How to fix this crack

yomax4 · Sep 15, 2016

Just a Weld, no matter how you prep it may not be enough if you don't stop the crack from spreading onward. cast, Steel, Aluminum or what ever. As long as you are tearing it down it wont hurt to drill a hole at the ends of the crack to stop them in their tracks.. Nip it now and don't look back.

Mark @ Everlast · Sep 15, 2016

First, get it steam cleaned all over before you do it. Then grind, grind grind. I wouldn't worry about the oil that much in the tank. It isn't that volatile. But for safety's sake, you could flood the tank with some pure CO2 or argon and keep a little bit running in while welding.
A plate over the corner like shown would be a good idea, just round the edges of the triangle. Also, weld one inside the frame too (or more). It looks like the crack continues onto the inside and underneath side of the weld possibly.

Get some fresh out of the can 7018 for this and get them hot before using. You should be able to burn the flat area in at 130 amps or so with ease. MIrror what you do on the other side as well before you finish too.

woodlandfarms · Sep 15, 2016

OK, so the consensus is it might be reparable by an idiot like me. THats good.

So my engineering question. Why do you use an oval instead of a square for a binding plate?

Second, my neighbor whom I do trust wanted me to use angle iron along the edge (maybe 2.5 feet of it) to "rigidize" that side and then the other. But it soundes like this would be a bad idea structurally. Why?

Finally, the fishplate (that is what you all it, right? an oval is a fishplate)? What thickness would be prescribed?

IslandTractor · Sep 15, 2016

woodlandfarms said:
OK, so the consensus is it might be reparable by an idiot like me. THats good.

So my engineering question. Why do you use an oval instead of a square for a binding plate?

Second, my neighbor whom I do trust wanted me to use angle iron along the edge (maybe 2.5 feet of it) to "rigidize" that side and then the other. But it soundes like this would be a bad idea structurally. Why?

Finally, the fishplate (that is what you all it, right? an oval is a fishplate)? What thickness would be prescribed?

Stress "accumulates" at sharp corners and sharp corners are the classic spot to find fractures. Rounding the edges distributes the forces so they don't concentrate.

I'm not sure the angle iron idea would have been bad before there was a crack but it won't solve the crack issue.

There are probably engineers here who can tell you what thickness the plate should be. I note that such plates on new equipment is usually about the same gauge thickness as the surrounding metal.

woodlandfarms · Sep 16, 2016

Also, Drilling. I saw this done on Aircraft Aluminum. Is it something I should do here or will the fishplate stop the cracking? If I do drill do I weld the drill hole?

IslandTractor · Sep 16, 2016

woodlandfarms said:
Also, Drilling. I saw this done on Aircraft Aluminum. Is it something I should do here or will the fishplate stop the cracking? If I do drill do I weld the drill hole?

Standard recommendation is to drill the end of the crack and then weld the hole closed along with the V'd out crack.

Shield Arc · Sep 16, 2016

I have always been told a fish plate should be the same thickness as the material it is being welded to.
When drilling holes at the end of a crack. Start the weld in the center of the crack, and weld towards the hole. Feather / grind down the start of that weld. And then weld towards the other hole.

ray66v · Sep 16, 2016

I don't think a "fish" plate will help, unless you're hungry.

A flitch plate could be very helpful though.

sd455dan · Sep 16, 2016

ray66v said:
I don't think a "fish" plate will help, unless you're hungry.

A flitch plate could be very helpful though.

Mmm...Fishplate - Wikipedia, the free encyclopedia
Flitch plate flitch plate - Google Search

have always heard and used the term fish plate ( generically) for these type repairs- but looks like a new term and variation to remember, especially when using thru bolts.

IslandTractor · Sep 16, 2016

Shield Arc said:
I have always been told a fish plate should be the same thickness as the material it is being welded to. When drilling holes at the end of a crack. Start the weld in the center of the crack, and weld towards the hole. Feather / grind down the start of that weld. And then weld towards the other hole.

That makes sense but what is the rationale for welding from center out? Is that just a general point or specific to crack repair?