Cutting Metal With a Plasma Torch ( With Accuracy)




Introduction: Cutting Metal With a Plasma Torch ( With Accuracy)

About: Owner, Operator of Steelshell Fabrication

I recently built 5 foot plates for a customers railing posts.
This is how I cut steel with a Plasma Cutting Torch

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Step 1: Equipment

You will need:
* a Plasma Cutting Torch. ( I'm using a Northern Industrial 275 that I got at Harbor Fright
* leather gloves
* Sun Glasses ( shade #5 if you have them, or a welding hood with a torch setting)
* Safety glasses
* A piece of angle iron long enough for your length of cut.
* A piece of metal to cut ( approx. 1/4" thick)
* A hammer and chisel
* A compressor capable of 70 psi or more
* A bright marking pen
* Measurement tools

Step 2: Set Up

* First, turn on your compressor, and make sure it's set to at least 70psi output.
* connect the air hose to the back of your Plasma
* Plug the plasma's power cord directly into the wall if possible. ( any extension cords will sap power from the plasma. if you must use an extension cord, use the thickest and shortest one you have. small household extension cords are not recommended.)
* Flip on the plasma's power, and set the air pressure. ( for 1/4" thick steel material, I set mine to 65psi. If yours has a power adjustment knob, check the manual or back side of the unit for thickness setting.)
This is fairly important. If the air pressure is too high or low, you will get messy or incomplete cuts.
make adjustments as you practice.
* Attach the negative lead either to the metal table that your part is clamped to, or directly clamp the Negative lead to your part.

Step 3: Line Out

* Its a good idea to make clear bold lines for your cuts.
I recommend a silver or white marker, which is easier to see thru sunglasses when cutting. ( mine wouldn't work)

Step 4: Clamp Up

* Clamp the steel off of the edge of your table, so that you don't cut thru your table, and on the end of the cut.
I'll be cutting right to left, so I clamp the left side top corner.

Step 5: Guide

now clamp the piece of angle on the start side of the cut, so that the angle sits back about a half inch back from your cut line.

Step 6: Cutting Technique

This is really the most difficult part of using a plasma, and I wished some1 would have shown me my first time, so forgive my thoroughness here, but this could make things a lot easier if followed.

Get your gloves and shaded lenses on.

I'm sitting comfortably to the left of the piece, so I can see the line, and pull towards me slowly.

with my right hand I rest the end of the torch just off the edge, and angled back.

My left hand is on top of the torch so that my pointer finger is on top, and my other fingers are on the other side of the angle ( pic 4 n 5 )

Your right hands job is to pull the trigger, and apply a little pressure down. ( pic 6)

your left hand pulls the torch back.
Your left pointer finger closes in and stops. then you scoot your 3 fingers back by opening your fist, and again close up with your pointer.
your basically scooting along in short movements over and over.

When cutting metal this thick, you have to move at a snails pace, and your hands will shake and jitter if not braced like this.

I always do a quick practice pass with no trigger, to see if my tip stays on the line, and to see if I can bend my hands and elbow smoothly for the entire length of the cut.

Step 7: Pull the Trigger

So now rest the tip off of the edge, and pull the trigger with your right pointer finger.

slowly start dragging the tip back towards the left, using both hands, but mostly your left ( or top hand)

If sparks start to fly up in the air, your moving too fast.

try to find that snail pace that it needs to cut all the way thru.

this is where having your hands braced, and you sitting in a comfortable position becomes important.

If you start to cut away from your line, just rotate the torch with your right hand slightly, and continue dragging.

try not to look at the light. this will help you to see your line.
If you focus on the back of the tip where it touches metal, you can see if your on target.

if you have to stop and look, make sure to start again with the tip in your old cut, or you'll have sparks spray up into the air. ( maybe face)

slow down at the end to make sure it cuts to the end.

You can make a lot of adjustments just by rotating the torch with your right hand a tiny bit.

Step 8: Clean Up

I was able to cut this notch out, and got some pretty straight lines.

Now I advise you to let the plates cool a bit, and Chisel the slag off of the back.

If you try to grind this slag off, you'll be there all day.
I found that clamping the piece like this, and chiseling at an angle, to cut the slag off goes really quick. ( pic 2 )

if your fighting it, you need to change your angle, this stuff should break off easily.

Step 9: A Word on Clean

If your going to weld these pieces together, you gotta get rid of the cut marks.

This material left in the cut lines is no good to weld to. It's full of contamination, etc., and will give you terrible porosity if you weld on it, so grind it until its shiny.

Step 10: Tanks for Reading !

I wanted to explain the important part of plasma cutting, because I spent years ruining tips and electrodes by doing this wrong.

If you just keep it dragging at a slight angle, you will save tons on replacement parts.

If you try to keep the tip hovering off of the part, without a guide, you will easily make contact, and zap the tip and inside parts into melted junk really quick.

For thinner sheet metal, the technique is the same, accept that you can move much faster.

for irregular curves, you can modify your hand like a pool que bridge, and drag it along.

I hope this was helpful!

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    3 Discussions


    Question 1 year ago

    "If you try to keep the tip hovering off of the part, without a guide,
    you will easily make contact, and zap the tip and inside parts into
    melted junk really quick."

    I have a plasma cutter that I haven't used yet. Pretty sure I'll electrocute myself. Among many questions I have is in regards to the above statement in the article. So...the tip should or should not touch the metal? It can touch the metal at an angle? Why? Is it because the tip won't actually be in contact with the metal if held at an angle?


    Answer 3 months ago

    First, it's pretty difficult to electrocute yourself with a plasma cutter. I have several hours on them and have never experienced this. Second, try NOT to touch the tip to the metal you are cutting. You are using an ARC of electricity to melt the metal while the compressed air pushes the molten metal and slag through the surface. If your tip touches the metal you're cutting, it's not the end of the world. It's kind of like getting a welding rod stuck while you're stick welding. The arc disappears once the tip touches the metal and the cutting will stop and your tip will be temporarily stuck to the metal. You can usually pull it off fairly easily and continue with the cut. Try to minimize the amount of contact because it can warp the and distort the cutting arc. Tips can be replaced if this occurs. That being said, there are guides you can attach to the tip that you can rest on the surface you are cutting. As far as what angle to hold the torch while cutting, it takes some practice to figure out what works best with which direction you're pulling or pushing the torch. Practice makes perfect!


    3 years ago

    I've welded cut joints with no cleanup and not noticed any porosity anywhere . Did you just hear that or have you tried it yourself . Turn your welder up and it burns through anything on the surface .Sounds like you set it too low which is a common problem