I dare say the poor Roland was not mean't to do what you're asking of it. As mentioned elsewhere, you'll need to get the carbide bit spinning real fast with an air drill or dremel. The Roland may not like the weight of the Dremel though! For carbide bits, pay a visit to your local pcb manufacturer - they'll have heaps! I used to grab a bag full of used drills and mills for zip. Besides, if you have no luck with your roland, you might have to use the pcb manufacturer's services! Really, for the cost of a single sided pcb, it's hardly worthwhile doing your own.