I'm starting to do designs meant for printing, but I'm fairly new to this medium so I don't really understand how bleed works and how much bleed should I specify for:
Should I extend the design into the bleed areas?
Yes, ideally all files that need bleed should have it on all sides.
The bleed is an extra area that you add to your design to make sure there's no "white border" once the card or flyer is cut. The cutters that print shop use is not 100% perfect, pages might not be aligned or printed perfectly; when you add bleed, you make sure there's color everywhere no matter what.
That goes for business cards, postcards, flyers, covers, banners, etc. Even giant size banner need it unless you don't mind having a banner that is a bit smaller; it will be trimmed smaller if there's no bleed added to your layout!
The minimum amount of bleed should be around 0.125" (3mm) outside your document final size, ideally 0.25" (6mm). Each printer has his own requirement for this.
The only time you don't need to use bleed is when there is absolutely nothing printed on all sides (eg. a design with a white border.) Some small ads in magazine or newspapers don't require it but it's better to provide a file with some bleed if you're not certain.
In this case, you can simply provide your final print-ready at its final size, without any extra bleed.
Another situation where you might not need to add bleed on all sides is when your file is provided as a "printer spread"; for example, a book cover design with the spine, front and back cover on the same layout OR a brochure with a fold OR a greeting card. The bleed will only be necessary for the printer on the outside edges. It's still a good idea to create your own designs (front cover and back cover) with bleed on all sides; it will be easier for you to merge them together later when you'll prepare the final print-ready file.
For magazine, they usually provide a template or precise instructions for bleed but the file still need to have bleed on all sides. The part where the fold or binding is will still be cut or folded. Printers also need bleed if the magazine or book is thick because they need to adjust the "creep"; pages are not cut exactly at the same exact width on thicker magazine or book, otherwise the pages in the middle would look wider than the pages that are closer to the covers.
For the same reasons, you need to be careful and keep your texts or important elements within the "safe margin" of your design and nothing important should be on the "bleed" part!
The safe margin should be 0.125" (3mm) inside your design. With books, some printers can even require up to 0.5" (13mm!)
Extra info about trim/crop marks
A commercial printer can not print right to the edge of a sheet of paper. In other words, there's really no such thing as "borderless" printing on a commercial press. In order to combat this, you print a little over the edge of the design on larger stock (paper). This is called a bleed.
If you have content that you want to be right at the edge of a design (or just go off the edge), you must use a bleed. What a bleed does is extend the content beyond the paper edge. This way when the piece is printed then cut down to size, the cut chops off the extra (bleed) allowing content to appear to sit right at the edge of a printed piece (or trail off of it).
There's no such thing as "too much" bleed, but a good minimum to stick to is 1/8" or .125" (1p6 picas). Generally anything between .125" and .25" is used.
Essentially, if you have anything that goes beyond the edge of a printed piece, that item should bleed. It can be on one side of a page, two sides, three sides, or all four. These are commonly referred to as "quarter", "half", "three-quarters", and "full" bleeds.
At least 1/8" - 1/4" to be on the safe size. No printer should ask for half an inch - that's really extreme! The bleed is only necessary to ensure that the paper doesn't show when it's trimmed.
I always work with a 3mm bleed around my artboard (Illustrator) or page (Indesign)it is just to ensure that the printer prints "over" the page if you require a borderless design.
With anything large format, it's prudent to ask the printer how much bleed they require; it's often in excess of 0.5". This is especially true if it's going to be mounted. Dry mounting a 8'x 4' duratran on perspex with only 2mm bleed is no joke. And there have been numerous occasions where I've rejected entire rolls of print because someone in pre-press decided you only need 0.25" bleed for wrap-mounted prints on 0.5" panels.
If the finished product is intended to have color bleed to the edge of the substrate without any white/unprinted/uncovered material, it requires a bleed to be included in the art for print production. The bleed allows for error in finishing. The bleed size should be determined by the expected quality, difficulty of the finishing required, precision and set-up of the equipment used to finish. The finishing department should be consulted when determining the required bleed.
Business cards, letterhead, cut-sheet digital/offset printing, in general, need a minimum bleed of 0.125" and up.
Posters, banners, decals, wraps, large format printing, in general, need a minimum bleed of 0.25" and up.
In any case, if you are not sure what is required to ask someone who is. You will have the best shot at getting the finished product as expected. There is a lot of fudging things because the project was started without the finish in mind....ask the finishers!
Bleeds, Margins, live area... I think I heard something about those things all working together somehow in some mythical alignment of the Planets and Moon's...Customer art is shart. Train your in house designers and if a customer's art does not meet your requirements you have to express the possible quality issues and train them a little also.
