Hi, we are new to plasma cutting. I got a cheap one off of eBay to get started, hoping to make cleaner cuts than the oxyacetylene torch does. How clean a cut can we expect? Is weld-ready possible? Any pointers? Thanks, Joel
Depends on how steady your hand is. Should cut clean enough that just wiping the edge with a grinder should do it.
Dry air is essential. An in-line drier attached to the plasma or you will burn out tips. had a cheap plasma , it was cheap and horrible nasty. A straight edge is your friend, as is clean metal.Unlikely you could get the metal perfectly accurate straight from the plasma and have a nice weld. There will always be some slag. But pretty darn close in the right conditions.
A good plasma will be pretty close to weld ready. There is usually slag on the bottom of the cut that can be knocked off with a hammer then a quick pass with a flap disc and it would be good to go. If the cut itself is so rough you need to clean it up you are either moving too fast or have a machine not capable of what you are asking it to do.
Oddly, the thicker metal I cut the better the result, and you can angle the cutting head to provide a nice bevel for welding. Aluminum cuts like butter. I have never tried SS.
Plasma cutter is capable of making very good cuts, good setup and operator is the key to making great cuts with it! It's like a welder, the machine is not what will give you good welds, it is the person running it!
My dad made me a “torch positioner “ for a lack of a better term. Two rounded arms, one on each side of the torch to hold the height of the tip. That, and as mentioned before, a straight edge (angle iron, etc) make the best cut. Then it’s a matter of amps and speed travel. I cut circles with a similar clamp, 1/4 inch rod, bent at 90*s that adjusts for size. But as said, a flap disc, etc with a quick pass should be all that’s needed. My large machine has an air dryer/filter on it. But I’ve also have a small machine that’s never used a filter/dryer I ran with my oilless small compressor with no issues.
It depends on the “oomph” the machine has and how thick the material is. If you use a straight edge on thin material, it should cut fast and leave a pretty clean edge. Thicker material means slower travel speed and more slag to clean off. I have an old OTC machine, 110 volt, built in air compressor. It is great on sheet metal. It will cut 1/8” but slow with lots of clean up.
One important step is using a constant speed, a constant cut speed is necessary if you want a really nice cut. I've seen guys use them with a excellent finish cut and a different guy do the exact same cut with the same equipment and have a cut that looked like a torch cut. As stated above use a straight edge, I used a piece of angle iron, gives me a high wall to put the gun against..... ...
I agree with everyone above. I have a miller 625 that is like 30 years old now but still performs flawless. only thing i haven't seen mention is using a new tip or like new tip on very important cuts you want a straight edge on. when i start leaving a jagged cut or alot of extra slag those tips are removed and i save those old tips for cutting up scraps, cutting condensers open, etc, just basicly stuff that don't need a perfect cut i finish burning my tips until the light comes on my machine and tells me the tip is junk then i replace it with another half worn tip. but whenever i cut important pieces for a project i put a new or like new tip in. i mainly use mine for cutting scrap up. cutting stainless steel is easy with the plasma where the sawzall blade goes dull within a foot or so. once you get it, it doesn't take long to get the hang of the speed you want
We chopped the top on Clarence (avatar) in 1992. All cuts, excepting A pillers and doors/door openings was done with a plasma cutter. A straight edge and "torch positioner (see Budget36 above) were used. And the cuts were made by the plasma cutter's owner. BTW, he has been restoring high end cars all his adult life. No clean up was required. Pieces were butt-welded "as-was".
I have made patterns out of 1/4 inch fiber board or ply wood. Compensate for the diameter of the tip and go to it. If you are steady it will make a nice cut. The are a fun tool.
I’ve found the biggest problems resulted from air not dry enough or poor ground, after that cutting speed. Guides are your friend for best results, like most everything practice practice practice
After a cut I will flip the piece and take a piece of 2" flat bar and slide it over the cut to knock off the slag. A quick pass with a sanding disc and it's done.
@atch I'm guessing the guy that chopped Clarence is the same guy who chopped my 54. Kenny b. As far as cutting with plasma I agree with what others have said.
@fastcar1953, Well, while I consider Kenny (& his brother Reggie) to be good friends, Clarence got chopped before I met him/them. Last I heard Mr. B has chopped over a thousand cars. Quite the craftsman. He gets more done in that itty bitty shop of his than I could do if I had a NASCAR shop. He used to visit here but I haven't seen him here in a long time. I can't even remember his screen name.
For a "proper" weld, you CANNOT weld after any cut with heat, without grinding off "slag". Or what's also known as "recast layer". It WILL contaminate the new weld. Something you learn in the Aerospace industry, among other industries requiring "certified" welds. Mike
Lay out the cut. Clamp a guide offset for the torch head and cut. Nice straight lines. Grinding necessary? Well, I consider light grinding part of the prep. Much less than with a torch. I’m no welding professor. Some off shore steel welds poorly anyway. Welding wire selection can help. I haven’t had issues for “around the farm” welding with a cut and weld. But so much of the stuff we do require cleanup or fine tuning to fit. The amount of grinding is greatly reduced with our plasma over the torch. I only rough cut sheet metal with a plasma. I’ve got a bench plate sheer and hand shears to make the final cuts. Plasma is faster than the electric shears to rough cut.
If you are going to build a cart for your plasma cutter, here is a suggestion. I got a cheap HF cart and modified it. Added a pressure regulator and a water separator to the back of it so that moisture is removed right before entry and pressure can be regulated right at the machine for consistant pressure. I'd also recommend getting a plasma cutter rated for a thickness thats more than you plan to cut......and don't get one thats only rated for 3/16 or so. From my experience the smaller ones struggle when used near their thickness rating. Air Hose simply snaps onto fitting on back of cart. Clear hose with loop allows you to see if any moisture is passing thru.
best case, just knock the dross off and weld. more likely involves prep before and after cutting before welding one of the greatest advantages for me is cost of consumables compared to Ox/Acc
these only needed a light touch with hammer and chisels to knock the minimal dross off, zero grinder work. only other weld prep was to remove mill scale and add a few bends.
Most plasma cutters will only cleanly cut thicknesses up to about 1/2 its rated capacity. Once you get past that 1/2 of the rated thickness, the time gets longer (you slow down the movement), you get more slag, and the cut itself is more jagged. Tips (the thing that starts the spark) and nozzles (the part with the hole in it) are consumable parts. Every time you press the button on the handle, you burn away a little of the spark starter (that burns away) on the end of the tip. That flame (the burning air) is melting away the material around the hole in the nozzle. The nozzles are usually only good for about an hour of cutting time (I use about 2 nozzles to every tip). Cutting makes the diameter of the hole in the end of the nozzle larger, and as the diameter grows, the cutting point spreads out and the quality of the cut goes away. You really need to hold the nozzle away from the metal while cutting, if the nozzle is against the metal (you can buy a standoff attachment to help with that), it melts the material around the nozzle much faster until a hole is made in whatever you are cutting and the sparks can blow through the material. Dirt, rust, and paint also shorten the and the nozzle and the tip life. Dry air and a good clean ground are necessary. Aluminum tends to cut a bit harder. Stainless and steel cut about the same. Just like with welding, you want to have fresh air to breath, plasma cutters tend tp put a lot of yellow/brown dust into the air. You need to be aware of what is under whatever you are cutting. The plasma will burn anything flammable within its full rated range (if its rated at a 1/2" cut, it will burn or melt anything within a 1/2" of the cut point (even if it efficiently only cuts 1/2 that metal thickness), and the melting metal sparks thrown by the plasma will also damage things for some distance that is under what you are cutting. As far as cleanup, the slag needs to be removed, I hand slide a wide sharp edged chisel (long edge on the steel) across the cut edge from the uncut part towards the cut, and it usually removes the slag easily. Then both sides get hit quickly with a flap disc, you need to remove the discolor from both sides. A straight edge is helpful for a straight cut (a straight edge that is longer then the straight cut you want to make is helpful), you need to be sure to keep the plasma handle at 90 degrees to the metal, or that straight line won't be very straight. A very steady hand works for a smooth curve, but I might suggest leaving a little extra material to clean up the curved edge. With a plasma cutter, you will find out very quickly how steady your hands are. I have cut a lot of stuff with my plasma cutter, some of it at the cost of killing a nozzle pretty quickly. I always have extra tips and nozzles on hand.
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