welding a cracked mower deck

My buddy has done a bunch of things for me, and now he wants his cracked mower deck fixed. The deck has an angle iron bracket welded on, and the welds have cracked 3/4 of the way around. My plan is to vee out the cracks and weld from the under side. I have a 140 amp mig with a big spool of ER70S-6 on it. Anything I should watch out for? He wants to put a patch over it, but I don't see the need for that.
thanks Dave Wilson www.davewilson.cc

    Greetings and Salutations.
On 26 Jan 2004 07:42:14 -0800, snipped-for-privacy@evcom.net (Dave Wilson) wrote:
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    Well, I suspect this will work pretty well. As a matter of fact, this same problem with my John Deere deck got me back into welding seriously. In my case, one of the support brackets had broken loose, thanks to rust and metal fatigue. I first looked at buying a replacement, but, just the metal shell would have cost me $500 from the dealer (and that was WITH a decent discount). Instead, I picked up an old Lincoln AC-225 buzz box, and after a bit of practice, got some solid if ugly welds on there. It has worked fine for several years now, although I have had to go back and fix some OTHER fatigue cracks...which leads me to suggest that it would be a VERY good thing to save time and energy, and, wirebrush down the metal to check for other cracks forming. Much easier to find them now and fix them while the deck is off the machine once, than make three trips or so to pull it off, weld a bit, and put it back on. I am pretty sure that if there is ONE crack, there is going to be others. The deck is under quite a bit of stress and vibration...both of which are hard on metal.     Regards     Dave Mundt

Hi Dave, This is what I would do
1) Remove any paint, grease, dirt etc from surrounding area. 2)Locate and find the ends of the crack and drill a small hole at those locations. 1/8" (This will hopefully prevent the crack from continuing) 3)Like you say "V" out the crack, but if possible weld from both sides. 4)do not grind the weld flush to the deck, as this will add reinforcement. 5)Get the area x-rayed when finished. (KIDDING)!
You could also weld over the crack and if it is accessible from both sides, back gouge with a grinder on opposite side and weld.
Hope this helps.
A
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It also adds what I call stress concentrations, but I gather others call stress risers. Increases the liklihood of cracking right beside the bead.

Aaron wrote:
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In addition to what Ecnerwal said, this dosen't help.
The base metal is weaker than the weld metal - A36 has Fu = 58 ksi and the ER70X has Fu = 70 ksi. Note that these are both minimums. From a strength perspective, the weld should be _thinner_ than the base metal. Problem is, this invites stress and fatigue. This is why partial penetration joints are used sucessfully.

Did the repair today. All went well. Thanks for the suggestions, I followed all of them. Pictures and commentary at www.davewilson.cc/Welding/MowerDeck. Would appreciate any suggestions on how to make my welds look better.
Dave Wilson www.davewilson.cc

On thin metal subject to high vibration you will typically find that the metal next to the cracks has been work hardened. Welding them up will not last very long unless you add some metal that moves the stresses away from the original points. Adding a plate underneath works as well as a couple pieces of strap iron on top. Even so, the cracks will just migrate.
My mower deck is vintage 1964, it is getting quite ragged after 40 years of hard use. I weld on it every other year, inbetween a new bearing or two in the off years.
Dave Wilson wrote:
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I like gas welding for such projects precisely beacuse of that reason. Seems the heating from the gas softens the area enough that it will not crack easily.
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I actually like O-A brazing for thin sections that have vibration induced fatiigue cracks. The braze material flows out nicely and provides fillets, lots of soft heat to soften the base metal.
Ole-Hjalmar Kristensen wrote:
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