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Making Cast iron forge welding powder


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How to easily quickly make Cast iron powder or shavings, for adding to borax and create a better forge welding flux.


1. 80 grit thin diamond stone 

And a 100-300 grit small hand held whetstone

2. Drill bit between 5-10mm

4. Cast iron


Run your drill press at the low speed, high torque setting,

Securely fix/vice the cast iron, 

Lay a piece of paper beneath to catch the shaving.

Resharpen the drill it every 4-8 holes, if you're using stones for this, use thin stones that can be held like a file, rest the drill bit against your bench and file with stones following the angle, check if your filing correctly by looking at the scratches left by the two stones.(ideally this takes -1min)


After that, mix it to the borax.

One recipe I heard says 2/3 cast iron to 1/3 borax


Hope this helps.







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I use a bandsaw with a magnetic pan under the blade to catch the swarf.  Well, I used to, until a friend gave me a large tub of milling machine swarf from Harley Davidson heads.  I found drilling to be too tedious.  I mix it about half and half with anhydrous borax, adding a squirt of boric acid.


However, if a drill is all you have, that's the best way to do it!

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4 hours ago, Brian Dougherty said:

Curious why cast iron swarf rather than iron filings?


Good on you for sharpening your twist drills by hand.  I'm not very good at doing that, and have to resort to a drill doctor.

Cast iron has more carbon in it, this allows for forge welding at lower temperatures, thus preserving the highcarbon steel and also preventing it from bleeding carbon into the softer cladding in the case of laminations.


Least so I heard, haven't tried yet.

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Well, I sort of meant both.  Iron filings are cheap, and finer so I thought they would be easier to use in flux than drill swarf.  However, I also assumed iron filings were not really pure iron, and were either cast iron or steel.  I may be wrong about the last part.



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Get a bowl and go to your nearest shop doing car/truck brakes ..ask for some of the turnings off the rotors/drums put them into a cylinder and pound them with an iron rod to make them fines.. Cast iron will melt on your iron in a layer of borax just tale your "L" shaped poker and move the piece of cast iron round and you will have a thin layer..carbon content is a big variable in welding but so is time , TIME is important.

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For the record, for those who are wondering why the heck someone would put foreign substances in a weld seam, Leon is correct in that the cast iron melts before the steel, carbon diffuses, and the welding temperature is lowered.  So far so good, but it also leaves a visible line unless you thermally cycle the billet or hold at heat to allow the carbon to diffuse.  It is not typically done for damascus or other pattern-welding operations, in other words.  If you're using high carbon steel to begin with, it is not necessary and can even be a bad thing. You really don't want graphite between your layers, which you can easily get if your cast iron source is really high in carbon. Lots of thermal processing is required to clear that up.


So where is it useful?  For me, I use it in mild-to-mild welds on things that just don't want to stick otherwise, i.e. A36 mild wrapped axes and tomahawks.  Some batches of A36 just will not weld to themselves without some assistance.   It can also save a mild-to high-carbon weld that isn't sticking as a last resort.  For that, though, and for high-carbon to high-carbon weld repairs that will be etched afterward, a bit of brown sugar works even better than cast iron. Leaves less of a line in the pattern.


Forge welding is a function of heat, clean steel, and pressure, and of those three variables heat is the least important.  The rest is mental.  If you think it will work, it does.  If a little magic powder helps you believe it will work, there's no harm in doing it.  B)  Clean steel is by far the most important thing, which is why we use flux to dissolve the surface oxides.  If you're running a reducing atmosphere, you can weld without flux because no oxides form.  Daryl Meier once welded at room temperature with freshly polished steels and a large hydraulic press just to prove the point about oxides and surface preparation being the real issue.  Heat just gets the electrons more excited, which allows them to form bonds as the steel surfaces come into closer contact.  


Since most of us aren't trying to weld things in a "clean room" setting after hours of surface prep, we use heat and oxide control methods. 

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I don't know if I can trust machine shops to not have the shavings or swarf mixed with other metals, also haven't been able to find a source to buy cast iron powder, most of it was labeled as cast iron powder but always turned out the fine print read (Fe)


I think most people have a drill press or drill and some throw-away cast iron, and producing 100g literally took me only 20-30minutes, which is certainly shorter than what I spend online looking for real cast iron powder.


I'm intending to use it for japanese style toolsmithing(iron+hc steel), that's where I heard it's being used.


Edited by J.Leon_Szesny
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8 hours ago, J.Leon_Szesny said:

labeled as cast iron powder but always turned out the fine print read (Fe)

That's odd that a company would do that, because iron powder is more expensive then cast iron powder. 

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On 12/14/2021 at 4:50 PM, Gerald Boggs said:

That's odd that a company would do that, because iron powder is more expensive then cast iron powder. 

Is it? 

the only times I found "cast iron powder" the items detail description said (Fe) 


Iron powder seems easy to buy, it's being sold as food, for chemistry and paint/art stuff.

For cast iron powder tho...no idea where that would be applied on the open consumer market.


I guess I would have to directly order it from the source?

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