drilling ambidextrous holes on gearbox
 

apparently to have an ambidextrous selector, you would need this tiny hole on your gearbox.

now every gearbox I got or want to buy, does NOT have this hole. so here goes my question:

How easy is it to add it on my own? Will a simple drill tool do the trick? What are the risks in long run?

I really want this for my project now.

This might interest you: http://www.airsoftcanada.com/showthread.php?t=126429

A drill will work fine. Use a proper bit with lubricant to minimize the risks of cracking, warping and metal shavings. Afterwards gently emery-cloth the hole smooth. Your hole has to be exact, close won't cut it. Make sure that it'll work with the parts you've selected though, drilling a mechbox is easy, drilling a hole for no reason is also easy.

Use a split point drill at high speed and low feed on a drill press. Don't need any lubrication for pot metal. If you go too fast or use a typical twist drill with a big chisel edge, you'll oblong the crap out of that hole.
Problem is you need the exact location of that hole, and despite the loose tolerances in airsoft, I suspect you'll have to be within about .015"
So you'd need an ambi mechbox to measure anyway.

..or you can assemble the halves and go through the opposite side with an angle gauge and a center pin punch to locate. If you don't have machine tool experience, never mind. lol

the whole accuracy part worries me. I have the tools and drill bit for this purpose but I am worried if I it is not in the exact place it would cause problem. has anyone ever done this before?

you need a drill press, also the issue is that the half shell will often not lay flat so that can throw off the squareness of your drill. If you have a sacrificial gearbox I would maybe try it, but if you have a nice shiny new gearbox, I'd be much more hesitant to try. Is it impossible to get the correct gearbox shell?