I just thought I'd add to the post Jim Riser talks about the whetstones.
The way I use the whetstone to round the corner of a stripper deck differs a little from Jim's.
I don't use a vice, and I actually use a different type of whetstone than the type Jim's link shows.
I move the deck against the stone, not the stone against the deck.
I prefer whetstones with a continuous surface and not the dimpled type, although I have used both. This type has a solid flat surface made up of diamond grit. I use a medium grit 6", one sided stone, and a cheapo one at that.
You will need to keep it ONLY for rounding corners of playing cards. (Unless you want to vigorously and repeatedly clean it after sharpening blades.)
Simply place the whetstone, diamond side up narrow end of the stone nearest yourself, on a surface that will stop it from slipping about.
Holding the deck in a sort of sideways biddle grip-
Square the edge of a newly cut deck on the stones surface, the corner you want to round farthest away from you, and simply slide the deck still squared towards yourself at the same time as lifting the corner of the deck nearest yourself, off the stone, and allowing the other (cut) corner to slid across the diamond surface as you continue to hinge the deck upwards.
Shuffle the deck (I faro them), and repeat as necessary.
If a small burr occurs- repeat the same actions but this time instead of keeping the deck squared, bevel the deck to the right and slide this bevelled edge along the surface. Then bevel the deck to the left and do the same.
You should end up with a round corner in no time.
Smaller whetstones can be (double sided) taped to a table.