Bolt seizes when theaded into welded nut.

[HotRodMan]

Spot welded a 1/2 inch grade 8 steel nut to 11 gauge steel plate. Spot weld only lasted 1/2 second. Inserted a dowel rod into the nut to keep spatter out of threads. Ran a tap thru the nut several times after the weld. Applied anti seize lube to the threads of the bolt. Bolt was difficult to thread into the nut and eventually gauled the threads. Nut and bolt worked fine before the spot weld. Never had this problem before. Any ideas on how to remedy this? Thanks

 

[Bigblue&Goldie]

When you say spot weld, are you using a MIG? I've done a bunch lately (even fine thread) without issue and I've welded the whole perimeter.

 

[mike93lx]

Maybe the tap was out of spec? Can't see why it would have worked before but not after it you chased the threads

 

[HotRodMan]

I used a flux core welder with .030 wire with the machine set for 1/8 inch steel. I plan to get a new tap and try it again. This is a course threaded nut. I have been doing this for years and never had a problem before. Its a real mystery.

 

[Downwindtracker 2]

A grade 8 is higher carbon steel, maybe you hardened it ? just a WAG

 

[Bogie1632]

I'm with moke93 lx... Bet the tap is out of spec. If you insert it do you get a fair amount of slop wiggling it? If the tap is loose you aren't really cleaning it up any.

In this case try a new bolt and cut a groove or two along the length of the treads. I've run into similar dilemmas welding new backup nuts on steel plate before. Always chalked it up to too much heat welding it on. This is kind of like making a homemade thread chaser. See if that cleans up the nut any as it's likely a tighter fit than the tap you used.

Good luck.

V/R
Bogie

 

[Doug Arthurs]

You didn't grab a metric bolt close to the fractional size by accident did you. And no I myself have never done that.

 

[Stooge]

I don't have an explanation as to why your tap isn't fixing it, but I always, (after yrs ago when I didn't do it and was having issues) thread a bolt into the nut then weld it to keep the nut from shrinking or distorting. usually tightens up a little bit and sometimes need to use a socket to get it back out, but will thread in fine afterwards

 

[rlitman]

A grade 8 is higher carbon steel, maybe you hardened it ? just a WAG

That's a reasonable guess. I seriously have no clue why people spend good money on grade 8 hardware that they then destroy by welding on it.

If you want to weld on it, buy something made for the purpose.

 

[aka Larry]

I don't have an explanation as to why your tap isn't fixing it, but I always, (after yrs ago when I didn't do it and was having issues) thread a bolt into the nut then weld it to keep the nut from shrinking or distorting. usually tightens up a little bit and sometimes need to use a socket to get it back out, but will thread in fine afterwards

I typically have a bolt threaded into the nut when MIG welding to:

a) hold it in place
b) keep any weld spatter out of the threads

If I do a full perimeter weld on the nut, it often shrinks very tightly on the bolt, and makes it hard to remove. Sometimes running the bolt in and out helps, sometimes not.

I need to try the cutting a slot into the bolt trick to make a thread chaser. Any technique involved with this? How long does the slot need to be? Use a grinder with a cut-off wheel or something smaller like a Dremel?

 

[MoonRise]

Any ideas on how to remedy this?

Remove the galled nut-bolt and replace with new ones.

When I need to weld a nut, I usually try to coat the mating bolt with either a good coating of NeverSieze or Anti-Spatter and thread it into the nut BEFORE welding. Helps to keep the nut's threads clean better than just sticking a dowel in the hole AND it helps to reduce the inevitable thread distortion on the nut caused by welding (you can still booger up the nut with all of the heat and solidification contraction when welding).

And a Grade 8 fastener IS certainly a heat treated (and thus heat treatable) medium carbon steel material (per the spec that applies to Grade 8 fasteners).

Of course, your coarse threads should have been 'cleaned' up if you ran a tap through the nut after welding. If the threads were not put back into the size spec after running the tap through, then the tap 'failed' in some way (possibly worn out).

And if I'm welding a nut/bolt, I usually just use a Grade 5 and not a Grade 8 as the welding heat is going to modify/change the nut/bolt mechanical properties after welding no matter what. So why use a harder/stronger and more expensive Grade 8 when it won't usually be a Grade 8 after welding anyway?

You DID remove the usual yellow zinc coating from the Grade 8 nut before welding, right? Zinc in the weld puddle is not what you want to have for a 'good' weld.

And "spot weld"? Although it kind of is possible to "spot weld" a nut to a plate, most of the time you are putting some "tack welds" or a weld bead around the periphery of the nut to weld it to the plate.

 

[Barrymaxx]

I had this happen too actually.

I think the welding slightly anneals the nut material. If the nut and the bolt are both soft they will gall.

 

[metlmunchr]

The hardness spec on grade 8 nuts is Rc24-30. The weld can distort the nut by a few thousandths and make a tight fit, but the nut can also have enough spring at that hardness level to allow a tap to walk the distortion around the hole and not cut anything. This is particularly true in cases where the tap isn't in new and dead sharp condition. If the tap happens to be of the hardware store variety, then its chances of skimming a few thousandths out of a heat treated thread are near zero.

If the OP has just a couple of these to do, he can take a bolt and use some valve grinding compound to lap the hole. I've done this several times in repairing parts having threads with minor distortion, and for a 1/2 inch nut it would be a sub-5 minute process.

Its really not a good idea to use grade 8 nuts for welding, and particularly so with tacks. For a nut to be significantly hardenable, it has to be a medium carbon steel regardless of whether its a straight carbon or an alloy steel. The immediate area of the weld is raised above the hardening temperature and the mass of the surrounding metal then pulls the heat away fast enough for the metal in the weld area to go to full hardness rather than remaining in the tempered state. Metal migrates within the weld area and the weld bead itself gains enough carbon that the weld itself becomes hard. This leads to a brittle weld that has a much greater chance of cracking or breaking over time.

OTOH, if you run a full hot bead all the way around the nut, the resulting heat in the nut will anneal the nut to the point where it would no longer have grade 8 strength.

In reality, a low carbon nut gets you away from these problems in welding. If you look at the tensile strength of a cast iron engine block as compared to the tensile strength of mild steel, they're in the same range of strength. Yet grade 8 head bolts are used regularly threading into cast iron with no problems related to the strength of the cast iron.

 

[Kenstone1]

I switched to square nuts after having same such problems.
Tacking the 4 corners that are further away from the thread
works for me,

 

[FTG-05]

I don't have an explanation as to why your tap isn't fixing it, but I always, (after yrs ago when I didn't do it and was having issues) thread a bolt into the nut then weld it to keep the nut from shrinking or distorting. usually tightens up a little bit and sometimes need to use a socket to get it back out, but will thread in fine afterwards

This is what I do when I weld nuts. I like to use blind nuts for fastening, so I do it quite often.

The only thing you need to be careful is getting weld splatter on the bolt threads, then trying to unthread it.

 

[zmotorsports]

Like others, I do this often for captured nuts or nut plates and don't have any issues with either MIG or TIG although I prefer to TIG them. I thread a bolt in and just snug the fastener and weld a couple of flats then remove the bolt before completing the rest of the perimeter of the nut. I'll run a clean-up tap through the nut and good to go. After powder coating I usually have to run a clean-up tap through again but still no issues.

Thinking maybe there is some issue with the tap because that should cut it back to spec and take the weld out of the equation.

 

[creativecars]

If the tap was cleaning out the threads to spec. I wonder if the bolt was sitting near by, had some spatter get into the threads without noticing and caused damage as it was going in?? Might try a die on the bolt to clean up those threads.

 

[Downwindtracker 2]

I find carbon steel taps dull pretty easily . Until they break, I prefer HSS.

 

[zmotorsports]

I find carbon steel taps dull pretty easily . Until they break, I prefer HSS.

Agreed. I generally use my standard carbon steel taps for cleaning threads and use my HSS for cutting new threads. Even at that when the carbon steel taps start dragging I replace them.

 

[fordkid88]

I used a flux core welder with .030 wire with the machine set for 1/8 inch steel. I plan to get a new tap and try it again. This is a course threaded nut. I have been doing this for years and never had a problem before. Its a real mystery.

Fluxcore is electrode negative so it puts 70% of the heat into the work piece. I would bet its the welding process

 

[matt_i]

I also think certain platings/coatings get changed with the heat of welding and ball up in the thread form to cause instant galling. The nut does get very hot in this step, and while its good to sand the hex faces to remove plating its impossible to remove it all. I usually don't stock "raw steel" hex nuts since they would be a rust-liability for so many things that have to go outside. But if you do this regularly it might be worthwhile to get a population and not mix it with your usual plated versions.

I've sort of given up welding hex nuts and instead go to drilling and tapping. Usually a clearance hole has to be drilled in any case and so just downsizing it and making sure that the material is thick enough to support a reasonable amount of threads (1 dia in steel, 2 dia in aluminum)

 

[joe49]

I use flange/washer nuts. Also you can inset them from the face side using a step drill.

 

[eyeball]

I use flange/washer nuts. Also you can inset them from the face side using a step drill.

That’s a great idea. I often weld flange nuts for projects but for some reason it never dawned on me to recess them.

I actually have a project in the works this morning that this idea will solve a clearance problem I have been sorting through.

Thanks again.

 

[danielbuck]

is your tap HSS? or Carbon? If it's Carbon, it might not touch a grade 8 nut. Also if the tap is dull, it might not be cutting deep enough, even for regular (somewhat loose) fitting hardware.

Try running a die over your bolt, if you have a split die that can be closed down a bit.

 

[SGKent]

was the nut still hot when you tapped it? If so it shrunk. Once a bolt galls you need to run either a thread chasing die or a regular die over it to clean its threads too. Then use a little extra oil on the threads. I'd chase the nut at room temp, chase the bolt, add a little extra oil and try again. If you are using cheap die and taps that can do it too.

 

[larry_g]

One other mode of failure is that the welded nut turned into a teardrop shape and then you run a 3 lobed tap through it. A 3 lobed tap will not round out a teardrop shaped hole and a round bolt will not fit in it.

lg
no neat sig line