What's the best technique for perpendicular cuts through thick stock?

What is the best way to maintain perpendicular cuts through thick card stock?

I printed out hull parts for my skipjack design and realized that cutting 1mm slots through the 2mm keel to accept the hull formers will be challenging. I foresee difficulty keeping the slot cuts perpendicular to the keel.

Any tips?

Thanks,

--jeff

Attached Images

slots.jpg (20.2 KB)