows the number of items on a page, the dimensions of the item and the bleed box etc, that it could then tell me the sequence of cutting and the measurements to use. I would expect there to be a bit of manual adjustment necessary based on various things, but that it should get me into the right ballpark, which i see more as fine tuning.

yesterday i was trying to do a card imposed 6 up onto a sheet (2 columns with 3 rows), but i couldn't get my head around how to calculate the trimming points for the three rows as i normally half things. In the end i got the card reworked removing a lot of excessive bleed which meant in the end i could do it 8 up, and was able to easily halve the measurements. That's just an example where there is no doubt a straightforward calculation to be done but I was not aware of it and google was failing me, as was my tired brain!

 

[kslight]

yeah i was hoping that if the imposition software knows the number of items on a page, the dimensions of the item and the bleed box etc, that it could then tell me the sequence of cutting and the measurements to use. I would expect there to be a bit of manual adjustment necessary based on various things, but that it should get me into the right ballpark, which i see more as fine tuning.

yesterday i was trying to do a card imposed 6 up onto a sheet (2 columns with 3 rows), but i couldn't get my head around how to calculate the trimming points for the three rows as i normally half things. In the end i got the card reworked removing a lot of excessive bleed which meant in the end i could do it 8 up, and was able to easily halve the measurements. That's just an example where there is no doubt a straightforward calculation to be done but I was not aware of it and google was failing me, as was my tired brain!

Re: managing three (or however many) rows. I would normally cut the foot here (the bottom mark of the bottom row), then rotate the stack back 180 degrees into the cutter - then assuming your first cut was accurate, the calculation is simply the length of the piece + your gutter. Then rotate back and just input the length of the piece, to chop the head (remaining gutter) off.

I am sure you could create a book making a step by step guide for cutting the common sizes you use, assuming you always impose consistently. Or likewise, you could probably set up an excel spreadsheet to do a rough calculation. Or many people choose to save common programs on their cutter. But I think you might be making it out as more complicated than it needs to be.

 

[bcr]

Re: managing three (or however many) rows. I would normally cut the foot here (the bottom mark of the bottom row), then rotate the stack back 180 degrees into the cutter - then assuming your first cut was accurate, the calculation is simply the length of the piece + your gutter. Then rotate back and just input the length of the piece, to chop the head (remaining gutter) off.

I am sure you could create a book making a step by step guide for cutting the common sizes you use, assuming you always impose consistently. Or likewise, you could probably set up an excel spreadsheet to do a rough calculation. Or many people choose to save common programs on their cutter. But I think you might be making it out as more complicated than it needs to be.

thank you!

 

[pippip]

I think cutting can be done in a number of ways depending on your accuracy versus economic needs.

I started with litho printing so my first cut out of habit would always be based off grip and lay, so with our digital press I'd be the same even though this isn't fully the same.

Using the above approach and templates in Fiery Impose and our programable guillotine means most jobs are straight forward.

We aim towards accuaracy so I do tend to use gutters and bleed on every job as it means I can manually adjust last minute. Also helps when the guillotine isn't 100% sharp.

At the end of the day a good guillotine operator doesn't even have to think about it once they have a ruler and a bit of OCD.