I read the post on installing ca hinges, it says to drill a hole to let the glue flow into the hinge. My hinges have a slot cut out in the middle, I think it's there to help the glue flow into the hinge, do I still need to drill a hole?

Probably not but if you have a drill available - do it.

What Bruce said. Even with the slots it doesn't hurt to drill the holes. The most important factor when installing CA hinges is to get a good bond of the hinge to the wood of the plane. The only way to do that is to get CA to all parts of the hinge, and that's why the slot and drilling a hole are done. It helps the CA wick into the entire hinge.

Ken

I also cut the covering away from the slot, just a little, so it doesn't impede the flow of the CA.

Drilling the hole is just a little insurance to give the glue a channel to wick deeper into. The slot in a slotted hinge does the same thing.

I often do not even drill the hole if the fit seems right - it's more important on a tight-fitting slot. But then, I've been doing this for a long time and I can judge when it's necessary and when it's not.

So the bottom line is - If you've got a slotted hinge, the hole is not necessary.