View Full Version : How to Machine a Weld?

12-22-2010, 08:45 PM
How does one best machine a weld? Let's say I have an unattractive bead sticking up from my recent O/A weld job on mild steel. Can I just "plane" the bead flat on my mill with an endmill? Or is your typical weld too hard to machine?

12-22-2010, 09:23 PM
Machining welds is easy.
You can always grind the weld off with an angle grinder.
If not, any facemill with carbide inserts will plow thru weld like butter.
Steel endmills cut weld too, just run them slower.

12-22-2010, 09:40 PM
It all depends on the base metal and the filler and how the two interacted.

Since you say OA welding,then I would assume the weld would be annealed and probably no harder than the surrounding base metal.Should machine easy with HSS.

If it were arc welded and a high or medium carbon steel for base metal,it could range from dead soft to glass hard.

Also if a weld is hard,no sweat,they can be annealed before machining.

12-22-2010, 10:16 PM
Start off by using a "Machinable Electrode"

Al Messer
12-22-2010, 11:01 PM
I'm with JoeFin.

12-23-2010, 12:13 AM
Knock off 95% of the bead with a grinder then flush it up on the mill sharp tool steady feed.

12-23-2010, 12:17 AM
Start off by using a "Machinable Electrode"

A machineable electrode (rod) exists for O/A welding??

12-23-2010, 01:57 AM
It all depends on the base metal and the filler and how the two interacted.

You really have to watch this. I built up the worn out lower area of a T-slot on a lathe compound. Cast iron of course, tigged it up. The resulting weld was so incredibly hard I could not even scratch it with carbide. Ended up having to grind to shape. I had to use a abrasive cut off wheel in an arbor to cut the under side of the T-slot flat.

12-23-2010, 09:43 AM
A machineable electrode (rod) exists for O/A welding??

Oxy-acetylene welding of cast irons
For successful oxy fusion welding, it is essential that the part be pre-heated to a dull, red heat (approximately 650C). A neutral or slightly reducing flame should be used with welding tips of medium or high flame velocity. The temperatures should be maintained during welding. As with Shielded Metal Arc Welding preparation it is necessary to use a furnace to ensure even heating of large castings. It is important that the casting be protected from draught during welding and provision should be made to ensure that the required preheat is maintained. It is important to avoid sudden chilling of the casting otherwise white cast iron may be produced which is very hard and brittle. This may cause cracking or make subsequent matching impossible.

Oxy welding is suitable for grey cast irons with an AWS A5.15 RCI (Aufhauser RCI), RCI-A type electrode and should used with a suitable flux such as Aufhauser Cast Iron Flux.

Austenitic cast irons can only be oxy welded with an AWS RCI-B type consumable.

Personally I've always done it with stick. I referenced this article for you - but i have no personal experience making machiable welds with Oxy/Ac. All I know is the welds I do with Ni 55 or Ni 95 are very strong and easily machined

12-23-2010, 11:10 AM
A machineable electrode (rod) exists for O/A welding??


"Machinable electrode" refers to Ni-Rod (nickel rod) for welding cast iron. The OP is asking about O/A welding on mild steel. O/A filler rods are just mild steel alloyed with a fluxing agent.

"Pure" nickel rods (99% nickel) are machineable. On the 45-55% nickel Ni-Rod, the balance is steel, which leaches out the carbon content of the cast iron, and gets hard as a witch's heart.

12-23-2010, 10:11 PM
macona: I asked my welding supplier - who may not know, of course - that same question today.

I asked him what process causes a weld on mild steel with a mild steel filler using a Tig weld to go hard, when I couldn't get the same metals hard without introducing carbon.

He replied that if I had enough gas around my weld, then it shouldn't get hard. I assume he means that atmospheric CO2 gets in to the weld if the gas flow is too low, or is too high and intrains the air, although how the small percentage of CO2 in the air can provide enough carbon to allow mild steel to become drill rod beats me.

I'm going to experiment with more gas flow sometime.

12-24-2010, 02:33 AM
No, he is wrong. Gas wont have anything to do with it. And considering how little of the atmosphere is CO2 is wont contribute to the carbon content in the steel. If you dont have enough gas you will know it though the porosity of the weld and it looking like crap in general. This applies to mig and tig.

Best guess for me i there is carbon concentration from the parent metal, or something like that. The effect is worst with cast iron which has the most carbon. Dont know for sure.

12-24-2010, 03:16 AM
Knock off 95% of the bead with a grinder then flush it up on the mill sharp tool steady feed.

LOL..Yup. Thats all there is to it. I dont get all the talk about "hardening joints", "special fillers or processes".

Its just mild steel right? Knock off the high parts of the bead with a grinder and finish it up with an endmill. Whats the issue? JR

12-24-2010, 06:37 AM
One thing you can do if you are unsure if it is hard or not, is run a file over the weld. If the file cuts it so will a HSS tool.

12-24-2010, 07:21 AM
If you are doing anything but cast iron with O/A and want a pretty weld just run the torch over the weld area again. This time keep the puddle width and speed consistent. Probably won't even need any filler rod. O/A welding doesn't have as many of the HAZ problems that arc welding produces. Unless you just want to machine it smooth. If I remember I read someplace that the raised bead actually adds strength and if it is removed the weld zone isn't as strong? One of the weldors would have to answer that question though.

12-24-2010, 10:46 AM
Its just mild steel right? Knock off the high parts of the bead with a grinder and finish it up with an endmill. Whats the issue? JR

That's what I do. Knock most of it off with an angle grinder, and blend it in with a flap disc. Then it mills like the parent material.