If you've built a custom classic truck, chances are you've had to deal with cutting metal-it may have been removing or modifying something old or installing something new. And, if you're like most hobbyists, you've tried a variety of tools to do the job including hacksaws, cutting torches, and abrasive wheels. But if you haven't used a plasma cutter you're missing the best tool yet and one that should be in your home shop.
What is plasma?
A common question is: "What is plasma?" The scientific answer is that it's the fourth state of matter: there's liquid, solid, gas, and plasma. OK, but what is plasma? Basically it is a gas that has been heated to such a high temperature that it is no longer a gas, and it becomes plasma.
Plasma cutting as actually an offshoot of the plasma welding process that was used during WWII to cut down production time in some applications. Similar in some respects to the TIG process, with plasma welding the arc is intensified by the injection of a gas into the electric arc stream. So much heat is generated that the plasma stream cuts, or "keyholes," the metal making a small hole as the torch is moved down the weld seam. During this cutting action the melted metal in front of the arc flows around the arc stream and is drawn together behind the hole (making something that looks like a keyhole, hence the name) as the metal cools it creates a solid bead. This process will weld material 1/2-inch thick or more without filler rod.
Like the welding process, plasma cutters use pressurized gas (such as compressed air) and electricity from an electrode to create a plasma stream that's approximately 30,000-degrees F moving at 20,000 feet per second. That's hot enough to melt the metal being cut while the pressure is great enough to blow the molten material through the cut rather than let it reform. The process can be up to 10 times faster than a conventional oxyacetylene cutting torch, and a cleaner cut is easier to achieve.
Plasma Cutting Tips
Use a straight edge, piece of flat stock, or virtually anything with a nice straight edge clamped to the metal to make a straight cut. If you are trying to build something out of 16-gauge or thinner, and it has to fit in a given space, make it out of cardboard first, and use the cardboard pieces for a cutting template. The plasma cutter can move so quickly the cardboard does not burn.
Maintenance
Remove the cover of the machine and blow the dust and dirt out of the unit every six months or a year based on usage. Make sure the unit has been disconnected from the power supply.
Check the cutting tip and electrode for wear frequently. If they are used beyond their service life, cut quality will be diminished, cut speeds will decrease, and you can damage the torch head.
Plasma Cutter FAQs
Q. If I need to cut a piece of 1/2-inch steel, can I cut one side, then flip it over and cut the other side?
A. No, for the plasma process to work properly without damaging the cutting torch, the air, and the metal removed, must pass completely through the metal being cut. If you were to cut 1/4-inch on the first pass, all the molten metal would be blown back up into the torch head, causing damage.
Q. If I turn the air pressure up, will the machine cut thicker?
A. No, you should only set the air pressure to the manufacturer's recommended setting.
Q. How far off the work should I hold the torch?
A. It all depends on the plasma cutter. Many machines have a "drag tip" design where you can actually rest the cutting tip on the work. Consult your owner's manual for the correct distance.
Q. How dry does the air have to be?
A. Most plasma cutters have a water separator/regulator, which is used to adjust the incoming air pressure. Generally speaking, the water separator supplied with most plasma cutters will filter out most of the moisture. However, if you see a lot of moisture building up in the water trap, then you should consider an additional drier for your system.
While the technical aspects...
While the technical aspects of plasma may not be fully appreciated by all of us, the results certainly are. The process brings new meaning to the phrase "cuts like a hot knife through butter."
Plasma cutters work by sending...
Plasma cutters work by sending pressurized gas through a small channel that contains a negatively charged electrode. Current passing from the electrode to the metal heats the gas until it reaches the fourth state of matter, plasma, which conducts electrical current and creates an arc, which does the cutting. Additional channels in the torch release a constant flow of shielding gas to control the radius of the plasma stream.
With a little practice a plasma...
With a little practice a plasma cutter can produce results like this. Those familiar with oxyacetylene cutting will find that plasma is much faster.
This is the control panel...
This is the control panel on an HTP 301 plasma cutter. The dial adjusts the amperage from 5 to 25 amps; the cutting current light illuminates when the trigger on the torch is depressed and the cutting arc has been activated; the thermo switch light illuminates when the duty cycle of the machine has been exceeded-it resets automatically when the machine has cooled sufficiently.
Using 16-gauge sheetmetal...
Using 16-gauge sheetmetal as a reference, CCT editor Ryan Manson cut 11/2-inch lines using five different amp settings on an HTP 301. As the amperage was increased, so was the speed of cutting, making it easier to run a straight line freehand.
The MicroCut 201 is a great...
The MicroCut 201 is a great entry-level plasma machine for the homebuilder. Operating on standard 110-volt power and weighing only 14 lbs., it'll cut 3/16-inch steel at 10-inches/minute and sever 1/4-inch steel with adjustable cutting amperage from 5 to 15 amps.
The MicroCut 301 is the unit...
The MicroCut 301 is the unit our editor uses and it's handled everything he's thrown at it with power to spare. Similar in size to the 201, it operates on 220-volts and will cut 5/16-inch steel at 12-inches/minute and sever 3/8-inch steel with adjustable cutting amperage from 5 to 25 amps.
HTP's new Micro Cut 625 packs...
HTP's new Micro Cut 625 packs a whopping 40 amps of high tech cutting power capable of cutting 5/8-inch steel in a small package.
Since the key to a properly...
Since the key to a properly working plasma cutter is clean, dry air, HTP offers this Super Dry desiccant air drier that incorporates a sintered bronze element that removes dust and dirt particles down to 5 microns. Changing from dark blue when new to clear when the desiccant has absorbed all the moisture it can, it's easy to tell when the Super Dry element needs to be replaced.
How to Select the Correct Plasma Cutter
Jeff Noland of HTP
The most important consideration when selecting a plasma cutter is the thickness of the material you will need to cut. Don't just say 1/2-inch because it is a nice round number that comes to mind-get a ruler, caliper, micrometer, or some measuring device and actually measure the thickness of the material you will be working with.
An analogy I like to make is it's like buying horsepower-the more amperage you have, the thicker you will be able to cut. However, more is not always better! A higher amperage machine will have a larger plasma cutting torch to dissipate the higher heat involved with cutting thicker material. The bigger torch is bulkier and won't get into tight places.
Another consideration is cost-a higher amperage machine will cost more money. A 25- to 30-amp machine gives you the ability to cut thin sheetmetal all the way up to 1/4-inch steel. And how much cutting are you really doing beyond that? This should tackle pretty much any automotive project you would be doing in your garage.
If you move up to a 40-amp machine, it will give you the ability to cut 1/2-inch steel. A benefit of a 40-amp machine over a 30-amp machine is it will cut any given thickness faster. So if you were doing a lot of cutting in the 1/4-inch range you would be able to cut at 25 inch/min vs. 12 inch/min.
A 60-amp machine is probably at the top end of the spectrum for anyone doing automotive work. These machines give you the capability to cut 3/4- to 1-inch steel. You better be building a lot frames in your garage to cost justify one of these cutters.
Two more things to take into consideration are air consumption and power supply. Some plasma cutters will operate on 110 volts, some operate on 110 and 220 volts, and some are 220 volts only. Make sure you have the correct voltage and amperage to run the machine you intend to purchase. Don't buy a cutter and then have to spend hundreds of dollars to upgrade your electrical service.
Generally speaking, for those working in their garage, air consumption usually is not an issue. The reason I say that, is because more than likely, you won't be doing "production" cutting at home. Let's say you have a 25-amp machine and are cutting a bracket out of 1/4-inch steel and need to make a 4-inch cut. At 12-inch/min that is a 15-second cut. A 25-amp machine will need about 31/2 cfm at 60 to 80 psi. Even if you have a small air compressor, you probably have enough air in your tank to get the job done. And with cutting speeds in sheetmetal upwards of 100-inch/min, you can cut a lot of sheetmetal before your air compressor will kick in.
The Super Dry filter is attached...
The Super Dry filter is attached to the provided pressure regulator at the inlet side of the 301 plasma cutter. The regulator is adjusted to 72 psi with the inlet air attached and the trigger of the torched depressed.
Editor Manson already had...
Editor Manson already had a pair of 220-volt, 30-amp outlets in his shop so he changed the plug that came installed on the 301 to the existing style. An easy job for the average person, but if there's any doubt in your mind, consult a professional before burning your garage down!
The plasma torch is fairly...
The plasma torch is fairly simple: The electrode is at the center, and the nozzle is just below it. The swirl ring is the second from the right; it causes the plasma to turn rapidly as it passes by.
A Plasma Parts Kit is a must...
A Plasma Parts Kit is a must have, especially if you're using one for the first time as you might go through some of the consumables faster than an experienced user. The kit consists of a spare gas diffuser, two extra cutting tips and electrodes, and an extra swirl ring. We also added an extended electrode and cutting tip, useful for getting into tight corners and great for pattern cutting.
Like any kind of work in the...
Like any kind of work in the shop or garage, safety is an utmost concern. A good, heavy-duty set of welding gloves are a must have and a pair of safety glasses that are shade-rated for using a plasma cutter are necessary. HTP offers a welding helmet that features a weld, cut, and grind function that has an adjustable lens that makes it simple to go from welding to grinding to plasma cutting with a flick of the switch, all the while offering full face protection while letting visible light through at a shade of 2.75 while offering UV and IR protection to a shade of 14.
Proving he's as talented as...
Proving he's as talented as he is good looking, our fearless leader uses the MicroCut 301 and a straight edge to cut a piece of 14-gauge sheet metal to repair the front valance panel on his F-1.
The MicroCut 301 allowed a...
The MicroCut 301 allowed a patch piece to be cut accurately with a gap close enough to weld up easily.
Unlike a cutting torch a plasma...
Unlike a cutting torch a plasma cutting machine will slice through any material that will conduct electricity, which makes cutting stainless steel, copper, brass, or aluminum plate as shown here, a breeze.
The MicroCut 301 allowed a...
The MicroCut 301 allowed a patch piece to be cut accurately with a gap close enough to weld up easily.