Saturday, October 16, 2010

Cutting Steel With The Plasma Cutter - Like Cutting Through a Piece of Cheese!!

The sparks were flying this morning, fer shur, at Science & Tech!! Got to cut 1" thick steel with the plasma cutter. Love that machine!! Cuts thru steel like it was cutting thru cheese!!  
 
The plywood being held down with the C-clamps is the pattern for half a pair of "rail tongs" - instead of lifting salad, they'll be used to lift rails (as in railway track). Cut the pattern 5/8" smaller than the final shape. Hold the plasma cutter vertically against the pattern. Squeeze the button and run the cutter around the edge of the pattern. Sparks and liquid steel blow out on the underside. Voila - half a pair of rail tongs!!!

The job started several weeks ago when Ross R asked me to cut out some patterns in 3/4" plywood from full-size drawings.  Using good old-fashioned carbon paper, I transferred the pattern onto the plywood and then cut out the full-size pattern on the band-saw.  

Interior Cuts (Pattern Is Our Final Product) - Reduce Pattern Size By 5/8"
The head of the plasma cutter is 1" wide and will make a 1/4" wide cut in the steel.  We therefore have to account for this in making our wooden pattern.  We can have two different types of cutting situations.  In the first situation, the final piece of cut steel will be underneath our wooden pattern.  I call this an "interior cut" because the cut steel will be inside our pattern.  

On an "interior cut" where the steel is underneath our plywood, we have to reduce the size of the plywood pattern by 5/8".  The plasma cutter will then be cutting the steel right along the edge of the final cut.   The centre of the plasma cutter has to be 5/8" away from the edge of the pattern.  

So, using my T-square and a pencil, I traced a 5/8" pattern around the edge of the full-size plywood pattern.  Again, using the band saw, I reduced the full-size pattern to what you see in the photo below.  
 Most of our cuts will be interior cuts where the cut steel will be underneath our wooden pattern.  

The plasma cutter produces a very rough and ragged edge.  If the edge needs to be ground smooth, the pattern will only be reduced by 9/16", rather than 5/8".  This additional 1/16" will leave sufficient steel for a smooth grind. 


Exterior Cuts (Pattern Is NOT Our Final Product) - Reduce Pattern Size By 1/2"


In the second cutting situation, it may not be possible to have the cut steel underneath our pattern.  For example, our pattern may be too small for the plasma cutter to easily go around the pattern.  In this case, the pattern is outside the final cut steel and NOT on top of the final cut steel the pattern.  

On an "exterior cut"we have to reduce the pattern by 1/2".     

Plasma Cutter Settings
We've been looking at the business end of the plasma cutter.  Let's take a look at the end that makes it all possible.  Here's a "back view" of the plasma cutter.  
A large extension cord is wound up on the left side.  The extension cord is only used if the work is far away from a wall plug.  The regular cord, the ground wire, and the cutter gun are wound up on the back of the plasma cutter as shown in the following order:
  1. the regular cord
  2. the ground wire
  3. the cutter gun
 Let's now take a look at the front end of the plasma cutter.  This is where me make the adjustments (if any) to control our cut.  
Let's take a closer look at the control panel.  
To set up the controls, and with the plasma cutter plugged into the proper wall plug:

  1. Press the green "On" button
  2. Wait until both "Ready" lights are lit ("Ready" and "DC Power")
  3. Set the amps to 100%.  (If you are cutting sheet metal, see instructions below)
  4. Normally, we would be doing "stop-and-start" cutting as we move our position around the pattern and steel.  Set the "Continuous" switch to "Off"
  5. Flick the "Air Pressure" switch to "Test" and make sure it shows 75 psi.  If required, adjust the pressure to 75 psi.  flick the "Air Pressure" switch back to "Run"
THERE IS NO NEED TO OPEN UP THE BOX!!  YOU AREN'T QUALIFIED TO ENTER THE BOX!

To cut steel, 
  1. Connect the ground wire clamp to the steel to be cut
  2. Hold the plasma cutter gun on the steel but with the electrode off of the steel
  3. Squeeze and hold the trigger button
  4. Air will immediately come out under pressure
  5. In one or two seconds, a blue arc will emerge from the gun.  
  6. Slowly move the gun into the steel and against the pattern.  
  7. Move the gun slowly, always making sure that the liquid steel is blowing down.  
  8. Always "drag" the gun towards you.  Never away from you or sideways.  This will result in smoother cuts.  
  9. Take your time!
  10. Move your body placement so that you are always "dragging" the gun towards you.  
  11. Stop and start your cutting as required.  
  12. Release the trigger button before you lift the gun from the steel!!
  13. ALWAYS WEAR AN AUTO-DARKENING WELDING HELMET!!
To be continued.

6 comments:

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