Nice work. I'm always impressed when folks carve a rounded handle without a lathe. Not sure I'd want to try that. To the cracking issue - the hole diameter will usually shrink if the wood is not completely dry - @less than 10% or so. I've often had to enlarge holes after brush handles have sat around for a month or more before they get a knot. A $30 moisture meter is a good thing to have, if you are going to make brushes. Hope to see more of your work in the future.