"Cutting a t-slot with a dremel is going to be tough on the dremel and slow. "
I reccon

But thats what I have, and
"I'd suggest borrowing or renting a router and you can zip the whole t-slot out in 2 minutes."
I dont know anyone with a router, and I dont think there are any rentals around

"Of course then more than likely your going to have to also purchase the t-slot bit." And the router.
I'll check up on the dremel first. If its a no-good, I hope my friendly hardware store accepts Mastercard
