# Welding thin tubing with a HF 125 flux core welder



## mickri (Nov 9, 2019)

My HF 125 has been modified with a bridge rectifier and a capacitor so it is a DCEN welder.  I am using 030 wire that came with the machine.  Spent most of the afternoon watching videos on flux core welding and practicing welding electrical conduit thin wall steel tubing.  It's what I have on hand.   Cleaned the conduit to bright and shiny before welding. Tried all kinds of different settings.  Min and Max power and wire speeds from 1 to 5.  Except when the wire speed was set to 1 I didn't really notice much difference in the welding.

Out of all of the videos I watched only one gave the settings being used.  Power on max and wire speed on 5 welding exhaust tubing.  He was doing overlapping tack welds.  All the rest mentioned adjusting the settings to suit the material.  Yet no demonstration on how different settings impacted the weld or the settings being used.

I found that it was real easy to blow a hole in the tubing no matter what the settings were.

First question is power setting.  Intuition suggests that you should be using the min power setting when welding thin tubing.  But what about penetration?  Should I see the weld on the inside of the tubing.  Only about half of my tacks looked like they had penetrated all the way through.  If you are tack welding would max power be better to get quick penetration without blowing a hole?

How does wire speed effect the weld?  Is it dependent on how thick the material is?  Or how fast you are welding?  Or some combination of the two.

Some of my tacks would be a small flat circle.  I think this is what I am striving for. Others would have a dent in the center.  What causes this?  Others would have a bulge in the center or a bulge around the edges with a deeper dent in the center.  What causes this?

Sorry no pictures.  They were too blurry to show anything.  I'll try again tomorrow.

Thanks for any advice you can share.


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## 4ssss (Nov 10, 2019)

The HF welder works well, but the wire they sell or comes with the welder is supposedly junk, and all of the guys I've talked to have said the same thing. If you're new to welding, I would think that's where you should start first.


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## Dudemanrod (Nov 10, 2019)

For thin material  use gas and .025 wire and get good wire. The setting you have to adjust for the material and the machine your using. Fluxcore is better on thicker 1/8 and up. Watch welding tips and tricks on you tube he has the best tutorials. Practice is key if something is not working change what your doing if it looks bad it usually is bad. Good luck


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## mickri (Nov 10, 2019)

The HF welder is what I have and there is no money in the budget for a mig or tig welder.

I will be getting some more wire in the next week or so.  I am almost out of the HF junk.  Will probably get some Lincoln NR211 MP.  That is what I see most of the people using in the videos and has been recommended by people on this site.


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## C-Bag (Nov 10, 2019)

i don't even try to mig thin wall tubing anymore. I oxy/acetylene and use steel rod or braze it. Either one is stronger than the tubing and I get a much nicer weld and way easier to control.


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## Old junk (Nov 10, 2019)

Thin steel is hard with flux core for a beginner.flux burns hot no matter what setting,solid wire with gas is way to go or oac


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## MontanaLon (Nov 10, 2019)

Conduit is galvanized so be careful with exhausting fumes out of the area. If you are actually grinding off the zinc on the outside you still have the zinc on the inside to off gas. This will make you feel like you have the flu. It won't make you chronically ill, like getting cancer or silicosis but you will feel like crap afterwards.

Not sure what effect the zinc will have on the welds themselves but it seems like the zinc would be vaporized anywhere the steel is melted so likely not be creating the issues you are seeing.


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## savarin (Nov 11, 2019)

Having mig welded a lot of thin wall steel tubing when building recumbent bicycles. I would suggest the best method is to weld vertically downwards.
Get the tubes to butt nicely, start the bead on the join and travel downwards.
It will probably burn through but dont worry thats what you want, just keep the arc in the middle of the bead weld and do not go side to side (weaving)
The bead should just keep forming and traveling downwards filling / fusing in as it goes.
Stay too long in one spot and the weight of the weld/bead will collapse and form a bigger hole.
Keep moving vertically  downwards.
If after the run is finished just go back and do the hole, still vertically.
I expect when you look inside the tube there will be heaps of wires inside, I used a small grinding wheel on a long shaft to remove them.
I used the thinnest solid wire (0.6mm) with mig gas, the zinc will leave a white fluffy powdery residue and as previously mentioned do not breathe in the fumes.
By vertically downwards I really do mean vertically, once it starts getting towards the horizontal the hole will collapse.
I would not attempt this with flux core.


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## Aaron_W (Nov 11, 2019)

I'm just a welding student and haven't done any flux core, but conduit is usually coated with a galvanized like coating and that is probably causing some of your issues. Assuming it isn't aluminum instead of steel which would be a whole different issue (wrong welding method). 

I've MIG welded galvanized a couple times when not thinking about the fact that they are galvanized (nuts, bolts etc) and it definitely causes issues. I get black sooty deposits and a lot of porosity (pinholes) similar to forgetting to turn on the gas. 

The gasses produced by welding on galvanized metal are also really bad for you, so you really want to remove any coating from the weld area, and some distance up inside and out both for the weld quality and your health.


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## mickri (Nov 12, 2019)

This is what the inside looks like.  Is this sufficient penetration?


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## DAT510 (Nov 12, 2019)

I believe most steel conduit is galvanized.  If your's is , be careful welding it, as the burning zinc can give you zinc poisoning.  The galvanization (zinc) could also be effecting/contaminating the quality of your welds.


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## Cooter Brown (Nov 12, 2019)

Take the HF mig welding wire and  throw it in the trash then go get some Crown Alloys, Weldcote, or Lincoln Electric mig welding wire..... If you try to use the HF wire you will think that mig welding is impossible..... DO NOT WELD GALVANIZED METAL WITHOUT A RESPIRATOR...... You can get metal fume fever from breathing the smoke when welding galvanized or other coatings....







						Metal fume fever - Wikipedia
					






					en.m.wikipedia.org


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## savarin (Nov 12, 2019)

mickri said:


> This is what the inside looks like.  Is this sufficient penetration?
> 
> View attachment 305695


that all depends upon whether you have sufficient bead upon the outside, there is no real strain in the joint, your not grinding the outside flat again.
As it stands there does not look to be any penetration that is fusing both edges together.


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## mickri (Nov 12, 2019)

Why I am going through this is I would like to weld up the exhaust header and tailpipe/muffler on my 66 midget myself instead of taking it to a muffler shop.  The outside will be ground for appearance on the header but not on the tailpipe/muffler.  I will be welding 1 3/8 OD .065 tubing and 1 7/8 OD .065 tubing.  This will be a mostly stock engine and not making any attempt to tune the exhaust piping other than the OD.  I will most likely use one of these two designs.  Which one will depend on clearance between the #4 tube and the foot well.





I won't get to this project until next spring and plan to spend lots of time practicing this winter.  Depending on how the practicing goes will determine if I have to go to a muffler shop or do it my self.


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## fixit (Nov 12, 2019)

mickri said:


> Why I am going through this is I would like to weld up the exhaust header and tailpipe/muffler on my 66 midget myself instead of taking it to a muffler shop.  The outside will be ground for appearance on the header but not on the tailpipe/muffler.  I will be welding 1 3/8 OD .065 tubing and 1 7/8 OD .065 tubing.  This will be a mostly stock engine and not making any attempt to tune the exhaust piping other than the OD.  I will most likely use one of these two designs.  Which one will depend on clearance between the #4 tube and the foot well.
> 
> View attachment 305711
> View attachment 305713
> ...



Get a mig or tig welder & do it right


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## Latinrascalrg1 (Nov 12, 2019)

Welding on proper exhaust pipe compared to welding on Galvanized conduit is Not At All a good comparison to practice with IMHO but then again what do I know.


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## mickri (Nov 12, 2019)

As I have said before there is no money to buy either a tig or mig welder.  The HF 125 is what I've got.  And I don't do much welding so the HF 125 suits my needs.

The only reason that I am using the conduit is I had some.  Next time I go to town I'll check with the muffler shop to see if they have any scrap that I can have for free or minimal cost.


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## homebrewed (Nov 13, 2019)

Modding your welder to DCEN shows you're not afraid to tinker with things.  I found a web site you might be interested in here.  It describes modifying a similar welder to use inert gas.  If you already have a bottle and regulator you already could be a long way down that road.

I did the DCEN mod to my HF welder and it definitely improved my welds, although I'm not proud of their appearance.  I don't have Argon but I do have a CO2 bottle and regulator (my moniker sort of gives away the why of that) & I've been thinking about trying it to see how it would work.


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## brino (Nov 13, 2019)

@mickri 

That's an excellent and ambitious project!

Since you want/need to stay with the welding process you have then my advice is the smallest diameter quality wire you can find, and practice, practice, practice.

When forced to do something like this I usually find that once I get a little spot deposited, I let off the trigger and let it cool a bit. Then I can come back and add a little more. It really is a patch-work of overlapping tacks. The extra mass of metal heats slower and helps avoid blow-thru. It doesn't look pretty, but can get you out of a tight place. It can also be slow since you'll want to clean/brush off the flux-core slag between tacks.

If you need to continue with galvanized, you can simply soak the pipe ends in a jar of muriatic acid (hydrocloric acid).
I used it to strip the galvanized coating off the ends of some (chain-link) fence posts for a project, it worked faster than I expected and stripped both the inside and outside to the depth that was immersed.
You can find that at pool supply stores, see: https://en.wikipedia.org/wiki/Hydrochloric_acid
Keep it away from your good tools though, just the vapor will rust steel in the same room.

For practice how about picking up some exhaust couplers/adapters at your local auto-parts place.
They would be more representative of the actual work piece. Like these:




But those look galvanized too.........

Best of luck, and please keep posting your progress!

-brino


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## mickri (Nov 13, 2019)

I am just about out of the HF wire.  I have purchased some Lincoln nr211mp wire and should get it next week.  Will keep practicing with the HF wire until it is gone.  My practice butt joints so far seem to be very strong.  Beyond ugly but strong.  Will be in town tomorrow and will try to get some scrap exhaust tubing from the muffler shop.  There is a small junkyard in town that might also have some scrap exhaust tubing.   I'll scrounge something somewhere.

If my exhaust system goes as planned I will only have 3 butt joints.  The rest of the joints will be lap joints.   A total of 12 joints.  I am going to make the flange that goes on the engine out of either 1/2 or 3/8 flat bar.  The exhaust ports are a rectangle.  1 1/4" x 1."  The common practice is to weld a short piece of tubing that has been pounded to the shape of the port and then weld to that.  I am going to machine a 1 3/8 hole 1/4" deep in the flange and then grind the flange to match up to the exhaust port.   This will give me a slip joint.





That will make it easier to align the tubes and easier to weld.  The collector that I will buy has a similar slip fit where the tubes enter the collector.  If I can get the welding dialed in than this a doable project for me.

Thanks for the lead on the mig conversion.  I have been to Mike's workshop in the past.  Lots of usable info on his site.


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## Aaron_W (Nov 13, 2019)

I mostly got my welder to do some body repair (rust) on an old Land Cruiser. I was given similar advice for welding sheet metal from my welding teacher as Brino gives. Short welds and then move to a different spot so it can cool. Basically a series of long tack welds.
He said he has also used a wet sponge to help the area around the weld cool faster. Not on the weld, but a few inches away where it won't contaminate the weld bead, or cause too rapid of cooling which can weaken the weld.

Aluminum also works as a good heat sink. Where I've had sheet laying on an aluminum plate, and then pass onto an area not in contact with the aluminum the difference is immediately apparent. Easy on sheet or flat parts, not so much with tubing, but maybe if you were able to make a collar that closed tight around the tubing that might help?


A less caustic way to remove the zinc coating than muriatic acid is soaking in white vinegar. It takes longer, perhaps overnight but it is safer to handle. The vinegar you buy in the cleaning aisle is more concentrated than the kind sold for cooking. You can buy industrial white vinegar as strong as 30%, cooking vinegar is usually around 5%, the % being how much acetic acid is in the solution.


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## mickri (Nov 13, 2019)

On this practice tubing I have been using the wire wheel on my grinder.  Takes less that a minute to remove the galvanizing to get the metal bright and shiny.


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## pontiac428 (Nov 13, 2019)

Wire wheel works great for zinc.  It takes a pretty good dose to get metal fume fever.

When you start working with exhaust tubing, you'll probably be dealing with stainless or aluminized tube.  Both weld like a dream compared to galvy.

You'll definitely have to face your header flanges on the mill when you're done to get them flat.  Until you get experience, you won't know which joints will want to warp from the heat or pull from the shrinking weld.  Headers are what I consider "fine work" where minutia and nuance are what will get the result.

I bought a 240v/50Hz overseas version of that same HF machine a few years ago when I realized buying the blue fortune cookie welder was cheaper than buying a new exhaust to pass vehicle inspection.  I barely made that repair happen for lack of heat control.  I was either burning through or spattering the arc out most of the time.  The little bamboo box welder was about as useful as a car battery, a pair of jumper cables, and a wire coat hanger when it came to burning metal together, but it could do thicker work easier than thin with a passable amount of integrity.  I was interested in the DCEN straight polarity modifications that you've done, seems like a big help, but now that I'm back in the states with my big welders I don't think I'll ever get around to it.

I understand working within constraints, especially budget.  Welders aren't cheap from the dealer, but craigslist seems to be a great place for welding equipment.  If that's out of the question, I get it.  I'm not saying fabricating a header is an impossible task with what you have, it'll just take effort, patience, and lots of extra grinding discs.  Let us know how it goes, I'd like to see the project!


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## mickri (Nov 14, 2019)

Local muffler shop had a huge scrap pile of exhaust tubing.  Got a couple of pieces for free and can take as much as I want in the future.  Should have my Lincoln nr211mp wire on Monday and have also ordered a magnifying lens for my helmet that I should get by Tuesday.  More practice next week.


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## mickri (Nov 18, 2019)

Between splitting more firewood this morning I took a break and did some practice welding on the exhaust tubing that I picked up last week. This is using the HF wire.  Much easier to weld than the conduit.  Did not get good penetration on the min setting on my welder.  Switched over to the max setting with the wire speed at 3.  Very easy to do tack welds.  I was also able to run some beads without blowing thru.  I think that I am getting this down.  Still lots of practice ahead of me before I try to weld headers for my midget.






A little while after this the UPS truck arrived with my Lincoln wire and the flux core nozzle.  I bought this from Home Depot and it was shipped directly from Lincoln.  Lincoln sent me the correct nozzle but the wrong wire.  I got mild steel mig wire.  Not flux core.  Lincoln is sending the correct wire and told me to keep the mig wire.  They didn't want it back.  Cost more for the return shipping than their cost on the wire.  Should have the correct wire in a couple of days.


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## brino (Nov 18, 2019)

mickri said:


> Lincoln sent me the correct nozzle but the wrong wire. I got mild steel mig wire. Not flux core. Lincoln is sending the correct wire and told me to keep the mig wire.



That will make a possible future gas conversion even easier/quicker/cheaper!
-brino


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## Cooter Brown (Nov 18, 2019)

With that HF welder leave it set to max and just adjust the wire feed until its welding nicely.....


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## Asbestos (Nov 23, 2019)

As far as the HF unit being not up to the task. Well every time I hear people say things like that I wonder how they ever managed to do these things before all this equipment.  or how they manage to do this stuff in third world countries.  Flux core is pretty lame, but it's what you have.  We tend to forget that we can do things like this, it is just going to be not as pretty or take longer or have a longer learning curve (exceptions apply) 
I would continue to raid the exhaust scrap pile. Also the amount of wire stick out can have some effect of the puddle due to the wire being heated by the current running through it.


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## C-Bag (Nov 23, 2019)

Funny how just the other day I had to weld up something similar thickness and decided to go for it rather than go to OA. What I did was tack weld it together with 3-4 tacks then fill in with basically tacks, never trying to run a bead. Having a good helmet with an auto lense is key. That way i can overlap the tacks to make them into what looks like a solid weld for me. FYI my mig is a Lincoln 175T running .030 flux wire.


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## mickri (Nov 25, 2019)

Got the nr211mp wire today.  I finished repairing my patio deck today.  Needed to get it done before the rains arrive tomorrow.  Will do more practice on the exhaust tubing tomorrow and also more welding on my 1966 midget.


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