If your cuts are like a tuna can, I suspect there is something amiss with your machine. Not getting your settings right or using a dull bit can do that. You might even have excessive machine flex, or even machine slop due to wear of parts. I just had to replace some gear rack on one of mine last Thursday. Think about it, if you have a lot of wear somewhere, that will translate into sloppy movement, that will translate directly to your cut. Check out all your components and see if there is any slop due to wear.