Hope you find a good sharp knife. For very hard veggies like sweet potatoes, and squash don't waste time trying to cut them into chunks. Just cleave them in half. Just wash, oil and roast with cut side down. the skin will slide right off after cooled and they will taste so much better than if they are boiled.
To cut in half I use a big knife and wack the veggie once. The knife will stick in the veggie which is what you want, then on a cutting board, lift the knife with the veggie on it and give it one more wack and the veggie will split just like a log.