If you're using two different weights of yarn in the same project you'll probably have some trouble -- worsted weight yarn knits to 16-20 stitches per 4", and chunky knits to 12-15 sittches. They also require different needle sizes. There's a great chart here
that explains the different weights. As a general rule of thumb you should use the weight the pattern calls for, and not mix weights within the same pattern unless the pattern tells you to.