If you search for tech airsoft videos on YouTube, or if you read forums, I’m sure you have seen people talk about gearbox “radiusing. ” What exactly is it, and why do we do it? Yes, it is a modification you will do yourself, but it is actually one of the easier and quicker modifications you can do with just a small rounded file. The front of your gearbox takes a lot of force from the piston slamming in to the front of the gearbox, and if you are running a heavy spring, or have a weak gearbox, they can crack right on the edge of that gearbox. Rounding the edges of your gearbox will remove some of the stress on the corners of the gearbox.
In the above photo, you can see a stock V3 gearbox shell, and the edges of the gearbox are pretty much at a 90 degree angle.
In the above photo, you can see how the cylinder is resting on the edges of the gearbox. That front rounded part is where your cylinder head will sit in, and you can see there is much more surface area than the edges of the gearbox; so it would make sense that we want the energy from the piston travel to be in this area, rather than the corners.
In this photo, I have a small file in place to show you the position and area you actually want to file. Try to use as small of a file as possible. Start small, and then gradually work your way bigger slowly.
In the above photo, this should be your end result. You can see the edges are rounded.
Above, this is the cylinder at rest in the gearbox. You can see that the edges are no longer going to take the force of the energy transfer from piston to piston head, because the edge of the cylinder is not touching directly on the edge of the gearbox.
The pictures below are some additional shots of how the cylinder is resting in the gearbox, showing you the radiuses. This usually should take you less than 15 minutes to do, and could save you from the headache of replacing a gearbox shell. You always want to make sure you are using a high quality gearbox shell. Especially if you are running a high powered set up. Hope this helps, and thanks for reading!