I purchased a SIG LT 40 ARF and am having trouble with the CA hinges bowing up in the middle. I have opened up the precut slots but to no avail. I read the CA hinges how to but still not getting very far with it. Any suggestions? Other types of hinges maybe? Any help most appreciated.

Make the hinge slots deeper.

The hinges might be too long, cutting the corners diagonally helps their insertion, if you get about 3/8 of an inch into the wood, you're OK, if you test on a scrap piece of balsa, you'll notice that the Ca doesn't go as far into the wood as one would imagine, if the wood is very soft and with poor grain, the aileron can come loose in the air, not that the hinge fails, the wood does, to avoid this, always after installing (I do this on any type flat hinge) insert from the bottom of the surface a seamstress type of steel pin, cut them just long enough to go through the hinge but short enough as not to protrude on the other side, I like to push them in with the back portion of an Xacto knife, you'll get the hang of it right away, after it is in, a drop of Ca on the pin's head will keep it there for ever. The hinge will be very secure and the pin is not visible, a little more work, but better be safe than sorry!

If you're using an exacto blade to cut the slots, make sure they're deep enough, and at least 1/4" wider than the hinge.