For a large block like the 5kg ones that callebaut makes, first drop the wrapped block on the floor or whack it against the edge of a table a few times to break it up into manageable pieces. Then use a large knife to cut down the corners of all the large chunks.
Sometimes I sift things through a sieve to get rid of the dust then a perforated hotel pan to get the right size chunks.
For flakes of chocolate in ice cream, I melt chocolate, spread thin on parchment, and freeze, then crumble into freshly spun ice cream. No need to temper if it’s going in a frozen product.
But yes, trying to get uniform chip sizes from a large block is a pain and often not very successful. I only buy chocolate in small pieces anymore (feves, rondo, pistoles, anything except blocks!)