When you can't find a fastener exactly like this, but the chores need done right now... it could be time to weld.

  2018 August 19    Metal & Shop

Introduction


This is a quick welding project to re-attach the jaw liner on the 1979 Taiwan bench vise.  Since this is just a yard vise, I'm not looking for the nicest welds or the most careful cast-iron repair. 

This time around, though, I used special electrodes meant for cast iron welding.  1/8" Nomacast.

Let's see how it went.  (Metalworking can have some hazards;  please read the Disclaimer.)





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In This Article

The Old Welds

Prep and Pre-Heat

The New Weld

Conclusion


The Old Welds


Originally I had welded the jaw liner on with 1/16" 7018, later switching to 3/32" 7018.  The welds didn't so much break;  it's more like they just fell off the cast iron because they didn't really bond to it (not enough amps, too-thin electrodes).  The weld zone looked grainy, finely-porous, and more like cast iron than steel. 



Cast iron has a lot of carbon, and some of that migrates into the molten weld.  If the surrounding metal is too cool, some of the cast iron nearest the weld will also get very brittle.  That's because it basically forms white cast iron.  (Any time you heat cast iron to 1400 F or more, you can form white cast iron if it cools too fast.  Arc welding temperature is a lot hotter than 1400.)

Put all this together with cast iron that's already brittle enough, and this is why a lot of hack repair projects end up with cracked welds.

Those welds were also a bit thin for a project like this.  And I'm sure the preheat was insufficient.

The Easy Weld can handle surprisingly thick metal when it's done right (unlike here.)  But 1/8" Nomacast requires more amperage.  This calls for an AC stick welder.  For thick steel and cast iron, an AC stick welder is the most cost-effective solution.



Table of Contents



Prep and Pre-Heat


First step was to remove as much rust as possible convenient using a flap disc.  (It's gotta be done this afternoon, remember?)  I also beveled the weld area a bit so the weld would (hopefully) take better.



Electrodes work much better when you're not welding cold iron.  So I pre-heated the cast iron to what I think was about 300 degrees F.  This is not really enough preheat, but it's better than none at all.

If you can only preheat to 300, it's better to get the entire piece to 300 Fahrenheit than just locally heating to a much higher temperature.  Otherwise the colder surrounding metal would just draw the heat away too fast.


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The New Weld


Nomacast is good for welding dirty, sooty, or oily cast iron, and for joining cast iron to steel.



I'm fairly certain that nomacast is a low-carbon steel.  The flux probably has a lot to do with how it works with cast iron.

1/8" nomacast ran OK at 105 amps AC, but the arc would go out a bit easily.  This was thick metal;  it could also be that the preheat was not sufficient.  (We'll talk about that more, shortly.)

Peening the welds with a hammer is a good idea immediately after welding.  Another method is to use a needle scaler (I don't have one, though.)  Either of these reduce the chance of stress cracking as the welds cool.  These become even more important when the air is very cold, because the faster surface-cooling produces larger temperature differentials.

After the vise jaw was welded, I just put a welding blanket over the metal after hammering on the welds.  (Don't use a regular blanket... you knew that.)  The piece was still hot several hours later. 







The welds aren't the smoothest, but from what I understand this is common with cast iron welds.  This electrode is about as easy to use as 7018, but it produces welds that look more like 6011.  That might change at a different amperage, though?


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Under Ideal Conditions


To do this right, I should have had some of those temperature crayons.  One made for 450 degrees Fahrenheit would be a good place to start.  Lincoln Electric lists 500 degrees as the low end of the preheat range, but a lot of people use 450 with good results.

With a charcoal grill, a workpiece can be heated to 500 Fahrenheit without difficulty.  A gas grill set on "high" should be able to achieve 450 with no problem.

For higher temperatures, the piece would be placed directly in the coals.  This would be in a temporary oven made of firebricks, built on dry flat ground where you don't care about the lawn.  (I would make the floor of that oven out of the firebricks too.)  After the weld, you could probably just shovel the coals back over the cast iron.  Then maybe cover it with some dry dirt, and leave it sit for a couple days.  (Disclaimer, again.)


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Conclusion


As before, the preheat was probably not enough, but it should work for the intended purpose.  It should hold for a while, and if it doesn't, I'll just weld it again.

The nomacast welded nicely, from what I can see.

The point of this repair was not to do the best weld possible;  the point was to do a "good enough" weld to get the vise back in service the same day.  There are advantages to using cheap stuff sometimes.  If it breaks again, I'll weld it again. 

Nomacast requires preheating the metal, but it seems to go through rust and oxidation easily.  It makes a non-machineable weld, but on a piece like this there would be no need to pretty it up on a milling machine anyway (even if I had one).  So I'd say it worked for the intended purpose.


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