All about plasma cutting

Lets talk plasma cutters, all names and colors don't matter to me.

There are a lot of plasma cutters on the market today from the cheap $200 special to the $4000 top of the line units. And trying to figure out what you need or want and the cost seems to some times get you the wrong plasma cutter for your needs.

That's why I am here, to try and help you get the plasma cutter that fits your needs with out breaking the bank.

So if your looking for your first plasma cutter, thinking of upgrading or just need some answers on the one you have, then here's the place to do it.

I will start off by saying you will need a air compressor that will run your plasma cutter efficiently. Most plasma cutters run on between 60 and 80 psi "cutting" air pressure. I recommend a compressor that will put out 5cfm at 90 psi or more, at least a 20 gallon tank and top out at 120 psi or more. The bigger the plasma cutter the bigger the air compressor. I also recommend using a 3/8" hose at 120 psi to your plasma cutter for best results.

A filter/water separator to take out most anything in the compressed air, you don't have to spend a lot to get clean air for your plasma cutter as far as filters.

Consumables

I really don't recommend after market consumables for your plasma cutters. I have found that you will not get very good life out of most aftermarket consumables.

Aftermarket or copy consumables may look like a good deal and your saving money, but your really not in the long run. They may not be made from the same materiel or be machined to the same tolerances as the factory one. This can cause all kinds of trouble from wearing out fast, shorting out, bad cuts or just not working and this could damage your plasma cutter.

DRAG OR STAND OFF

This may help you under stand it better.

A few things regarding standoff vs drag cutting with a plasma torch.

- The two major consumable parts in a plasma torch are the electrode and the tip/nozzle. Some users call the cutting tip the nozzle.....so for less confusion I will refer to them as electrodes and tip.

- Electrode is inserted into the torch....where it makes an electrical connection to the Negative output from the plasma power supply. The electrode (in an air plasma torch) has a slug of hafnium bonded to its copper body, the hafnium in the electrode is used as the electron Emitter.....it is where the 25,000 degree plasma arc is formed. The hafnium slug can reach temperatures of 3000 F., so it is air cooled in air plasma torches below 130 amps, liquid cooled in higher power plasma systems.

- The tip fits accurately over the electrode and is spaced by a swirl ring (or some sort of non conductive insulator) in order to maintain proper electrical and air flow spacing between the two parts. The tip makes an electrical connection to the pilot arc control circuitry inside the power supply. This circuit attaches the tip to the positive output of the power supply during arc initation and non-transferred pilot arc modes. During conventional cutting the tip is disconnected from positive, essentially "floating" from an electrical point of view. The primary function of the tip is to shape the arc into a perfectly round high speed jet of super heated gas. It's secondary function is to get the arc started by allowing electrical energy to pass from the negative electrode to the positive tip...creating a temperature rise in the air flow that ionizes the air making it more electrically conductive, this allows a pilot arc to initiated and exit through the tip orifice.

- As soon as the pilot arc is established and assuming the plasma torch is close to the material to be cut (the material is attached to the positive output of the power supply via the work cable, often (incorrectly) referred to as a "ground cable". If the pilot arc is close (generally less than 1/4") from the material, then the pilot arc will transfer some energy to the material and electrical current will flow through the work cable back to the positive side of the power supply. The power supply senses electrical current flowing, tells the pilot arc control circuit to disconnect the tip from the positive connection....and at this point all of the power transfers from the pilot arc path (negative electrode to positive tip) to the transferred arc path (negative electrode to positive material or work piece). The power supply now ramps up the power from low pilot arc amperage to high cutting amperage....the plasma cutting process has begun!

- Early plasma torches always had an exposed tip....in other words the tip protruded out the front of the torch. With any plasma torch over 40 amps during transferred arc cutting (the nozzle is floating electrically)....if the nozzle touches the work piece (connected via the work cable to positive).....expect that the tip will change its potential from "floating" to positive (same as the work piece). So dragging any exposed nozzle plasma torch on the material causes the tip to switch back to positive, allowing the negative potential from the electrode to jump from electrode to tip (inside the torch), then through the copper body of the tip down to the positive work piece. This is a phenomenon known as "double arcing". Expect that when any plasma torch operating at 40 amps or above with an exposed tip touches the plate that double arc will occur. This causes "current splitting" (some energy goes to the cutting arc, some splits off and shorts to the material), lowering your cutting power. The double arc to the material also cause "sticking", which is an effect of the copper trying to weld itself to the material...typically roughening the smooth motion of the torch and providing a very rough cut edge. Last, but probably the worst effect: the tip wears out very rapidly...you will see an out of round, cratered nozzle orifice after just minutes of drag cutting.....the orifice is supposed to shape the arc....so imagine what the cut will look like with an out of round orifice. (widely varying angularity, rough edges, slower cut speeds).

- Shielded torch technology. The shield is another component that attaches to the front of the torch. While the original shielded plasma torches were introduced by Hypertherm in the mid 1980's...most of the patented technology has expired (there are some exceptions!) and anyone can use shield technology to eliminate double arcing and allow drag cutting without stiction and longer tip life. The shield attaches on the torch to non conductive threads that allow the shield to electrically float, the front of the shield has an orifice and often some bleed holes as some cooling air flow passes between the shield and the tip. Shields are designed for hand cutting with the correct arc length when dragging directly on the surface of the workpiece, and there are mechanized or "standoff" shields that are designed for keeping the torch at the correct standoff using some sort of automated torch height control system for mechanized cutting.

-There are a lot of other things the shield is used for in modern torches today that improve height control, pierce thickness, arc energy density as well as allowing for different shield gasses for better metallurgy on certain materials.

Bottom line: There are some exposed tips available for certain torches that are advertised as "drag" tips, often these tip have a castleation machined into the face to allow dragging...instead of the smooth face noticed on other tip designs. If the tip is exposed (as described above), regardless of the shape on the front end....expect double arcing, sticking and shorter life. If you can get shielded technology for your torch...this is always the best bet for drag cutting...best quality, best life.

Under 40 amps you can drag cut with an exposed tip with most torches with acceptable results...the double arcing still occurs but at low enough power so the side effects are not as noticeable. Higher amperage dragging with an exposed tip will produce poor results!

Hope this helps with understanding drag vs standoff with Plasma cutting!

Common Plasma Cutting Faults

1. Insufficient Penetration

a. Cutting speed too fast

b. Torch tilted too much

c. Metal too thick

d. Worn torch parts

e. Cutting current too low

2. Main Arc Extinguishes

a. Cutting speed too slow

b. Torch standoff too high from workpiece

c. Cutting current too high

d. Work cable disconnected

e. Worn torch parts

3. Excessive Dross Formation

a. Cutting speed too slow

b. Torch standoff too high from workpiece

c. Worn torch parts

d. Improper cutting current

4. Short Torch Parts Life

a. Oil or moisture in air source

b. Exceeding system capability (material too thick)

c. Excessive pilot arc time

d. Air flow too low (incorrect pressure)

e. Improperly assembled torch

f. Incorrect torch parts for the operation

g. Non-Genuine parts used

When to change the electrode

I recommend to change the electrode every time you change the tip/nozzle. This is not always the why it works but it does keep you out of trouble.

With out getting into all the technical stuff I will put it in my own words, so it should make it easier to under stand. ( I hope, maybe )

The electrode is the part that gets the heat and keeps the fire burning so to speak. The heat is controlled by the Hafnium installed in the leading end center of the electrode. The Hafnium is only about 1/8" long or deep, with out it the electrode would just melt as its mostly copper.

There are a few reasons to change the electrode, even if it does not look bad. It is not firing dead center, this will cause poor cutting and excess tip/nozzle wear. Also a bad electrode will cause miss fires or pilot arc problems.

NOTE: YOU CAN NOT SAVE THE ELECTRODE BY SANDING, GRINDING, FILING OR WIRE WHEELING IT!!! SO GET THIS OUT OF YOUR HEAD!!!!

The time to change the electrode is when the divot/pit/hole in the end of the electrode get to be 1/16" deep or so. If you do not change the electrode before it losses its center core it will cause damage to your torch head. I have seen them worse they have burnt right into the torch head. This will cost you the price of a new torch head because of changing out a few dollar electrode.

I hope this will help you with your plasma cutter to get better performance out of your electrodes and consumables as well as saving money.

Here is a little tip for everyone with a plasma cutter with the IPT/PT 40/60 back striking torch. The electrode has its own built in gauge in the threaded end, if your electrode divot/pit/hole looks like that change it.

Plasma cutter air pressure, how to set it and when and why to change it.

As I posted earlier in this thread I recommend 120 psi with a 3/8" hose to the plasma cutter. This is because you need the pressure and volume to set and run your plasma cutter efficiently.

How to set your air pressure on your plasma cutter can differ from one to another, but this is the basic why to set it.

Most but not all plasma cutters have an adjustable regulator and gauge. Turn your plasma cutter on, if it has a set switch or set setting this will let the air start to flow from the torch. On some plasma cutters you have to bump the trigger to get it to post flow. With the air flowing set your regulator to the recommend pressure in the manual if it has a setting listed ( most manuals give you a range from say 60 to 80 psi) so set it at about 75psi this setting will give the 20,000fps coming out of you tip/nozzle to ionize the air( so it will ignite ). Set the switch back to the cut position, look at the gauge it can read from 80 to 95 psi or more. Note: MORE AIR PRESSURE then listed in the manual will not make it cut better...

This is because the pressure in the hose has increased. This is why you will get a quick burst of air when you pull the trigger till the pressure equalizes and will stay study at the 75psi setting you need for cutting.

Why the 75psi, well I have found out that most plasma cutters in the 40 to 60 amp range work best at this setting for cutting mild steel up to 1/2".

Most but not all plasma cutter company's/retailers work on the K.I.S.S. (keep it simple stupid) system. Case in point the 62204 plasma cutter sold by Harbor Freight. This is a good plasma cutter and will do a lot of great cutting, but HF only sells one size tip/nozzle (0.9mm, 40 amp) for that plasma cutter to do all your cutting. And yes that works if your a scrapper or just cut metal then grind to size and don't care about extra doss, clean up time, clean straight cuts, sharp corners, etc. this system works. So the 62204 has a IPT40 torch on it you can get tips/nozzles in 20, 30 and 40 amps, as well as 40 amp drag and shielded consumables. So why don't HF sell them? Well most buyers wouldn't now what all those consumables were for and you know that the sales person would never even have a clue what they were for, so the K.I.S.S. system works here.

So now your in the garage and you want to cut out some flowers for some yard art that your wife would like from 1/16" sheet, you fire up the plasma cutter, (maybe even) install a new tip/nozzle and start cutting, yea, the flowers look like (zombie snow flakes) not flowers. So you try different air pressures and amp setting, things still ain't getting any better, so now you start thinking this piece of junk plasma cutter. Well its not the plasma cutter the K.I.S.S. system is not going to cut it in this case. (pun intended)

This is were the 60 to 80 psi comes into play, as well as using the right size tip/nozzle and amp settings for the cutting job at hand. The rule of thumb is the thinner the metal, the smaller the tip/nozzle orifice size, the less amps and air pressure you need to do the cutting. I will cover these setting later.

This is what I have found to work with most plasma cutter nozzles/tips that most people have in their shops or garages. NOTE: Orifice hole size 1mm = .03937"

20 amp tip - 0.6mm/.025" - 15 to 20 amps - 50 to 55 psi

30 amp tip - 0.8mm/.030" - 21 to 30 amps - 55 to 60 psi

40 amp tip - 0.9mm/.035" - 31 to 40 amps - 65 to 70 psi

50 amp tip - 1.0mm/.040" - 41 to 50 amps - 65 to 75 psi

60 amp tip - 1.1mm/.044" - 51 to 60 amps - 65 to 75 psi

70 amp tip - 1.2mm/.047" - 61 to 70 amps - 75 to 80 psi

80 amp tip - 1.3mm/.051" - 71 to 80 amps - 75 to 80 psi

Or check with your owners manual for settings.

Ok then when was the last time you changed the filter/separator filter on your air compressor?----------------I'm waiting------------------------------------------

I have to admit it but I don't change them as offtin as they should be. The last time I changed the element on my compressor was a few years ago, the element was around $129 from Grainger.

I get plasma cutters in for repairs and about 25% are air related problems. Plugged filters, air lines, regulators and torch's full of rust, water, ice, dirt, sand, etc.

Now if you read most plasma cutter manuals they don't have anything on when to replace the filter or even if it has one.

Some have a filter number listed and how to replace it but don't say when to do it.

I get a lot of calls and emails from people having trouble with their plasma cutters. Bad cuts, lots of doss, can't cut thick metal and so on.

Now, I have went over this a few times but I will cover it here again, hopefully in more detail that everyone can under stand.

I have read a lot of plasma cutter manuals on air requirements that should I say is not bad but misrepresented or no information that really works. Here is what I have found out over the many years of plasma cutting to work the best for almost all plasma cutters on the market today.

Flow, its how much air you get out of a certain size hose at a set pressure. Think of it this way, a 1/4" water hose at 55 psi can fill a 5 gallon bucket in say 10 minutes, with a 5/8" hose takes a little over 4 minutes to fill the 5 gallon bucket. (this is an example only for the topic at hand)

So here is what I recommend for most plasma cutters, 120psi with a 3/8" hose to the fitting or regulator on the back of the plasma cutter. With air flowing from the torch (a lot of plasma cutters has an air set button or switch) set your regulator at the plasma cutter between 60 and 80psi. 60psi would be for low amp thin metal say 22 gauge and 80psi would be for max amps and thick metal cutting say 3/4" to 1". I set all my plasma cutters at 70psi flowing as this covers most cutting from 30 to 40 amps and adjust as the need requires.

I hope this helps answer some of the questions you may have about your plasma cutters air requirements.

Now to throw a monkey wrench into the workings of what I just posted. All this depends on what metal your cutting, what amps you are trying to cut it at and what kind and size consumables you are using.

Why do people do this!!!!!!!!!!!!!!!!!!

Got a plasma cutter in for repair the other day. First thing is to take the cover off and clean it as well as check it over before plugging it in. Cleaned out the cob webs and metal dust everything looked good, checked the torch for consumables, checked the work clamp and cable everything seems ok. Hook up the air and see the regulator was cranked up to 120psi way over the 60 to 80psi it called for ( I should have known something was wrong right then ), adjusted that, installed a plug and plugged it in. Turned it on, fan was running but nothing else was working. Did a few power tests and found the power divider transformer was bad. Installed a new transformer, turned it on and it came alive. Set it up for a cut and it worked for the first cut but would not re-trigger (start the pilot arc) for the next cut.

Now here is were things take on a whole new meaning in pulling your hair out trying to find out why it wont restart the pilot arc. Remove the tip and electrode and install new ones, still won't work. Remove the torch head and clean it, still won't work. Remove the complete torch assembly and clean it as well as plow air backward through the torch cable to make sure there is nothing in the air lines., put it all back together and still not working. Next take the regulator and air valves off, take them apart and clean them, reinstall them and you guessed it, no workie.

Now I have 4 hours in this and its 100+ degrees in the shop so I am getting really hot, so I go to the office to cool down a little. Sitting there in the AC having some ice tea thinking about this and then the light bulb comes on, I remember I had this with a plasma cutter a few years ago. Back out to the shop and remove the consumable retaining cup, there it was the answer to why it won't work. Cheap Chinese copy retaining cup, installed a new original retaining cup and low and behold it works.

People do not get it, using these cheap aftermarket copy's will cause you more trouble and money in the long run then just buying the right original consumables in the first place.

I can tell you the customer won't be happy with this bill because of a cheap copy retaining cup.

I got a email the other day asking why the metal he was cutting was warping when he was cutting it and how to stop it from warping.

When you cut thin strips off of a sheet of metal it will warp or curl out away from the larger piece as it gets the most heat from the cutting process. With a O/A torch it will warp/curl a lot but it will also warp/curl with a plasma cutter some.

Say you want to cut a 2" strip of metal off a 3' long plate. To help stop the warp/curl clamp on your straight edge, start your cut about 1/2" or so in from the edge, cut about 10" then stop, move ahead 1/2" then make the next 10" or so cut stop and leave 1/2" and make your last cut but leave the last 1/2" uncut. Let it cool for a few minutes then come back and cut all the 1/2" parts.

Your cut piece will be almost perfectly straight.