Version 2 mech box fix?

[brently0725]

I heard from a fairly reliable source that if you take a small round file and file the corners where the cylinder goes in a V2 mech box is it will be stronger cause the stress will be applied equally in the circle not all at the square point?

Just a thought.
I think it makes sense!!!

[LUTNIT]

I've seen two broken V.2 mechboxes in person and a couple examples online, about half of the breaks occur at the points that picture says to file down but some still occur at different points, seems to be pretty random.

[MadMax]

It looks to me that the wrong corners are indicated. The offending areas are the front upper and lower corners where cracks develop. I'm not sure, but it looks like the rear corners are indicated. There are no cracking issues on the rear corners to my knowledge.

I would suggest filing forward only and not downwards. There is not much material in the up-down direction at either front corner. While rounding may reduce stress concentration, filing in the up/down direction will reduce the cross sectional area of metal pulling against the piston impact. Filing forward will leave a rounded corner, but not reduce forward arms area under impact tension.

I would suggest a single cut file pointed 1/8" file. Use the smaller dia pointed tip and file a 1/16"-3/32" round. Doublecut/crosscut files will leave small "V" notches which will themselves induce stress concentration. You want a smooth surface not a ridgy one.

[brently0725]

Thanks guys for your imput. The pic was just an example. It was the only one I could find in a hurry. Yes the front would be the ones I meant to be filed. The constant hammering from the piston causes cracks there in some folks cases.

[Greylocks]

Removing metal from an already weak joint is not really bright. Whoever told you that needs a clue about physics and metallurgy.
The only way to implement that idea is at the casting and manufacturing level, not after.

[Dracheous]

JUST BUY REINFORCED!


I yell this because a PDI 150 destroyed TWO TM mechboxes in less than a month apart of each other. The first only one side split up, in the front. On the second after a good fire fight at a game with the Warmongers and only one really. I got into sneaking around after that and just didn't encounter any contacts and any I did I wasn't sure who they were so I just hid and tried to to be discovered, or get any attention to the other two guys that I was with. Anyway the whole front end had be broke right off. When I opened the M4 the morning after to do routine cleaning ((Reason it got left till morning was this was a night game and by the time everything was said and done it was nearly 2 in the morning that I got home. Didn't want to do it tired and miss something. Anyway after cracking the gun open I found the front of my mechbox was being pushed up against my upper receiver because the whole front was broke off and being pushed by the spring.

Save yourself the headache get in on a group order or call up one of the retailers on the list at the top here and get a reinforced.

[MadMax]

Originally Posted by Greylocks

Removing metal from an already weak joint is not really bright. Whoever told you that needs a clue about physics and metallurgy.
The only way to implement that idea is at the casting and manufacturing level, not after.

It's a fairly standard trick in manufacturing to drill or mill corner rounding features to reduce sharp corner stress concentration.

You're right that such features can reduce available cross sectional area and reduce the strength of an already critical alrea. This is why I recommend cutting forward only to keep the cross section across the usual breakage direction from being reduced. Since I have only seen cracks perpindicular to the cylinder axis, I am inferring that the cross section in the forward direction is much more than adequate. The fatigue strength in that direction is much higher than in the vert' direction anyways.

If you closely examine pics of TMs new Type 89 mechbox (V8 you can see stress relief corners at the front windows of the mechbox.



Look at the upper shell and zoom in on the image to see two small round features at the front corner windows. TM put the hole centre right on the original corner which reduces cross section in the vertical direction. I think TM does lifecycle testing so they either know that the hole placement improves fatigue strength or they are trying to limit the fatigue life for some bloody minded ASGK promise to limit use of high powered springs. Not much material is removed so I am leaning towards the former. Sharp corners can significantly reduce fatigue strength, a touch of rounding goes a long way to improve things. I would have made the holes tangent to the upper and lower window edges though.

I also note a heavy pad of metal at the top so I think TM has modified their design for V8 to address fatigue issues.

[Greylocks]

If we were talking about good steel instead of aluminum or pot metal used for airsoft, machining the corners may help, but I would not do it for this game.

And it requires skill and good tools to do it well, something most of us dont have.

So if it's not done at the factory, my point is it's not a good thing to try it after the fact. You are more likely to remove whatever hardening was done.

MadMax, you are an exception to this comment; you know your shit, we know you do, but really, again, most of us dont even come close.