USA Weld
usaweld.com
Lincoln Electric Company
lincolnelectric.com
Miller Electric Manufacturing Co.
millerwelds.com
Photography by Carl Heideman
Cutting metal is no picnic. Thinner metals can be cut with hand tools, but once the material thickness starts to build, so does the difficulty of cutting—and more drastic tools become necessary.
These heavy-duty tools usually involve a saw blade, an abrasive wheel or directed heat. Each has its advantages and disadvantages, but directed heat is probably the most versatile.
Historically, oxygen/acetylene torches were the preferred method for cutting metal with heat, but they weren’t the most accurate tools and they left a lot of damage and cleanup in their wake. Today we have something better: the plasma cutter.
Most plasma cutters blow compressed air through an electric arc. The arc ionizes the air and turns it into a very hot, very tightly directed plasma arc—ideal for cutting metal. These cutters cost more than a basic welder and most also require that you own an air compressor of sufficient capacity.
Few tools match the plasma cutter. Its speed, agility and ability to cut tight shapes are a real boon to quality work. Plus, it eliminates the need to spend big time and money on larger equipment, such as a serious band saw.
We’ll admit that we don’t have a lot of use for plasma cutting until the metal gets around 1/8-inch thick or we have a lot of concave cuts to make. For thinner metals and straight or convex cuts, we often find that an air or electric grinder with a quality cutoff wheel will give us a slightly cleaner, more accurate cut with just a bit of a time penalty.
Nonetheless, if you do a lot of fabricating with thicker metal, a plasma cutter is a pretty wise investment. Follow along as we share some tips for using one of these versatile machines.
We really like this HTP MicroCut 301. It’s compact in size, though not extremely portable. It cuts up to 5/16-inch steel and requires 220 volts and an external air compressor feed.
Miller, Lincoln and other companies have some nice portable 110-volt cutters with built-in air compressors, but they are more costly. The HTP requires hooking up the air line and electric power. Then, much like with a welder, the ground strap is attached to the work, and a hand-held torch makes the cuts.
It’s a good idea to draw the cuts with a dark marker before cutting. Then, just follow the line with the torch.
The torch is held at a 90-degree angle to the work. Speed varies depending upon thickness: The thicker the metal, the slower the cut. Want to make sure you’re not cutting hastily? The sparks should be flying below the work, not up at you.
Working freehand over drawn lines works well if you’ve got a steady hand, but it’s typically beneficial to use a guide to get a really nice cut. We usually make a guide out of a 1/2-inch-thick piece of plywood. The plasma cutter excels when making a concave slice around a guide. This would be difficult with an angle grinder.
Here are three straight cuts in 1/4-inch steel. The first cut was with an angle grinder and a cutoff wheel; it took us just over 30 seconds to get a nice result. Our second cut was with the plasma cutter and didn’t require a guide; it’s not quite as straight, but we made it in 20 seconds. The third cut was made with the plasma cutter and a guide—very nice work done in 20 seconds.
While the plasma cutter often offers some improved speed in cutting—as demonstrated by our 1/4-inch steel cuts—it does require some additional cleanup work to remove the kerf from the edge. This comes off pretty quickly; a chipping hammer can take care of most of it, but we prefer to use a grinding disc to dress the edge nicely.
Should the tip rest on the workpiece?
fearlesfil said:Should the tip rest on the workpiece?
My Miller has a drag tip that is meant to touch the work. I assume other brands offer similar.
fearlesfil said:Should the tip rest on the workpiece?
My Miller has a drag tip that is meant to touch the work. I assume other brands offer similar.
fearlesfil said:Should the tip rest on the workpiece?
I always cut with the tip slightly above the workpiece. My old Hobart used to have a metal coil that clipped on the torch and kept the torch the perfect distance from the workpiece. My new Hypertherm doesn't have that but is otherwise superior in every way.
One thing you need to have, that wasn't mentioned was a quality moisture trap right before the cutter where the air line goes into the cutter. And when I say quality I mean it. The little ones that you get at Harbour freight or home dept won't cut it, I use one of the industrial ones that you would use in a paint shop, that have the removable paper filters in it. If you don't use a proper moisture trap you will go though the consumable tips very rapidly.
Rumnhammer said:One thing you need to have, that wasn't mentioned was a quality moisture trap right before the cutter where the air line goes into the cutter. And when I say quality I mean it. The little ones that you get at Harbour freight or home dept won't cut it, I use one of the industrial ones that you would use in a paint shop, that have the removable paper filters in it. If you don't use a proper moisture trap you will go though the consumable tips very rapidly.
Thank you for that reminder! I use the small desiccant traps that Milton sells (model s1173). I probably need to try a few of those inline and pay closer attention to drying out the desiccant inside. These Milton traps can be dried out if you put them in your oven all night and keep the temp around the boiling point. They're plastic and they're glued together so you can't replace the desiccant without destroying them. (edit: the desiccant turns pink when saturated and dark blue when dry and the case is clear plastic)
In reply to fearlesfil :
Re tip
Varies by manufacturer. My Thermal Dynamics says touch for under 1/4 Inch, hover if over.
In reply to Rumnhammer :
Dry air!
In reply to Carl Heideman :
I'm not fond of sparks on my feet....or elsewhere.
Grab an old clothes dryer....make a shop heater, and a roll-around plasma work-station. Reinforce the top, and do some heavier work with the lid closed.
Fill the bottom with a pan and 2 inches of wet sand.
Use bricks to hold work up off the old BBQ or oven racks.
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