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Norton, MA


Learning to Weld

First steps towards learning how to weld with oxyacetylene.

Early 2014

While pulling the engine on the DeLorean, I found a couple of holes a few inches across in the frame (which I'll detail in another post).  It can be hard to find someone who is willing to weld repairs on a frame due to liability concerns, especially on a fairly rare thirty year old car.  Luckily none of the damage to my frame was structural, but I did want the holes plugged.  After some questions on DMCTalk, I decided to learn oxyacetylene welding.

DISCLAIMER:  Oxyacetylene welding deals with pure oxygen and acetylene gases, both of which can be extremely dangerous, not to mention the incredibly hot flame that can melt steel. This post is not an instruction guide to welding, and you should do your own research and ideally take classes before trying to weld anything.


I went with oxyacetylene because it was recommend on DMCTalk when working with the kind of thin sheet metal used on the frame (16 gauge low carbon mild steel, apparently, which is common for car frames), and is less likely to burn through than MIG or TIG welding.  MIG is supposed to be pretty easy, but I'm limited to a 120v power source, and many MIG welders need 240v to do any reasonable thickness of metal.

After search around the net, I found some recommendations for a small portable Uniweld kit on Amazon for around $400.  It included a carrier, a cutting head and two welding heads, a mixing handle, hoses, regulators, an oxygen tank, an acetylene tank, flip-down welding goggles, and a striker to light the flame.  The tanks are the most expensive part of this whole thing; if you prefer, you can just rent tanks from your local welding supply store and buy a set with a handle and heads for around $150, but I didn't know how long I'd be using this stuff for so I wanted to have the supplies on hand.

I also picked up flash arrestors for both the torch side and the regulator side, just to be as safe as I possibly could be.  Flashback is a condition where the pressure drops and the flame goes back inside the torch, possibly running up the lines to the tanks.  This can happen when tank pressure gets too low, or when you touch the tip to the material (thus blocking the flow of gas) instead of holding it just off the surface.  This is Very Bad, and can lead to serious fires or explosions.  The arresters help keep this from happening.  The arresters for the torch side are different from those on the regulator side, so you need to get the right ones.  This wound up costing me another $150 or so, but I think it was worth it.

I also bought a bunch of safety clothing, keeping in mind that I'd eventually be welding while lying on my back under the car: a welding jacket that buttons up at the neck to keep sparks out of my shirt.welding gloves with long sleeves, a welding cap to keep sparks out of my hair, welding sleeves (just in case), and a welding apron.

I also wanted to protect my garage.  I already had two fire extinguishers, and I added a fire blanket in case I needed to smother any flames.  I also picked up four fiberglass welding blankets and covered anything I didn't want to be damaged by sparks and molten metal with them.  I don't have running water at the garage, so I brought some jugs of water to put out any small flames or hot metal bits that might show up.  I also got a spray bottle filled with water to dampen any surfaces around where I was going to eventually be welding under the car to keep them from being affected by the heat.

I bought some small 1/16" (16 gauge) small metal plates ranging from 2"x2" to 6"x6" and RG45 welding rods from McMaster-Carr to practice with.  Googling said that RG45 was the correct rod to use with low-carbon mild steel.  I also picked up a couple of house-shaped welding magnets from Home Depot to hold my test metal in place while I worked.

Basic oxyacetylene setup with flashback arrestors installed.

Flashback arrestors installed at the handle and the regulators.


A lot of people suggested taking classes, but I really don't care to do that.  It would have been nice to learn from someone around who knew what they were doing, just a friend if not an instructor, but I didn't know anyone who knew how to weld with gas.  I decided to teach myself.

This meant that I spent quite a lot of time looking for information on how to weld.  There are many YouTube videos on oxyacetylene welding that explain safety, how to light the torch, heat the metal, insert the filler rod, and so on.  I also found some web sites and PDFs guides explaining how to safely use a welding torch.

I found all sorts of important safety tips, too:

  • Acetylene connections are left-handed and the tanks and hoses are red, while oxygen are right-handed and green.
  • Acetylene is a fuel that decomposes into its component compounds and spontaneously combusts at 15 PSI, so you must always keep it below that.
  • Oxygen is an accelerant, and won't burn itself, but makes it much easier for things around it to burn -- notably, grease and oil.  You can't light oxygen, but it's very easy for something in the vicinity of the oxygen to ignite, and fed by the oxygen this will lead to a huge flame or explosion almost instantly.
  • You need to check all the gear for leaks, most simply by opening the regulators and making sure they don't drop over a period of 10 minutes, but more usefully by using leak detector solution (soapy water or a similar solution sold for the purpose).
  • Make sure to purge the lines by opening the valves on the handles for a few seconds before lighting, to avoid possible flashbacks.
  • Make sure that you have enough ventilation (I set up a fan blowing towards the open garage door).
  • Don't tip over the acetylene tanks, as they contain acetone that must sit at the bottom.  If they lay on their sides, they must be placed upright for a few hours before you can use them, or else the acetone can plug the nozzle.
  • Oxygen is under very high pressures.  Care should be taken when transporting the tanks to avoid accidentally snapping off the valve and turning the tank into a missile.  There are metal caps that can be used to protect them, although mine didn't come with any.
  • Some people shut off the oxygen first, some the acetylene.  I decided to shut of the acetylene first, since it's the fuel and that's what burns.
  • Popping sounds aren't that bad -- it's squealing you have to watch out for.  Squealing means that the flame is inside the torch, and that could mean a flashback.  Flashbacks can result in serious injury or death.  If you hear squealing, turn off the valves immediately and run away.

That's a small subset of the tips I found.  This is something you really want to do your research on so you don't blow yourself up.

Filling The Tanks

I googled and found a small welding supply store about 20 minutes away that was open on Saturday mornings.  I wasn't sure if every place provided fuel for hobbyists, so I made sure to find one that did.  In Massachusetts they won't refill acetylene; they simply replace the tank.  It was a bit disappointing to have my nice new red acetylene tank replaced with a rusty old tank, but it wasn't really that important -- I just wanted the gas.  They refilled the oxygen easily enough.  The total cost was about $30.

You're not supposed to transport the tanks in the cabin of your vehicle, but you also can't really lay them down either -- especially acetylene, due to the acetone in the tank, at least if you want to use in the next few hours.  However, my only other car is a four door sedan, so my only real options was to wedge the tanks in their carrier on the floor between the back and front seats.  I had no problems getting to the garage.

You're also supposed to store the oxygen and acetylene tanks separately.  I've completely forgotten about this and have been storing them right next to each other in the carrier.  I should probably put them on opposite sides of the garage, though.  I do remove the key used to open the acetylene tank when not in use, as you are supposed to do.

Lighting The Torch

My first experiment was going to be to cut some metal with the cutting torch.  This was before I had the flash arrestors, so I was exceedingly paranoid.  I had no problem lighting it, other than the fact that I forgot to tighten the cutting tip onto the head -- flames shot out from the sides as well as the end.  I quickly shut off the gas, tightened it correctly, and tried again.  I failed to get the oxygen mix to work properly; I never got a blue flame.  I'm still not sure what I was going wrong, but when I tried a few weeks later I was able to get it to light, but it didn't seem strong enough -- holding the handle down made the blue flame more green, and it wouldn't cut anything.

I gave up on cutting and moved on to welding.  At this point I'd installed the flashback arrestors and was feeling a bit more confident.  It took me a bit to realize that the arrestors quire you to increase the pressure from the tanks; 5 PSI of acetylene wasn't enough to get past them, but 10 PSI worked fine, for example.  The torch lit easily with the striker, and I had no trouble adjusting the oxygen to a neutral flame.  I did learn not to close the oxygen too tightly when shutting off the torch, as it made it difficult to open again, and opening it too quickly would blow out the acetylene flame.


I actually found welding to be fairly straight-forward.  I set up my practice metal on the house-shaped magnets at a 90 degree angle to each other.  I held the torch in my right hand and the rod in my left.  I hovered the neutral flame near the right edge of the metal plates, making sure to evenly heat both plates they glowed orange and formed a molten puddle.  Then it was just a matter of inserting the rod into the puddle and moving both the torch and rod from right to left to weld the two plates together.

It took a few minutes for the metal to cool, much longer than I expected.  You're not supposed to try to hurry it along with water, since that flash-cools the metal and makes it brittle.  You just have to wait.

Eventually I used Vice Grips to pick the two pieces up and put them in a vice.  I tested the quality of my weld by pulling up as hard as I could -- it easily bent at the weld and finally snapped.  So that was a failure. I used my angle grinder to clean the surfaces off and tried again.

My second weld was much better, and I couldn't break it no matter how hard I pulled.  I had to cut it off with a cutting wheel on the angle grinder.  My third and fourth welds were better still, and I wound up just bending the metal instead of breaking it.

My beads need work; they're not very consistent, but at least the welds are strong.  Unfortunately, at this point my angle grinder broke.  I'll practice for a few more weekends before I try to weld the frame.

My first weld.  The bead isn't very good, and the weld was not strong, but at least it worked.

Second weld.  Still pretty ugly, but much stronger than the first weld; I had to cut the two plates apart.

Third weld.  Getting better, and it's fairly strong.

Fourth weld.  Getting there...

Lap Joints

After a few months of working on my engine I went back to practice lap welding, which is what I really should have been doing this whole time, being that my goal is to weld plates over the holes in my frame.

The basic principle is the same, in that you want to heat both pieces of metal evenly, insert the filler rod, and let it cool.  I practiced with two pieces of metal I had, cutting them and welding them repeatedly.

My welds were horrible.  While some of my earlier ones were fairly strong, the later ones were just bad and could be pulled apart with my hands.  Only later did I realize my problem -- I wasn't cleaning the surface after I cut them apart to practice again.  

During this time I also tried to do a few welds with an auto-dimming helmet my friend let me borrow.  The problem with that was that the helmet only went down to 9; oxyfuel welding only needs lenses at 4 or 5.  9 was so dark that I couldn't really see the work well enough to tell how things were going -- all I saw was the brightest bits of the puddle.

An attempt with my friend's auto-dimming welding helmet.  Combined with other problems with the cleanliness of the metal itself, the helmet was meant for electrical welding, and only dimmed to 9 -- oxyfuel welding uses lenses of 4 or 5.

An example of a very poor weld.  It was not hard to break this.

An absolutely worthless "weld".  This one was easily pulled apart with my hands as though the two pieces of metal were held together with tape.  Everything about this weld is bad.  Really, only the top piece of metal melted; the bottom had glowed under the heat, but really hadn't bonded, most likely because it was dirty from previous practice welds.