On steel grinding is fine for prep. I think Tigging over a Mig weld would also require grinding to clean it up a bit. You could try a little without grinding. Sometimes the tungsten can be cleaned on a grinder but use a dedicated grinding wheel just for the tungsten. If you have to break the tungsten use 2 pairs of pliers and break only as much as needed and consider it slso has to be ground to a point afterwards. Some pics. would help greatly to see what your dealing with. I can't remember if it works for Tig welding steel but going on reverse polarity and striking an arc on a piece of copper for a second can clean minor contamination. Knew someone who did it on pennies if they didn't have a piece of copper scrap. The copper needs to be pretty clean too. Not sure about the boiled hot steel. One of the Tig experts like Shovelon or Timmy Tig should be along shortly.

 

My answers are probably not authoritative: I have never had to have a weld x-rayed and these responses are based on my experiences and the way I was taught:

If after a few minutes the tungsten is smoky or covered in soot- how important is it to stop and clean it off?

Probably yes, but it is more important to determine why that is happening. Actual soot? That shouldn't be happening. If the tungsten discolors from the heat, that is a problem but less worrisome...just turn up your post flow.

Does the whole rod need to be ground/sanded clean or can you just re- grind the tip?

By "rod" if you mean the tungsten, I would personally grind the tip then use sandpaper on the rest of the tungsten. Let me explain. I chuck my tungstens in a cordless drill and sharpen them on a belt sander. The drill is to spin them. Once the point is dressed, I wrap a piece of medium or coarse sandpaper around the tungsten and spin it to remove any contamination (usually aluminum that has wicked up the tungsten). If by rod you mean welding rod or filler rod, then no I just wipe it with acetone before I begin welding.

Do you have to snap off the last inch to get it really fixed or what?

No, not at all..that wastes money

Does the dirty tungsten contaminate the grinding wheel? (I'm using a Dremel with a diamond disk mounted in a tungsten holder - 3D printed.

No, and honestly tungsten contamination is seriously overplayed. I sharpen mine on a belt sander that I also use for general use, like sharpening my lawn mower blades. I have never had an issue with tungsten contamination

Can you tig weld mild steel that has been mig welded or ground on with contaminated flap disks? ( could have been used on galvanized steel parts)

You could, but why would you? TIG welding is not an acceptable way to repair a bad MIG weld.

If the weld puddle looks like it boiled hot steel what should you do to fix it? Are you needing to throw the whole thing in the dumpster or can you grind away the fried parts and use the filler rod to weld over it again?

just grind out the bad weld, and re-do it.

By the way, how you prep the metal being welded is probably a lot more important than how you prep your tungsten. On steel, you need to get all the mill scale and oil off. I hit everything within an inch of the weld with a flap disk then wipe with acetone. Back side of the weld joint as well.

 

I'm baffled by the "tungsten is smoky or covered in soot" and "weld puddle looks like it boiled hot steel"

I've never seen the former and only seen the latter with insufficient/no gas flow.

What gas are you using and what is the flow rate?

I see a lot of emphasis placed on cleanliness. I have found this to be important with aluminum, much less so with steel. With steel I never bother to clean the filler and MAY remove the hot-rolled scale with a wire wheel, but not always. Sometimes I will even TIG steel with paint on it.

I've never been very steady, so dipping the tungsten in the puddle is something I just live with. I don't run to the grinder every time it happens, I'd never finish the weld. I re-grind when the arc becomes difficult to control. I've found that thoriated tungstens tolerate this much better than lanthanated.

Flame on.

 

I do commercial TIG welding part time.
The metal has to be clean and dry. You can't tig weld paint, oil or rust. Come on. It will make porous welds, and spit and contaminate your tungsten.
Nor does it have to be absolutely spotlessly clean... But it helps, if you want those perfect welds.
I use acetone to clean my stainless steel jobs when it matters, but i don't bother on quick n dirty jobs.
I weld until my tungsten blunts, which takes quite a while, or until i dip, which sometimes is quickly or slowly. I like high quality low heat input welds, so i swap to a freshly sharpened tungsten.
Regarding tungsten contamination, you can sometimes grind it off and then sharpen it normally, but you're much better off chopping it and regrinding.
Just carrying on welding with a blunt tungsten is a bit like trying to drill something with a blunt drill, or cut down a tree with a blunt axe. It takes more effort and does a worse job.

 

I'd recommend watching Jodi on YT his channel is "welding tips and tricks". Great arc shots and explains it so even a cave man could do it!

 

Black soot and boiled metal indicate gas coverage issues too. Could be technique, joint, gas flow, cup size, leak….

As a newb, you should remove as many variable in your control as possible. So, clean.

 

Well thanks guys! you answered my most important questions! It's not easy starting from scratch up here in the North woods. I know I am facing some gas coverage issues and I'm working on switching torches to a CK 17 flex with a Fupa 10 glass diffuser of the shorty type. The torch that came with my VEVOR 210P was a WP 26 with the on/off switch on the handle. I kept accidently hitting the trigger and was wasting gas left and right, so I moved the switch to a foot switch I had for wood working.
So now my control is a lot more deliberate and much safer. I can wrestle the heavy cord and big torch much easier since I don't have to fiddle with the switch being in the way of my index finger. This also makes the torch cord a bit lighter, but the real improvement will be with the CK superflex cable and the CK 17 flex head torch.

I am fabricating an adapter to accomodate the CK hose fitting to my M16 x 1.5 chinese welder. It's mostly ready to go, including a nice insulator cover as soon as I get the CK stuff in I can finish fitting up the insulator. I don't know why nobody is selling these, as they ought to be available for the CK owners out there. This way, you don't have to modify your CK superflex hose at all and you can use the premo stuff on your cheap chinese equipment!

I want to be able to tig weld the thin wall steel tubing for a bicycle project I started, and most of it is like .050" wall or even a little less.

I have to do butt joint welds and extend or add pre-bent sections of old drop handlebars that I re-cycled for my wife's sling recumbent seat frame.

It looks like this project is pretty daunting for a Tig beginner with my cheap equipment, but I'm learning fast and enjoying the ride.

I'm trying to include a short piece of tubing inside each joint which absorbs some of the heat and prevents a burn thru in most cases.
But it's tough to get the joints 100% touching on all the edges before I can tack them down. I have a lathe and a mill, but even then there can be a tiny gap somewhere that will blow thru at the worst possible time.

At one time I considered using an OXY torch instead of TIG, but I had a friend who burned his motorcycle shop to the ground last year using OXY equipment and I don't want any chance of that happening to me!

 

Well thanks guys! you answered my most important questions! It's not easy starting from scratch up here in the North woods. I know I am facing some gas coverage issues and I'm working on switching torches to a CK 17 flex with a Fupa 10 glass diffuser of the shorty type.

you don't need a fancy diffuser or cup. What you need, is the basics.

A standard gas lens and no6 or 7 cup will work for 99% of everything. And I mean EVERYTHING. (apart from titanium maybe)

A no10 cup will just get in the way and waste loads of gas.

 

Tig through paint? That's a new one on me. :dizzy:

 

Forty years ago, a lot of high end steel bicycle frames were TIG brazed.

 

I agree with Munkul, save yourself some cash and skip the fancy cups.

It sounds like you either have bad gas, leaks in the gas lines, the wrong flowrate or your post flow isn't high enough. Those are the typical causes of oxidized (sooty/discolored tungsten) although if your tungsten is contaminated by weld wire or something that isn't tungsten, it can get discolored as well.

Usually contamination while prepping the tungsten isn't a problem as long as no one has used the wheel on something that smears. Aluminum/copper/brass all like to smear, so if you booger a tungsten up with aluminum and grind it off on the same wheel that you use to prep tungsten you can contaminate other tungsten electrodes that way.

Contamination reduces the longevity of the tungsten and generally makes welding harder since the arc will be less focused and steady.

It sounds like you're getting heavy porosity in the welds as well, which to me sounds like a rather serious problem with gas coverage. You should sort that out before you go building anything.

As someone else mentioned, the youtube channel "Welding Tips and Tricks" is a great resource for newbies.