Screw The Core Boxes!!
One of the tricks-of-the-trade I learned with the Sodium Silicate/ CO2 experience was a better way to make core boxes. My first attempts resulted in a core box built in two pieces with wooden pegs to join the together - the same way you fasten the two halves of a split-pattern together.
That was a complete failure - for two reasons. Firstly, trying to pull apart two halves of a 3-sided core box (one end, half of one side and half of another side) didn't work. The sand core got stuck in the core box and had to be broken out. Secondly, without realizing it (remember this was my first experience making sand cores!), one of the core boxes had an extremely large "undercut". I ended up with a solid chunk of sand stuck in this angled core box. The only way to get the sand core out was to dig it out with a screwdriver. So much for that sand core!
Then I hit upon the idea of fastening the sides of the core box together with screws. This way, when the sand core had solidified, it was a simply matter of undoing the screws.
The solidified sand core easily released from the sides of the core box as each pair of screws was undone. This way, I could give the sand core an extra couple of shots of CO2 with all 6 sides of the sand core exposed.
All in all, a great first-time experience. No muss, no fuss, no cleaning up my wife's oven, eh!?