Some important things
I just trimmed two Thoths and they turned out pretty good, but when tried the 'borderectomy' on some of my other decks the results weren't that great (fortunately I tried on the title cards that come with the deck and are pretty much useless, so no harm done). I have to warn you on some things if you decide to cut the borders off:
1) Use a good paper cutter with a sliding blade
2) Use corner scissors for the rounding the corners
3) Practice on a blank card if you can
This is important because you can't be absolutely sure how close the blade will cut unless you try it first (I didn't and ended up with a couple of 'close shaves'). Also, you can't know if the edges of the cards will fray or not. In my experience, some of the heavily laminated decks have raggedy edges after being cut (might have something to do with blade sharpness too)
4) Try to cut as fast as possible but remember to have a firm grip on the card to prevent it from sliding off
If you cut it too slowly, the blade won't cut through the card but leave a small line on the surface. I don't recommend trying to cut by sliding the blade back after cutting the first time because this might make the edge raggedy
5) After rounding the corners with corner scissors pick one card (if you have a card where you sliced off more than from the others, use that one) and align it with another card one at a time and carefully even out the overlapping edges with the card you picked out
Be careful not to cut too much off or to cut the card you use as a guide. Every once in a while align the the cards you have cut already and see if they are even (or as close as they can, they are hand cut).
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So, there's what I've learned yesterday and today. The beginning was nerve wrecking and when I sliced a bit too much... i thought that would be the end of the deck, but it wasn't! The difference was so tiny that now my cards seem like they were born that way! i didn't cut away anything important or make the edges totally crooked, so.. GO FOR IT!!!