Here you can see a model of the gearbox shell and how it's shaped around the cylinder. The darker red the color, the more pressure and force that's on the metal. You can see on the left picture, how the cylinder edges aren't radiused, there's lots of orange, and even a little red. The red means that it's a breaking point. Now, when you look at the right picture, you see that the cylinder's edges have been radiused, and everything is a much nicer color, less stress, and less likely to break.
The corners there, on a stock gearbox, are pressure points. All that pressure slams into the front, and those points take a lot of it. By rounding them out, you are making those "points" larger, so all that pressure is spread over a larger area. This is similar to why AoE is good. Larger contact pressure, less likely to break. Now, obviously, there is a limit to how large they need to be, you don't want paper thin walls.
So, that's where I'll help out a little more, MORE PICTURES!!!
This picture here, is a stock Classic Army M16 X-Series gearbox shell. Just like any other version 2 gearbox shell you'll find in a stock gun. Note how the edges of the cylinder hole are not rounded, they're corners, corners are bad.
I use this dremel tool to remove material from the gearbox shells. I believe it's a steel cutting Tungsten Carbide Cutter, piece 9901 for those of you with a dremel. For those of you without, a rat tail file will work, it just takes a lot longer.
Now, you are going to want to get a little creative with how you take out the material. You don't want to damage other parts of the gearbox, and you don't want to damage your dremel either. Here is how I remove material:
You basically, only want to remove enough material, to get rid of the corners that are there. Once they are 100% gone, then stop, you don't need to take any more away from the gearbox. Anything extra will only lead to problems.
And then, once you're done with that:
You have a properly radiused cylinder.
A few notes before I wrap this up.
Be sure to remove the metal shavings from the gearbox, you don't want that getting around, it'll cause problems.
Remember to always use eye protection, metal shards + eyes, no fun there either. I also find that sometimes gloves, or doing this in an easy to clean up area is a good idea as well. Metal shards can act as splinters, and those won't decay like wooden ones will. Be careful. Take your time and take it slowly.
For archive's sake, here is the old post:
So, It's a boring day at work, and I've got the time to type this up. I've been suggesting to several people to try and round the edges of your cylinder port on the gearbox to increase the integrity of the gearbox shell. Most of the time I get the "how do I do that" Well, I can't show you how to do it, but I can show you the differences of what happens with your gearbox with and without the mod.
This is the gearbox of an Ares Tavor. It's shaped differently, but it is still a gearbox, and still goes under the same forces that normal gearboxes go under. You can see around the cylinder, everything comes to a point, closing in around the cylinder. Well, this causes a pressure point, and therefore a point for the gearbox to crack. This is also the cause of the infamous V2 Gearbox crack.
Well, this is a program called solid works. This is a simple example of a gearbox with the cylinder removed. The outside is simply a block of metal, the inside is cut out in the same shape of a cylinder. It has been overly simplified so you can see what happens.
I have put it under a stress test, with the force being on the far inside wall of the cylinder. The object is being held in place by the back outside wall, the one with the green arrows. Blue is good, it means the area has been unaffected by the force, and isn't experiencing much, if any stress.
As the colors shift from blue to red, you get more and more stress. You see how at the front corners of the gearbox, they are very red. Those are the pressure points. Those are where the cracks start, and gearboxes break.
The fix is to round the corners. What it does is spread out that force from one point, to a much larger point, because of the rounding.
This for example, is a gearbox that has rounded corners. The ones in the back aren't necessary, but the ones in the front are very good. It spreads out that force of the piston hitting the cylinder head.
In this image, I have rounded out the front of the cylinder head area as shown in the above gearbox. See how blue everything is now, that means it isn't experiencing near as much stress as it was when those corners where still corners. Those red marks are still there, but they are much, much smaller, not to mention how little stress the rest of the gearbox is in. This is the reason why this is such a good mod for high powered set ups, and for V2 gearboxes, for those of you who are paranoid about them breaking.
This can be done with a dremel, or just a round file that you may or may not have lying around the house. It's not very hard, just don't take off too much material.
Edited by Star_folder, 12 November 2012 - 07:26 PM.