how to get a clean cut with miller 375 ??

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Well, I finally broke down and bought a 375 extreme expecting to replace my abrasive disks for most jobs.  20 pounds of scrap metal later I finally decided that I must be missing something  My next project will be cutting a few dozen pieces of 3"X3"X1/4" angle and about as much 10ga square tube.  I'd like to put the plasma cutter to use but I can't get my cuts clean enough or straight enough.  I'd sure appreciate a little help on set up and operation - thanks
Reply:How fast are you running your hand speed?I have a Hypertherm Powermax 380 and it cuts great but you have to watch how fast you pull your hand across the cut.Also, watch the tip-to-work distance. These don't have drag tips so finding the right height is key to a good cut.You may also want to check the basics first. What type of air supply are you running? Is it enough? Is it "dry" air? Do you have good ground contact?Hope this helps.- Paulhttp://all-a-cart.comWelding Cart Kits and accessories
Reply:I need to use all kinds of jigs and guides for a torch or plasma either one if dead on straight is critical. Heck, the more I think about it, I don't know of anything I can use to cut with that I don't need a guide. As for clean, I haven't had much problems yet. What small amount of dross that does remain is mostly in the knock off range. Tube can be problematic depending on dimensions. You can get an interior full of packed plasma dust. Oh, I've got a miller 625.
Reply:625's are nice machines. I'm thinking of selling my 380 and getting a 625 but I like the portability of the 380 since it's dual voltage.I use a 2x4 for a lot of my straight cuts so I don't get any arc wander.- Paulhttp://all-a-cart.comWelding Cart Kits and accessories
Reply:Thanks guys - I'm using a good filter so the air is clean but pressure may be too hig at 90psi.  I'll try lowering it this afternoon.  What about tips and stand off?  How do I tell when the tip is shot / are there different style replacements?
Reply:I have the same machine and don't have any complaints as long as you stay within the recommended parameters. 3x3x1/4" should take about 8 seconds per leg to cut, and you could knock the slag off entirely with a hammer. I made up a small wooden "square" to guide the tip. The thickness of the wood lifts the tip off the metal by 1/16", and when it gets too burnt (takes a while), you make a new one. If you could find a piece of bakelite (high temp stuff) it would last longer. Your pressure going in can be up to 100psi I think, I added another filter/dryer to the inlet of my machine. For thin sheet (up to about 1/16") you can drag the tip, over that you need stand-off to get full power. Also crank the voltage to the max and leave it there, unless you are gouging.Man invented metal, he can do whatever he wants with it.KMAC
Reply:I suppose each design has its own ideal working parameters, but if you have 90 psi at the torch inlet that may be a tad high. Mine calls for around 75 lbs ±.. I've tweaked it up and down just for giggles and haven't noticed a big difference. It's all about producing a nice little circular tube of air that becomes a plasma jet when everything works the way it should. Get outside those parameters and you could get either a lot of back splash or venturi maybe. I suppose all that varies as the hole in the tip enlarges anyway tho. The tip being usable or not is a matter of perspective and the needed results. The tip starts out with the worlds tiniest hole which enlarges from the point closest to the work back up through the tip to the interior in sort of a cone configuration. It's far less than a perfect shape so the cut gets wider and messier as the tip opens up.  You swap when it doesn't do what you want it to do. Big difference between blowing apart some 1/4 inch galvy channel and cutting artsy doo-dads out of some 20 gage or cutting a circle that needs to be darn close. On mine, with the freehand tip I should run about 1/8th inch standoff. That's pretty tight when you are wanting to see the line you are following. I've run wider, but you'll notice some O/A type slag when you start getting too far off the piece. And of course the thicker the material the more critical this becomes. I don't know if you can get a drag tip for yours or not. A drag tip takes all the guess work out of it as far as stick out goes but makes guides and templates more necessary. Drag tips are kinda tuff to roll around sharp corners and edges too. I'm still stuck back in the O/A mode where I want to see the pierce and leading edge of the cut with one eye and the spray trail with the other (lizard eyes)..  With plasma you need to become more robotic, learn the travel speeds for differing thicknesses and trust it to do what you know it can do. Variable thicknesses like that angle you are wanting to do will be a slight learning curve but you'll get it.
Reply:You want 80-100 PSI going to the machine, so that should be good.  The machine´s internal regulator you then adjust to inside the green lines on the gauge.If your air is clean and dry, then work on your technique and travel speed, using a homemade combination standoff/straightedge.
Reply:All good advice .... HoweverThe Miller 375 Extreme has a pressure switch inside which turns the machine off if the pressure drops below 90 psi.Drag tips are available ... but Miller is quite proud of them, as I recall I paid approx 35 dollars for the retainer cup. The drag shield and the drag shield tip were more reasonable in price.Washman Attached Images
Reply:For the square tubing you could cut a short piece that'll slide over the tube you're cutting to use as a guide. and maybe a piece of slightly bigger angle to use as a guide for the 3 x 3 angle.DewayneDixieland WeldingMM350PLincoln 100Some torchesOther misc. tools
Reply:Originally Posted by camobobWell, I finally broke down and bought a 375 extreme expecting to replace my abrasive disks for most jobs.  20 pounds of scrap metal later I finally decided that I must be missing something  My next project will be cutting a few dozen pieces of 3"X3"X1/4" angle and about as much 10ga square tube.  I'd like to put the plasma cutter to use but I can't get my cuts clean enough or straight enough.  I'd sure appreciate a little help on set up and operation - thanks
Reply:It's all in how you hold the torch..... my technique is very unorthodox but it is the best free hand grip I have found. If you refer to this thread you will see an example of how I hold the torch.http://www.weldingweb.com/vbb/showthread.php?t=11061By holding the torch the way I do my hand acts as a stand off, my thumb and first finger stabilize the torch while my second finger works the trigger. When making cuts I have very little pressure on my hand so that I can slide it easily across the plate. It takes a bit of practice to get used to it but I think you will find in the end, you have a lot more control over your cuts._________________Chris
Reply:Sounds like I need to learn annother skill. I had to use abrasive cuts to get this particular project rolling but as soon as it's painted and out the door I'll start working on my technique and maybe get a drag tip.  Thanks for all the advice.  Hope you don't mind if I ask one more stupid question - Is plasma really worth the effort?  I've been doin okay for a long time using abrasives and steel blades.  I actually do very little O/A cutting.  This little gem was well over a grand and it hasn't done me anything yet.
Reply:Sometimes I feel the same way.  When cutting 1/8" thick angle or square tube, I prefer the machined (super clean cut) look I get from my abrasive chop saw.  Maybe with more practice I can duplicate the same cut quality with my plasma.  Overall, I am still glad I have mine.MetalBob
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Reply:Camobob. For what it's worth, for that kind of work I think a bandsaw or drycut saw is going to win over plasma any time for repeatability and precision of cut. Really depends on what you're building of course. I love my plasma. It's great for making long straight cuts in sheet and light plate. But for a hunk of angle or channel or tube the chopsaw usually gets the task even though I hate the noise.
Reply:this is an old thread that's been spammed.  admin please shutdown agelkom