Optimum Distance for a plasma cutter between torch and material?

admin

I have a Miller Spectrum 300, its about 10 years old, but works like a champ. The consumables are a minor fortune to replace and I no doubt go through too many because I drag the torch directly on the material that I am cutting. I am going to make a few straight edge guides to hold the torch against and to standoff the material.  I am thinking that about an 1/8" between tip and material would be about right? I base this on its brother plasma cutter the 650 with a drag tip that provides 1/8" standoff.1/8" sound about right?
Reply:I'd think less for a smaller unit...around 1/16?Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:The torch you have is a Hypertherm manufactured non shielded torch. It can be used for drag cutting....but as you have discovered nozzle life is affected by doing this. For best quality on most materials....about 1/16" is good for this particular torch for standoff. Some have fabricated a wire divice that clamps on the retaining cap...extending past the nozzle about 1/16" as a guide.Newer technology torches are either designed for drag cutting specifically and provide better consumable life (Hypertherm Powermax30) or have shielded front end parts that allow direct drag cutting with little effect on nozzle life.You may also want to ensure your air is clean and especially dry. Any moisture will cause very short life...filters and air dryers are a necessary evil for plasma cutting.Jim Colt
Reply:Unfortunately, I don't know much about your torch (which is the most important variable in this question), but your tip seems familiar.I do know that my torch sells with several types of nozzles.  The nozzles that look like yours (with a "pointier" tip), require a standoff of at least 1/16" when running at 20A, and at least 1/8" when running at 40A, and should not be dragged under any circumstances (or you'll get very rapid deterioration)The nozzles with the "blocky" tip that I use have the nozzle hole recessed 1/16", so they are designed to be dragged at 20A, and require only a slight 1/16" standoff at 40A.So, what I'm saying, is that if your nozzle hole just looks like a drilled hole in the center of the tip, then its not made to be dragged.  If the nozzle hole is recessed (one style), or if the nozzle tip is kind of flat with the hole drilled in the center, but the circumference of the tip has bumps kind of like a crown (another style), then its made to be dragged at lower currents (since it has a built-in standoff of sorts).While this varies from torch to torch, about how many nozzles are you going through, before replacing your electrode.  Both of these are wear items, and I get about two nozzles to the electrode.  Dragging doesn't really add too much to the electrode wear, but can really increase the nozzle wear, so if you are going through 3 or 4 nozzles before you kill an electrode, then that may be a sign that you're doing something wrong.Also, because of the nature of the swirling gases coming out of the nozzles, they tend to cut more on one side.  So, with use, the hole will enlarge, first into an egg shape, and if left too long, into a keyhole (where it just won't cut any more).  If you notice the hole enlarging on one side, you can rotate the nozzle 180 degrees, and almost double its life.If the wear is highly asymmetric, there could be something wrong with your swirl ring.Back to the different types of nozzles.  For my torch, they make long and short nozzles too (with corresponding long and short electrodes).  The long style (which looks a lot like yours), has much better cutting visibility, and can be used on a concave surface (like the inside of a pipe), but costs me about 2x as much.  I tend to use the short type of electrode for that reason.  Picture an electrode that sticks out from your cap only about 1/8".  It does make it very hard to see what you're doing, but its so much cheaper.
Reply:You may also want to ensure your air is clean and especially dry. Any moisture will cause very short life...filters and air dryers are a necessary evil for plasma cutting.Jim Colt
Reply:Moisture causes a couple of issues in a plasma torch.....first when the moisture is broken down it creates a different gas mixture (water is made from oxygen and hydrogen).....the air cutting consumables are designed for air cutting.....electrode erosion is accelerated. Also....internal pressure and turbulence is also created when the moisture vaporizes....likely creating issues with the electrode emmitter.Jim
Reply:Gentlemen --as usual you guys are outstanding, and I greatly appreciate the assistance with this question, hopefully this may help others also.  In terms of the air supply and keeping it good and dry, I have a dedicated Motorguard filter that only runs when using the plasma and is valved off all other times. Supposedly it is made for plasma cutting operations.  The tip I have is pictured below, it is definitely dead flat across the top and I would assume not meant for dragging operations that I have been subjecting this poor thing to.  You can see the old and new.  I get the crater erosion forming fairly quickly when new.  I bet the nozzle pictured below does not have more than 50 feet of 16 gauge steel on it. Riltman--I can't say what the life span of my tips are, I have never estimated hours of cutting time or total length of cuts, but in my subjective opinion, they seem to go faster than perhaps they should.  Now I know why.  Why didn't you tell me sooner that I could possibly go 3:1 on the nozzle vs the electrode.  Miller must love me pitching both each replacement.  Thanks for the advice.  I will also look into different tips that might be available, perhaps there is a drag tip.  The max output for my unit is 25 amps (3/8" max cutting capacity) so it sounds like a 1/16" standoff is appropriate for most of my applications.  Again, gentlemen my thanks for your help.  My consumable cost is about $3.00 for the nozzle and $6.00 for the electrode.  So I am going to save a few bucks here using that tip the way it should be with a standoff.
Reply:If money is an issue, I think you can get tips for a bit less.I'm still not completely sure what model you have, take a look at weldingdirect.comThis picture shows what I was talking about for drag tips:http://ep.yimg.com/ca/I/weldingdirect_2063_11622651Both of those tips are of the "short" variety.  You showed a "long" tip, which is usually a little more costly.If you like to drag (and who doesn't?), then its probably a good idea to just get the drag style tips.  They're the same price, and don't reduce your visibility any more than a homemade standoff.As for re-using electrodes.  Your electrode should certainly outlive one nozzle.  When its time to change the nozzle, look closely.  A new electrode (at least, the ones I get), start with the hafnium (silver dot in the center), flush with the surface.  The hafnium will erode, leaving a "pit" on the electrode tip.  You can usually let that pit go as much as 3/32" deep.If there is ANY damage (from arcing) to the rounded shoulders of the electrode (or the matching surface around the inside of the nozzle hole, or if the hafnium is just plain gone, then your electrode is shot.  Run it like this, and it can arc to the side, and ruin your swirl ring (which is not usually considered a "consumable", and is one of the more costly parts to replace).
Reply:Miller has an excellent guide on how to use a plasma torch properly.  Every time you start the torch in air and the arc does not immediately arc to the base metal you lose around ten starts.  Depending on the make and style of torch you get a max of 1000 starts.  Similarly if you run the torch past the edge of the plate into the air you again cause damage to the torch tip.