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Tim Cook

Evil air pocket

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Yikes!  Used a lost foam technique and poured a bronze drag for a scabbard.  There was a small dimple on the tip.  I thought no problem, I will grind it away.  But the more I ground the larger it got!  Is there a way to fill this in or fix it somehow?  Or am I condemned to have to start over?  Could really use some help.

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Hmmm....

 

With the correct rod (corresponding alloy, one assumes) you should be able to braze that. Fill the hole in and grind it flush. 

 

Do you know the exact alloy of bronze? That will be crucial for color matching. 

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Considering he cast the piece, I would assume he still has scraps of the same.  An oxy/acetylene torch or TIG welder should take care of it nicely with some filler.  Pile it on, melt a puddle. enjoy.  

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I was thinking TIG as well. I've never ran one on bronze. Should be pretty straight forward. 

 

TIG would be better than oxy-acetylene. Brazing melts the filler, while TIG will melt surface material as well as filler, results in a stronger weld. 

 

Set it to DC, I would imagine AC would be a little aggressive on bronze, might end up blowing more away then you want. This is all assuming you have access to a TIG welder. 

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1 hour ago, Will W. said:

Set it to DC, I would imagine AC would be a little aggressive on bronze, might end up blowing more away then you want.

I don't know squat about welding, but I can make two pieces of metal stick together. I was under the impression that AC was specifically for aluminum and nothing else.

I always seemed to make a mess of everything I ever tried it on.

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@Joshua States it is mostly used for aluminum, yes, but is also used for magnesium and a few niche applications. It can also be used for rusty steel, but youre better of just cleaning the steel and using DC.

 

The reversing polarities of AC have an inherent cleaning action, cutting through the oxide layers which melt at much higher temperature then the base metal itself. 

 

One assumes you could just clean metals like aluminum or magnesium before welding, but they form an oxide layer immediately on contact with air, which means any time between cleaning and welding just builds more oxide, and these metals are very touchy about welding with oxide layers present. 

 

During the electrode positive (EP) portion of the AC cycle, the current is flowing from the workpiece to the electrode, thus "blasting" or "pushing" the oxide layer away. The electrode negative (EN) portion of the AC cycle then has a clean section of metal to fuse, free from oxide, when the current pushes from the electrode to the work. The shielding gas used (argon or helium usually, depending on the situation) prevents more oxide from forming by pushing away the ambient air, forming a cloud of shielding gas, essentially. 

 

Keep in mind that many, many AC cycles are happening every second, and you can adjust the number of cycles per second on most higher end machines, as well as the balance control, which is whether it favors more cleaning or more penetration (EP or EN, respectively.)

 

You want to use as little EP as possible, if you can adjust it. EP tends to cause excessive heat build up, which is not good for your tungsten or your material being welding. 

  

A quick note on shielding gases; argon, which is heavier than air, is typically used when you're welding downwards, like on a welding table. This encompasses 90% of all TIG welding, I would bet. But this is so the heavy shielding gas is pushed down onto the weld. Helium is used if you're welding above yourself, so the light helium rises up into the weld.

 

Hope that wasn't too long winded. I'm having flashbacks to welding school :lol:.

Edited by Will W.
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I do have some more of the alloy.  Problem is I only have a mig welder.  Didn't know a handheld propane torch would get hot enough to melt it.

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Propane probably won't get hot enough.  Acetylene will.

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15 hours ago, Will Wilcox said:

TIG would be better than oxy-acetylene. Brazing melts the filler, while TIG will melt surface material as well as filler, results in a stronger weld. 

 

I was intending to melt the base metal with oxy/acetylene, too; a full bronze weld, not just a braze operation.  

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2 hours ago, Jerrod Miller said:

 

I was intending to melt the base metal with oxy/acetylene, too; a full bronze weld, not just a braze operation.  

 

Which is pretty tricky; the heat transfer of bronze, while far lower than pure copper, is enough that unless you use a very small tip the point at which the filler and base metal unite is about the point the whole thing dissolves into a puddle.  Been there, done that, said the bad words.  TIG is much safer, but I don't have that either.  This is a job for the Smith Little Torch, the one that jewelers use.  https://store.cyberweld.com/smlito231.html  It'd be cheaper to take it to a welding shop that does bronze, unless you intend to go into jewelry.  If you have the regulators, you can get just the torch body and tips for about $125.  I may do that... 

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That is exactly the setup I've done that with.  I'm pretty sure it also works to submerge most of the part in water to act as a pretty good heat sink.  

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There are some youtube videos on how to convert your MIG welder to a TIG welder.  Basically, you modify a MIG tip to accept a short tungsten electrode and do not use the wire feed function.  I've never tried it but thought it an interesting hack.

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1 hour ago, Gazz said:

Basically, you modify a MIG tip to accept a short tungsten electrode and do not use the wire feed function.  I've never tried it but thought it an interesting hack.

 

That is interesting.  I'm going to have to run that by our weld engineer and get his thoughts on it.  I would much prefer to TIG my damascus stacks together rather than MIG and have to grind the welds back off.

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@Alex Middleton the nice thing about tig welding damascus stacks is that you dont even need to add filler, just use the torch to melt all four corners together. Works really well and it doesnt seriously disturb the pattern. 

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That's why it's an attractive idea.  I have a meeting with him later today. I'll see what he says.

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Sorry for hijacking the thread, but I ran the idea past him and his general impression, after he figured out that I was serious, was that it should be safe enough to try, both for me and my equipment.  He cautioned me not to make physical contact with the workpiece while welding at first.  His words were "Most likely nothing would happen, but it would be a good idea to be careful." 

He also cautioned not to expect much in the way of nice welds, went off on a tangent about volt/amp curve something or others, but said that it might just do a good enough job to tack together a billet.

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So long as you are not in between the tungsten and its ground clamp, you probably wont get shocked. Path of least resistance and all that. But yes, exercise caution when modifying anything that pushes the kind of power a welder uses. 

 

Make sure you have good gas flow too, up your regulator a bit from what your MIG was set at. And use pure argon, not the 50/50 that MIGs typically use. You could probably get away with the 50/50 short term, but tungstens are expensive, and deteriorate quickly without proper shielding. I have never TIG welded with 50/50, so I'm not certain what effect it will have. 

 

It wont make as nice of welds as a dedicated TIG will, probably wont have as steady of a current, and you wont have access to many of the "quality of life" features that come on most TIGs, but it should make passable welds for the application at hand. 

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18 hours ago, Alex Middleton said:

Sorry for hijacking the thread, but ... it might just do a good enough job to tack together a billet.

 

I'd love to hear how this works, I've been starting to save for a TIG welder, but this is probably much less out of pocket.

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@billyO I picked up a Vulcan ProTIG 200 about a year ago from harbor freight for a bit under 1000 dollars, and it is a remarkable machine for the price. I highly recommend it for a hobby welder, or even light production. Can be used on a 110 circuit or hooked up to 220 for more power output. AC or DC capability, and with a lot of nice features. Can also be used as a stick welder, comes with the stinger and everything. 

 

Its nothing like the 15,000 dollar Miller I used to run, but that's to be expected ^_^.

Edited by Will Wilcox
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Thanks for the info, Will.  Good to know, and hopefully I'll remember this when I'm ready to pull the trigger.

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