Plasma Cutting Guide
Once you have used a plasma cutter you will never want to go back to using oxy-fuel cutting, grinding discs etc it is an amazing tool to have
in any metal working environment, they are easy to use and cheaper to run than oxy-fuel cutting.
Plasma cutting is a quick and simple way to any metal that conducts electricity. It will cut steel, stainless steel, aluminium, copper, brass etc
Operating a hand held plasma cutter is actually very simple, you connect your plasma cutter to an air compressor and 240V or 415V supply depending on machine purchased, connect the earth lead to workpiece, connect torch to machine, select cutting amperage (more amps for thicker materials) and press the switch on torch handle and move the torch across work as the plasma arc cuts the metal.
You can start from the edge of work or pierce a hole in middle of metal, cut perfect circles with a circle cutting kit and make unique shapes using a template.
As there are no heavy gas bottles to lug around, plasma cutters are fairly portable and the minimized heat affected zone with small cut width compared to oxy-fuel cutting is a great benefit.
Plasma cutters use DC voltage to heat compressed air to a very high temperature where it ionises the atoms and creates a "plasma arc", this flows through the narrow hole of cutting tip (normally 0.9mm - 1.5mm) at a temperature of about 25,000 - 30,000 degrees Fahrenheit. The small jet
of plasma pushes through and melts the metal and pushes the molten metal away. It is highly focused when compared to oxy-fuel cutting and results
Selecting the right machine for you.
What input voltage do you have in workshop 240V, 415V ?
What is the maximum thickness of metal you want to cut?
You will need an air compressor to supply compressed air to plasma cutter.
Our P30C plasma cutter requires a 240V 13A supply so is very portable and suitable for DIY & light industrial use and has automatic cutting start via HF contact start and feature 8mm clean cut and 12mm severance cut on mild steel.
Our P50HF plasma cutter requires a 240V 32A supply which is generally found in most workshop environments, this has automatic cut starting via HF pilot arc starting with auto-restart and features a generous 18mm clean cut and 24mm severance cut on mild steel.
Plasma Arc starting differences.
HF Contact start
HF contact start uses high frequency generated inside the machine to jump the gap between torch cutting tip and workpiece so you simply rest the tip onto workpiece, press the trigger and the machine will automatically start cutting.
HF Pilot Arc Start (with auto-restart)
HF Pilot arc start again uses high frequency generated inside the machine and when trigger is press a pilot arc flame will come out of cutting tip about 1 inch long, when this pilot arc touches the workpiece the machine will sense this and start main cutting amperage. This has the benefits of being able to start on heavily painted / rusty surfaces etc.
It also features pilot arc re-start which is ideal for cutting mesh etc, when you have come to end of metal, the machine will sense this and re-engage the pilot arc so when you move torch to next piece of metal it will sense this and re-start main cutting power. This saves you having to release trigger and re-press to start arc again.
What is the different between Clean Cut and Severance cut.
This is where the machine will cut all the way through the material and the cut parts will fall away from each other leaving only minimal dross on bottom edge which can easily be pulled of using pliers etc.
The cutting marks will start of straight and then slope of a small angle towards bottom of cut.
The metal should require no extra working before being welded together etc.
This is where the user is using the machine close to its maximum cutting thickness capability.
The cutting speed will be much slower compared to a clean cut and the metal will require some cleaning up towards the bottom edge
Cutting speed, amperage and cutting tip size.
Cutting speed is dictated by the amperage used and size of material to be cut.
If you are cutting say 4mm with a 30A machine, you could either set the amperage to 20A and have an average travel speed or you could set the machine to maximum 30A (which will cut 8mm clean) and enjoy a faster travel speed, however you may experience slightly more dross at bottom of cut this way.
Cutting too slow.
If you cut too slow you may experience the arc cutting out with a contact start HF machine, or if using a pilot arc machine it may start to splutter (going between pilot arc and main cutting power, you will also get heat input into work and experience more dross at bottom of cut- So increase travel speed or reduce cutting amperage.
Cutting too fast.
If you cut too fast you will experience two things
Poor cut quality - As you have not cut all the way through material it will not break away from each other at end of cut and it will require a lot of cleaning up before use.
Blow back of dross - As you have not cut all the way through and have moved torch the dross (cut metal) will not be able to blow out the bottom as so will blow at a severe angle at bottom and if you are moving far to fast it will blow back towards the operator.
How to tell if you're cutting at the right speed
When starting from the edge of work take ensure the metal has been cut through and the dross is coming out at a maximum of a 10-20 degree angle and then start moving torch along work ensuring the dross angle does not increase, if the angle starts to increase close to 45 degree angle slow down the cutting speed, if you struggle to get a good clean cut and small angle of dross coming out the bottom of cut, try increasing the cutting amperage.
Piercing (Not starting cut from edge of metal)
When piercing metal at the start, this will result is dross being blow back up so the normal practice is to hold the torch at a 45 degree angle to work so dross blows away from operator, once the cut has started slowly move the torch to the 90 degree angle to work to enable the cut to go all the way through material - Once you have gone all the way through, you may start to move the torch.
Piercing will shorten tip life due to more dross blow back.
You can normally pierce metal up to 1/2 the maximum cutting thickness the machine is capable of.
This is uses where you may want to remove an old weld or defect in metal and is suited to machines with HF pilot arc starting. You will need to uses a special gouging tip which has a much larger hole than standard cutting tip.
Hold the torch at about 45 degrees to work and adjust arc length (distance between cutting tip and metal) and speed to blow away unwanted metal, do not attempt to gouge too much at one time, multiple passes may be required. Be aware that sparks / dross will be generated in this process and to guide dross away from torch / user and take care with other staff in cutting area.
A plasma torch head has 3 main consumables which will require replacing the most - Cutting tip and electrode and stand off spring.
The other parts which are the outer retaining nozzle and swirl ring (gas distributor) require less frequent replacement.
Stand off spring or pointed spacer - This fits onto end of outer nozzle and keeps a distance of 1-2mm between tip and workpiece. This can be removed if you wish to use a straight edge or template for cutting shapes.
Outer Nozzle - This screws onto head and holds the tip/electrode in place.
Compressed air requirements.
Select a suitable air compressor to be able to supply the correct amount of air flow to the plasma cutter. Using too small an air compressor will result in the air compressor running all the time and also lack of correct air pressure to plasma cutter resulting in a poor consistent cut. For our machines we recommend the following air compressors as a minimum to achieve good cutting results.
All plasma cutters required a clean dry compressed air supply, ensure you air compressor is drained regularly. All our plasma cutters come fitted with a air pressure regulator with water trap on rear of machine. If this water trap has signs of water, drain water trap and air compressor more often or fit an in-line compressed air dryer like our Aqua Purge Compressed Air Dryer.
Post flow air / gas
When cutting has stopped air will continue to flow from torch tip for a preset time, this is to allow the torch components
to cool down.
You can easily cut perfect circles using a circle cutting kit.
This comprises of a 2 wheel guide that attached to head of plasma cutter which incorporates a bearing so head can rotate in the guide. You then have extension bars which screw into head guide and into the centre of hole holder which can be magnetic, secured via a drilled hole or a small indent in work. These will generally cut circles from 70mm to 800mm
Cutting from a template
If you wish to cut the same shape in multiples, you can make a template from non-conductive material and hold the cutting tip against the template. As there is an offset from side of tip to centre hole, you will have to allow for this when making your template.
Cutting straight lines
If you wish to cut a very straight line, simply use a non conductive material with straight edge to run the cutting tip along.
Spacer Spring / wheel guide
To enable easier cutting and pro-longing tip life our machines come with a stand of spring which holds the tip about 1-2mm from workpiece.
You can also use the 2 wheel guide from circle cutting kit which allows smooth travel across the work as is less affect by bumps in metal when compared to a stand of spring.
Follow the correct safety procedures as stated in owners manual.
You will require safety goggles like our Flip Front Plasma Goggles
to protect eyes from the plasma arc and suitable welding gloves and non-flammable work clothing.
Please ensure you follow all relevant health and safety procedures as stated by your company.
Video reviews by Doubleboost showing setup and cutting with our R-Tech P50HF Plasma Cutter