Drillling & Tapping MIG Weld

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Grind it down if you can. Use a new drill bit and oil, lots of pressure and not too fast on the speed. Maybe better to avoid it if you can - it will be hard as can be and will not tap well.
 
Depends on the nature of the weld. Do you have a torch? Can you anneal the weld affected area?
 
That is going to be a double barrel bastard. The best advice I have is heat it cherry red with a torch and then try it.
 
I cant imagine what it will be like to tap it. Thickness,diameter and
Pitch will all affect the outcome.
A new, high quality tap may be your only shot,tapping fluid and go slow.
 
what kind of metal is the weld on ? and will you be boring through the whole weld or just catching the side like half the hole or less ?
 
Thanks for the input guys. I've got the hole drilled. Now hopefully I can tap it.

jimjimjimmy said:
what kind of metal is the weld on ? and will you be boring through the whole weld or just catching the side like half the hole or less ?
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The metal is mild steel (0.25" thick). Unfortunately, the entire hole to be tapped is through the weld.

toolmanmike said:
Tell us what you're up to. May be we can help.
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I have to tap a 7/16-20 in a hole in 0.25" thick steel that was previously drilled to 29/64" (slightly larger than the - hopefully soon to be threaded hole). I welded it shut in order to drill and tap it to the new smaller size. In hindsight, I probably should have just installed a helicoil in the original hole.
 
Try the hard stuff but you could always use a thread-sert in a larger hole. Wont hurt to try. Isnt MIG weld very brittle? I can barely tap cast iron with crap taps.
 
If the part can handle the heat, getting it cherry red and then slow cooling it should soften it and make it drill/tap easier. Quality cobalt drills and a good tap will make a difference too.

Maybe a question for another thread, but.....Is there a "soft" MIG wire or is the hardness a product of the process? TIG welds are workable, why are MIG such a bear?
 
I got the hole tapped. The threads aren't great - some of them chipped out - but it'll get the job done.

I was also curious about filler wire that that results in a more easily-machinable weld.
 
pishta said:
Try the hard stuff but you could always use a thread-sert in a larger hole. Wont hurt to try. Isnt MIG weld very brittle? I can barely tap cast iron with crap taps.
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You know why? Because most "crap taps" are made from cast steel, or even sometimes cast iron. That's why they wear out so fast and or break easily.
 
gzig5 said:
If the part can handle the heat, getting it cherry red and then slow cooling it should soften it and make it drill/tap easier. Quality cobalt drills and a good tap will make a difference too.

Maybe a question for another thread, but.....Is there a "soft" MIG wire or is the hardness a product of the process? TIG welds are workable, why are MIG such a bear?
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I've seen talk from old timers and farmers about using 'hay wire' (iron wire) to make 'soft' welds. No idea whether it's a good idea or what, but the lack of alloying materials seems to make the welds easier to deal with. I wouldn't do it for anything that's strength-critical obviously.

Mig welds use the heat of the filler metal to fuse to the surrounding metal. Versus TIG or torch which melt the base metal and heat the filler using the base metal and/or arc/flame. In a Mig weld, the material being welded will draw heat away from the weld and cause a faster temperature drop which can cause harder deposits or hardening of the base metal due to the relatively 'quick' cooling.

I remember reading years ago some guidance from the FAA on homebuilt aircraft that post weld normalizing of mig welds (heat with oxy/acetylene until red, let air cool, do not force cool) should be practiced by most any fabricator for tough joints. Also that MIG is the least reliable method of welding high-strength joints and is a method of last resort (they cited lack of penetration, fusion rarely exceeding more than 40% of the joint, etc). Their guidance was being given as a 'best practices' type deal recognizing that people will use Mig even when they shouldn't and were trying to help make things less-bad.
 
gzig5 said:
If the part can handle the heat, getting it cherry red and then slow cooling it should soften it and make it drill/tap easier. Quality cobalt drills and a good tap will make a difference too.

Maybe a question for another thread, but.....Is there a "soft" MIG wire or is the hardness a product of the process? TIG welds are workable, why are MIG such a bear?
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There is a wire called Easy Grind. I have never used it and yes the process of welding TIG and MIG heat the base metal differently so MIG cools faster hence a harder metal than the TIG that heats the base metal more so it takes longer to cool.
 
I searched for a mig wire equivalent to 6018 rod which is easily machined. There isn't any available in major wire manufacturers. I did find the easy grind wire though.
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Phreakish said:
I remember reading years ago some guidance from the FAA on homebuilt aircraft that post weld normalizing of mig welds (heat with oxy/acetylene until red, let air cool, do not force cool) should be practiced by most any fabricator for tough joints. .
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I don't know much about metallurgy but I'd agree with this.
 
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