I don't cut up grapes, or anything else small. They eat whole grapes with no trouble at all. I cut big stuff in chunks just so I can spread it around, and everybody gets a chance to get some. When I give them a new item, like cucumbers at the beginning of cuke season, I cut them open, quartered longways, so whichever way they land, they can find the inside easily. Otherwise, they peck the skin a couple of times and walk away. But after a few days, they know what a yummy thing a cucumber is, then I don't cut them up anymore. They peck away at them until they get past the skin. They don't like orange rind, so oranges that are going bad, I cut off the bad part, and quarter the rest, so they can get right at the pulp. They love 'em. I know some say not to feed them citrus, but mine have never had any problem from it.
There are a few things mine won't eat raw, like squash, green beans, pumpkin, though they will eat the seeds of squash and pumpkin. I started keeping a big enamel pot in the kitchen for scrapes during squash season, my excess and overgrown summer squash got cut in big hunks and tossed in there. Then before I went to bed I'd stick it in the oven and turn it up to 450F. Let it heat while I brushed my teeth and got ready for bed, then turned it off before I turned in. The oven stayed hot long enough to partly cook it, and it was cold when I got up, and I'd toss it out to the birds, and some, to the pigs, in the morning. The pigs wouldn't eat it raw, either. They love it, cooked.