The side of an A5 is 148 x 210 mm. That means all 3 pages have the same size. This is oly possible, if you fold like a Z but not folding inward, than the third sheet has to be smaller due to technical reasons.
Set up an indd with 6 page, facing pages.
In the page panel menu don't allow to shuffle pages, then move the pages to spreads of 3.
Thanks for that. I am confused on two things still.
When you say spreads of 3, is this correct: https://workspace.imperial.ac.uk/edudev/Public/spreads3.png
If so, I am confused as to which page is which. With saddlestitch, it is easy to work out, but this is confusing me! Which is the front page and what would become the back page when folded?
Do I have to change the dimensions of two pages to 146 or 147? I so which pages and how do I do that?
I only went through that link quickly, but I think it's misleading. My impression is it didn't mirror the guides front and back, and I didn't check to see if they were trimming the last panel short.
Tri-folds are actually trickier than you might think to set up, depending on if you want the same spacing between columns as you have on the outside edges for margins (and that might be different inside than out since you view the outside first as a folded piece), and whether you have the ability to trim the edge off the panel that will fold in. Are you printgn this yourself, or sending it out? Will there be color breaks at the folds?
If you are not going to trim, and you want to set up as two A5 sheets with no trimming, I'd put guides for the folds at 147mm and 295.5 mm from the left edge for the outside and 148.5 and 297 from the left edge for the inside, which will make the inside foleing panel 1.5 mm narrower than the two outside panels. You'll need to add additonal guides spaced either side for of these for the text margins of your choice on the panels.
If you are willing to trim the edge of the last panel so it will fold, you can either set up as 2 A5 pages with three equal columns and add a guide on the opposite edges inside and out to mark what you plan to trim off (and adjust the width of any text frames on the inside folding panel), or make 6 A4 page, turn off page shuffling inthe Pages panel, drag them into two 3-page spreads, and use the Page tool to adjust the width of the left page in the first group (the outside of the brochure) and the right page of the second group (the inside).
Many thanks for this - most helpful. The finished document will go to our in-house print unit and so they will trim). What I might do is take your info and go and speak to them and see if they can guide me through the InDesign setup.
You'd have thought there might be nice trifold InDesign templates somewhere you could just download!
Thanks again - still struggling to get my head round this tricky venture!