Hi,

For hinges, you need to ensure they are all parallel and operating on the same axis. But one will always be higher / lower than the others, and one will always be at an angle to the rest. You get better with practice! Mis aligned hinges will result in binding.

I love GP hinges!

You can get a set of hinging tools from Du Bro, and I beioeve Carl Goldburg once made a set. A set of 2 prong forks & a gouger (to remove the wood froem h e\center of teh slot)

There is also a parallelogram 'hinge slot centering tool' that helps guide teh above tool into the center of teh TE, and paralleel to teh TE. But I ralrey use it. As long as teh hinge pin is parallel to each other and to the axis of rotation

There is also the center finder marker. Both GP & CG make them.. a lttiel device, with two tabs, and a central point. The tabs ride on teh top & bottom of the TE, while the cdnter point scribes your center line.

Once teh slots are cut, drive th inhnes hiome, and give a bit of a opush to 'dent' teh balsa. this, for me, is enough of a groove. Then try teh control surface, adn ensrue all fits & works as intended.

Next, you need to glue them hinges in. Typically I use epoxy, and as you've seen, gettin gehright amount in the slot takes expericent (i usually get too much in!!) a sanded donw popcicle stick helps get the epoxy into the slot. I glue the hinges into the control surface, let cure, then glue teh control surface to teh airframe.

Grease teh hinges at teh pin. Brush a bit of vaseline on the hinge knuckes (both sides). This prevents teh epoxy from sticking the hinge halves together.

Glue teh hinge in place. Wipe up any excess with a rag & Methyl Hydrate (denatured achohol) flex the hinge a few times, and wipe again. Ensure it is well seated.

There is usually a bit of stiffness when you first flex the surface.